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Direct and indirect relationships between logging intensity and regeneration of two timber species in the Dry Chaco of Argentina

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... Por otro lado, estos indicadores de uso del suelo en el área de estudio (i.e., hornos de carbón vegetal, número de bovinos, distancia a cultivos), no necesariamente implican un constante uso tradicional en la región, y contemplar la intensificación y avance tecnológico de estas actividades es importante para observar las respuestas sobre el carbono de las comunidades boscosas chaqueñas. Debido a esto, en la última década hubo un avance en los estudios a nivel local y regional para determinar los efectos de los disturbios y actividades productivas sobre las comunidades leñosas, como por ejemplo los efectos de rolado para prácticas silvopastoriles (Kunst et al., 2012;Ledesma et al., 2018), manejo del pastoreo (Cavallero et al. 2019), aprovechamiento forestal (Tálamo et al., 2020), y las diferentes historias de manejo o conservación en bosques del Chaco seco (Loto & Bravo, 2020). ...
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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.
... The restoration of degraded forests has become increasingly important [12][13][14]. As the first step for restoring degraded production forests, it is necessary to identify the different states of degradation, such as the remaining stock and regeneration status of commercial tree species in relation to understory vegetation [12,15,16]. ...
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In this study, we determined the effects of selective logging on the abundance of the last remnant populations of two tropical timber species with a restricted distribution, Caryocar costaricense and Peltogyne purpurea. We conducted a census of adult tree densities for these species on 94 selectively logged sites located in a tropical rain forest on the Osa Peninsula, Costa Rica. We compared the abundance of juveniles and seedlings for both tree species on 11 logged and unlogged sites. In addition, we analyzed the growth and mortality rates of adult trees of P. purpurea (>10 cm dbh) in a 4 ha permanent plot that was selectively logged once in 1992. Both species presented a heterogeneous density distribution over the Osa Peninsula (166,668 ha) and the highest density of both species is located in the region of the highest logging activity. For C. costaricense, seedling (height < 50 cm) and juvenile (height > 50 cm, dbh < 2 cm) abundance was greater in unlogged areas, while trees 2–10 cm dbh were more abundant in logged areas. For P. purpurea, seedlings were more abundant in unlogged areas, but small and large juvenile abundance did not differ between selectively logged treatments. The density of P. purpurea adult trees remained constant 15 years after selective logging but the density of trees 10–30 cm dbh decreased in the same period. We predict that recurrent 15 year cutting cycles of 50% of timber trees with restricted distribution, as it is practiced by conventional logging in Costa Rica, may lead a significant reduction of the main reproductive individuals, decreasing the regeneration of the populations subjected to exploitation and fragmentation.
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Over the past two decades, sets of timber harvesting guidelines designed to mitigate the deleterious environmental impacts of tree felling, yarding, and hauling have become known as “reduced-impact logging” (RIL) techniques. Although none of the components of RIL are new, concerns about destructive logging practices and worker safety in the tropics stimulated this recent proliferation of semi-coordinated research and training activities related to timber harvesting. Studies in Southeast Asia, Africa, and South and Central America have clearly documented that the undesired impacts of selective logging on residual stands and soils can be substantially reduced through implementation of a series of recommended logging practices by crews that are appropriately trained, supervised, and compensated. Whether reducing the deleterious impacts of logging also reduces profits seems to depend on site conditions (e.g., terrain, soil trafficability, and riparian areas), whether the profits from illegal activities are included in the baseline, and the perspective from which the economic calculations are made. A standardized approach for calculating logging costs using RILSIM software is advocated to facilitate comparisons and to allow uncoupling RIL practices to evaluate their individual financial costs and benefits. Further complicating the matter is that while there are elements common to all RIL guidelines (e.g., directional felling), other components vary (e.g., slope limits of 17–40° with ground-based yarding). While use of RIL techniques may be considered as a prerequisite for sustaining timber yields (STY), in particular, and sustainable forest management (SFM), in general, RIL should not be confounded with STY and SFM. This confusion is particularly problematic in forests managed for light-demanding species that benefit from both canopy opening and mineral soil exposure as well as where harvesting intensities are high and controlled primarily by minimum diameter cutting limits. These qualifications notwithstanding, since logging is the most intensive of silvicultural treatments in most tropical forests managed for timber, some aspects of RIL are critical (e.g., protection of water courses) whether forests are managed for STY, SFM, or even replacement by agricultural crops.
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"Traditionally, sustained yield (SY) has been viewed as a pillar of sustainable forest management (SFM), but this has been increasingly questioned. Ensuring SY of some species, i.e., a 'strong sustainability' paradigm, could be an inadequate criterion if consideration of the social and economic components of the SFM concept are desired. SFM was translated into the ATO/ITTO set of principles, criteria, and indicators (PCI) for forest management in the Congo Basin; it resulted in the necessity for a certified logging company to ensure that no significant change in structure and floristic composition would result from logging operations. Besides raising the question of where to place the change threshold, we argue that sustainability must be considered from three indissociable viewpoints: ecological, social, and economic. The issue is how to balance these criteria, knowing that this assessment will involve potential conflicts of representations and beliefs. To discuss these questions, we used the example of two heavily logged timber species in the Congo Basin, sapelli (Entandrophragma cylindricum) and ayous (Triplochiton scleroxylon). Using long-term data collected from permanent sample plots in Mbaiki, Central African Republic, we calibrated a matrix model and performed short- and long-term simulations to examine (1) the potential effect of repeated logging of the species under the current national regulation system and (2) the rules that should be set to reach long-term SY. Ensuring long-term SY would require a 22% and 53% decrease in the felling intensity of E. cylindricum and T. scleroxylon, respectively, at first cut, together with an increase in overall logging intensity targeted toward less-used species. Light-demanding E. cylindricum and T. scleroxylon require open forests to regenerate and grow. This new set of rules is probably economically unsustainable for the current African forest industry, and will not meet the ecological requirements encapsulated in the ATO/ITTO PCI. We thus stress the following points: (1) the importance of most exploited species for the current industry may change as wood processing capacities become more efficient and markets change, potentially providing conditions for harvesting a greater number of species; (2) floristic change is unavoidable in these conditions, but this problem should be addressed at a broad scale, notably by ensuring a network of protected areas; (3) as long as the timber industry remains one of the few sources of employment and revenues in marginalized countries, reducing SFM to SY of the most exploited species on every concession appears questionable."
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Plant cover plays a major role in shaping the nature of recruitment microsites through direct (resource mediated) and indirect (consumer mediated) interactions. Understorey plants may differentially affect seedling establishment, thus contributing to regeneration-niche separation among canopy tree species. We examined patterns of early tree seedling survival resulting from interactive effects of understorey bamboo (Chusquea culeou) and resident consumers in a mixed temperate Patagonian forest, Argentina. Newly germinated seedlings of Nothofagus dombeyi and Austrocedrus chilensis were planted in bamboo thickets and non-bamboo patches, with or without small-vertebrate exclosures. We found species-specific patterns of seedling survival in relation to bamboo cover. Nothofagus survival was generally low but increased under bamboo, irrespective of cage treatment. Desiccation stress accounted for most Nothofagus mortality in open, non-bamboo areas. In contrast, Austrocedrus survival was highest in non-bamboo microsites, as most seedlings beneath bamboo were killed by small vertebrates through direct consumption or non-trophic physical damage. There was little evidence for a negative impact of bamboo on tree seedling survival attributable to resource competition. The balance of simultaneous positive and negative interactions implied that bamboo presence facilitated Nothofagus early establishment but inhibited Austrocedrus recruitment via apparent competition. These results illustrate the potential for dominant understorey plants to promote microsite segregation during early stages of recruitment between tree seedlings having different susceptibilities to water stress and herbivory. We recognise, however, that patterns of bamboo-seedling interactions may be conditional on moisture levels and consumer activity during establishment. Hence, both biotic and abiotic heterogeneity in understorey environments should be incorporated into conceptual models of regeneration dynamics and tree coexistence in forest communities.
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In semiarid regions, livestock is concentrated around water sources generating a piosphere pattern (gradients of woody vegetation degradation with increasing proximity to water). Close to the water source, livestock may affect the composition, structure and regeneration strategies of woody vegetation. We used the proximity from a water source as a proxy of grazing pressure. Our objectives were (1) to compare woody vegetation attributes (richness, diversity, species composition, density and basal area) and ground cover between sites at two distances to a water source: near (higher grazing pressure) and far from the water source (lower grazing pressure), and (2) to quantify and compare cases of spatial association among the columnar cacti Stetsonia coryne (Salm-Dyck) Britton and Rose (Cactaceae), and the dominant tree Bulnesia sarmientoi Lorentz ex Griseb. (Zygophyllaceae). We used a paired design with eight pairs of rectangular plots distributed along a large and representative natural water source. We found lower total species richness, plant density and soil cover near than far from water source, and more cases of spatial associations between the two species studied. Our results show evidence of increased livestock impacts around water sources. However, we found no difference in terms of species composition or basal area at near versus far sites. We conclude that grazing pressure might be changing some attributes of the woody plant community, and that the association of young trees with thorny plants (grazing refuge) could be a regeneration mechanism in this semiarid forest with high grazing pressure.
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Ecologists and evolutionary biologists are relying on an increasingly sophisticated set of statistical tools to describe complex natural systems. One such tool that has gained increasing traction in the life sciences is structural equation modeling (SEM), a variant of path analysis that resolves complex multivariate relationships among a suite of interrelated variables. SEM has historically relied on covariances among variables, rather than the values of the data points themselves. While this approach permits a wide variety of model forms, it limits the incorporation of detailed specifications. Here, I present a fully-documented, open-source R package piecewiseSEM that builds on the base R syntax for all current generalized linear, least-square, and mixed effects models. I also provide two worked examples: one involving a hierarchical dataset with non-normally distributed variables, and a second involving phylogenetically-independent contrasts. My goal is to provide a user-friendly and tractable implementation of SEM that also reflects the ecological and methodological processes generating data.
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NE WIN R, SUZUKI R & TAKEDA S. 2012. Effects of selective logging on the regeneration of two commercial tree species in the Kabaung Reserved Forest, Bago Mountains, Myatunar. The density and growth of two commercial tree species from shoot recruitment after selective logging were studied for 13 months in the Kabaung Reserved Forest, Myanmar. The highest density and greatest initial height growth of Tectona grandis (teak) were observed in log landing and logging road sites. These were areas with disturbed soils and increased light intensity. Despite the higher light availability in felling gaps compared with areas unaffected by logging, the density and height of recruited teak shoots at both sites were not significantly different. Among disturbance types, log landing created the highest canopy openness and caused the greatest recruitment and growth of new teak shoots. These findings suggest that the level of disturbance in felling gaps caused by current selective logging practices may be inadequate to promote satisfactory teak regeneration. Activities that increase light and control interference from competing vegetation in felling gaps may be necessary. Xylia xylocarpa did not resprout because of the damage to both stems and roots of shoots caused by the construction of logging roads and log landing sites. This resulted in a much lower post-logging recruitment than mortality of pre-existing shoots.
Article
Chaco Chachalacas (Ortalis canicollis) in the semi-arid Chaco forest region of northern Argentina fed mainly on herbaceous leaves (37% of the dry mass of its diet) and fleshy fruits (25%). Leaves and fruit were consumed year round. The rest of the diet consisted of caterpillars and flowers. The Chaco Chachalaca consumed all the fruit species available to it during this study period. Fruits most frequently eaten were: (1) fruit thickly bunched on the plant with long availability, even though of lower quality and (2) fruit of good quality (judged by pulp and total solids content). Low quality fruits not clumped together were less used in spite of their abundance in the forest. Received 24 Feb. 1993, accepted I Mar. 1994. Guans (Penelope) and chachalacas (Ortalis) feed on leaves and fruit and probably are seed dispersers (Delacour and Amadon 1973, Terborgh 1986, Strahl and Grajal 1991). Marion (1976) found that fleshy fruit makes up approximately half of the diet of the Plain Chachalaca (0. vetula), a species also described as herbivorous-frugivorous by Christian-sen (1978). Similarly, the Crested Guan (P. purpurascens) is one of the dispersers of wild nutmeg (Virola surinamensis), whose seeds it regur-gitates (Howe and Vande Kerckhove 1980). In the forests of Northwest Argentina (El Rey National Park), the Dusky-legged Guan (P. obscuru) feeds on various species of fleshy fruit in both summer and autumn (Brown 1986). The Chaco Chachalaca (0. canicollis) inhabits the thorny Chaco forest of Bolivia, Paraguay, and Argentina where it is relatively abundant. There are no previous records of its feeding habits. In the woodlands of the western Argentine Chaco forest, the fruit supply is markedly seasonal and is most concentrated in the wet spring-summer season (Protomastro 1988). Winter is a time of shortage, both of water and of fruit and insects. The Chaco Chachalaca is the only fruit-dispersing bird living in the Chaco woodland throughout the year, Its diet is comprised mainly of plant leaves and fleshy fruits. Seeds pass through its digestive system intact and are probably viable at dispersion.
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Specific features of the forest cover formation after industrial timber cutting during a period of 50 years in southern taiga spruce forests (Kostroma oblast) are described. The statistical analysis of the forest use intensity, the forested area, and the dynamics of the age and species structure of forests was performed. Plans of forest stands obtained for five inspections and taxation databases of 1954 and 1997 were also used. The potentialities of analyzing the structure of forest mapping units using means of overlay in the geoinformation system are considered. Parameters for distinguishing forest compartments were calculated. The dynamics of these parameters reflect the natural development of forest, effects of adverse environmental factors, economic history of the region, and specific features of individual interpretation of the survey materials in forest management.
Article
Vegetation research in boreal forests has tended to focus on the tree component, while little attention has been paid to understory components such as dwarf shrubs, mosses, and reindeer lichens. However, the productivity of understory vegetation is probably comparable to that of the trees. We review recent research in the boreal forest of northern Sweden to highlight the ecological importance of understory vegetation, both in the short term by influencing tree seedling regeneration, and in the longer term by affecting belowground processes such as decomposition, nutrient flow, and buildup of soil nutrients. Wildfire resulting from lightning strike is a primary determinant of understory vegetation, and as such is a major driver of forest community and ecosystem properties. Forest management practices that alter the fire regime and the composition of understory vegetation may have long-term consequences for both conservation goals and commercial forest productivity.
Article
We studied the composition and structure of the woody plant community in a logged/grazed forest, an abandoned road, a burned forest, and a primary forest as a control. The disturbances occurred 10 years prior to the study. The logged/grazed forest was similar in physiognomy to the primary forest, whereas shrubs dominated the abandoned road and burned forest. Using rarefaction techniques, the total species richness (adult, >0.5 cm diameter, and saplings, <0.5 cm diameter) was significantly highest in the logged forest. Basal area and adult plant density were similar in the logged and primary forest, and considerably higher than those of the burned forest and abandoned road, the last two types having more stems per individual. Species composition differed among communities; most notably some pioneer species were absent from the primary forest. For saplings, the abandoned road had the lowest species richness and plant density. Sapling density was highest in the logged forest due to one shrub species that was abundant in disturbed areas. Saplings of one valuable timber species, Aspidosperma quebracho-blanco, were abundant on all sites, probably due to the capacity of this species to sprout after root damage. Stem densities in the primary and logged forests were higher than on the abandoned road and in the burned forest except for the smallest diameter class (0.5-1 cm). Logged forest tended to have higher densities, but smaller individuals than the primary forest. Considering the paucity of well-conserved areas in the Argentine Chaco, the management of extended accidental disturbance (i.e. forest fires) should be considered for long-term use and conservation planning.
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a b s t r a c t Reduced-impact logging (RIL) is a set of techniques aimed to maintain forest structure and functions of the harvested forest as similar as possible to pre-logging status, while reducing adverse impacts from log-ging activity on the remaining forest. We analysed the mid-term effects of RIL on the regeneration of the long-lived pioneers (LLP) Bagassa guianensis and Jacaranda copaia; the partially shade tolerant (PST) Hymenaea courbaril, Dipteryx odorata, and Carapa guianensis and the total shade tolerant species (TST) Symphonia globulifera and Manilkara huberi. This study was carried out in an intensive study plot in the 600,000-ha Tapajós National Forest, Eastern Amazon – Brazil (03°02 0 S and 54°56 0 W). Three transects split in 10 Â 10 m plots, adding up to 2.37 ha were sampled in an area where RIL was applied, and com-pared with a same size sampling in an unlogged area. The regeneration of individuals 620 cm in dbh was inventoried and measured before logging in 2003 and three times after logging (2004, 2006, and 2009). RIL modified the forest structure creating more gap-phase plots, with the consequences of such distur-bance still remaining after 6 years. Densities of B. guianensis, J. copaia, and S. globulifera increased, while C. guianensis diminished. The positive effect on the density of LLP species was, however, ephemeral and disappeared 2 years after logging. RIL had a positive effect on the height growth rate of S. globulifera and on the dbh growth rate of C. guianensis. Plants growing in the gap-phase plots had higher height growth rates (ANOVA, F 2;2980 = 33.3, p < 0.001) than plants growing in other phases, but the same difference was not observed for dbh growth rates (ANOVA, F 1;364 = 0.9, p = 0.33). Crown position had positive effects on height and dbh growth rates: the higher the crown position, the faster the plant grows in height (ANOVA, F 3;2979 = 148.4, p < 0.001) and dbh (ANOVA, F 3;362 = 26.1, p < 0.001). The application of RIL following the Brazilian regulations, may be considered a silvicultural technique for increasing density and growth rates of commercial species, but additional silvicultural interventions, as liberation for example, might be required for maintaining the ecological outcomes of RIL in the long run. Ó 2012 Elsevier B.V. All rights reserved.
Article
Tropical forest ecosystems are threatened by habitat conversion and other anthropogenic actions. Timber production forests can augment the conservation value of primary forest reserves, but studies of logging effects often yield contradictory findings and thus inhibit efforts to develop clear conservation strategies. We hypothesized that much of this variability reflects a common methodological flaw, simple pseudoreplication, that confounds logging effects with preexisting spatial variation. We reviewed recent studies of the effects of logging on biodiversity in tropical forests (n = 77) and found that 68% were definitively pseudoreplicated while only 7% were definitively free of pseudoreplication. The remaining proportion could not be clearly categorized. In addition, we collected compositional data on 7 taxa in 24 primary forest research plots and systematically analyzed subsets of these plots to calculate the probability that a pseudoreplicated comparison would incorrectly identify a treatment effect. Rates of false inference (i.e., the spurious detection of a treatment effect) were >0.5 for 2 taxa, 0.3-0.5 for 2 taxa, and <0.3 for 3 taxa. Our findings demonstrate that tropical conservation strategies are being informed by a body of literature that is rife with unwarranted inferences. Addressing pseudoreplication is essential for accurately assessing biodiversity in logged forests, identifying the relative merits of specific management practices and landscape configurations, and effectively balancing conservation with timber production in tropical forests.
Article
Abstract Three experiments were conducted to verify if an increase in environmental stress level would affect the interactions between two species of nurse shrubs and seedlings of Aspidosperma quebracho-blanco. This is a mesic species with a generalist distribution over an extensive environments gradient. The relationship between Larrea divaricata and seedlings of A. quebracho-blanco was studied in two contrasting soils, a silty loam soil with higher surface clay content and a sandy loam soil. The effect of seasonal variability of rainfall on the initial establishment of seedlings under the shade of L. divaricata was evaluated in three consecutive years. The effect of nurse plant shade was tested comparing two shrub species with different types of leaf life span (sclerophyllous-evergreen and leguminous-deciduous). The natural establishment of A. quebracho-blanco depended on shaded microsites, but not on the type of shade provided by different nurse shrubs. Emergence and initial establishment depended on interactions of soil type and seasonal rainfall variation with nurse plants. The importance of facilitation increased with clay soil (CS). Sandy soil was ‘less humid’ than CS under shrub shade. However, establishment success depends on opportune even rainfall distribution in interaction with nurse plant presence.
Article
Abstract Tree regeneration and understory response to selective cutting of DC, and Sim, was measured outside Katavi National Park, Tanzania. Contrary to expectations, a selective harvest had no effect on tree recruitment for either species in this miombo woodland. In unlogged plots along transects taken at increasing distance from a main road, the stand densities of young trees declined away from the road. Since anthropogenic activity along the road results in a high fire frequency but low native ungulate densities, the increased rate of tree regeneration near the road may result from either reduced grazing and browsing pressure by native ungulates, or reduced fire intensity and severity along roads. These effects appear to mask any possible effect of selective harvest on tree recruitment. Currently, there is no evidence of compensatory recruitment of trees of any species into the canopy to replace logged trees and this will lead to a gradual thinning in overstory stand density. French Résumé Introduction
Article
The impact of skidder disturbance on recruitment of commercial tree regeneration within logging gaps was studied using paired scarified and unscarified plots as well as whole-gap surveys of scarified and unscarified areas in a Bolivian tropical humid forest. More than a year following gap creation, variability in the density of regeneration among logging gaps was high, but commercial tree regeneration density tended to be greater in scarified areas than in unscarified areas within gaps for most species. Height growth was also significantly greater for trees in scarified compared to unscarified areas, despite a near doubling of soil compaction in scarified areas. The principal species benefiting from soil disturbance by skidders was Schizolobium amazonicum, which had nearly 10× higher density and 2× greater height growth in scarified compared to unscarified areas. Although initially devoid of vegetation and litter cover, scarified areas had vegetation and litter cover levels similar to unscarified areas after 7 months. Vegetation cover on scarified areas tended to be dominated by early successional tree species while unscarified areas were dominated by forbs and grasses.
Article
We studied the structure of a primary and a secondary forest in the driest portion of the South American Chaco (average annual precipitation 400 mm) and the forest evolution after exploitation. The work was conducted in Chancaní Provincial Natural Park and Forest Reserve, Córdoba, Argentina, where the best preserved forests of the region are found. The secondary forest was subjected to moderate and selective exploitation of the most important forest species of the Dry Chaco region, Aspidosperma quebracho-blanco Schlecht., over 30 years ago. Density of trees and shrubs (>5 cm dbh) was similar in both forests, but total basal area and volume were markedly lower in the secondary forest. Also density of saplings and shrubs (<5 cm diameter) was similar in both forests. A. quebracho-blanco dominated in the primary forest, representing 85% of the total basal area (8 m2) and 92% of the total stand volume (54.03 m3). The secondary forest showed a relative increase of the second most important species, Prosopis flexuosa D.C., and significant differences (P < 0.05) in total basal area (4.72 m2) and total stand volume (24.77 m3) with respect to the primary forest. Furthermore, a tendency towards an increase of less abundant species of lower economic value as well as invasive shrub species was observed. Total basal area and stand volume of the primary forest are indicators of the possible maximum values expected, and may be used as a reference to develop management plans to regenerate forests.
Article
The differences in species composition and horizontal and vertical vegetation structure between a natural forest edge and the adjacent forest interior were analyzed in an old-growth Chaco forest of Argentina. Total basal area in the shrub stratum was slightly greater at the edge, whereas total basal area in the arboreal strata was slightly greater in the forest interior. The abundance of trees and thick stems were significantly greater in the interior, and total stem density, species richness and abundance of thin stems were significantly greater at the forest edge. Compared with the interior, the edge showed greater cover at low heights in the shrub layer and lower cover in the canopy. Edge-interior differences are similar to those reported for both tropical and temperate forests, and appear to be related mainly to the environmental conditions at edges and perhaps to vertebrate-related dispersion mechanisms associated with edges. The similarity of this forest edge with other modified areas elsewhere in the Chaco forest and the relationship with fragmentation processes are discussed.
Article
This paper describes how to test, and potentially falsify, a multivariate causal hypothesis involving only observed variables (i.e., a path analysis) when the data have a hierarchical or multilevel structure, when different variables are potentially defined at different levels of such a hierarchy, and when different variables have different sampling distributions. The test is a generalization of Shipley's d-sep test and can be conducted using standard statistical programs capable of fitting generalized mixed models.
Atlas climático digital de la República Argentina. Instituto Nacional de Tecnología Agropecuaria
  • A Bianchi
  • S Cravero
Bianchi, A., Cravero, S., 2010. Atlas climático digital de la República Argentina. Instituto Nacional de Tecnología Agropecuaria, Buenos Aires.
Los bosques del Chaco Semiárido. Propuestas para la conservación de bosques degradados
  • Brassiolo
Brassiolo, M., 2001. Los bosques del Chaco Semiárido. Propuestas para la conservación de bosques degradados. IDIA 21, 23-28.