Browsing by Autor "Z. Villegas"

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Beyond reduced-impact logging: Silvicultural treatments to increase growth rates of tropical trees
(Elsevier BV, 2008) Marielos Peña‐Claros; Todd S. Fredericksen; Alejandro Alarcón; Geoffrey M. Blate; U. Choque; Claudio Leaño; Juan Carlos Licona; Bonifacio Mostacedo; William Pariona; Z. Villegas
Clearance and Fragmentation of Tropical Deciduous Forest in the Tierras Bajas, Santa Cruz, Bolivia
(Wiley, 2001) Marc K. Steininger; Compton J. Tucker; Peter J. Ersts; Timothy J. Killeen; Z. Villegas; Susanna B. Hecht
Abstract: The Tierras Bajas is an area of 20,000 km 2 of lowland deciduous forest in eastern Santa Cruz, Bolivia, that has undergone rapid change during the past two decades. As part of the largest remaining area of intact deciduous tropical forest in the world, it has been nominated a priority area for conservation by several environmental organizations. We quantified the spatial and temporal patterns of deforestation in the area by digital processing of high‐resolution satellite imagery from 1975 through 1998. The estimated rate of deforestation was among the highest in the world for such a limited area, ranging from 160 km 2 /year in the early1980s to almost 1200 km 2 /year in the late 1990s. Although most deforestation up to 1984 was in Bolivian peasant and Mennonite colonies, most deforestation after 1984 was in non‐Mennonite industrial soybean farms. The level of fragmentation of uncut forest, caused by the spatial patterns of deforestation, also differed among these broad land‐use types. Deforestation in planned and spontaneous peasant colonies was complex in shape, forming relatively large areas of edge‐affected forest, whereas that in Mennonite and other industrial farms was in large, rectangular increments, creating relatively less edge. But the distribution of these farms and the practice of initially clearing around the peripheries of properties resulted in the isolation of large areas of forest. In 1998 four‐fifths of the remaining forest were either within 1 km of a clearance edge or in isolated fragments of <50 km 2 . Compared with deforested areas, the areas of isolated and edge‐affected forest were disproportionately large during the early stages of frontier colonization. These results imply that if the fragmentation effects of deforestation are to be minimized, conservation planning must occur at the earliest stages of frontier development.
Silvicultural treatments enhance growth rates of future crop trees in a tropical dry forest
(Elsevier BV, 2008) Z. Villegas; Marielos Peña‐Claros; Bonifacio Mostacedo; Alejandro Alarcón; Juan-Carlos Licona; Claudio Leaño; William Pariona; U. Choque
Tendencias de la deforestación en las municipios de San Javier y Concepción, Santa Cruz-Bolivia
(2002) Timothy J. Killeen; Z. Villegas; Liliana Soria; Britaldo Soares‐Filho
The importance of wood traits and hydraulic conductance for the performance and life history strategies of 42 rainforest tree species
(Wiley, 2009) Lourens Poorter; Imole McDonald; Alfredo Alarcón; Esther Fichtler; Juan‐Carlos Licona; Marielos Peña‐Claros; Frank J. Sterck; Z. Villegas; Ute Sass‐Klaassen
*In a comparative study of 42 rainforest tree species we examined relationships amongst wood traits, diameter growth and survival of large trees in the field, and shade tolerance and adult stature of the species. *The species show two orthogonal axes of trait variation: a primary axis related to the vessel size-number trade-off (reflecting investment in hydraulic conductance vs hydraulic safety) and a secondary axis related to investment in parenchyma vs fibres (storage vs strength). Across species, growth rate was positively related to vessel diameter and potential specific hydraulic conductance (K(p)), and negatively related to wood density. Survival rate was only positively related to wood density. *Light-demanding species were characterized by low wood and vessel density and wide vessels. Tall species were characterized by wide vessels with low density and large K(p). Hydraulic traits were more closely associated with adult stature than with light demand, possibly because tall canopy species experience more drought stress and face a higher cavitation risk. *Vessel traits affect growth and wood density affects growth and survival of large trees in the field. Vessel traits and wood density are therefore important components of the performance and life history strategies of tropical tree species.