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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). ...
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 . 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]. ...
The restoration of degraded forests is the focus of global attention. Effective restoration requires information on the condition of degraded forests. This study aimed to understand the conditions of illegally logged stands that had also experienced inappropriately short rotations between legal logging cycles in natural production forests in Myanmar. Four rectangular plots (each 0.64 ha) were established in 2013. The plots included illegally logged stumps in three compartments where the latest legal logging was conducted in 2011 after very short rotations between legal logging cycles (up to five harvests between 1995 and 2011, compared with a recommended 30-year logging cycle). Using data from the field measurements in 2013 on the legal and illegal stumps and living trees, we reconstructed stand structure just before and after legal logging in 2011. Before the legal logging in 2011, there were variations in stand structure and the composition of commercial species among four plots. Illegal logging (14–31 trees ha−1) was much higher than legal logging (0–11 trees ha−1). Illegal logging targeted six to nine species that were suitable for high-quality charcoal from various sized trees, while legal logging targeted one or two timber species with a diameter at breast height (DBH) larger than 58 cm. The number of remaining trees in 2013 ranged from 33 to 181 trees ha−1. There was a negative relationship with the number of bamboo clumps, which varied from 6 to 145 clumps ha−1. Bamboo-dominated stands with a low remaining stock of commercial trees may need active restoration such as bamboo cutting and replanting of commercial species. Bamboo cutting could generate income for the local community.
The knowledge of the diversity of species which integrate the goat’s diet is a strategic input to improve the productivity and sustainability of the range extensive systems of the Arid Chaco in the province of Catamarca. The diversity of native forage which is used by goats is studied in this work for a representative area on the second level of the low hill of the Arid Chaco, in the province of Catamarca. The study of the forage vascular flora was made on 145 ha without grasser animals and settled in the southeast of Capital County. It was used the classical methodology for de the systematic determination of the plants. The register of the forage plants and its parts eaten by goats was basically made on direct observations between the years 2008 to 2014 on the extensive grazing regions of La Paz, Valle Viejo, Capital, Capayán and Fray Mamerto Esquiú counties. It was consigned the scientific and common name, the botanical family, habit, status, and the part eaten by goats. It was founded that goats consumed 110 species (72 %) of the 152 total native vascular plants observed in this work. The high diversity of the forage species founded in the low hill botanical communities of the Arid Chaco shows the aptitude of these ecosystems for the development of a sustainability goat keeping.
KEYWORDS: Native forage plants; Goats; Low hill; Arid Chaco; Diversity.
The forest in the Central Argentine Chaco has been dramatically fragmented and persists only as isolated patches in an agricultural matrix. In this study, we evaluated the effects of fragmentation on total density, recruitment and size-class structure of its dominant tree species, a key issue, although little explored, for forest conservation in the region. We particularly analyzed the effects of fragment size and forest cover at landscape level on seven of the most important tree species of the forest. Our results suggest that forest cover at landscape level is more important than fragment size to explain the population patterns of the main tree species. Fragment size was relevant in only one species, Cordia americana, whereas forest cover resulted relevant in five species. The size-class structure of Schinopsis balansae, one of the dominant species of the upper stratum, appeared to be affected in landscapes with less forest cover, showing lower densities of the smaller classes. Our results show that for the conservation of the forest it would be important to increase their protection degree against the expansion of agriculture, attempting to preserve as much of the forest as possible, to promote the forest cover at landscape level and give relevance even to the smallest fragments.
Charcoal production has been widespread in the past and is still common where poor societies and dry forests coexist. For the Dry Chaco in South America, one of the largest remaining dry forests of the world, we describe the geographical distribution, type of production systems, environmental and social context and output of charcoal based on remote sensing (charcoal kiln detection); together with existing environmental (forest cover/biomass), social (population density, poverty), and infrastructure (roads) data. While most of the region has low kiln densities (b1 kiln every 1000 km 2), foci of higher production were found in the north of Santiago del Estero and the west of Chaco provinces (N 1 kiln every 5 km 2). Individual or small groups (up to three units) prevail over the regions (58.2% of all kiln sites), frequently associated with a forest land cover. Large groups of kilns (≥12 units, 15.5% of all kilns) were associated with land cleared for cultivation. For a subset of kiln sites for which forest biomass data was available, we found that typical kiln sites (1–3 kilns) had half of the average biomass of the region within a radius of 125 m. Although charcoal production in the whole region has been stable for 50 years, a strong redistribution from richer to poorer provinces has taken place. At the county level, kiln density and charcoal production records showed a linear association that suggests an average output of 11 tons of charcoal per year per kiln. Comparing counties with high vs. low charcoal production with similarly high forest cover, the first had higher population density and poverty levels. Today small scale charcoal production by poor rural people represents the only significant use of forests products that provides some market incentive for their preservation. However this situation is associated with marginal social conditions, inefficient production, and forest degradation. Developing charcoal production under environmentally and socially virtuous conditions should be seen as a unique opportunity and an urgent challenge in the face of the fast deforestation of dry forests.
Lacking of detail data, forest carbon stock estimation with forest inventory data usually excludes or underestimates understory carbon storage. To quantify the effects of understory on carbon sequestration in a natural secondary Pinus tabulaeformis forest, organ biomass models for arbor, shrub to their growth indices were regressed. Biomass of herbage was estimated in a stratified sampling method. Soil respiration in forest land was measured. Based on above data, carbon budget of Pinus tabulaeformis forest was assessed as 1.882 CO2 Mghm−2year−1, 37.04% of the entire vegetation’s yearly net carbon storage belonging to understory.
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.
Selective logging of tropical forests is increasing in extent and intensity. The duration over which impacts of selective logging persist, however, remains an unresolved question, particularly for African forests. Here, we investigate the extent to which a past selective logging event continues to leave its imprint on different components of an East African forest 45 years later. We inventoried 2358 stems ≥ 10 cm in diameter in 26 plots (200 m × 10 m) within a 5.2 ha area in Kibale National Park, Uganda, in logged and unlogged forest. In these surveys, we characterized the forest light environment, taxonomic composition, functional trait composition using three traits (wood density, maximum height and maximum diameter) and forest structure based on three measures (stem density, total basal area and total above-ground biomass).
In comparison to unlogged forests, selectively logged forest plots in Kibale National Park on average had higher light levels, different structure characterized by lower stem density, lower total basal area and lower above-ground biomass, and a distinct taxonomic composition driven primarily by changes in the relative abundance of species. Conversely, selectively logged forest plots were like unlogged plots in functional composition, having similar community-weighted mean values for wood density, maximum height and maximum diameter. This similarity in functional composition irrespective of logging history may be due to functional recovery of logged forest or background changes in functional attributes of unlogged forest. Despite the passage of 45 years, the legacy of selective logging on the tree community in Kibale National Park is still evident, as indicated by distinct taxonomic and structural composition and reduced carbon storage in logged forest compared with unlogged forest. The effects of selective logging are exerted via influences on tree demography rather than functional trait composition.
Successful persistence of dry forests depends on tree regeneration, which depends on a balance of complex biotic interactions. In particular, the relative importance and interactive effects of shrubs and herbivores on tree regeneration are unclear. In a manipulative study, we investigated if thornless shrubs have a direct net effect, an indirect positive effect mediated by livestock, and/or an indirect negative effect mediated by small vertebrates on tree regeneration of two key species of Chaco forest (Argentina). In a spatial association study, we also explored the existence of net positive interactions from thorny and thornless shrubs. The number of Schinopsis lorentzii seedlings was highest under artificial shade with native herbivores and livestock excluded. Even excluding livestock, no seedlings were found with natural conditions (native herbivores present with natural shade or direct sunlight) at the end of the experiment. Surprisingly, seedling recruitment was not enhanced under thornless shrubs, because there was a complementary positive effect of shade and interference. Moreover, thornless shrubs had neither positive nor negative effects on regeneration of S. lorentzii. Regeneration of Aspidosperma quebracho-blanco was minimal in all treatments. In agreement with the experiment, spatial distributions of saplings of both tree species were independent of thornless shrubs, but positively associated with thorny shrubs. Our results suggest that in general thornless shrubs may have a negligible effect and thorny shrubs a net positive effect on tree regeneration in dry forests. These findings provide a conceptual framework for testing the impact of biotic interactions on seedling recruitment in other dry forests.
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.
The Chaco Árido region of Argentina has suffered strong desertification. Some 95% of the area is now covered by deciduous plant species that form dense, spiny shrubs, many of which are of little forage value. Lack of forage during winter leads to economic losses, contributing to the overall low profitability of the regions small goat-producers. The incorporation of appropriate shrub plants into the production system might help ensure and make more uniform the supply of feed to goats over the year. However, it is first vital to determine the preferences of these animals in order to prioritise such incorporations. The preferences of local goats for the native shrubs of the Chaco Árido region were therefore established over the different seasons of the year by means of a "cafeteria" experiment. Preferences were determined using the Di Rienzo, Guzmán and Casanoves means-comparison test. Maytenus spinosa, Celtis pallida and Lippia turbinata were frequently chosen in Summer and Autumn. The consumption of Condalia microphylla was low year-round while Larrea divaricata was consumed strongly throughout the year. The latter species and Capparis atamisquea were particular favourites during the winter reduction in forage availability. It is suggested that these species be incorporated into local goat production systems.
Forest cover change directly affects biodiversity, the global carbon budget, and ecosystem function. Within Latin American and the Caribbean region (LAC), many studies have documented extensive deforestation, but there are also many local studies reporting forest recovery. These contrasting dynamics have been largely attributed to demographic and socio-economic change. For example, local population change due to migration can stimulate forest recovery, while the increasing global demand for food can drive agriculture expansion. However, as no analysis has simultaneously evaluated deforestation and reforestation from the municipal to continental scale, we lack a comprehensive assessment of the spatial distribution of these processes. We overcame this limitation by producing wall-to-wall, annual maps of change in woody vegetation and other land-cover classes between 2001 and 2010 for each of the 16,050 municipalities in LAC, and we used nonparametric Random Forest regression analyses to determine which environmental or population variables best explained the variation in woody vegetation change. Woody vegetation change was dominated by deforestation (−541,835 km²), particularly in the moist forest, dry forest, and savannas/shrublands biomes in South America. Extensive areas also recovered woody vegetation (+362,430 km²), particularly in regions too dry or too steep for modern agriculture. Deforestation in moist forests tended to occur in lowland areas with low population density, but woody cover change was not related to municipality-scale population change. These results emphasize the importance of quantitating deforestation and reforestation at multiple spatial scales and linking these changes with global drivers such as the global demand for food.
El nombre Schinopsis fue establecido por Engler (1876) a partir de la unión del antiguo nombre Schinus (i.e. ‘lentisco’, Pistacia lentiscus L.) con la partícula -opsis (i.e. ‘parecido a’); es decir, plantas semejantes/
parecidas al ‘lentisco’ (Muñoz, 2000). Se trata de un pequeño género de mucha importancia económica nacional e internacional, cuya madera es reputada por su durabilidad y extrema dureza (de allí el nombre vernáculo de varias de sus especies: ‘quebracho’, derivado de ‘quiebrahacha’).
El quebracho colorado es una especie de antigua explotación y de gran importancia comercial y cultural. Por ello ciertos aspectos
como su distribución geográfica, su morfología, taxonomía, etnobotánica y regeneración se conocen acabadamente. Tal vez lo más estudiado de esta especie refiera a la multiplicidad de
aspectos concernientes a sus taninos (origen y composición, producción, efectos y usos agroindustriales), pero curiosamente existe muy poca información sobre sus efectos tóxicos y la dermatitis
que provoca en humanos ante el contacto a campo. Otros aspectos, como sus procesos reproductivos comienzan a ser comprendidos en
contextos ecológicos, mientras que la verdadera naturaleza del híbrido putativo entre esta especie y S. lorentzii aún resta ser develada. Por otra parte, se conoce muy poco sobre la ecofisiología
y las interacciones biológicas de la especie, de modo tal que sea posible comprender mejor el rol de la especie en las comunidades de las que forma parte, a lo largo del Chaco Húmedo desde el suroeste del Brasil hasta la provincia de Santa Fe en la Argentina.
La presente contribución pretende sintetizar y recopilar la información existente sobre este espléndido árbol, emblemático de la flora argentina y sin dudas de la Ecorregión del Chaco Húmedo.
La pérdida de bosques naturales y su fragmentación en el paisaje por actividad agrícola pueden afectar procesos ecológicos como la dispersión biótica y también el mantenimiento de la diversidad de especies nativas y la invasión de plantas exóticas. En el contexto de la fragmentación del bosque chaqueño de la provincia de Córdoba se evaluó remoción y frugivoría de frutos carnosos en especies de dos fragmentos con superficie menor a 5 ha y dos de bosque continuo superior a 300 ha. Una vez por semana durante dos meses los frutos de cada individuo se contabilizaron tomándose como indicador de la dispersión biótica a la probabilidad de supervivencia de los frutos (PSF). Los elementos florísticos ornitócoros incluyen a 15 especies, principalmente leñosas. En todas las especies ornitócoras presentes en cada sitio se encontraron diferencias en la PSF, siendo mayor en los fragmentos pequeños respecto a los sitios de bosque continuo. Asimismo, la PSF fue menor en la especie arbustiva de origen exótico en relación con la nativa. Contrariamente, en las especies exóticas leñosas la PSF fue mayor que en las nativas. Estos resultados sugieren que la dispersión de frutos es afectada por la reducción del bosque chaqueño y que los fragmentos pequeños son aún utilizados por las aves como áreas de alimentación. Este comportamiento de las aves sería importante para la persistencia y colonización de nuevos sitios por las plantas con frutos carnosos, así como para la conservación de los pequeños fragmentos de bosque inmersos en los agroecosistemas del centro de Argentina.
This discussion paper assesses the state of knowledge on tropical dry forests1 as it relates to CIFOR’s strategy and identifies research opportunities that align with CIFOR’s strategic goals. Over the past two decades, CIFOR has accumulated a substantial body of work on dry forests, with a particular focus on African dry forests. This paper is intended to build on that work, by gathering wider research from around the world, as CIFOR seeks to widen the geographic scope of its research on dry forests. The present assessment explores five themes: climate change mitigation and adaptation; food security and livelihoods; demand for energy; sustainable management of dry forests; and policies and institutional support for sustainable management.
These themes emerged as priority areas during discussions on dry forest research priorities held at CIFOR’s Dry Forests Symposium in South Africa in 20112. Research on these themes should be considered a priority, given the importance of dry forests to people and ecosystems around the world and the threats posed to them.
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.
Logging activities generate microsites that can be colonized by different woody plant species whose regeneration may be influenced by biotic and abiotic factors. This work describes three microsites created by logging (main roads, skid trails and logging gaps) in two sites with different recovery time (one and two years) in the semi-arid Chaco of Argentina. Woody plant richness and diversity are compared and the relationship of plant density as a function of microsite type, recovery time, soil compaction, canopy cover and herbaceous cover is evaluated. Richness and species composition were similar in all microsites, which were dominated by the same species. Main roads presented more compacted soil, skid trails had denser canopies and logging gaps had soils with larger herbaceous cover. Woody plant density depended on the interaction of the covariates (soil compaction, canopy cover and herbaceous cover) with microsites and recovery time. Road plant density was low and was negatively related with soil compaction and positively related
Little is known about the impacts of selective logging on herbaceous plants
of tropical forests. If logging impacts on nontimber species are low and little time is required
for recovery, logged forests could be compatible with conservation of some elements of
the understory flora. As many nontimber species may have commercial value, knowledge
about the impacts of different logging intensities is necessary to determine levels of timber
extraction compatible with multiple use of forests. In this study, we examined the effects
of logging intensity, time after logging, and skidder tracks, on the composition and diversity
of the ground-level herb community of a terra-firme forest in central Amazonia. Logging
was carried out at varying intensities in eight 4-ha experimental plots in 1987, three plots
in 1993, and five plots were controls. Herb community composition, analyzed with hybrid
multidimensional scaling (HMDS), was not significantly affected by logging intensity, but
was significantly related to the area covered by logging gaps and skidder tracks. There was
no significant difference in community composition and richness between treatments with
different times after logging. Species richness was also not related to the logging intensity.
Some species (18.2%) were found only in logged plots and were mainly from habitats
outside the rain forest. There were significant differences in herb composition between
controls and skidder tracks, but recent and old skidder tracks were mixed in the ordination
space, suggesting that recovery in skidder tracks is slower than in other areas affected by
logging. Overall, our results indicate that the ground herb community is not severely affected
by selective logging at the intensities used in this experiment. The alterations in composition
are mainly local, and restricted to the most disturbed patches. We conclude that forests
managed with logging intensities similar to those used in this experiment could be compatible
with conservation of understory herbs. Skidder tracks should be minimized, as they
have the greatest long-term impact and allow species from other habitats to invade the
A major impediment to the sustainable management of tropical dry forests in Bolivia is the scarcity of natural regeneration of commercial timber tree species. Where regeneration is present, true seedlings of many species are outnumbered by vegetative sprouts from roots, broken stems, and the stumps of felled trees. This study evaluates the importance of resprouts promoted by logging operations for the regeneration of commercially important canopy tree species. The objectives of the study were: (1) to characterize stump and root sprouting behaviors of canopy tree species harvested for timber; (2) to quantify the effect of logging on relative abundances and growth rates of stump sprouts, root sprouts, and true seedlings; (3) to relate the species-specific probabilities of stump sprouting to stump diameter and stump height; and (4) to explore how sprouting varies with the ecological requirements of canopy tree species. The study was carried out 1–5 years after logging of a privately owned land in a Bolivian tropical dry forest. Twenty-seven of the 31 species monitored resprouted at least occasionally, among which Centrolobium microchaete (Leguminosae-Fabaceae) and Zeyheria tuberculosa (Bignoniaceae) were the most frequent stump sprouters, and Acosmium cardenasii (Leguminosae-Fabaceae) and C. microchaete were the most frequent root sprouters. In all species the number of sprouts declined with increasing stump diameter and stump height. The probability of stump resprouting differed among species but did not vary consistently with stump diameter, except in Z. tuberculosa in which it declined. Approximately 45% of juveniles
In forests characterized by a dense woody and herbaceous understory layer, seedling recruitment is often directly suppressed via interspecific competition. Alternatively, these dense layers may indirectly lower tree recruitment by providing a haven for seed and seedling predators that prey on neighboring plant species. To simultaneously test for resource competition and indirect, habitat-mediated effects, we factorially manipulated understory plant cover (removed versus intact) and predation (exclosures versus controls) at three forested sites. We found that vegetation cover created privileged foraging areas that increased seed removal and seedling predation rates. Predator preference was directly related to seed size with larger seeded species including Prunus serotina Ehrh. and Fagus grandifolia Ehrh. removed more readily than smaller seeded species such as Fraxinus americana L. We found strong species-specific evidence for habitat-mediated indirect effects; establishment of P. serotina and Acer saccharum Marsh.was significantly lower under an intact hay-scented fern (Dennstaedtia punctilobula (Michx.) T. Moore) canopy when small mammals were present. Competition also played a strong role; both P. serotina and Acer rubrum L. survival as well as A. rubrum emergence were reduced under a fern canopy with or without seed predators. The impact of habitat-mediated indirect effects and resource competition appear to vary predictably based upon predator preferences and differences in the timing of woody seed dispersal and germination relative to vegetation cover phenology. Overall, our results suggest that habitat-mediated indirect effects may be common and occur wherever vegetation provides the potential for creating privileged foraging areas.
The aim of this work was to determine the seasonal variation of botanical composition and diversity of the goats' diets grazing during the day, in a forest of the Chaco semiarid region, Argentina. This area has clearly defined seasons, dry during the winter-spring and wet during summer-autumn. The goats are a very important resource in the region because of their good adaptation. The trial was conducted with 2,5 animals/ha, grazing during the day, and kept at corral in the night. The botanical composition of diet was determined using the microhistological method of feces; diversity Index was estimated using Shannon and Weaver Index, and the preference Index was estimated using Krueger Index. The herbage components of the diet were organized as: dicotyledonous herbs, grasses, woody species and epifitic species. The dicotyledonous herbs were preferred by the goats in the wet seasons, and grasses and woody species were preferred in dry seasons. The diversity index suggests the specialistic behavior of goats in the dry season, and generalistic behavior in the wet season, in function of availability of forage.
Sustainable management of selectively logged tropical forests requires that felled trees are replaced through increased recruitment
and growth. This study compares road track and roadside regeneration with regeneration in unlogged and selectively logged
humid tropical forest in north-eastern Bolivia. Some species benefited from increased light intensities on abandoned logging
roads. Others benefited from low densities of competing vegetation on roads with compacted soils. This was the case for the
small-seeded species Ficus boliviana C.C. Berg and Terminalia oblonga (Ruiz & Pav.) Steud. Some species, e.g. Hura crepitans L., displayed patchy regeneration coinciding with the presence of adult trees. Our results suggest that current management
practices could be improved by intensifying logging in some areas to improve regeneration of light demanding species. Sufficient
seed input in logged areas should be ensured by interspersing large patches of unlogged forest with logged areas. This may
also assist regeneration of species that perform poorly in disturbed areas.
The vast plain known as the Gran Chaco is a natural region of more than 1·3 million square kilometres, the second largest natural biome in South America, with only the Amazon region being larger. It extends over parts of Argentina, Bolivia, Paraguay and, marginally, Brazil. The original landscape of the region was mostly a park land with patches of hardwoods intermingled with grasslands. Increasing human encroachment, largely by poor campesinos, with associated overgrazing, excessive timber harvesting, charcoal production and over-exploitation of wildlife, is transforming the region into a dense and unproductive shrub land and is contributing to increasing rural poverty. A management system for the sustainable use of the Chaco has been developed based on a multiple-species ranching system that includes beef, timber, charcoal and wildlife production. An evaluation of the management system finds that it is capable of protecting and enhancing the resource base, while providing higher economic returns in a sustainable manner. However, high initial costs, as well as a divergence between the «best» interests of campesinos and society, jeopardize the feasibility of the managed system.
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.
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.
"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."
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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
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, M., 2001. Los bosques del Chaco Semiárido. Propuestas para la conservación de
bosques degradados. IDIA 21, 23-28.