Post on 29-Jan-2020
CARACTERIZACIÓN DE LA INFLAMABILIDAD DE ESPECIES LEÑOSAS EN EL
CHACO SEMIÁRIDO DE ARGENTINA, A PARTIR DEL ANÁLISIS DE RASGOS
FUNCIONALES
AUTOR: ANA CAROLINA SANTACRUZ GARCÍA
DIRECTOR: DRA. SANDRA BRAVO
UNIVERSIDAD DISTRITAL FRANCISCO JOSE DE CALDAS
FACULTAD DE MEDIO AMBIENTE Y RECURSOS NATURALES
MAESTRÍA EN MANEJO USO Y CONSERVACIÓN DEL BOSQUE
BOGOTA
2018
Nota de Aceptación
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Firma de la Directora
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Firma del Jurado
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Firma del Jurado
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Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
DEDICATORIA
A quienes extraño con el alma y adoro con mi vida:
A quienes nunca se han cansado de creer en mí y
han estado siempre presentes, mi par de
viejitos: Bertha y Alberto
A quienes son mi motor, mi principal motivación día a día, mi par de fotocopias:
Sofi y mi Negra
A mi abue, simplemente por ser tan peculiar como solo
puede ser él
A mis amigos de siempre, los que creyeron que este día
llegaría y a los que no, también...
A los amigos que he ido
haciendo día a día, a medida que avanza esta
travesía
A quién siempre persevero, tuvo infinita paciencia y me
apoyo a terminar este proyecto y emprender otros más, mi directora de tesis:
Sandra
Y sobre todo, a Dios, a la virgen y a la vida por la luz y la fuerza que me brindan
cada día...
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
TABLA DE CONTENIDO
RESUMEN…………………………………………………………………………………….. 1
ABSTRACT…………………………………………………………………………………….. 2
I. INTRODUCCIÓN GENERAL…………………………………………………… 3
II. CAPÍTULO I: “Flammability characterization of woody species in semiarid Chaco
region, Argentina, through functional traits analysis” ………………………..…. 7
Abstract…………………………………………………………………………..….7
Resumen……………………………………………………………………………..9
Highlights…………………………………………………………………………..11
1. Introduction……...…………………………………………………………….12
2. Material and methods……………………………………………………….…14
2.1 Study area……………………………………...………………………….14
2.2 Functional traits of plant flammability……………………………..…….18
2.3 Seasonal variations of flammability……………………..………………..18
2.4 Statistical data analysis……………………………………………………19
3. Results……………………………………………………………………..…..19
3.1 Disturbance effects……...…………………………………………...……19
3.2 Interspecific variation of flammability…………………………… ……...22
3.3 Seasonal variations of flammability……………………………………... 23
4. Discussion……………………………………………………………………..27
5. Conclusions……………………………………………………………………31
6. Acknowledgements…………………...……………………...………………..32
III. CONCLUSIONES GENERALES…………………………………………...…….33
IV. RECOMENDACIONES GENERALES………………………………………..…34
V. REFERENCIAS…………………………………………………………………...35
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
INDICE DE TABLAS
Table 1.Botany family, foliar phenology and growth habit for the studied species……………16
Table 2.Average (A) and Standard Deviation (SD) for six flammability functional traits evaluated
in eleven native species from Western Chaco region, Argentina, during three sampling dates for
fire season (June, August and October) in forest with different disturbance history. CF= Forest
under closure, without disturbances over three last decades, considered as reference condition;
DF=Disturbed forest with fires and roller chopper applications. References: TDMC=Twig dry-
matter content (mg*g-1); TDT= Twig drying time (days); LDMC=Leaf dry-matter content (mg*g-
1); TMC= Twig moisture content (%); FMC=Foliar moisture content (%); DR =Number of
ramifications orders; FD=1 to 5 categories following Pérez-Harguindeguy et al. 2013…..……21
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
INDICE DE FIGURAS
Figure 1. Study sites localization in (A) American Chaco Region, (B) Santiago del Estero
Province included in South extreme of American Chaco Region, (C) Sampling sites localization
at Experimental Ranch Francisco Cantos belonging to the National Institute of Agricultural
Technology (INTA)……………………………………………………………………………..14
Figure 2. Temperatures (continuous line), monthly rains (vertical bars) and average dates of the
first and last frosts in the Experimental Ranch “Francisco Cantos”, INTA EEA Santiago del
Estero. The rectangle indicates fire season in the Chaco region’s central zone. Climatic data period
1981-1990, EEE Meteorological Observatory Santiago del Estero, INTA. Source: Kunst & Bravo,
2003………………………………………………………...…………………………………..15
Figure 3. Study sites: (A) Satellite image of the Experimental Ranch “Francisco Cantos”
belonging to the National Institute of Agricultural Technology (INTA), Argentina, (B) Control
plot, a forest under closure, without disturbances over three last decades (C) Disturbed plot,
disturbed forests with fires and roller chopper applications…………………….……………….17
Figure 4. Flammability degree (FD) in native woody species from Western Chaco region,
Argentina, during three sampling dates along fire season (June, August and October) in forests
with different disturbance history. CF= Forest under closure (without disturbances over three last
decades, considered as reference condition) DF=Disturbed forest with fires and roller chopping
with management goal. Different letters indicates significant differences between sampling dates,
according to LSD Fisher, Tukey and Di Rienzo, Guzmán, Casanoves (DGC) pair-wise
comparison procedure with α: 0,05, n=66 individuals by site each sampling
date………………………………………………………………………………………..…….20
Figure 5.Flammability degree (FD) in native woody species from Western Chaco region,
Argentina, following Pérez Harguindeguy et al. (2013). Same letters indicate no significant
differences between species, according to LSD Fisher pair-wise comparison procedure with α:
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
0,05, n=66 individuals. References: 1=S. gilliesii; 2=L. divaricata; 3=C. microphylla; 4=S.
lorentzii; 5=S. johnstonii 6=M. spinosa; 7=C. ehrenbergiana; 8=A. quebracho-blanco; 9= A.
emarginata; 10= S. mistol; 11=C. praecox……………………………………………………………..22
Figure 6.Dendrogram resulting from cluster analysis (Ward method and Euclidean distance) for
eleven native woody species from Western Chaco region, Argentina; based on six functional traits
related to flammability, foliar persistence and growth habit. References: SG=Senegalia gilliesii;
AQB=Aspidosperma quebracho-blanco; AE=Atamisquea emarginata; CM=Condalia
microphylla; LD=Larrea divaricata; SJ=Schinus johnstonii; MS=Maytenus spinosa; CE=Celtis
ehrenbergiana; SL=Schinopsis lorentzii; CP=Cercidium praecox; SM=Sarcomphalus
mistol……………………………………………………………………………...……..………23
Figure 7. Average flammability degree of 11 native woody species from Western Chaco region,
Argentina, at different sampling date along fire season (May to October) and rain season
(December to March). Same letters indicate no significant differences in flammability degree,
according to LSD Fisher pair-wise comparison procedure withα: 0,05, n=66
individuals…………………………………………………………………………….….……..24
Figure 8.Principal Component Analysis (PCA) of functional traits associated to flammability,
foliar persistence and growth habit for eleven natives woody species in Semiarid Chaco Region
(General trend). The ordination was based on six functional traits in six individuals per species.
FD=Flammability degree; LDMC=Leaf dry-matter content; TDMC=Twig dry-matter content;
DR=Degree of ramification; TDT=Twig drying time; PCO1= First principal coordinate,
represents growth habit; PCO2= Second principal coordinate, represents foliar persistence.
References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A. emarginata; 4. C. ehrenbergiana; 5. C.
microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S. lorentzii; 10. S. johnstonii; 11.
S. mistol…………………………………………………………………………………………………….25
Figure 9.Principal Component Analysis (PCA) of functional traits associated to plant
flammability, foliar persistence and growth habit, for eleven native woody species from Western
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
Chaco region, Argentina, at different sampling dates during fire season (A) May; (B) October;
and rain season (C) December; (D) March. The ordination was based on six functional traits in
six individuals per species. FD=Flammability degree; LDMC=Leaf dry-matter content;
TDMC=Twig dry-matter content; DR=Degree of ramification; TDT=Twig drying time; PCO1=
First principal coordinate, represents growth habit; PCO2= Second principal coordinate,
represents foliar persistence. References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A. emarginata;
4. C. ehrenbergiana; 5. C. microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S.
lorentzii; 10. S. johnstonii; 11. S. mistol…………………………………………………………26
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
1
RESUMEN
El conocimiento sobre las estrategias de las plantas para adaptarse y tolerar las perturbaciones
ambientales es un propósito fundamental para promover la conservación de la biodiversidad, en
el actual escenario de cambio climático. Nuestro objetivo fue evaluar la inflamabilidad de
especies nativas del Chaco semiárido desde un enfoque funcional, analizando variaciones
estacionales y el efecto de los disturbios. Se evaluaron ocho rasgos funcionales, 6 de ellos
vinculados a la inflamabilidad y dos referidos a persistencia foliar y hábito de crecimiento, en
once especies leñosas nativas de la región. Los mismos se compararon en bosques con diferente
historia de disturbios (BDHF): clausura y con disturbios como el fuego y rolados. Los resultados
indicaron que el 80% de la cobertura vegetal del Chaco Semiárido tiene grado de inflamabilidad
(GI) de media a elevada. Los rasgos funcionales de mayor influencia en la inflamabilidad fueron
el contenido de materia seca en ramas y hojas (CMSR y CMSH), la fenología foliar y el hábito
de crecimiento. La especie con mayor GI (Muy Alta) es Senegalia gilliesii, un arbusto de
arquitectura ramificada y elevado CMSR y CMSH, mientras que las especies con menor GI
(Media), se caracterizan por ser especies arbóreas con bajo CMSR. Se identificaron 2 picos de
inflamabilidad uno a finales de la temporada de fuego y otro al final de la temporada de lluvias,
relacionados a la fenología foliar y las condiciones climáticas durante la temporada de fuego. No
se encontraron diferencias significativas en la inflamabilidad de las especies en BDHF. Esto
representa un avance significativo para el estudio de la inflamabilidad de combustibles en bosques
chaqueños y contribuirá a mejorar las actividades de gestión de combustibles, prevención y
extinción de incendios.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
2
ABSTRACT
Knowledge about plant strategies for adapting and tolerating the environmental disturbances is a
fundamental purpose to promote biodiversity conservation, in the current climate change
scenario. Our objective was to evaluate the flammability of native species from Western Chaco
region through a functional approach, analysing seasonal variations and the effects of disturbances
on flammability. We evaluated eight functional traits, six of them related to flammability and two
referred to growth habit and foliar persistence, in eleven native woody species of the region. Those
traits were compared in forest with different disturbance history (FDDH): closure and
disturbances as fire and roller chopper applications. The 80 % of plant cover from Western Chaco
region forests have Medium to High flammability degree (FD). Functional traits more incident
on flammability were twig and leaf dry-matter content (TDMC and LDMC), foliar persistence
and growth habit. The unique species with Very High FD was Senegalia gilliesii, a shrub with
complex architecture and high TDMC and LDMC. Lowest flammability species (Medium FD)
were tree species with low TDMC. We identified two flammability peaks, one at the end of fire
season and the other at the end of rainy season, related to foliar persistence and climatic conditions
during fire season. There were no significant differences in the FD for studied species in FDDH.
These results represent a significant advance for fuels flammability studies in the Chaco region
and it will contribute to improve the activities of fuel management, prevention and firefighting.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
3
I. INTRODUCCIÓN GENERAL
Los incendios forestales se han convertido en un fenómeno recurrente que afecta la
dinámica poblacional de los ecosistemas tropicales; se estima que aproximadamente el 50% de
la superficie global actualmente afectada por el fuego corresponde a áreas tropicales. A
pesar de ello, las causas y efectos sobre la vegetación no han sido estudiados con profundidad en
gran parte de los países tropicales y subtropicales de Latinoamérica (Neri, Rodríguez y Contreras,
2009). El conocimiento sobre el comportamiento del fuego y sobre las características y
propiedades de los combustibles forestales es fundamental para el planeamiento de
estrategias preventivas y de las actividades de restauración de áreas quemadas. Es así como
instituciones como el INTA (Instituto Nacional de Tecnología Agropecuaria), emplean los datos
proporcionados por investigaciones de esta naturaleza, para la elaboración de manuales,
protocolos y capacitaciones con el fin de mitigar los efectos del fuego y la ocurrencia y
propagación de incendios forestales (Instituto Nacional de Tecnología Agropecuaria [INTA]
2014).
El fuego no constituye una amenaza a los ecosistemas, por el contrario, es un proceso natural
de los mismos (Agee, 1993); sin embargo, su recurrencia ha aumentado a causa del cambio
climático y de cambios en el uso de la tierra. Los factores antropogénicos como la transformación
y degradación de zonas forestales ocasionada por la expansión de la frontera agrícola, la
sobreexplotación de los recursos naturales y la deforestación, entre otras, han conducido a la
alteración de los regímenes naturales del fuego, lo que se ha convertido en una problemática a
nivel mundial aún en grandes áreas boreales y tropicales (Neri, Rodríguez y Contreras, 2009;
Conafor, 2012).
Los combustibles forestales son uno de los factores determinantes en la severidad y
recurrencia de los fuegos. Se define como combustibles forestales a “(…) cualquier
sustancia o compuesto susceptible de encenderse y mantener un proceso de combustión”.
Están constituidos por materia orgánica, abarcando tanto la biomasa de las plantas vivas y como
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
4
sus restos muertos; éstos combustibles al interactuar con el tiempo atmosférico y las
condiciones topográficas conducen el fuego, cuya intensidad, velocidad y dirección de
propagación puede variar de acuerdo a la disponibilidad y distribución espacial de estos
combustibles (Conafor, 2012).
Un rasgo determinante del comportamiento del fuego es la inflamabilidad, la cual es un aspecto
clave para las tareas de gestión de incendios forestales. La gestión forestal preventiva considera
la necesidad del manejo de combustibles atendiendo a las características que le son propias,
con el fin de reducir los efectos ecológicos, sociales y económicos de los grandes incendios
(CREAF, 2003). La inflamabilidad se entiende como la capacidad de un combustible para entrar
en ignición y sostener el fuego. Esta considera cuatro aspectos: la combustibilidad que hace
referencia al calor desprendido durante la ignición, la ignitabilidad, que aborda la facilidad de un
material para entrar en ignición, la consumibilidad, que consiste en la proporción de un
combustible que entró en combustión y la sostenibilidad que analiza la duración de la
combustión (Anderson, 1970; Martin et al., 1994). Estos componentes de la inflamabilidad se
encuentran en estrecha relación con el contenido de agua de hojas, ramillas y ramas y con la
arquitectura del canopeo (Cornelissen et al., 2003; Pérez Harguindeguy et al., 2013) y es
considerado un concepto complejo, ya que puede ser analizado a escala individual como de
comunidad (Pausas y Moreira 2012).
Algunos trabajos han puesto énfasis en el efecto de los rasgos foliares sobre la
inflamabilidad de los combustibles, estudiando entre otros el contenido de humedad y tamaño de
las hojas, área foliar específica y resistencia de la lámina en diferentes especies (Gill et al., 1996;
Blackhall et al., 2012). Otros, se han enfocado en los aspectos bioquímicos vinculados a la
inflamabilidad de los combustibles como la presencia de resinas, aceites, terpenoides
considerados promotores del fuego (Ormeño et al., 2008; Zhao et al., 2012), y otros compuestos
como la presencia de sales de calcio, fosfatos de amonio, sulfatos de amonio, silicatos, entre otros,
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
5
que parecen actuar como retardantes del fuego y podrían contribuir como elemento de
prevención (Liodakis et al., 2006; Scarff y Westoby, 2008).
Pausas y Moreira (2012), han sugerido que la inflamabilidad puede variar acorde a la recurrencia
de fuego y que en sitios con una baja frecuencia de estos eventos las especies son menos
inflamables y de menor densidad específica, lo que contribuye reducir el tiempo de residencia
del fuego.
El Chaco semiárido de Argentina es una de las regiones donde el fuego y las inundaciones
constituyen los disturbios más frecuentes, responsables ambos del modelado del paisaje de
bosques, sabanas y pastizales (Bucher, 1982). Entre pastizales y sabanas, algunos corresponden
a formaciones de origen edáfico y otros de carácter antropogénico, producto del uso del
fuego desde tiempos precolombinos (Bravo et al., 2001; Kunst y Bravo, 2003 ;Torella yAdámoli;
2005). Los incendios se originan en pastizales y sabanas dominadas por especies altamente
inflamables como Elionurus muticus, Schinus molle y algunas latifoliadas herbáceas como Lippia
turbinata y Aloyssia gratissima. En los bosques del Chaco que han sido sobreexplotados o
sobrepastoreados, las especies arbóreas y arbustivas de madera dura coexisten con distintos
grados de dominancia, lo que crea diferentes situaciones de susceptibilidad a la ocurrencia y
propagación de incendios.
Como otras regiones semiáridas de América, los incendios podrían ser considerados una amenaza
para la conservación de la biodiversidad, de la estructura y funcionamiento de los bosques
(Kennard y Putz 2005). Sin embargo, hay antecedentes que sugieren una elevada capacidad de
resistencia al fuego de las especies de leñosas nativas del Chaco (Pinard y Huffman, 1997; Bravo
et al., 2001; 2006; 2008, 2014, Kennard y Putz 2005) lo que podría indicar una evolución bajo
condiciones de fuegos recurrentes. Sin embargo, no existen muchos antecedentes sobre la
influencia de rasgos morfológicos y estructurales sobre la inflamabilidad de los combustibles en
bosques del Chaco semiárido. Jaureguiberry (2012) analizó este carácter como rasgo funcional,
entre especies de leñosas y herbáceas nativas del Chaco seco de Argentina, determinando una
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
6
estrecha correlación entre la inflamabilidad y la altura de la planta y la forma de crecimiento.
Estudios a nivel de comunidad son muy interesantes, sobre todo en bosques discetáneos
multiespecíficos como los del Chaco. Las características climáticas de la región chaqueña
Argentina, caracterizada por un clima semiárido marcadamente estacional, produce
seguramente variaciones en la inflamabilidad de combustibles a lo largo del año (Kunstet al,.
2012, 2014). Por ello, la valoración de cambios estacionales en los rasgos morfológicos y
estructurales vinculados a la inflamabilidad es otra demanda de información básica, en la temática
de la ecología de fuego.
El propósito de este trabajo es evaluar la inflamabilidad de once especies leñosas nativas de
bosques del Chaco semiárido mediante la estimación de rasgos funcionales, analizar cambios
estacionales en la inflamabilidad de los combustibles vegetales y evaluar el efecto de los
disturbios en la inflamabilidad. Estos resultados se encuentran en el Capítulo I del presente trabajo
y podrían contribuir en la gestión futura de los bosques chaqueños, ya que permitirán comprender
el comportamiento del fuego en estos ambientes y mejorar las tareas de control.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
7
II. CAPÍTULO I
FLAMMABILITY CHARACTERIZATION OF WOODY SPECIES IN SEMIARID
CHACO REGION, ARGENTINA, THROUGH FUNCTIONAL TRAITS ANALYSIS
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de
Argentina, a partir del análisis de rasgos funcionales
Ana Carolina Santacruz-García1, Sandra Bravo2
Abstract
The increasing tendency of wildland fires in the tropics have generated the urgent need of
knowledge about species flammability as an important input for risks management and prevention
plans of fires. The present work characterized the flammability of native species from Chaco
region through functional traits, analysed its seasonal variability and the effects of disturbances
on flammability. We selected eleven native woody species considering their representation within
native forests. A set of eight functional traits, six of them related to flammability (leaf dry-matter
content –LDMC-, twig dry-matter content -TDMC-, twig moisture content –TMC-, foliar
moisture content –FMC-, degree of ramification –DR- and twig drying time –TDT-) and two
describing growth habit and foliar persistence were evaluated at first time along fire season (May
to October) and then considering also rainy seasons within Chaco region. The 80 % of plant cover
from Western Chaco region forests have Medium to High flammability degree (FD) and the
functional traits more closely related to plant flammability were TDMC, LDMC, foliar
persistence and growth habit. The highest flammable species was Senegalia gilliesii, a shrub with
high DR and high LDMC and TDMC. The lowest plant flammability was observed in Cercidium
praecox, a tree species, with herbaceous and low LDMC. There was seasonal variability on plant
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
8
flammability with two peaks, at March and October but fuel desiccation was greater at the last
date accompanied by the lowest TDT. Flammability peaks at March could be related to high
foliation period and high LDMC in perennial species. There were no significant differences in
species flammability among forests with different disturbance history. Our results provide
valuable information that will contribute to improve efficiency of prevention activities, and
evaluations of fire behaviour.
Keywords
Disturbance effects, flammability, functional traits, seasonal variations.
1Consejo Nacional de Investigaciones Científicas y Técnicas CONICET and Instituto de Silvicultura y Manejo de Bosques –INSIMA.
Universidad Nacional de Santiago del Estero –UNSE. Belgrano 1912, Santiago del Estero (Capital),
Argentina..anacaro.santacruz@gmail.com. Corresponding author.
2 Instituto de Silvicultura y Manejo de Bosques –INSIMA. Universidad Nacional de Santiago del Estero –UNSE. Belgrano 1912,
Santiago del Estero (Capital), Argentina, sandrabrav@gmail.com
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
9
Resumen
El aumento de incendios forestales en los trópicos ha generado la necesidad de información básica
sobre características y comportamiento de combustibles para fortalecer los planes de prevención
de incendios. El conocimiento de la inflamabilidad de las especies se considera una valiosa
información para la determinación de la vulnerabilidad de las comunidades vegetales, la
prevención de incendios y en la restauración de áreas afectadas. El presente trabajo caracterizó la
inflamabilidad de once especies de leñosas nativas del Chaco semiárido a través de rasgos
funcionales, analizó su variación estacional y los efectos de los disturbios en la inflamabilidad.
Se seleccionaron once especies considerando su representatividad dentro de los bosques nativos
de la región de estudio y se evaluaron seis rasgos funcionales relacionados con la inflamabilidad
(contenido de materia seca en hojas –CMSH-, contenido de materia seca en ramas –CMSR-,
contenido de humedad en ramas –CHR-, contenido de humedad foliar –CHF-, grado de
ramificación –GR- y tiempo de secado de las ramas –TSR-) y dos que describen el hábito de
crecimiento y la fenología foliar. Se midieron atributos funcionales inicialmente a lo largo de la
temporada de fuego (mayo a octubre) y luego se considero la temporada de lluvias dentro de la
región chaqueña. El 80% de las especies que representan la cobertura vegetal del Chaco, se
caracterizan por tener inflamabilidad de Media a Muy Alta. Los rasgos funcionales de mayor
efecto sobre la inflamabilidad fueron CMSR, CMSH, fenología foliar y hábito de crecimiento. La
especie de mayor inflamabilidad fue Senegalia gilliesii, un arbusto con alto GR y alto CMSH y
CMSR. La especie con menor inflamabilidad fue Cercidium praecox, una especie arbórea, con
hojas herbáceas y bajo CMSH. Hubo variaciones estacionales en la inflamabilidad, y se
registraron dos picos, uno en marzo y otro en octubre. Sin embargo; la desecación de los
combustibles es mayor ésta última fecha en coincidencia con el menor TSR. El pico de
inflamabilidad en marzo podría estar relacionado con la foliación plena de todas las especies
estudiadas y con el alto CMSH en especies perennes. No se identificaron diferencias significativas
en la inflamabilidad de las especies en bosques con diferente historia de disturbios al menos con
los rasgos considerados en este estudio. Nuestros resultados proporcionan información valiosa
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
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que contribuirá a mejorar la eficiencia de las actividades de prevención y las evaluaciones de
comportamiento del fuego.
Palabras clave: Efecto por disturbios, inflamabilidad, rasgos funcionales, variaciones
estacionales.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
11
Highlights
- Native woody species from Western Chaco have medium to high flammability degree.
- The LDMC, the foliar persistence and growth habit influence species flammability.
- Foliar functional traits influence the seasonal variation of plant flammability.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
12
1. Introduction
The flammability of plant is defined as the propensity to burn and it represents a significant
functional trait especially in fire prone ecosystems such as those developed under Mediterranean
climate (Pausas et al. 2004; Pausas & Moreira, 2012). As a global tendency, wildfires are
increasing even in those ecosystems (rainforest, jungles) where they were no frequent
disturbances (FAO, 2016)
The vegetation structure and plant leaf traits are the main variables considered in fire behavior
models. Moisture content of branches, twigs and leaves influence plant flammability through the
drying-time of fuels. Expected flammability will be greater with high dry-mass content leaves
and low diameter twigs, which contribute to the fast fire propagation under dry atmospheric
conditions (low air humidity and standing winds) (Bradstock, 2016). Other plant attributes closely
related to plant flammability are volatile oils, waxes and resins contents, canopy architecture and
degree of ramification (Ormeño, 2008; Blackhall et al., 2012; Burger & Bond, 2015; Wyse et al.,
2016).
The common methods to plant flammability assessment involve measurements of small pieces of
plants under laboratory conditions. However, the entire plant flammability could vary broadly of
these assessments. As an alternative to these methods, a functional approach has been postulated
by Cornelissen et al. (2003) considering plant attributes related to flammability such as leaf and
twig moisture content, the dry matter content of twigs and leaves, ramification degree, among
others. This approach proposes five plant flammability categories considering variations ranks of
attributes related to plant flammability. More recently, Pérez-Harguindeguy et al., (2013)
following this approach, recommended the use of a low technology device (Jaureguiberry et al.,
2011) and functional attributes, to assign five categories of plant flammability obtained by
average (rounded to one decimal) of the each class scores. These flammability classes consider
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
13
quantitative and qualitative traits obtained by measuring standardized methods. The selected traits
are relatively easy to measure, closely related to flammability determined at laboratory (Pérez-
Harguindeguy et al., 2013).Therefore this combination of traits allow good estimation of plant
flammability at field and it has been checked in other studies on this issues (Jaureguiberry, 2012;
Wyse et al., 2106). This estimation are valuable for fuel management plans destined to as fire
forest prevention and extinction activities.
The native vegetation of Chaco region comprises a mosaic of forests, grasslands, savannas and
shrublands, where fire has been a frequent ecological event, at least during the last two centuries
(Morello & Adamoli 1974; Prado, 1993; Bravo et al., 2001),). These vegetation units currently
are experimenting strong changes in land uses and disturbances regimes (Tálamo & Caziani,
2003; Grau et al., 2005; 2014; Gasparri & Grau, 2009, Bravo et al., 2010). Chaco forests are
considered as a high priority conservation area (Dinerstein et al. 1995, Torrella et al., 2015).The
continuity of grasslands, savannas and forests in Chaco region represents wide contact surfaces
of different types and fuel models and land uses. Elionurus muticus Spreng. (aibe), is the grass
species dominant in these open areas with values of plant cover among 30 to 90%. This species
propagates easily wildfires and fires initiated by farmers. Its flammability has been attributed to
a high content of citral terpenes in its foliage and a high rate of fine fuel production(Burkart, 1969;
Bravo et al., 2001; Kunst et al., 2012). Fires can propagate into forests according environmental
conditions and fuel moisture content (Argañaraz et al., 2016).
The objectives of this work were to characterize the flammability of eleven native woody species
from Argentine Chaco region through functional traits, to evaluate the seasonal variability and
the effects of disturbances on plant flammability.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
14
2. Material and methods
2.1 Study area
The study area was located in Argentine Western Chaco region (Fig. 1). This region is
characterized by a seasonal semiarid climate, with the most rainfall concentrated from October to
March. The average temperature of the coldest month (July) is 10.6 ºC and the average
temperature of the hottest month (January) is 26.1 ºC (Boletta et al., 2006). The Western Chaco
region includes the South American heat polo with maximum temperatures of hottest month
above 47 ºC (GTZ, 2006).
Figure 1. Study area and sites localization in (A) American Chaco Region, (B) Santiago del Estero Province
included in South extreme of American Chaco Region, (C) Sampling sites localization at Experimental
Ranch Francisco Cantos belonging to the National Institute of Agricultural Technology (INTA).
C
A B
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
15
The average annual precipitation is 574 mm (annual series from 1934-2000, INTA climatic
record). The dry season extends from May to October, with a notably diary thermal variation and
strong deficit moisture, increasing over dry season.(Fig.2)The fire season coincides with dry
season in Western Chaco region, but some fires can occur out it under unusual environmental
conditions or human activities such as residues burns in urban-rural interfaces
Figure 2. Temperatures (continuous line), monthly rains (vertical bars) and average dates of the first and
last frosts in the Experimental Ranch “Francisco Cantos”, INTA EEA Santiago del Estero. The rectangle
indicates fire season in the Chaco region’s central zone. Climatic data period 1981-1990, EEE
Meteorological Observatory Santiago del Estero, INTA. Source: Kunst & Bravo, 2003.
The sampling sites were located in the Experimental Ranch “Francisco Cantos”, belonging to the
National Institute of Agricultural Technology (INTA), Santiago del Estero, Argentina (28°03’S
64°15’E) (Fig. 1). This Experimental Ranch has an extension approximated of 8000 has and
contents patches of forests, grasslands and savannas typical of Chaco region, in good conservation
state.
Aspidosperma quebracho-blanco Schltdl. (quebracho blanco) and Schinopsis lorentzii (Griseb.)
Engl. (quebracho colorado) are the two dominant tree species of the upper stratum reaching over
20m height. The medium forest strata can reach 7 to 12m height and are common Prosopis nigra
Griseb (algarrobo negro), Sarcomphalus mistol (Griseb.) Hauenschild (mistol), Cercidium
praecox (R. et P.) Harms (brea) and Geoffroea decortican sGillies ex Hook. &Arn, (chañar).In
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
16
the understory are common several Acacia, Celtis and Prosopis species, Atamisquea emarginata
Miers ex Hook.&Arn(atamisqui), Moya spinosa Griseb.(abreboca),accompanied by juvenile
individuals of S. lorentzii and A. quebracho-blanco (Brassiolo, 2005).In the herbaceous layer, the
most common grass species are Trichloris crinite (Lag.) Parodi, Trichloris pluriflora E. Fourn.,
Pappophorum pappiferum (Lam.) Kuntze, Setaria leiantha Hack., and Gounia spp among others
broad leaf species (INTA,2015).
The woody species selected for this study were: A. quebracho-blanco and S. lorentzii, dominant
of upper forest stratum; S. mistol, C. praecox and Celtis ehrenbergiana,representing medium
forest stratum and C. atamisquea, Schinus spp., Larrea divaricata Cav., M. spinosa, Senegalia
gilliesii Steud.,and Condalia microphylla Cav.,typical of understory. The species selection took
account floristic inventories of the study area (Araujo et al. 2008) and the criteria of the most
abundant species defined by those that, together, make up about 70- 80% of the standing biomass
of the community (Cornelissen et al., 2003). The Table 1 shows botany family, growth habit and
foliar persistence for species selected for this study due to this traits will be used in discussions
about plant flammability. Names of species are according to classification system of Darwinion
Institute, National University of La Plata, Argentina. The foliar persistence was assigned
following botany descriptions of species by Palacio & Roger (2016).
Table 1. Botany family, foliar phenology and growth habit for the studied species.
Species Botany Family Growth Habit Foliar Persistence
Aspidosperma quebracho-blanco Schltdl. Apocynaceae Tree Perennial
Atamisquea emarginata miers Ex Hook.
&Arn.= Capparis atamisquea Kuntze Capparaceae Shrub Perennial
Celtis ehrenbergiana (Klotzsch) Liebm Celtidaceae Shrub Deciduous
Cercidium praecox (R. Et P.) Harms. Fabaceae Tree Deciduous
Condalia microphylla Cav. Rhamnaceae Shrub Perennial
Larrea divaricata Cav. Zygophyllaceae Shrub Perennial
Maytenus spinosa (Griseb.) Lourteig &
O´Donell= Moya spinosa Griseb. Celastraceae Shrub Deciduous
Sarcomphalus mistol (Griseb.)
Hauenschild Rhamnaceae Tree Deciduous
Schinopsis lorentzii (Griseb.) Engl. Anacardiaceae Tree Deciduous
Schinus johnstonii f.A. Barkley Anacardiaceae Shrub Perennial
Senegalia gilliesii Steud.) Seigler &
Ebinger = Acacia gilliesii Steud. Fabaceae Shrub Deciduous
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
17
Sampling sites were selected employing satellite images and a record of recent land uses of
Experimental Ranch of INTA. Sampling sites were located in forests with two different
disturbance histories: a) disturbed forests (DF) with by wildfires and roller chopping applications
to control of shrub encroachment and improve the pasture growth for livestock (Kunst et al. 2012)
and, b) forests under closure (CF) without disturbances over three last decades (Fig. 3). Past fire
events were detected by fires scars, charred barks and carbonized woods on soil. The roller
chopping was informed as low severity event by personnel of Experimental Ranch. The study
was performed in 2015 – 2016 and a 150 x 150 m plot was delimited in each sampling sites. The
control and disturbed plots were emplaced about 4000 m of distance among them. In each
sampling sites, six mature and healthy individuals from each species were selected for this study
(Palacio & Roger, 2016)
Figure 3. Study sites: (A) Satellite image of the Experimental Ranch “Francisco Cantos” belonging to the
National Institute of Agricultural Technology (INTA), Argentina, (B) Control plot, a forest under closure,
without disturbances over three last decades (C) Disturbed plot, disturbed forests with fires and roller
chopper applications.
A
B
C
B C
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
18
2.2 Functional traits of plant flammability
The variables related to flammability considered in this work were: leaf dry-matter content
(LDMC), twig dry-matter content (TDMC), foliar moisture content (FMC), twig moisture
content (TMC),twig drying time (TDT) and degree of ramification (DR). Measures were made
following Pérez-Harguindeguy et al. (2013), tacking account the functional approach of this
work. The foliar persistence and growth habit were considered as other explicative variables in
the statistical analysis.
The LDMC and TDMC assessments were made in two twigs with diameter <2.5 cm and 20 cm
length, extracted from each individual. The FMC, TMC and TDT assessments were made on the
same material and for the last variable we took account time (days) until reach constant weight.
The fresh weight of samples was recorded using a balance Sartorius with 0.001 g. Then, material
was dried in controlled temperature oven at 40°C, until reach constant weight. The LDMC and
TDMC (mg. g-1) were assessed by ratio among oven-dry mass (mg) and water-saturated fresh
mass (mg). The degree of ramification was used as a predictor of canopy architectural complexity.
We measured the number of nodes and/or branches along a 1 m length branch segment (from the
top to bottom) and we categorized values obtained in a scale from 0 (no branches) to 5 (four or
more orders of ramifications). Values obtained of each variable considered were used to assign a
flammability category of each species. Each flammability category was calculated as average
class value (rounded to 1 decimal) of overall traits considered in this work, identifying five
flammability categories (From 1 to 5).In this work, we considered the three (3), four (4) and five
(5) flammability degree, from Perez- Harguindeguy et al. (2013), as categories named as Medium,
High and Very High flammability.
2.3 Seasonal variations of flammability
The seasonal variations of flammability of species selected were studied considering the fire
season in Western Chaco region from Argentina (Fig. 2; Kunst & Bravo, 2003). At first step, the
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
19
assessments were carried out in three dates along fire season: June, August and October. Along
fire season the vegetation experiments changes in plant moisture content and phenological state
due to its extended duration (six months). This fact can modify the fuel conditions for fire
propagation (Kunst & Bravo 2003; Bravo et al., 2014). The sampling was carried out in both
types of forests (CF and DF), testing simultaneously disturbance effects. In a second step, we
studied the annual variation of flammability among species, selecting March. May, October and
December as sampling dates. These dates allowed us to analyze seasonal changes in functional
attributes of species closely related to flammability (Fig. 2).
2.4 Statistical data analysis
For assessment of disturbances effects on flammability, data were analyzed through a general
lineal model (GLM) using sampling site and fire date as fixed effects. When the study area was
delimitated to disturbed forest (DF), a generalized linear mixed model (GLMM) was performed
to the assessment of seasonal variations of plant flammability, using Poisson distribution and fire
date and species as fixed effects. A Cluster Analysis was performed, including growth habit and
foliar persistence, using Ward method and Euclidean distance, in order to establish flammability
groups. Correspondence analysis were performed to identify associations between categorical
traits and flammability groups. Principal Component Analysis (PCA) were used to determine the
association between FD and LDMC, TDMC, FMC, TMC and TDT. To incorporate growth habit
and foliar persistence in the PCA, a principal coordinates analysis were performed before. The
statistical software used was Infostat/2017 (InfoStat Group, Universidad Nacional de Córdoba,
Argentina) with a α= 0.05.
3. Results
3.1 Disturbance effects
The Table 2 shows the average of six functional attributes evaluated during three sampling dates
along fire season (June, August and October) in the eleven woody species studied. Results
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
20
considering LDMC, TDMC, FMC, TMC, TDT and DR, did not indicate significant differences
in the FD between sites with different disturbance history in neither sampling date. The 63.64 %
of species studied showed FD High and Very High according the categories given by Pérez
Harguindeguy et al. (2013). There were significant differences in the flammability throughout the
fire season (Fig. 4). Flammability degree increased from August to October, without significant
differences among these sampling dates. These preliminary results guided the selection of DF as
study area of plant flammability of native woody species and encouraged the study about seasonal
variations in functional attributes on a wider temporal framework.
Figure 4. Flammability degree (FD) in native woody species from Western Chaco region, Argentina, along
fire season (June, August and October) in forests with different disturbance history. CF= Forest under
closure (without disturbances over three last decades, considered as reference condition) DF=Disturbed
forest with fires and roller chopping with management goal. Different letters indicates significant
differences between sampling dates, according to LSD Fisher, Tukey and Di Rienzo, Guzmán, Casanoves
(DGC) pair-wise comparison procedure with α: 0,05, n=66 individuals by site each sampling date.
CF DF
June August October0,00
1,00
2,00
3,00
4,00
5,00
FD
BC
A A
C
AB ABC
A A
C
AB A
CF DF
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina, a partir del análisis de rasgos funcionales
21
Table 2. Average (A) and Standard Deviation (SD) for six flammability functional traits evaluated in eleven native species from Western Chaco region, Argentina, during three
sampling dates for fire season (June, August and October) in forest with different disturbance history. CF= Forest under closure, without disturbances over three last decades,
considered as reference condition; DF=Disturbed forest with fires and roller chopper applications. References: TDMC=Twig dry-matter content (mg*g-1); TDT=Twig drying
time (days); LDMC=Leaf dry-matter content (mg*g-1); TMC= Twig moisture content (%); FMC=Foliar moisture content (%); DR=Number of ramifications orders; FD=1 to 5
categories following Pérez-Harguindeguy et al. 2013.
Species Site TDMC TDT LDMC TMC FMC DR FD
A SD A SD A SD A SD A SD A SD A SD
A. quebracho-blanco CF 619,74 209,13 2 1 504,68 58,06 38,03 20,91 49,53 5,81 4,33 0,58 3,9 0,6
DF 469,66 48,90 2 2 557,64 24,17 53,03 4,89 44,24 2,42 4,33 0,58 3,8 0,3
A. emarginata CF 603,61 36,82 3 0 524,07 31,97 39,64 3,68 47,59 3,20 4,33 1,15 3,6 0,1
DF 495,96 54,01 3 2 511,87 23,07 50,40 5,40 48,81 2,31 3,67 1,53 3,5 0,3
C. ehrenbergiana CF 671,72 161,66 2 1 466,86 101,23 32,83 16,17 53,31 10,12 3,33 1,15 3,7 0,2
DF 550,99 166,25 1 1 484,37 106,92 44,90 16,62 51,56 10,69 3,33 1,15 3,6 0,5
C. praecox CF 645,08 98,99 4 1 421,00 0,00 35,49 9,90 57,90 0,00 3,67 0,58 3,6 0,5
DF 568,71 43,28 3 1 301,66 0,00 43,13 4,33 69,83 0,00 4,00 0,00 3,6 0,4
C. microphylla CF 575,85 246,44 2 1 507,29 46,37 42,41 24,64 49,27 4,64 5,33 2,08 3,8 0,6
DF 585,86 15,45 3 1 485,49 19,22 41,41 1,55 51,45 1,92 4,67 1,53 3,4 0,3
L. divaricata CF 512,14 108,38 2 1 515,98 32,59 48,79 10,84 48,40 3,26 5,33 0,58 3,6 0,3
DF 415,52 79,33 3 1 508,58 67,96 58,45 7,93 49,14 6,80 4,67 1,15 3,5 0,3
M. spinosa CF 593,58 37,73 3 2 546,10 22,50 40,64 3,77 45,39 2,25 3,33 1,15 3,6 0,3
DF 592,53 33,16 3 2 559,25 18,70 40,75 3,32 44,07 1,87 4,33 1,53 3,8 0,4
S. mistol CF 692,66 186,56 2 1 459,05 10,06 30,73 18,66 54,10 1,01 4,00 1,00 3,7 0,6
DF 563,01 126,95 2 1 470,66 52,31 43,70 12,70 52,93 5,23 4,00 1,73 3,6 0,4
S. lorentzii CF 576,44 92,75 3 0 467,40 20,27 42,36 9,27 53,26 2,03 4,00 1,00 3,5 0,4
DF 585,71 88,74 3 1 491,36 24,34 41,43 8,87 50,86 2,43 3,67 1,15 3,5 0,3
S. johnstonii CF 568,69 16,35 2 1 509,71 28,68 43,13 1,63 49,03 2,87 6,00 0,00 3,6 0,3
DF 518,95 78,59 2 1 519,93 30,76 48,11 7,86 48,01 3,08 5,00 1,73 3,7 0,2
S. gilliesii CF 567,57 68,84 2 1 516,99 71,28 43,24 6,88 48,30 7,13 5,67 0,58 3,8 0,2
DF 592,45 137,35 3 1 481,19 19,09 40,76 13,74 51,88 1,91 4,67 0,58 3,7 0,0
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
22
3.2 Interspecific variation of flammability
Flammability degree varied among 3,3 in C. praecox and 4,1 in S. gilliessi. )The 63.64 % of
species studied presented FD values are included in High to Very High flammability categories
according to Pérez-Harguindeguyet al. (2013). ANOVA did not indicated significant differences
in FD among eleven studied species, considering exclusively LDMC, TDMC, TDT, TMC, FMC
and DR (Fig. 5). A Cluster Analysis including the three FD categories assigned (Medium, High
and Very High), growth habit and foliar persistence of species studied allowed us a better
identification the three functional species groups with different flammability (Fig. 6).
Figure 5. Flammability degree (FD) in native woody species from Western Chaco region, Argentina,
following Pérez Harguindeguy et al. (2013). Same letters indicate no significant differences between
species, according to LSD Fisher pair-wise comparison procedure with α: 0,05, n=66 individuals.
References: 1=S. gilliesii; 2=L. divaricata; 3=C. microphylla; 4=S. lorentzii; 5=S. johnstonii-,
6=M.spinosa; 7=C. ehrenbergiana; 8=A. quebracho-blanco;9= A.emarginata; 10= S. mistol; 11=C.
praecox.
Medium flammability species are characterized by tree growth habit, herbaceous and perennial
leaves, with low dry-matter content. High flammability species are characterized by shrubby
growth habit, perennial and coriaceous leaves, with high leaf dry-matter content. Senegalia
gilliesii was the unique species with Very High flammability degree, with shrubby growth habit,
high degree of ramification, and high leaf and twig dry-matter content (Fig. 6)
1 2 3 4 5 6 7 8 9 10 110,00
1,00
2,00
3,00
4,00
5,00
FD
A
A AA A A A A A A
A
A
A AA A A A A A A
A
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
23
Figure 6. Dendrogram resulting from cluster analysis (Ward method and Euclidean distance) for eleven
native woody species from Western Chaco region, Argentina; based on six functional traits related to
flammability, foliar persistence and growth habit. References: SG=Senegalia gilliesii; AQB=Aspidosperma
quebracho-blanco; AE=Atamisquea emarginata; CM=Condalia microphylla; LD=Larrea divaricata;
SJ=Schinus johnstonii; MS=Maytenus spinosa; CE=Celtis ehrenbergiana; SL=Schinopsis lorentzii;
CP=Cercidium praecox; SM=Sarcomphalus mistol.
3.3. Seasonal variations of flammability
The analysis of generalized linear mixed model (GLMM) considering LDMC, TDMC, FMC,
TMC, TDT and DR showed significant differences in flammability along the year with two peaks
observed at March and October, without significant differences among them. The October peak
coincided with the maximum value of flammability observed in Chaco region fire season and
with the lowest values of drying time of leaves and twigs (Fig. 7). The lowest FD values
corresponded to May and December, without significant differences among them (Fig. 7).
0,00 1,52 3,04 4,56 6,09
SG
AQB
AE
CM
LD
SJ
MS
CE
SL
CP
SM
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
24
Figure 7. Average flammability degree of 11 native woody species from Western Chaco region, Argentina,
at different sampling date along fire season (May to October) and rain season (December to March). Same
letters indicate no significant differences in flammability degree, according to LSD Fisher pair-wise
comparison procedure withα: 0,05, n=66 individuals.
The Principal Component Analysis (PCA) of functional traits associated to flammability (LDMC,
TDMC, TDT and DR), and the two first coordinates of the Principal Coordinate Analysis for
foliar persistence and growth habit traits, explained for the two first axes the 75% of the data
variability, and showed that TDMC and growth habit (tree or shrub) are the functional traits more
incident on flammability (Fig. 8). In the Principal Coordinates Analysis, the PCO1 axis separated
tree growth habit species from shrub growth habit species. The PCO2 separated perennial species
from deciduous species. FMC and TMC were not considered in this analysis in order to avoid
redundancy in the PCA, owing to the strong association to LDMC and TDMC.
The first component principal (PC1) explained the 47,6% of variability and separated species
according their growth habit, considering the flammability groups established (Fig. 6). PC1
separated Medium flammability group, conformed by tree species from High and Very High
flammability groups, conformed by shrubby species. The second component principal (PC2)
explained the 28,4% of variability and separated species according their foliar persistence.
Regardless of season, general trend indicated that the more incident functional traits on
March May October December0,00
1,00
2,00
3,00
4,00
5,00
FD
A
C
AB
BC
A
C
AB
BC
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
25
flammability were TDMC, LDMC and DR, followed by growth habit, foliar persistence and
TDMC (Fig. 7).
Figure 8. Principal Component Analysis (PCA) of functional traits associated to flammability, foliar
persistence and growth habit for eleven natives woody species in Semiarid Chaco Region (General trend).
The ordination was based on six functional traits in six individuals per species. FD=Flammability degree;
LDMC=Leaf dry-matter content; TDMC=Twig dry-matter content; DR=Degree of ramification;
TDT=Twig drying time; PCO1= First principal coordinate, represents growth habit; PCO2=Second
principal coordinate, represents foliar persistence. References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A.
emarginata; 4. C. ehrenbergiana; 5. C. microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S.
lorentzii; 10. S. johnstonii; 11. S. mistol
According to seasonal variations of functional attributes considered in this study, on May the
more flammable species were S. gilliesii, M. spinosa and L. divaricata (Fig 9 A). On October,
the more flammable species were A. emarginata, M. spinosa, S. johnstonii and L. divaricata (Fig
9 B). All them are shrubs with perennial and coriaceous leaves, and both sampling dates
corresponded to the Chaco region fire season. On December more flammable species were S.
gilliesii and C. microphylla and this period coincided with the beginning of rainy season in the
region. At this sampling date, the degree of ramification (DR), leaf dry-matter content (LDMC)
and growth habit (GH) were the most important functional traits on flammability (Fig 9 C). On
March, S. gilliesii, C. microphylla and A. emarginata. were the most flammable species (Fig. 9
-5,00 -2,50 0,00 2,50 5,00
CP 1 (47,6%)
-5,00
-2,50
0,00
2,50
5,00
CP
2 (
28
,4%
) 1
2
3
4
5
6
7
8 9
10
11
LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
1
2
3
4
5
6
7
8 9
10
11
LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
26
D) and TDMC, LDMC and DR were the more determinant traits of plant flammability. At least
60% of the information (variances) contained in the data were retained by the first two principal
components.
Figure 9.Principal Component Analysis (PCA) of functional traits associated to plant flammability, foliar
persistence and growth habit, for eleven native woody species from Western Chaco region, Argentina, at
different sampling dates during fire season (A) May;(B) October; and rain season (C) December; (D)
March. The ordination was based on six functional traits in six individuals per species. FD=Flammability
degree; LDMC=Leaf dry-matter content; TDMC=Twig dry-matter content; DR=Degree of ramification;
TDT=Twig drying time; PCO1= First principal coordinate, represents growth habit; PCO2= Second
principal coordinate, represents foliar persistence. References: 1. S. gilliesii; 2. A. quebracho-blanco; 3. A.
emarginata; 4. C. ehrenbergiana; 5. C. microphylla; 6. L. divaricata; 7. M. spinosa; 8. C. praecox; 9. S.
lorentzii; 10. S. johnstonii; 11. S. mistol
-4,00 -2,00 0,00 2,00 4,00
CP 1 (36,2%)
-4,00
-2,00
0,00
2,00
4,00
CP
2 (
25
,3%
)
12
3
4
56
7
8
9
10
11 LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
12
3
4
56
7
8
9
10
11 LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
March
-4,00 -2,00 0,00 2,00 4,00
CP 1 (39,8%)
-4,00
-2,00
0,00
2,00
4,00
CP
2 (
26
,6%
)
1
2
3
4
5
6
79
10
11
LDMC
TDMC
TDT
DRFD
PCO1
PCO2
1
2
3
4
5
6
79
10
11
LDMC
TDMC
TDT
DRFD
PCO1
PCO2
May
-4,00 -2,00 0,00 2,00 4,00
CP 1 (38,8%)
-4,00
-2,00
0,00
2,00
4,00
CP
2 (
33
,1%
)
2
3
4
5
6
7
10
11
LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
2
3
4
5
6
7
10
11
LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
October
-4,00 -2,00 0,00 2,00 4,00
CP 1 (32,6%)
-4,00
-2,00
0,00
2,00
4,00
CP
2 (
26
,5%
)
1
2
3
45
6
7
8 9
1011
LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
1
2
3
45
6
7
8 9
1011
LDMC
TDMC
TDT
DR
FD
PCO1
PCO2
December
A
C D
B
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
27
4. Discussion
The set of woody species studied represent 80 % of plant cover from Western Chaco region forests
(Araujoet al., 2008).The percentage of species with High or Very High flammability (63,64%)
suggests the Chaco forests could be considered a fire-prone vegetation type. Even though
functional traits considered in this work are directly related to plant flammability (Kunst et al.
2012; Pérez Harguindeguy et al. 2013; Burger & Bond 2015), multiple morphological and
biochemical traits (Diaz et al., 2013) contribute to enhance the plant ignitability, fire spread rate
and combustion rate modifying its behavior as fuel. Landi et al. (2017) informed that forest cover
is less flammable than grassland and shrublands in Chaco region attributing that to fine fuel
availability and fuel desiccation. Some aspects usually does no considered determinant on plant
flammability as growth habit and foliar persistence seem influencing the response of plant as fuel
during wildland fire.
The lack of significant differences in plant FD among sites with different disturbance history
could be related to the short time period considered in this analysis (only 3 decades under closure
in CF),to the plant community heterogeneity or low severity of disturbances within DF. Blackhall
et al., (2012) communicated that foliar flammability properties such as leaf moisture, leaf size,
and specific leaf area and leaf strength varied according time since last fire. Carbone & Aguilar
(2016) found differences in foliar area and, specific foliar area in perennial herbs from Argentine
Chaco Serrano, in areas with different fire frequency. Therefore, it is probable that foliar traits
analyzed in our work be less sensible to changes promoted by disturbances or these were low
severity events. Rosenblun (2015) considered that plant communities and fire regimes
heterogeneity make it difficult to discerner what result from fire suppression, which generating
the need to stand level studies to better management decisions. Time from the last fire and low
severity roller chopper applications could not represent an enough environmental pressing to
promote changes in flammability traits analyzed. Tálamo et al.,(2013) informed a high resilience
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
28
of native vegetation from Argentine Chaco region to common disturbances as logging, wildfires
and livestock. Therefore, null or slight changes in plant flammability traits could be expected, at
least in this preliminary approach.
Nevertheless, the seasonal variation of flammability along Western Chaco region fire season
observed in our work, with an increasing tendency at end of this season, agreed with data from
experimental fires to study effects of fuel moisture content (Kunst et al., 2014), and to assess the
fire severity on tree species within the same study area (Bravo et al., 2014).High severity fires are
expected at fire season end due to lower moisture content of fuels than early fire season (Kunst
& Bravo, 2003). These results suggest that variables considered in our work may be useful to
detect seasonal variations in plant flammability but could be less sensible to changes promoted
by disturbances.
The absence of significant differences in the FD among species studied (Fig. 5) in ANOVA could
be attributed to the set of functional traits used for its characterization (LDMC, TDMC, FMC,
TMC, TDT and DR) and the analysis of FD as categorical variable. The standard methods for
measurement and the categories of plant flammability proposed by Pérez Harguindeguy et
al.(2013) using quantitative and qualitative variables allowed us to assign categories 3, 4 and 5 to
the species studied which we named as Medium, High and Very high FD species. The inclusion
of growth habit and foliar persistence in the Cluster Analysis improved the identification of three
species functional groups with different FD. These category names were reaffirmed through field
observations of fire behavior during experimental burns in native forests from the same study
area, where differences in flammability, spread rate and intensity have been observed among some
species studied.(Kunst et al., 2012; Bravo et al., 2014-, Ledesma et al., 2018. Liodakis
and Kakardakis (2006) found also three different categories of plant flammability in seven
dominant Mediterranean plant species from wildland/urban interfaces in Athens, Greece
considering the ignition delay time, heat content, combustion duration and mass residues as
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
29
analysis variables. These authors named flammability categories as FD categories identified in
our study.
Species from same plant community can differ strongly in flammability traits, fire resistance,
tolerance and postfire regeneration strategies (Burger & Bond, 2015). The Medium FD species
group included to S. lorentzii and S. mistol, two of the three more important tree species of canopy
and medium stratum of Chaco forests, respectively (Araujo et al., 2008). High FD species
included shrubby species with perennial sclerophyllous foliage (high dry matter content leaves),
open canopy with high density of low diameter twigs. The unique species identified as Very High
DF species, S. gilliessi, has caducifolious foliage but the plant architecture seems promoting its
ignitability. The shrub-vegetation types are one of the more relevant landscape units of
Mediterranean climate areas. Shrublands from New Zealand, Australia and South Africa are
particularly propensity to fire recurrence (Anderson et al., 2015). The combination of traits such
low plant height, fine-branching and dense canopy, perennial leaves with high dry matter content
could be related to high flammability of shrub species studied (Allen, 2008).
Bond & Van Vilgen (1996) considered that water content and drying rates of plant parts are one
of the most important properties affecting flammability at level both individual plants and the
entire plant community. The study of seasonal variation of plant flammability tacking account a
wider temporal framework showed the highest flammability values at October (the end of fire
season within Chaco region) and March (the end of rainy season). Antecedents about fire behavior
in Western Chaco region (Kunst et al., 2014; Bravo et al., 2010; 2014) and Chaco Serrano
(Argañaraz et al, 2016) referred the importance of fuel availability and fuel desiccation level in
fire recurrence and severity. However, the maximum FD values obtained in our work (October
and March) did not differ significantly among them and coincided respectively, with the minimum
and maximum moisture content of fuels from Chaco region (Kunst et al., 2014). Our results
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
30
suggest that different factors could contribute to plant flammability at different climatic seasons
(fire and rainy) at community level.
In fact, the first PCA analysis regardless season, showed the influence of TDMC and DR on
species FD (Fig.7). In both two sampling dates along fire season (May and October) also TDMC
and LDMC were the factors more closely related to FD. The influence of LDMC on FD during
fire season (in coincidence dryness season in Chaco region) could be related to the percentage of
perennials among species studied (45%) and the short time period without leaves in caducifolious
species.. The greater variability of data explained when PCO1 (growth habit) and PCO2 (foliar
persistence) were added to PCA, agreed with functional traits of species groups of High and Very
high FD in Cluster Analysis. According to that, shrubby growth habit and coriaceous and
perennial leaves are the more flammable combination of traits during Chaco region fire season.
Flammability is expected to be greater with lower moisture content and high leaf dry matter
content (Cornelissen et al., 2003). The shrubby species architecture promote the air flux
indispensable to hold the combustion (Dickinson & Johnson, 2001) and this growth habit
represent to the 55 % of species studied (Table 1). The community level analysis suggests a high
flammability of shrubby stratum of Chaco forests. The high FD observed on March are closely
related to TDMC and LDMC in coincidence to maximum foliation of caducifolious species and
woody growth modules fully differentiated. Low diameter twigs and fully expanded leaves
present a high ratio surface/volume, facilitating the fast loss of humidity of tissues, and fuel
desiccation, in coincidence with hot winds and high air temperatures characterizing summers in
Chaco region. These considerations are very important to fire prevention activities which always
were concentrated on dry climate period in Chaco region. Argañaraz et al. (2016) considered de
LDMC is a strong indicator of fire danger for Argentine Chaco Serrano, with a seasonal variation
related to the annual precipitation.
The influence of growth habit and foliar traits seems be confirmed in results of Cluster Analysis
that allowed identifying three groups with different flammability among studied species. Medium
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
31
flammability species included tree deciduous species with herbaceous foliage. These species loss
the foliage during the most fire season and recover it at ending of this season, in coincidence with
October flammability peak. High flammability species included shrubby species with
sclerophyllous foliage (high dry matter content leaves) and open canopy with high density of low
diameter twigs. These traits contribute to fast dehydrating in dry environmental conditions,
increasing the ignitability. Blackhall et al. (2012) informed that shrublands in Northwest
Patagonia are dominated by species with high foliar flammability. In our work, Senegalia gilliesii
was the unique species with Very High flammability and it is characterized by a deciduous leaves
and a shrubby growth habit, notably sclerophyllous. These result reaffirmed the importance of
TDMC, DR and LDMC on plant flammability since dry matter content has a strong effect on
heat release rate (Madrigal et al., 2012). Carbone & Aguilar (2016) determined a LDMC
increasing in three herbaceous species, in different fire frequency scenarios of Chaco Serrano,
Argentina. Blackhall et al. (2012) considered that initial burns create a positive feed-backs
towards increased fire occurrence since promotes the replacement of fire-resistance forests by
shrublands dominated by resprouting species.
5. Conclusions
Our results represent a significant advance in fire ecology knowledge from Argentine Chaco
region. The functional approach using traits related to plant flammability allowed to identify
species groups with different FD and a seasonal variation of FD beyond the fire season in Western
Chaco region. As well, the results indicated the importance of growth habit and foliar persistence
on flammability of native woody species of Chaco forests. The functional traits considered in this
work did not allow us to identify significant differences in plant flammability among species and
among forests with different recent disturbance history. These aspects will be considered in future
studies with other traits considered also related to plant flammability as foliar area, specific foliar
area and biochemical flammable compounds (terpenes, tannins, and essential oils, among others).
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
32
6. Acknowledgements
Authors are grateful with authorities of Universidad Nacional de Santiago del Estero (UNSE) and
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) for funding our research
and providing support for equipment. Special acknowledgement to Universidad Distrital
Francisco José de Caldas, (UDFJC) Bogotá, Colombia, for supporting our work and scientific
assistance of reviewers. To the assistant personnel and colleagues from Cátedra de Botánica
General, FCF, UNSE for help to field work and to Engineers Ana Belén Cisneros and Jaime
Andrés Herrán, and Dr Pedro Jaureguiberry for advising us during the statistical data analysis
and whole investigation.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
33
III. CONCLUSIONES GENERALES
-El 63,64% de las especies evaluadas tienen inflamabilidad de elevada (Corresponden al 80% de
la cobertura vegetal del Chaco Semiárido), lo cual podría explicar la adaptación y resistencia de
las especies chaqueñas al fuego y la recurrencia de éste disturbio en la región.
-Los rasgos foliares son indicadores de inflamabilidad, al estar relacionada directamente la
biomasa foliar con la cantidad de combustible fino. Las especies con alto grado de inflamabilidad
se caracterizan por tener bajo porcentaje de humedad y alto contenido de materia seca en hojas y
ramas, siendo el contenido de materia seca en ramas y hojas (TDMC y LDMC) los rasgos con
mayor incidencia en la inflamabilidad. El contenido de materia seca se asocia directamente con
la resistencia de la planta a los disturbios, entre más alto sea éste rasgo indica mayor adaptación
y tolerancia a factores ambientales como fuego y sequía.
-El hábito de crecimiento es un factor determinante en el grado de inflamabilidad de una especie,
se encontró que las especies arbustivas tienen mayor grado de inflamabilidad que las especies
arbóreas, lo cual remarca la importancia de la arquitectura de la canopia en la inflamabilidad de
las especies.
-Hay una variación estacional en la inflamabilidad que podría estar relacionada a la fenología
foliar sumada a las condiciones climáticas durante la temporada de fuego. Los meses con mayor
grado de inflamabilidad (marzo y octubre) coinciden con los meses de mayor expansión foliar en
la región chaqueña. No obstante, la inflamabilidad es mayor en octubre, debido a las condiciones
de sequía en la que se encuentran los combustibles vegetales al estar finalizando la temporada de
fuego.
-El conocimiento sobre las estrategias de adaptación de las especies al fuego, proporciona
información valiosa sobre el rol de éste disturbio en las comunidades vegetales. La susceptibilidad
o la tolerancia de las comunidades al fuego influye directamente en los cambios en la
biodiversidad del ambiente afectado.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
34
IV. RECOMENDACIONES GENERALES
El conocimiento sobre las estrategias de adaptación de las especies al fuego, proporciona
información valiosa sobre el rol de éste disturbio en las comunidades vegetales. Por esta razón,
se considera importante para estudios posteriores evaluar el contenido de hojarasca y el porcentaje
de ramas muertas. La proporción de biomasa muerta debajo de la planta durante la estación seca
es crítica para la inflamabilidad (Pérez-Harguindeguy et al., 2013). El material vegetal muerto
contribuye a bajas tasas de acumulación de agua, incidiendo directamente en la inflamabilidad de
la planta. Otros rasgos importantes a considerar son el área foliar y el área foliar específica, ya
que estos son indicadores de la adaptación y resistencia de las especies a factores ambientales
disturbantes.
Otra línea de investigación interesante es la composición bioquímica de las especies, compuestos
como resinas, aceites esenciales y terpenos, contribuyen marcadamente a la inflamabilidad de las
especies. El estrés producido por los incendios, sobre la mayor parte de las comunidades vegetales
promueve la síntesis y/o liberación de metabolitos secundarios, muchos de ellos volátiles, que
predisponen a la vegetación a nuevos eventos de características similares o aún de mayor
severidad.
Evaluar la respuesta metabólica y los rasgos funcionales propuestos, puede contribuir a la
interpretación del comportamiento de las especies frente al fuego, a nivel de poblaciones y
comunidades. La producción de información básica para determinar la vulnerabilidad de las
coberturas vegetales a incendios es una demanda de gran importancia para la gestión de
recursos naturales.
Caracterización de la inflamabilidad de especies leñosas en el Chaco semiárido de Argentina,
a partir del análisis de rasgos funcionales
35
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