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Direct versus indirect facilitation (herbivore mediated) among woody plants in a semiarid Chaco forest: A spatial association approach

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In arid environments, direct facilitation (microhabitat amelioration) and indirect facilitation (“associational resistance” via protection from herbivory) among plants of different species may act simultaneously. Little is known about their relative effects. One way to disentangle the effects is by evaluating spatial associations. We examined the relative importance of these two mechanisms of facilitation in the semiarid Chaco vegetation of north-central Argentina, through an eight-way observational study in which we quantified the degree of spatial association between saplings of each of two key tree species, Schinopsis lorentzii (Anacardiaceae) and Aspidosperma quebracho-blanco (Apocynaceae), with shrub neighbours either possessing spines or without spines and in both an ungrazed site and a site with a long history of cattle grazing. We analysed data across 400 subparcels at each site with SADIE (Spatial Analysis by Distance Indices). Saplings of both tree species showed positive spatial associations with spiny shrubs in the grazed site but not in the ungrazed site, and never with non-spiny shrubs. This result suggests that spiny shrubs may indeed provide associational resistance (AR) for saplings of key tree species in grazed habitats in these dry subtropical forests, that is, that indirect facilitation may predominate over direct facilitation. If confirmed by experimental studies, this result can have implications for the silvopastoral management of rapidly expanding ranches in the semiarid Chaco, where current practice includes the near elimination of native shrubs.
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... Facilitation (i.e., positive interactions) is the phenomenon through which one species improves the survival, growth or general state of another species [9,10]. In this sense, previous studies have shown the capacity of shrublands to influence the environment by creating microclimates or markedly different conditions in open spaces, thus allowing the settling of certain species [9][10][11][12]. ...
... Facilitation (i.e., positive interactions) is the phenomenon through which one species improves the survival, growth or general state of another species [9,10]. In this sense, previous studies have shown the capacity of shrublands to influence the environment by creating microclimates or markedly different conditions in open spaces, thus allowing the settling of certain species [9][10][11][12]. ...
... Plants 2020,9, 593 ...
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Most communities with the presence of Cistus ladanifer are characterised by the low richness of accompanying species, with C. ladanifer, in most cases, exceeding 70% of the coverage of woody species. This fact could be due to the allelopathic activity attributed to compounds present in the leaves of C. ladanifer, which may have a negative effect on the germination and growth of woody species that share its habitat. One of the possible ways of incorporating allelopathic compounds to the soil is the degradation of leaf litter. Therefore, the aim of this study was to determine how the presence of leaf litter from C. ladanifer affects accompanying species. Under controlled conditions, we analysed the effect of C. ladanifer leaf litter on the germination and growth of seedlings of five species that share their habitat with C. ladanifer (Retama sphaerocarpa, Cytisus multiflorus, Lavandula stoechas, Cistus salviifolius, and Cistus crispus). Additionally, the effect of leaf litter on the species itself, C. ladanifer, has been studied. The experiments were designed with different concentrations of leaf litter (UL) and leaf litter from which the compounds with allelopathic activity were extracted (WL). The results show that such effect greatly depends on the analysed species, with L. stoechas being the most negatively affected species. On the other hand, C. multiflorus and C. salviifolius were only negatively affected at the stage of seedling growth. The results reveal the involvement of leaf litter in the allelopathic activity attributed to C. ladanifer and that its presence has a negative influence on the germination and growth of accompanying woody species. This shows the need to delve into the potential relevance of allelopathy as an interaction that determines the composition, structure and dynamics of a community.
... shrubs. This phenomenon has been demonstrated many times, when seedlings are associated with thorny, unpalatable or dense shrubs (Baraza et al., 2006;Tálamo et al., 2015). Arbutus unedo is a thornless species regularly browsed by deer in Mediterranean systems (Perea, Girardello, & San Miguel, 2014), and consumption was also observed in our study area. ...
... In the early formulation of the SGH, direct (habitat amelioration) and indirect (associational resistance) facilitation are not expected to be found in the same system (Bertness & Callaway, 1994). However, herbivory pressure can be high in many harsh environments, and several studies regarding tree seedlings in xeric systems suggest that facilitation can occur due to habitat amelioration (Gómez-Aparicio, Zamora, Castro, & Hódar, 2008), associational resistance (Tálamo et al., 2015), or both (Boulant et al., 2008). A few recent empirical studies even suggest that associational resistance tends to be more important as water stress increases (Louthan, Doak, Goheen, Palmer, & Pringle, 2014;Verwijmeren, Smit, Bautista, Wassen, & Rietkerk, 2019). ...
Article
1.Using nurse shrubs to improve tree seedling establishment in stressed environments is a common practice in forestry. Recent refinements of the stress‐gradient hypothesis suggest that positive nurse effects occur under intermediate stress and decline in the harshest conditions. Additionally, indirect facilitation (e.g. protection from herbivory) is expected in low‐stressed/productive systems according to the initial stress‐gradient hypothesis. However, there have been fewer investigations into the use of nurse shrubs to decrease herbivore impacts in stressed systems compared with the role of nurses on stress alleviation. This raises the need to clarify conditions in which the use of nurse shrubs would be most appropriate. 2.We conducted a field experiment in the sand dune forest of southwest France characterised by severe summer water shortages and the presence of different types of wild herbivores. In 2015 and 2016, Pinus pinaster seedlings were planted under shrubs (Arbutus unedo) or in shrub‐removed locations, in fenced/unfenced areas. Survival, cause of mortality, and water stress were monitored for one year after plantation. 3.Summer drought was the main cause of mortality. Water stress increased in both years as summer progressed. We found direct facilitation only in July 2016 at intermediate water stress, due to a decrease in vapour pressure deficit under shrubs. These positive effects declined in late summer when stress was at a maximum. Rodent damage occurred under shrubs in spring whereas ungulate browsing was observed in open areas in autumn/winter. Overall seedling survival was equivalent under or outside shrubs during the first year, but was better under shrubs in the second one. 4.Synthesis and applications. Our results partially validate the refinement of the stress‐gradient hypothesis, with a decline of positive interactions in the most water‐stressed conditions. This draws attention to the difficulty of using shrubs as nurses to improve tree regeneration in the most xeric systems. In addition, we show that indirect associational effects, both positive and negative, could be as important as abiotic stress alleviation in a stressful ecosystem, and using shrubs to facilitate seedling survival could be efficient depending on the type of herbivore involved. This highlights the fact that considering plant‐plant interactions can help in the design of management options, providing that up‐to‐date ecological theories are considered and that the different biotic and abiotic constraints are accurately evaluated.
... pers.). Also, cattle can alter fruit production and change the spatial distribution and vertical structure of woody plants (Tálamo & Caziani, 2003;Tálamo et al., 2015). However, our results do not support this explanation because we did not find a relationship between foxes' activity index and fruit availability or understory structure (represented by shrubs density). ...
Article
Extensive livestock ranching is one of the main drivers of habitat degradation in terrestrial communities in the dry Chaco forest (Argentina). Grazing intensity could differentially affect native mammals and their interactions, which could impact both, native mammal communities and livestock production systems. Here, we determined how the activity index of grey foxes Lycalopex gymnocercus and capture abundance and richness of small mammals vary along a grazing intensity gradient in a particular region of the dry Chaco forest (Copo National Park, Argentina). Track plots were used to estimate the activity index of foxes and cattle, and Sherman traps for small mammals. Fresh scats were collected to analyse the diet of foxes and to assess possible changes in predator-prey dynamics. Fruit availability and shrub density were measured in 6 plots of 2 m x 50 m. We used generalized linear mixed models, Spearman’s nonparametric rank correlation, Chi-squared test, and Spearman’s partial correlation coefficient to analyse the potential effects of grazing intensity. We found that the activity index of foxes increased (0.06 ± 0.018) while small mammal abundance (-0.08 ± 0.024) and species richness decreased (rs = -0.94) with increasing grazing intensity. However, the proportion of scats with mammalian remains decreased with increasing grazing intensity. Also, we did not find a strong partial correlation between foxes and small mammals when we controlled for grazing intensity. This suggests that the abundance and diversity of small mammals in the study area are determined more by grazing intensity than by predator-prey interactions. Grazing intensity could negatively affect small mammals, but not through changes in fruit availability or shrub density, but possibly by affecting grass cover. Consequently, foxes’ activity could increase to meet caloric intake requirements. Our results suggest that specific cattle management recommendations depend on the wildlife species that serves as a conservation target. We recommend testing whether reducing cattle load can make this productive activity compatible with wildlife conservation in dry Chaco forests.
... Disturbances are known to affect both biotic and abiotic environmental conditions and, therefore, ecosystem structure and functioning (Mitchell et al., 2017). One of the most ubiquitous disturbances affecting dryland plant communities are domestic livestock practices, frequently reducing plant abundance, richness and cover (Tadey, 2006;Bär Lamas et al., 2013;Zhang et al., 2013;Pol et al., 2014;Tálamo et al., 2015). These changes in plant community may cascade up and down within the ecosystem, affecting both environmental conditions and biotic interactions through changes in resource availability and interspecific relationships. ...
Article
Questions Vegetation patches formed by interacting xeric species are the main drivers of dryland structure and function. Plant aggregation enhances microclimatic conditions and triggers abiotic and biotic processes, such as nutrient cycling and accumulation, and species interactions. However, vegetation patches may be modified by disturbances in unpredictable ways. We tested whether livestock grazing affects vegetation structure and plant spatial associations in a desert community, by considering the role of plant species in ecological succession. Location Patagonian Monte Desert, Argentina. Methods We used high‐quality standardized photographs along transects to characterize plant community structure (i.e., cover, abundance, richness), spatial patterns (i.e. plant‐plant associations), and classified species based on their successional role (i.e. early, intermediate and late species). We used regression models and network analysis to evaluate the effect of grazing on vegetation. Results In general, grazing modified community structure, reducing total cover, abundance and richness. Grazing modulated community spatial patterns, simplifying and removing vegetation patches. The impact of grazing depended on the species successional role. The abundance and cover of early species were less affected by grazing than intermediate and late species, the latter being the most affected. However, species richness significantly decreased with increasing stocking rates, regardless of their successional role. Late species were present in most plant spatial associations, indicating a major contribution to multi‐specific vegetation patches formation. Conclusions The reduction in species richness and low abundance of late species highlights the need to prevent irreversible degradation caused by overgrazing. Late species emerge as key structures of vegetation in desert rangelands facilitating the establishment and protecting other plant species. Due to the critical role of vegetation patches in maintaining desert ecosystem functioning, conservation and management practices should focus on late species, while early species, responsible for vegetation patch formation in overgrazed situations, should be preferred for restoration practices.
... Shrubs can provide an important source of fruits for wildlife (Caziani and Protomastro, 1994;Ponce et al., 2012), or offer forage biomass for native and domestic herbivores (Bucher, 1987;Catan and Degano, 2007;Cora et al., 2005;Quiroga and Esnarriaga, 2014). Also, shrubs can promote regeneration niches that other plants can use for their establishment, growth and survival (Barchuk et al., 2005;Caccia et al., 2009;Tálamo et al., 2015aTálamo et al., , 2015bTrigo et al., 2017). Understanding how forestry affects understory vegetation structure and the regeneration of timber species is key to assess the sustainability of logging and measure potential consequences to ecosystem function. ...
... For example, heterogeneity in grazing is enhanced by the presence of scattered shrubs because shrubs in pastures provide safe sites for some species (e.g. Tálamo et al, 2015). Because grazing may increase the contrast between patches close or under shrubs with open patches, we expect that grazing would enhance the effects of light availability on the community scale resulting in statistical interaction between the effects of grazing and light conditions. ...
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Shrubs in pastures are expected to adversely affect plant species diversity and community composition at various spatial scales. We recorded vegetation composition as well as light conditions and other environmental variables in 105 1 m2 plots nested in 35 sampling sites in shrubby pastures in Romanian Banat. We used generalized linear models, generalized linear mixed-effects models, and linear regression to find determinants of species turnover and richness at patch and community level. We expected shrubs to negatively influence species richness on the patch level but to introduce spatial heterogeneity to the light availability resulting in a unimodal relationship of light availability with species richness on the community level. Species turnover was significantly influenced by light conditions, grazing variability, and distance between the plots. We found a unimodal relationship between light availability and species richness consistently across the two spatial scales in grazed sites. However, the same relationship changed its shape from linear to unimodal in non-grazed sites. Shrubs in pastures may not be considered as a threat to plant species diversity. Instead, they contribute significantly to plant species diversity and vegetation heterogeneity.
... Here, heavy grazing intensity modifies density, richness, species diversity and structural diversity of woody plants (Macchi and Grau, 2012;Trigo et al., 2017). Moderate grazing intensity changes the spatial distribution of woody plants (Tálamo et al., 2015a), reduce tree emergence and survival (Tálamo et al., 2015b), and shrub abundance (Brassiolo et al., 1993;. And, seasonal exclusion increases grass cover and biomass (Cotroneo et al., 2018). ...
Article
Livestock grazing can be a problem for forest conservation because it can generate heterogeneous and unpredictable changes in plant communities. Understanding these changes is important for generating management strategies that are compatible with long-term conservation of threatened forests. Livestock exclusion is a useful experimental approach used to evaluate grazing effects. However, the evidence showing the effects of grazing on forests is mixed and little in know about the responses of different plant life forms, especially in dry forests. In this study, we evaluated the effects of a 7-8 year of livestock exclusion experiment on understory plant community structure in the dry Chaco forest (Argentina). We categorized understory plant life forms as shrubs, succulents (Cactaceae family + Bromelia hieronymi), and herbs (forbs, grasses and vines). Then, we compared the plant community structure (richness, diversity, density and cover) and understory structure (soil hardness, bare soil and vegetation vertical and horizontal structure) between five excluded plots and five grazed plots, in a paired design. We found that livestock exclusion lead to an increase in grass species richness and grass cover as well as an increase in lower understory biomass (0-0.5 m) and a decrease in percentage of bare soil. On excluded plots, dominant herbs were Setaria nicorae (grass), Trichloris crinita (grass), and Justicia squarrosa (forb). Grass species that were recorded exclusively on excluded plots were Gouinia latifolia, T. crinita, and Pappophorum mucronulatum, all forage species preferred by livestock. In contrast, on grazed plots, the dominant species was Stenandrium dulce (forb), a species with resistance strategies to grazing. As for the other variables, we did not find strong differences between excluded and grazed plots. Livestock grazing did not modify the ensemble structure of shrubs and succulents nor did it change the horizontal vegetation structure or soil hardness. Our evidence suggests that the assemblage composed by shrubs and succulents seems to be tolerant to livestock grazing, and that the grass assemblage has the ability to quickly recover when grazing stops. Finally, the effectiveness of exclusion as a management tool will depend on which attribute of the plant community to be conserved or recovered. In dry Chaco forests after many years of grazing at moderate stocking rates, livestock exclusion could help recover grass cover, generate opportunities for the establishment of certain grass species that are sensitive to grazing, and increase ground cover.
... Based on the everyday complementary uses that livestock farmers give to the trees demonstrate the need to implement an integral handling of the arboreal stratum that mitigates environmental degradation, promote diversified use and increased density per surface unit, because it may represent a savings in maintenance costs of fences, construction of artificial shade, herbal medicine and in buying feed for animals among other things (Guerreiro et al., 2015;Olivares-Pérez et al., 2016;Tálamo et al., 2015). ...
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RESUMEN: En el Trópico Méxicano se estudió la distribución, densidad y usos de los árboles Pithecellobium dulce Roxb Benth, Gliricidia sepium (Jacq) Steud, Haematoxilum brasiletto Karst y se agregó su follaje a las dietas de cabritos y midió la respuesta productiva y la digestibilidad aparente. Los ganaderos dieron seis usos (leña, postes, sombra, medicinales, consumo humano y artesanal). Los árboles estuvieron en cercas vivas y dispersos en potreros con densidades de 4,87 árboles 100-1 metros lineales y 1,79 árboles ha-1 ; P. dulce Roxb Benth tuvo mayor talla y se localizó entre 250 a 1332 msnm. Las cenizas (P<0,0001) y fibras detergentes (P<0,01) del P. dulce (T1) fueron más digestibles. La CA y GDP entre los cabritos fueron diferentes entre tratamientos. La temperatura rectal sólo se afectó (P<0,0001) por la hora de evaluación. El pH ruminal de los cabritos fue diferente entre tiempos de evaluación (P<0,0001) y tratamientos (P<0,0003). Se concluye que la densidad de árboles es baja y podría tener un impacto sobre la fertilidad del suelo y la aportación de biomasa para la alimentación animal; La digestibilidad de las dietas y respuesta productiva fueron más eficientes en los animales alimentados con P. dulce Roxb Benth (T1). ABSTRACT: In the Tropic of Guerrero Mexico the distribution, the density and uses of trees Pithecellobium dulce Roxb Benth, Gliricidia sepium (Jacq) Steud, 155 Haematoxilum brasiletto Karst were studied and its foliage was added to the diets of kids and productive response and apparent digestibility was measured. The livestock farmers have six complementary uses (firewood, poles, shade, medicinal, human consumption and artisanal). The species were identified in live fences and scattered in paddocks with densities of 4.87 trees per 100 linear meters and 1.79 trees ha-1 ; P. dulce was the largest size and identified from 250 to 1332 masl. The ashes (P<0.0001) and detergent fibre (P<0.01) of P. dulce (T1) had higher apparent digestibility. The feed conversion and daily weight gain of the kids were different due to the effect of foliage trees. The rectal temperature was only affected (P<0.0001) by the time of evaluation. The ruminal pH of kids was affected by time evaluation (P<0.0001) and the treatments (P<0.0003). It is concluded that the density of trees is low and could be of impact on soil fertility and the contribution of biomass for animal feed; the apparent digestibility of diets and productive response were more efficient in the animals fed with P. dulce (T1).
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The main objective of this study is to determine if Juniperus communis subsp hemisphaerica, a nurse plant, plays a facilitating role in the dynamics of the cedar forest in the mountain of Djurdjura (Algeria). In order to highlight the possible effect of the presence/absence of cedar seed trees on vegetation dynamics and the natural regeneration of this species, the choice of study sites takes into account three different phytoecological situations: a dense stand of cedar, a cedar-pasture ecotone area and a juniper formation without cedar seed trees. To appreciate the various correlations that may exist between the nurse plant, its biological traits and the facilitated species, through different parameters, such as plant diversity, number of tall scrubs and recovery of Cedrus atlantica individuals within juniper thickets, we used multi�variate analysis for the treatment of the data collected. The results allow highlighting the nature of the positive interac�tions of this juniper in the dynamics of the cedar forest. These interactions, rendered by the role provided by the patches of hemispherical juniper, favor the rise of a microhabitat adequate to the installation of the plant species linked to the ce�dar stand, thus protecting them from ecological stress in mountain and anthropogenic disturbances. Among these latter, overgrazing remains the major problem threatening the biological recovery and biodiversity of the National Park of Djurd�jura. It would be likely to use this facilitation process for ecological restoration of the degraded cedar forest in Djurdjura. Keywords: positive interaction, nurse effect, Mediterranean mountain, Juniper shrub, Atlas cedar, Djurdjura Mountain.
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Domestic livestock are widespread in seasonally dry forests, likely causing forest degradation and limiting tree seedling establishment. Shrubs can play an important role in facilitating tree regeneration, by protecting trees from livestock damage and ameliorating unfavorable abiotic conditions. We aimed at disentangling the relative contribution of grazing exclusion, long-term forest conservation, and the potential facilitation effect of shrubs on the performance of saplings of the native tree Kageneckia lanceolata. We planted 400 saplings in grazed and ungrazed areas situated both in a preserved and a degraded forest. In each situation, we established planting plots in three accompanying vegetation treatments: herbs, a non-leguminous spiny shrub and a leguminous spiny shrub. Survival of three-year-old saplings was 10-fold higher in the preserved than in the degraded forest and two-fold higher in the ungrazed than in the grazed site. Differences in survival among accompanying vegetation treatments were much smaller than between grazing treatments. Survival significantly increased with increasing protection by shrubs only in the degraded site. Sapling growth patterns were fairly similar to survival patterns, with no growth in the degraded forest, except for limited growth under both shrubs in the ungrazed site. We conclude that, in selecting plantation sites for the study species, forest condition and grazing exclusion should be prioritized over microsite selection based on neighboring vegetation. This article is protected by copyright. All rights reserved.
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Terrestrial herbivory in the Chaco, Monte and Patagonia natural regions of Argentina shows similar pattems to equivalent regions of North America, as weil as distinctive features. Peculiarities include the near absence of native large her-bivores, itre ttlg1t diversity and abundance of leaf-cuting ants, and a considerable number of plants showing adaptations against predation and for dispersion by large herbivores. All these features might be linked to evolutionary interactions ."ith th" diverse fauna of laige herbivores which became extinct during the Pleistocene. Overgrazing fiom domestic ungulates in the Chaco has transformed the original parkland landscape provoking widespread encroachment of woody u.gltutiott, the near extinction of grasslands and some of their largest herbivores, and an increment of medium-sized rodents, which, in turn, can keep the system in a new "disclimaxic" equilibrium. In the Monte and Patagonia the results of overgtazing on the natural vegetation have also been dramatic, although les spectacular in terms of landscape alteration. These characteristics suggest lines along rvhich future tesearch efforts could be focused. RESUMEN La herbivoria terrestte en las regiones naturales del (haco, Monte y Patagonia de la Argentina muestra patrones simila-res con regiones equivalentes de Norte America, asi como caracteristicas peculiares. Estas iltimas incluyen una marcada pobnza di grandei herbivoros, la gran abundancia y diversidad de hormigas cortadoras de hojas, y un considerable nri-mero de plantas que muestran adaptaciones contra la depredaci6n y parc la dispersi6n por grandes herbivoros. Todas estas caracteristicas pueden ser vinculadas con la diversa fauna de grandes herbivoros que se extingui6 durante el Pleis-toceno. El sobrepastoreo por ungulados domdsticos ha transformado el paisaje de parque original del Gtaco, a trav6s de una invasi6n generalizada de la vegetaci6n lefrosa,1a casi extinci6n de 1os pastizales y de algunos de sus grandesherbi-voros, y un incremento de roedores de tamafro mediano, los cuales pueden mantener el sistema en un nuevo equilibrio "disclimdxico". En el Monte y Patagonia los efectos del sobrepastoreo han sido tarnbitjn intensos, aunque menos espec-taculares en t6rminos de alteraci6n del paisaje. Estas caracteristicas sugieren lineas a lo largo de las cuales pueden orien-tarse futuros esfuetzos de investigacion. Palabras clave: Regiones semiaridas neotropicales, Chaco, Monte, Patagonia, sabanas, herbivorfa, efectos del pastoreo, hormigas cortadoras de hojas.
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RESUMEN. En un camino abandonado del bosque chaqueño semiárido (Parque Nacional Copo, Argentina), comparamos la comunidad de plantas leñosas en dos sectores: uno de bosque secundario con presencia de ganado vacuno (“Vacas-Bs”), y otro de bosque primario sin presencia de ganado vacuno (“Sin Vacas-Bp”). Para esto, medimos atributos de la vegetación leñosa en parcelas dispuestas al azar en cada sector. La riqueza de especies, la densidad de plantas adultas y el área basal fueron similares en los dos sectores. En las parcelas del sector “Vacas-Bs”, Capparis retusa representó el 34% del área basal total, disminuyendo la equitatividad del ensamble de este sector. El número de ramas por individuo y la densidad de ramas fueron similares en ambos sectores. Achatocarpus praecox, Prosopis sp. y Ximenia americana estuvieron presentes sólo en las parcelas del sector “Vacas-Bs”, mientras que Senna aphylla fue encontrada sólo en las parcelas del sector “Sin Vacas-Bp”, aunque estas diferencias podrían deberse a la variación intrínseca. En el tiempo considerado, no encontramos evidencias marcadas de que la comunidad de plantas leñosas difiera entre sectores con distinta historia de pastoreo y vegetación circundante. [Palabras clave: disturbio, diversidad, plantas leñosas, pastoreo, bosque, camino abandonado, Chaco] ABSTRACT. Woody vegetation of an abandoned road in the semiarid Chaco forest in relation to the surrounding vegetation matrix and grazing: In an abandoned road in of the semiarid Chaco forest (Copo National Park, Argentina), we compared the community of woody plant species in two areas: one with livestock, surrounded by secondary forest, and another without livestock, surrounded by primary forest. We measured characteristics of the woody vegetation in nine plots (2 x 100 m) selected randomly in the area with livestock and in six plots in the area without livestock. Considering the same number of samples, species richness was similar in both areas. No significant differences were found in species richness per plot, adult plants density and basal area between the two areas. In the plots with livestock, 34% of the total basal area corresponded to Capparis retusa, decreasing the assembly eveness in this area. The number of branches per individual and the branch density were similar in both areas. Achatocarpus praecox, Prosopis sp. and Ximenia americana were present only in plots with livestock, while Senna aphilla was found only in the plots without livestock, however these differences could be the result of intrinsic variations. The density and basal area per species were not different between areas. In the considered period of time, we did not find evidence of differences in the community of woody plant species related to the different grazing history and the surrounded vegetation matrix. [Keywords: disturbance, diversity, woody plants, cattle grazing, forest, abandoned road, Chaco]
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Quantification of global forest change has been lacking despite the recognized importance of forest ecosystem services. In this study, Earth observation satellite data were used to map global forest loss (2.3 million square kilometers) and gain (0.8 million square kilometers) from 2000 to 2012 at a spatial resolution of 30 meters. The tropics were the only climate domain to exhibit a trend, with forest loss increasing by 2101 square kilometers per year. Brazil's well-documented reduction in deforestation was offset by increasing forest loss in Indonesia, Malaysia, Paraguay, Bolivia, Zambia, Angola, and elsewhere. Intensive forestry practiced within subtropical forests resulted in the highest rates of forest change globally. Boreal forest loss due largely to fire and forestry was second to that in the tropics in absolute and proportional terms. These results depict a globally consistent and locally relevant record of forest change.
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In an abandoned road in of the semiarid Chaco forest (Copo National Park, Argentina), we compared the community of woody plant species in two areas: one with livestock, surrounded by secondary forest, and another without livestock, surrounded by primary forest. We measured characteristics of the woody vegetation in nine plots (2 × 100 m) selected randomly in the area with livestock and in six plots in the area without livestock. Considering the same number of samples, species richness was similar in both areas. No significant differences were found in species richness per plot, adult plants density and basal area between the two areas. In the plots with livestock, 34% of the total basal area corresponded to Capparis retusa, decreasing the assembly eveness in this area. The number of branches per individual and the branch density were similar in both areas. Achatocarpus praecox, Prosopis sp. and Ximenia americana were present only in plots with livestock, while Senna aphilla was found only in the plots without livestock, however these differences could be the result of intrinsic variations. The density and basal area per species were not different between areas. In the considered period of time, we did not find evidence of differences in the community of woody plant species related to the different grazing history and the surrounded vegetation matrix.