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Wood with fire wounds: (A, B) Fire scars A. A. quebracho-blanco. (B) S. lorentzii. (C, D) Discoloured wood C. P. nigra. D. A. furcatispina. (E, F) Fire marks E. A. quebracho blanco. F. S. lorentzii.
Source publication
The Chaco region is one of the most extensive areas of dry forests and savannas in South America and fire plays a major role in its ecology. We studied the types of wounds caused by fire on the native woody species of Chaco and evaluated their suitability for fire dendroecological studies. The selected species were “quebracho colorado santiagueño”...
Contexts in source publication
Context 1
... tissue at the edges of the wound contributing to the wound closure. In the field, fire scars showed the typical triangular shape when extending from the bole base, or lenticular shape when there were elevated from the ground level. Cross-sections with fire scars displayed kidney-type shapes of compensatory wood growth near the wound ( Figs. 2A and B). The wood formed before the fire action has improved discoloration due to heat transference during the fire event. Discoloured wood was separated from normal wood by the accumulation of dark substances (Fig. 2C). The compartmentalisation of discoloured wood by means of tannin and gum secretion was more notable in samples of S. ...
Context 2
... from the ground level. Cross-sections with fire scars displayed kidney-type shapes of compensatory wood growth near the wound ( Figs. 2A and B). The wood formed before the fire action has improved discoloration due to heat transference during the fire event. Discoloured wood was separated from normal wood by the accumulation of dark substances (Fig. 2C). The compartmentalisation of discoloured wood by means of tannin and gum secretion was more notable in samples of S. lorentzii and P. nigra than others species. Percentage of damage to the bole perimeter was highly variable among samples of the same specie. This variability was in part due to the presence of small, intermittent lesions ...
Citations
... Moreover, some native woody species in the Argentine Chaco region are particularly appropriate for dendroecological studies as they survive fires but are affected by different types of fire injuries or scars that remain identifiable for a long time (Bravo et al., 2008). Some common native trees in the Chaco forests, such as Schinopsis lorentzii and Aspidosperma quebracho-blanco, several of the medium-size species, such as Neltuma alba, Neltuma nigra and Neltuma pugionata, and some understory species, such as Vachellia aroma and Senegalia gilliessi, are suitable for such studies as they usually exhibit characteristic post-fire effects. ...
... In the Argentine Chaco region, plant survival is due to a combination of the protection of sensitive tissues and the resprouting ability. Some woody species in this region, such as A. quebracho blanco, S. lorentzii, Neltuma alba and Neltuma nigra, can diminish the negative effects of fire on the cambium through the combination of bark thickness and density and thus maintain the tree growth habit (Bravo et al., 2001(Bravo et al., , 2008(Bravo et al., , 2010Bravo et al., 2021), whereas shrubby species, such as Vachellia aroma, Senegalia gilliesii and Schinus fasciculatus, accentuate their shrubby growth habit and thus intensify their resprouting capacity . Although bark density and thickness contribute to fire resistance and tolerance (Bravo et al. 2014), plant species can also increase fire resistance by relocation of buds. ...
Fire is a natural element of some tropical dry ecosystems. However, during the last decades, fire occurrence has become more frequent and intense due, in part, to climate change and land use transformation. This is the case in the Gran Chaco Americano, one of the largest dry forests all over the world that extends across Argentina, Paraguay, Bolivia and Brazil. Fire has shaped the Gran Chaco landscape since ancient times, but today, as in many other regions, the pattern, frequency, severity and intensity are being dramatically altered. Based on information collected mainly over the last two decades, this paper presents a detailed review of the available literature on the fire regime across the Gran Chaco region. Here, we present a multi- disciplinary understanding considering fire behavior and dynamics in the study ecosystem within a very specific ecological, administrative and historical framework.
A noteworthy aspect of this review indicates the clear imbalance between regions in terms of available literature; while information about the Argentine Chaco is abundant, the literature for the Paraguayan or Bolivian Chaco is practically non-existent. The rainfall gradient and drought periods are key climatic drivers of fire ignitions while cattle ranching is the main socioeconomic activity of this region and key precursor of forest fires. In general, a substantial part of the available information focused on ecological aspects of the fire regime as the effect of fires on plant functional traits such as bark thickness, resprouting ability and flammability patterns. Other post fire effects on soil, invasive species, herbivory and soil seed banks have been also explored in detail to understand ecosystem recovery and research needs. We finally highlight current necessities and future prospects, mainly related to soil burn severity (SBS), invasive species and wildlife impact. Although our study specifically focused on changes in the fire regime of the Gran Chaco, some generalities were further discussed about fire regimes that could be relevant for diverse fire-sensitive ecosystems in the tropics
... Wildfires can produce tree mortality during the event or generate fire wounds on wood called scars or marks that constitute an access window to pathogens such as fungi and insects after fires ( Figure 3); [11,12,6]. The process of fire scars and marks formation has been described for native tree species of Argentina (Medina, 2003; [13][14][15][16]) but their long-time effect on health and tree mortality has not been analyzed yet. The formation of decolored wood, white and brown rots, and insect galleries on the bole and shoots are the signals often observed in burnt trees and shrubs ( Figure 3). ...
... The compartmentalization of fire wounds and aptitude for healing is greater among tree species than shrubby species [13]. Among anatomical responses to fire damage have mentioned the increase in parenchyma proportion and the diminishing in vessels and fibber proportion, which could be related to higher susceptibility to pathogens, and the deterioration of health conditions after fires [12][13][14][15][16][17]. ...
... En el Chaco serrano, también se ha determinado que las especies leñosas se regeneran principalmente por rebrote posterior al fuego (Torres et al. 2013;Herrero et al. 2013). La intensidad del rebrote y los cambios de hábitos de crecimiento responden a características específicas como el tamaño del banco de yemas su localización y el grado de protección de las cortezas (Bravo et al. 2008(Bravo et al. , 2014. ...
... S. gilliesi fue la más afectada, mientras que S. bumelioides lo fue en menor medida. S. bumelioides es una especie que muestra un potencial regenerativo superior a las otras especies, dado principalmente por su banco de yemas (número y posición), fisiología y estructura (Bravo et al. 2008;2018). ...
El incremento de la biomasa aérea, cobertura y densidad de las especies leñosas, especialmente arbustivas, en detrimento de las gramíneas y eventualmente otros grupos funcionales, es un proceso muy común en ambientes subhúmedos a áridos. La coexistencia pastos-arbustos puede ser explicada mediante distintos mecanismos ecológicos, agrupados bajo dos grandes enfoques: competencia y demografía. Los mecanismos competitivos involucran entre otros, separación de nichos por exploración radical, competencia balanceada, relaciones de competencia y facilitación, mecanismos regenerativos, efecto almacenaje. El enfoque demográfico sugiere que los disturbios gobiernan la coexistencia pastos-arbustos a través del control sobre la demografía. El objetivo de este trabajo fue comprender los mecanismos ecológicos que regulan la coexistencia pastos-arbustos en el Chaco semiárido, mediante un estudio que contempla ambos enfoques. Los experimentos se realizaron en dos sitios ecológicos en la provincia de Santiago del Estero: alto, con un bosque de dos quebrachos y bajo, dominado por sabanas de Elionurus muticus. Para estudiar el mecanismo de separación de nichos por exploración radical vertical (Hipótesis de Walter) se desarrolló un estudio descriptivo de la distribución de raíces en el perfil del suelo. Además, se realizó un ensayo de remoción de especies para analizar el tipo de interacción que ocurre entre los grupos funcionales, con los tratamientos: a) remoción de arbustos, b) remoción de pastos y c) sin remoción (control) usando un Índice de Interacción. El efecto almacenaje fue analizado mediante el estudio de la emergencia y la habilidad para rebrotar de los arbustos en respuesta a la secuencia sinérgica de dos perturbaciones: mecánica y fuego. Los principales resultados fueron: a) el patrón de distribución radical encontrado responde parcialmente a la Hipótesis de Walter, ya que existe en ambos sitios ecológicos superposición de los sistemas radicales de pastos y arbustos en el perfil del suelo; b) en el bajo prevalecerían las relaciones de competencia, mientras que en el alto las relaciones neutrales y de facilitación; c) la emergencia de las plántulas varió en función del sitio, de la intensidad del fuego y del grupo funcional y d) la habilidad rebrotadora de los arbustos estuvo condicionada por la intensidad de las perturbaciones y por la especie. Esta tesis contribuye a comprender qué mecanismos ecológicos prevalecerían entre pastos y arbustos en los sitios de bosque y sabana del Chaco semiárido, y cómo las perturbaciones (tratamiento mecánico y fuego) influyen en los procesos regenerativos. Este conocimiento permitirá explicar a futuro los cambios en la estructura de las comunidades y en las funciones ecosistémicas, con el fin de generar recomendaciones de manejo más conservativas y sustentables.
... Sin embargo, este corto período de 8 años aquí analizado, puede ser el reflejo de una larga historia de dinámica de fuegos. Otras herramientas como la dendrología y la dendrocronología de especies nativas chaqueñas (Bravo et al., 2008), serán necesarias para una completa caracterización de la historia de fuegos. ...
... De esta manera, el carbono de los grupos 4 y 5 tuvo ganancia en estos altos niveles de ganadería. La presencia de grandes árboles, implica una enorme contribución de carbono acumulado en sistemas ganaderos (Lindenmayer et al., 2012;Fernández et al., 2020), por un lado atribuido a la longevidad de estos grupos funcionales de plantas leñosas (Bravo et al., 2008), pero la dinámica natural de la vegetación puede verse comprometida por las dificultades que conlleva si el manejo ganadero no es controlado. ...
Ciclo de carbono en biomasa de bosque con relación al régimen de disturbios en el Chaco seco argentino TESIS PRESENTADA COMO REQUISITO PARA OBTENER EL GRADO DE DOCTOR EN CIENCIAS Y TECNOLOGÍAS FORESTALES por Dante Ernesto Loto Licenciado en Ciencias Biológicas.
... Wildfires and grazing are the main disturbances affecting the physiognomy of the landscape (Blanco et al. 2005). The representativeness and vigor of P. pugionata individuals -even in these stressed and disturbed environments -justify carrying out studies about their fire survival aptitude and potential for dendrochronological studies (Grau et al. 2003;Bravo et al. 2008). ...
... We hypothesize that: (i) P. pugionata has distinctive growth rings, allowing for the accurate dating of tree rings, (ii) P. pugionata forms identifiable fire scars in the wood, and (iii) the bark of P. pugionata sufficiently protects the cambial tissue to resist wildfires, and plant size influences the cambial damage percentage on bole. These considerations are based on: (i) the literature that reports that other Prosopis species form annual growth rings, identifiable fire wounds suitable for dating wildfires and feasible tree ring dating Morales et al. 2001;Medina 2003;2008;Bravo et al. 2008;Bogino et al. 2015), and (ii) in other Prosopis species, the bark thickness protects cambial tissue, allowing them to survive low to medium fire severity wildfires (Bravo et al. 2001b;2008). However, the exceptional environmental conditions of the distribution area of P. pugionata (dryness, saline soils, scarce seasonal thermal amplitude) may produce different wood anatomy than other Prosopis species. ...
... The greater frequency of fire scars than of marks could be related to high susceptibility to fire in P. pugionata due to its thin barks and scarce increase in bark thickness with age (Bravo et al. 2006;2008). Fires marks have been related to low severity events in fire chronologies due to the slight alterations on wood growth and low magnitude of fire wounds (Bravo et al. 2008;Medina 2008). The lack of significant effect of age, diameter, total bark thickness and cross-section height on bole damage percentages in the fire wounds in P. pugionata could be attributed to the small size of sampled individuals and the low bark thickness increase rate with age, which contribute to fire damage even in low-intensity fires. ...
Prosopis pugionata (Fabaceae) is a halophyte tree species that grows exclusively in Argentina's arid environments, whose woodlands are mainly affected by fires and overgrazing. Here, we describe the wood anatomy and fire wounds of P. pugionata and their relationship with plant size and bark thickness. Besides, we attempt to determine the potential of P. pugionata for dendrochronological studies in order to date fire events throughout time. We tested the hypothesis that P. pugionataforms datable fire wounds, allowing its use for dendrochronological studies. The study area is located in the arid Argentine Chaco region. Seventeen individuals, varying from 15 to 65 years of age, were randomly sampled and bole disks were taken at 0.3, 1.3 and 2.3 m high. P. pugionatais a diffuse and semi-ring-porous hardwood species with growth rings delimited by marginal parenchyma bands. The bark is longitudinally fissured, with an average thickness of 0.19 cm, and a scarce increase with age. Seventy-seven percent of the samples showed fire wounds (n = 46). We identified fire scars (70%) and marks (30%), and differentiated them by wood growth interruption in the former. Sixty-one percent of fire wounds affected less than 20% of the cambial perimeter and there were no significant effects of age, bole diameter, bole height and bark thickness on the cambial damage percentage. After cross-dating, P. pugionata showed a mean correlation value between series of 0.5, which represents an accurate potential for dendrochronological studies. Twenty wildfires were dated from 1943 to 2007 in the study area with a fire frequency of 0.40 fires/year and a mean fire interval of 2.5 years. Wildfires frequency increased from 1980 to 0.48 fires/year and a mean fire interval of 2 years. Our results indicate that P. pugionata has the potential to date fires, considering its potential for dendrochronological studies, its ability to survive recurrent fires and forms identifiable wound scars in the wood.
... Traits such as bark thickness, bud bank size, and reproductive mature age determine woody species maintenance in savannas. For example, A. quebracho-blanco is one of the most fire-resistant tree species in Chaco savannas, due to its thick bark (Bravo et al., 2008). Fabaceae species such as Prosopis nigra, P. kuntzei, Vachellia aroma, and Schinus sp., among others, have an important aerial bud bank, which allows these species to resprout from aerial organs after lowintensity fire events. ...
The Dry Chaco is mostly known as a forested ecosystem. However it includes natural grasslands, savannas, scrublands, and wetlands. With one of the highest global deforestation rates in the last two decades and only 12% of the area protected, the concern about land-use change in this ecoregion has raised exponentially; but conservation initiatives developed in last years almost exclusively targeted forests whereas natural grasslands and savannas remain as neglected ecosystem within scientific and governmental agendas. While currently the distribution of natural grassland and savanna area encompasses over 20,000 km2, historical records and spatial models indicate that natural grassland and savannas were more widespread in pre-European era. Two main reasons drove this reduction in natural grasslands and savannas: woody encroachment by fire suppression and overgrazing, and conversion to agriculture and implanted pastures. In this article, through a combination of analyzes and bibliographic revisions, we describe biotic and abiotic components of natural grassland and savannas of the Dry Chaco. We also present the current distribution and conservation status of these ecosystems, and describe the process of change and the ecological consequences for biogeochemical cycles and biologic interactions. To provide basis for management, we estimate current grazing stocking rates on natural grasslands and savannas of Argentine Dry Chaco and we propose an alternative approach to sustainably intensify the use of these ecosystems and improve cattle rancher livelihoods. Despite the existent knowledge about natural grasslands and savannas in the region, we believe that is necessary to motivate the scientific community and national institutions to increase efforts to reconcile the restoration and conservation of these particular rangelands.
... Lately, this forest land has been subjected to several fire incidents (Balducci et al. 2012), affecting its production potential. Even though fire is part of the natural regime in the region, the frequency of this phenomenon has been altered by climatic and anthropogenic factors (Bravo et al. 2008). ...
The rehabilitation of degraded subtropical natural forests is a global concern. A detailed assessment of their structure is a challenging and costly prerequisite because diverse structures exist depending on the cause and degree of degradation. Recent remote sensing concepts and technologies provide a detailed picture of actual forest structure, even in difficult terrain. When it comes to planning and implementing rehabilitation measures on the ground, however, meaningful forest management units (FMUs) must be created that are large enough to allow technical implementation, but which are also homogenous in structure. To date, the delineation of FMUs has, in most cases, been achieved qualitatively based on expert knowledge. The aim of this contribution is to develop and demonstrate a method for creating and delineating meaningful FMUs based on quantitative information acquired from remote sensing and spatial statistics. Therefore, a case study was conducted in a 3940-ha fire-degraded forest area in the Argentinean cloud forest of Yungas Pedemontana. A plot-based field inventory and an aerial survey with an unmanned aerial vehicle were conducted. The Adjusted Canopy Coverage Index (ACCI), as a metric for stand structure, was formulated to predict basal area from canopy height models. A SPOT6 image of the area was object-based segmented and classified into four fire-severity strata by training it with the ACCI values. The resulting classification presented a mosaic pattern in which the stands are homogenous but far too small (average 3129 m²) for planning adaptive management. Therefore, features in close proximity with similar structure (i.e. ACCI values) were aggregated using the Hot Spot Analysis (Getis-Ord Gi*) tool from the Arc geographic information system environment to create FMUs. Clusters were calculated at four scales: 10, 20, 30 and 40 ha (resulting in threshold radii of 178, 252, 309 and 357 m, respectively), using ACCI values as the variable of aggregation. As a result, average cluster areas were obtained of 33.9 ha for the shortest threshold distance of analysis and 138.5 ha for the greatest threshold distance. The tool significantly aggregated between 30.7% and 60.8% of the area into either coldspots or hotspots of ACCI, facilitating the delineation of FMUs for the planning of adaptive rehabilitation measures. There is a trade-off, however, between the gain in area of the FMUs and the loss of homogeneity: for a 357 m distance threshold, 12% more of the area was misclassified, compared with a 178 m threshold.
... La capacidad de rebrotar ha sido observada en las 23 especies de leñosas, identificadas en los censos de vegetación de bosques con diferentes historias de disturbios (bosques en clausura, con ganadería y fuegos, con rolados y fuegos y con rolados y aprovechamiento forestal). Sin embargo, la intensidad del rebrote y los cambios de hábitos de crecimiento responden a características específicas como el tamaño del banco de yemas, (Bravo et al. 2011), su localización y el grado de protección de las cortezas (Bravo et al. 2008(Bravo et al. , 2014. La regeneración vegetativa post fuego de ejemplares juveniles (< 15 cm de diámetro) de las tres especies de leñosas más representativas de los bosques chaqueños (S. lorentzii, A. quebracho-blanco y S. mistol), se establece a través de rebrotes basales o epicórmicos, luego de quemas experimentales. ...
La capacidad de resiliencia de la vegetación nativa, frente al sinergismo entre
disturbios plantea la necesidad de un enfoque funcional para fortalecer los planes
de manejo forestal, la restauración o rehabilitación de áreas degradas, así como las
actividades para mitigación frente al cambio climático. Actualmente, en el marco
del Proyecto de Cooperación Binacional SPU-CAPES, entre la Universidad
Nacional de Santiago del Estero de Argentina y la Universidad Federal do Paraná,
Curitiba, Brasil, se realizan estudios para cubrir en parte, estos aspectos relevantes
en la ecología de la regeneración de especies leñosas del Chaco semiárido
argentino. Se han establecido dos líneas básicas de investigación: regeneración
vegetativa con foco en la estrategia rebrotadora de especies de leñosas nativas, y
regeneración por vía sexual, enfocada en el estudio de bancos de semillas, ambas
en relación a los disturbios antes mencionados (fuegos, rolados, aprovechamiento
forestal y ganadero).
... A pesar de que el fuego no habría sido un factor evolutivo importante en el Chaco seco, diversas especies características de la región presentan estrategias adaptativas que facilitan la persistencia de las mismas frente a los incendios (Jaureguiberry, 2012). Por ejemplo, la presencia de una corteza gruesa es una estrategia de resistencia importante para especies arbóreas como el Aspidosperma quebracho-blanco Schlecht, Schinopsis lorentzii Schlecht, Prosopis nigra Griseb y Prosopis alba Griseb, ya que disminuye el daño generado por las llamas en la parte aérea de la planta e incrementa la probabilidad de sobrevivir luego del incendio (Bravo et al., 2008). A su vez, la capacidad de rebrote post-fuego es una importante estrategia de resiliencia, ya que permite a las plantas no solo sobrevivir sino también recuperar la biomasa consumida durante el incendio y restablecer la estructura del bosque (Clarke et al., 2013;Araújo et al., 2017). ...
... ). Mientras que los bosques secundarios están compuestos por especies deciduas como P. nigra, P. alba. A pesar de que las especies de Prosopis poseen características que le confieren cierta resistencia a los incendios los resultados reportados porBravo et al., (2008) sugieren que poseen una baja tasa de supervivencia a incendios de elevada intensidad; además estas especies poseen una mayor densidad de copa lo que incrementa la inflamabilidad del dosel del bosque. A su vez, Tiedemann, (2011) detectó que los bosques primarios tienen una duración dela estación de crecimiento entre 5 a 13 días más larga que los bosques compuestos por una mezcla de especies típicas de bosques primarios y secundarios. ...
Wildland fires are complex spatial-temporal processes which are able to modify distribution patterns, composition and structure of the vegetation across the landscape. The success of the ignitions and the posterior propagation of the flames are close related with the flammability level of the landscape. The last is determined by the flammability of the each species in each plant cover, also by environmental and structural characteristics of each plant cover and by the distribution of these troughs the landscape. Flammability is also determined the moisture and amount of each fuel present. All these factors along with the ignitions interact to determine spatial distribution of the wildland fires trough the landscape and the characteristics of these. Also wildland fires are disturbs that begin the succession, as a consequence are processes that are close related to vegetal succession. However, ecosystems have resistance and resilience mechanism that enable them to resist the flames damage and to recover. In the dry Chaco of the Argentine there have been great land cover changes that modified cover flammability. The main aim of this thesis were, 1) study flammability differences of the plant covers (forest, shrubland, grassland and crops), 2) determine the relative importance of the clime, land cover and human activities on the spatial distribution of the wildland fires in the dry Chaco and 3) study the structural resistance and functional resiliencia patterns of the forest in the dry Chaco.
To meet the objectives 1 and 2 we used MODIS images of burned area and MODIS hotspot, as well as vegetation maps, geospatial data bases about climate, human populations and productive activities. Results show that there are great flammability‘s differences between the arid and semiarid regions. Forest was the less flammable cover, also we detected that in the arid region shrubland had a flammability level similar to forest cover, and that in the semiarid region had a flammability level similar to grassland and crop cover. In the forest the biomass level did not promote the occurrence wildland fire, and that in grassland cover there were local drivers that faded the precipitations effect.
Regarding to the relative importance of the fire drivers that determine spatial distribution of wildland fires, results showed that grassland was the most important driver. Land clearance for crops and cattle had a great effect on the wildland fire incidence. Also we detected that the effect of the climatic conditions on the occurrence of wildland fires, was determined by the land cover. In areas almost all occupied by forest, wildland fires increased with water deficit, whereas in areas with a lot of grassland wildland fires were higher at intermediate water deficit levels. Results also showed that cattle raising could increase the forest flammability.
To meet the objective three a statistical methodology were developed to analyse time series of spectral vegetation index with the aim to select control sites with the same pre-fire photosynthetic activity pattern than burned sites. This is useful to select control sites, which is the one of the basic requisites to implement an appeared experimental design. The results show that from biological point of view the proposed methodology had a satisfactory performance; therefore it could be implemented successfully to study post-fire recovery patterns of the vegetation. Also, to meet the objective 3 were used Landsat 5 TM images to detect nine forest located in Santiago del Estero and were burned in 2003, inner of these burned areas 85 burned plots were located. Vegetation maps and Quickbird images were used to ensure that all burned plots was forest before the wildland fire, also the eight years after fires the maps and images were used to determine if the burned plots remained as forest or change to shrubland. With the aim to determine the effect of the factors related to structural resistance and functional resilience of the forest, pre-fire functional satellite attributes of the vegetation were estimated, fire intensity, fire severity and burned were also estimated, lastly post-fire precipitations were estimated. In addition eight years after fire there were compared the functional attributes of burned plots that remained as forest and those that changed to shrubland. Result showed that 53 % of forest burned plots changed to a shrubland successional stage. Forest probability to remain as forest after wildland fire was determined by fire severity and by the pre-fire characteristics of the foliar phenology of the trees. Functional attributes shown different post-fire recovery patterns between them, those attributes related with winter and early spring had lower resilience levels. Also, in burned plots with high severity, post-fire resilience of the aboveground primary production was determined by the pre-fire productivity, whereas in burned plots with moderate severity post-fire resilience of the aboveground primary production was related to pre-fire characteristics of the foliar phenology of the trees.
... Sprouting is a mechanism by which a species persists after a disturbance such as fire, herbivory, or mechanical treatment (Pausas and Keeley 2014). Species tolerate fire due to that ability, a trait determined by the development, protection and resourcing of a viable bud bank (Wright and Bailey 1982;Casillo, Kunst and Ledesma 2006;Bravo, Kunst and Grau 2008;Clarke et al. 2012). Heat released by fire, depending on the season and fuel load, may also increase soil temperature and reduce sprout number (Wright and Clarke 2007). ...
... Barchuk et al. (2006) reported that this species does not tolerate well the removal of apical buds by any disturbance. A. gilliesii is common in the upland ecological sites of the Chaco, where fire frequency is estimated to be lower than in the lowland sites, owing to the paucity of fine fuel load (Bravo, Kunst, and Grau 2008). On the other hand, although fire reduced the size of C. ehrenbergiana, it seemed to stimulate its resprouting ability and new growth, suggesting a large bud bank and confirming its high fire tolerance. ...
... The high wood density of the native Chaco species, a property that makes them very useful as firewood (Bravo, Kunst, and Grau 2008) likely enhanced fire effects on the ecosystem, especially in A. gilliesii. S. bumelioides, belonging to the family Anacardiaceae, also has a high content of oils, phenols, and other chemical components that increase fuel flammability (Kunst et al. 2012). ...
Shrub encroachment is frequent in grazing lands in the Chaco region, Argentina. Fire is used by cattlemen to reduce the dominance of the shrub stands, improve forage standing biomass and quality, and enhance grazing accessibility. In this research, we assessed the combined effect of roller chopping þ fire on the plant canopy of three native shrub species, Acacia gilliessi, Celtis ehrenbergiana, and Schinus bumelioides. We used a randomized design, with three factors, year, burn dates, and fine fuel load. Before the burn, the area received a roller-chopping treatment. Canopy volume reduction was assessed using, DifV ¼ −1*(V i − V a) and DifS ¼ −1*(S i − S a), respectively, where V ¼ plant volume and S ¼ sprout number. Suffixes i and a represent measurements taken before the roller-chopping treatment and one growth season after the fire, respectively. Fire intensity, headfire residence time, woody residues, and initial plant volume were evaluated as covariates. Results indicate a negative fire effect on canopy volume and sprouting. A. gilliesi was more susceptible to fire than the other two species. High fine fuel load and high fire intensity generated a severe effect on sprout number. The same trend was observed for coarse fuels. The canopy volume reduction was greater in A. gilliesi than the other species, reaffirming its high susceptibility to fire. Head fires were faster in 2009 than in 2008 and in the late than in the early burn dates. These results suggest that mechanical þ fire treatments can be useful management tools for controlling shrub encroachment in the western Chaco.
