Browsing by Autor "Gregory P. Asner"

Now showing 1 - 6 of 6

Amazon tree dominance across forest strata
(Nature Portfolio, 2021) Frederick C. Draper; Flávia R. C. Costa; Gabriel Arellano; Oliver L. Phillips; Álvaro Duque; Manuel J. Macía; Hans ter Steege; Gregory P. Asner; Érika Berenguer; Juliana Schietti
Individual-Based Modeling of Amazon Forests Suggests That Climate Controls Productivity While Traits Control Demography
(Frontiers Media, 2019) Sophie Fauset; Manuel Gloor; Nikolaos M. Fyllas; Oliver L. Phillips; Gregory P. Asner; Timothy R. Baker; Lisa Patrick Bentley; Roel Brienen; Bradley Christoffersen; Jhon del Águila Pasquel
Climate, species composition, and soils are thought to control carbon cycling and forest structure in Amazonian forests. Here, we add a demographics scheme (tree recruitment, growth, and mortality) to a recently developed non-demographic model - the Trait-based Forest Simulator (TFS) – to explore the roles of climate and plant traits in controlling forest productivity and structure. We compared two sites with differing climates (seasonal versus aseasonal precipitation) and plant traits. Through an initial validation simulation, we assessed whether the model converges on observed forest properties (productivity, demographic and structural variables) using datasets of functional traits, structure, and climate to model the carbon cycle at the two sites. In a second set of simulations, we tested the relative importance of climate and plant traits for forest properties within the TFS framework using the climate from the two sites with hypothetical trait distributions representing two axes of functional variation (‘fast’ versus ‘slow’ leaf traits, and high versus low wood density). The adapted model with demographics reproduced observed variation in gross (GPP) and net (NPP) primary production, and respiration. However NPP and respiration at the level of plant organs (leaf, stem, and root) were poorly simulated. Mortality and recruitment rates were underestimated. The equilibrium forest structure differed from observations of stem numbers suggesting either that the forests are not currently at equilibrium or that mechanisms are missing from the model. Findings from the second set of simulations demonstrated that differences in productivity were driven by climate, rather than plant traits. Contrary to expectation, varying leaf traits had no influence on GPP. Drivers of simulated forest structure were complex, with a key role for wood density mediated by its link to tree mortality. Modelled mortality and recruitment rates were linked to plant traits alone, drought-related mortality was not accounted for. In future, model development should focus on improving allocation, mortality, organ respiration, simulation of understory trees and adding hydraulic traits. This type of model that incorporates diverse tree strategies, detailed forest structure and realistic physiology is necessary if we are to be able to simulate tropical forest responses to global change scenarios.
Integrating Stand and Soil Properties to Understand Foliar Nutrient Dynamics during Forest Succession Following Slash-and-Burn Agriculture in the Bolivian Amazon
(Public Library of Science, 2014) Eben N. Broadbent; Angélica M. Almeyda Zambrano; Gregory P. Asner; Marlene Soriano; Christopher B. Field; Harrison Ramos de Souza; Marielos Peña‐Claros; Rachel I. Adams; Rodolfo Dirzo; Larry Giles
Secondary forests cover large areas of the tropics and play an important role in the global carbon cycle. During secondary forest succession, simultaneous changes occur among stand structural attributes, soil properties, and species composition. Most studies classify tree species into categories based on their regeneration requirements. We use a high-resolution secondary forest chronosequence to assign trees to a continuous gradient in species successional status assigned according to their distribution across the chronosequence. Species successional status, not stand age or differences in stand structure or soil properties, was found to be the best predictor of leaf trait variation. Foliar δ(13)C had a significant positive relationship with species successional status, indicating changes in foliar physiology related to growth and competitive strategy, but was not correlated with stand age, whereas soil δ(13)C dynamics were largely constrained by plant species composition. Foliar δ(15)N had a significant negative correlation with both stand age and species successional status, - most likely resulting from a large initial biomass-burning enrichment in soil (15)N and (13)C and not closure of the nitrogen cycle. Foliar %C was neither correlated with stand age nor species successional status but was found to display significant phylogenetic signal. Results from this study are relevant to understanding the dynamics of tree species growth and competition during forest succession and highlight possibilities of, and potentially confounding signals affecting, the utility of leaf traits to understand community and species dynamics during secondary forest succession.
Recovery Of Forest Structure And Spectral Properties After Selective Logging In Lowland Bolivia
(Wiley, 2006) Eben N. Broadbent; Daniel J. Zarin; Gregory P. Asner; Marielos Peña‐Claros; Amanda Cooper; Ramon C. Littell
Effective monitoring of selective logging from remotely sensed data requires an understanding of the spatial and temporal thresholds that constrain the utility of those data, as well as the structural and ecological characteristics of forest disturbances that are responsible for those constraints. Here we assess those thresholds and characteristics within the context of selective logging in the Bolivian Amazon. Our study combined field measurements of the spatial and temporal dynamics of felling gaps and skid trails ranging from <1 to 19 months following reduced-impact logging in a forest in lowland Bolivia with remote-sensing measurements from simultaneous monthly ASTER satellite overpasses. A probabilistic spectral mixture model (AutoMCU) was used to derive per-pixel fractional cover estimates of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and soil. Results were compared with the normalized difference in vegetation index (NDVI). The forest studied had considerably lower basal area and harvest volumes than logged sites in the Brazilian Amazon where similar remote-sensing analyses have been performed. Nonetheless, individual felling-gap area was positively correlated with canopy openness, percentage liana coverage, rates of vegetation regrowth, and height of remnant NPV. Both liana growth and NPV occurred primarily in the crown zone of the felling gap, whereas exposed soil was limited to the trunk zone of the gap. In felling gaps >400 m2, NDVI, and the PV and NPV fractions, were distinguishable from unlogged forest values for up to six months after logging; felling gaps <400 m2 were distinguishable for up to three months after harvest, but we were entirely unable to distinguish skid trails from our analysis of the spectral data.
Spatial partitioning of biomass and diversity in a lowland Bolivian forest: Linking field and remote sensing measurements
(Elsevier BV, 2008) Eben N. Broadbent; Gregory P. Asner; Marielos Peña‐Claros; Michael Palace; Marlene Soriano
Timber production in selectively logged tropical forests in South America
(Wiley, 2007) Michael Keller; Gregory P. Asner; Geoffrey M. Blate; John McGlocklin; Frank Merry; Marielos Peña‐Claros; J. Zweede
Selective logging is an extensive land-use practice in South America. Governments in the region have enacted policies to promote the establishment and maintenance of economically productive and sustainable forest industries. However, both biological and policy constraints threaten to limit the viability of the industry over the long term. Biological constraints, such as slow tree growth rates, can be overcome somewhat by management practices. In order to improve the likelihood of success for sustainable management, it is important to accept that forests change over time and that managed forests may be different than those of the present. Furthermore, education campaigns must convince decision makers and the public of the value of forest resources. We recommend that the forest sector be governed by simple, understandable regulations, based on sound science and consistent enforcement, and that governments work with, instead of against, industry. Problems of tropical forest management are far from being solved, so biological and social scientists should continue to generate new knowledge to promote effective management. El aprovechamiento selectivo es una práctica extensiva del uso del suelo en Sudamérica. Los gobiernos de la región han establecido políticas para promover el establecimiento y mantenimiento de industrias forestales económicamente productivas y sostenibles. Sin embargo, tanto restricciones biológicas como políticas amenazan con limitar la viabilidad a largo plazo de esta industria. Las limitaciones biológicas, tales como una baja tasa de crecimiento de los árboles, pueden ser superadas parcialmente a través de prácticas de manejo. Para aumentar la probabilidad de éxito del manejo sostenible es importante reconocer que los bosques cambian en el tiempo y que los bosques manejados podrían ser diferentes a los bosques actuales. Asimismo las campañas de educación deben convencer a los tomadores de decisiones y al público en general del valor que tienen los recursos forestales. Recomendamos que el sector forestal esté regido por regulaciones sencillas y comprensibles, basadas en una ciencia sólida y con aplicación consistente, y que los gobiernos trabajen con, y no en contra de, la industria. Los problemas de manejo de los bosques tropicales están lejos de ser resueltos, por lo que los científicos de las áreas biológicas y sociales deben continuar generando nuevo conocimiento para promover un manejo forestal efectivo.