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How do size distributions relate to concurrently measured demographic rates? Evidence from over 150 tree species in Panama
- Renato A.F. Lima, Helene C. Muller-Landau, Paulo I. Prado, Richard Condit
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- Journal:
- Journal of Tropical Ecology / Volume 32 / Issue 3 / May 2016
- Published online by Cambridge University Press:
- 11 April 2016, pp. 179-192
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In stable populations with constant demographic rates, size distributions reflect size-dependent patterns of growth and mortality. However, population growth can also affect size distributions, which may not be aligned with current growth and mortality. Using 25 y of demographic data from the 50-ha Barro Colorado Island plot, we examined how interspecific variation in diameter distributions of over 150 tropical trees relates to growth–diameter and mortality–diameter curves and to population growth rates. Diameter distributions were more skewed in species with faster increases/slower decreases in absolute growth and mortality with diameter and higher population growth rates. The strongest predictor of the diameter distribution shape was the exponent governing the scaling of growth with diameter (partial R2 = 0.20–0.34), which differed among growth forms, indicating a role of life history variation. However, interspecific variation in diameter distributions was also significantly related to population growth rates (partial R2 = 0.03–0.23), reinforcing that many populations are not at equilibrium. Consequently, although fitted size distribution parameters were positively related to theoretical predictions based on current size-dependent growth and mortality, there was considerable deviation. These analyses show that temporally variable demographic rates, probably related to cyclic climate variation, are important influences on forest structure.
Chapter Fourteen - Detecting and projecting changes in forest biomass from plot data
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- By Helene C. Muller-Landau, Smithsonian Tropical Research Institute, Matteo Detto, Smithsonian Tropical Research Institute, Ryan A. Chisholm, Smithsonian Tropical Research Institute, Stephen P. Hubbell, Smithsonian Tropical Research Institute, Richard Condit, Smithsonian Tropical Research Institute
- Edited by David A. Coomes, University of Cambridge, David F. R. P. Burslem, University of Aberdeen, William D. Simonson, University of Cambridge
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- Book:
- Forests and Global Change
- Published online:
- 05 June 2014
- Print publication:
- 20 February 2014, pp 381-416
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Summary
Introduction
Increasing atmospheric carbon dioxide, changing climates, nitrogen deposition and other aspects of anthropogenic global change are hypothesised to be changing forest productivity and biomass stocks in tropical forests and elsewhere (Clark 2004; Lewis, Malhi & Phillips 2004; Lewis et al. 2009a; Luo, 2007; Myeni et al. 1997). These hypotheses continue to be much debated, with contrary views on the plausibility of particular mechanisms and on the status of current evidence for or against them (Clark 2007; Friedlingstein et al. 2006; Holtum & Winter 2010; Körner 2009; Wright 2005, 2010). The influence of atmospheric and climate change on forest biomass is of particular interest because of the potential for positive or negative feedbacks. Increases in forest biomass and associated carbon pools would slow the rise in atmospheric carbon dioxide, producing a negative feedback, whereas decreases in forest biomass would have the opposite effect. Uncertainty surrounding these feedbacks is considerable at the global scale, with important implications for global carbon budgets (Luo 2007).
In view of this, it is essential to know whether forests are experiencing changes in productivity and biomass in excess of those typical for their age. Successional forests, those regrowing after disturbances, increase in biomass over time, with the trajectory and duration of this increase varying with forest type (Bormann & Likens 1979; Odum 1969). In the absence of global change, such forests are expected to eventually reach a dynamic equilibrium in which biomass gains from growth and recruitment are balanced by biomass losses from tree death and branchfall, and these old-growth forests thus experience no directional changes in biomass (Odum 1969; Yang, Luo & Finzi 2011). Accordingly, detection of directional changes in biomass in old-growth forests is generally considered evidence of global change influences. When and where such changes are detected, the next critical question concerns prediction of future net carbon fluxes and ultimate carbon stocks of such altered forests.
Dissecting biomass dynamics in a large Amazonian forest plot
- Renato Valencia, Richard Condit, Helene C. Muller-Landau, Consuelo Hernandez, Hugo Navarrete
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- Journal:
- Journal of Tropical Ecology / Volume 25 / Issue 5 / September 2009
- Published online by Cambridge University Press:
- 01 September 2009, pp. 473-482
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Above-ground biomass (AGB) is increasing in most of the Amazon forests. One hypothesis is that forests are responding to widespread and intense human intervention prior to the European conquest (>500 y ago). In this study we confront this hypothesis with changes in AGB over 6.3 y in a large western Amazonian forest plot (>150 000 shrubs and trees and 1100 species with dbh ≥ 10 mm in 25 ha). We examined AGB flux in different habitats and across diameter classes. The forest lost small stems (4.6%), gained large trees (2.6%), and gained biomass (0.7%). The change in AGB stock was due entirely to this upward shift in size leading to more canopy trees and fewer saplings after just 6 y. Across habitats, the biggest increment in biomass was in the secondary-forest patch (3.4% y−1) which we know was cleared about 27 y ago, whereas mature forest on ridges and valleys had small increases (0.10% and 0.09% y−1, respectively). In both censuses, AGB stocks were >50% higher on the ridge than in the valley while relative growth and mortality were higher in the valley. Mean wood specific gravity (WSG) decreased with increasing diameter class; WSG did not change much between censuses in mature forests and did not contribute to the change in AGB stocks. Our forest increased its standing biomass, but far less than the average reported for other Amazonian forests (i.e. 0.30 vs. 0.98 Mg ha−1 y−1). We find no evidence to support the notion that this forest is recovering from long-past human intervention. Instead of a long-term recovery, we believe the forest changed in response to natural fluctuations of the environment (e.g. changes in precipitation, higher CO2), windstorms or other more recent events. The significant differences in AGB stocks between valley and ridge suggest that the terra firme forests are a mosaic of natural habitats, and that this mosaic is in part responsible for the variation in biomass stocks detected in Amazonian terra firme forests.
Resumen: La biomasa aérea de la mayoría de los bosques amazónicos está incrementando. Una hipótesis es que los bosques están respondiendo a un disturbio humano intenso y ampliamente distribuido, anterior a la llegada de los conquistadores europeos (>500 años atrás). En este estudio se confronta esta hipótesis con los cambios en biomasa encontrados en 6.3 años en una parcela de gran escala de la Amazonia occidental (>150.000 arbustos y árboles con diámetro a la altura del pecho ≥10 mm y 1100 especies en 25 ha). Los resultados se examinan por categorías de diámetro y hábitat. En este período el bosque perdió tallos pequeños (4.6%), ganó árboles grandes (2.6%) y ganó biomasa (0.7%). La ganancia en biomasa fue debida enteramente al incremento de árboles de gran tamaño que significó más árboles de dosel y menos juveniles en apenas 6 años. Entre los hábitats, el mayor incremento en biomasa se encontró en un parche de bosque secundario de colina (3.4%/año), cuya edad es de 27 años, mientras el bosque maduro de las colinas y los valles incrementó escasamente (0.10% y 0.09%/año, respectivamente). Tanto al inicio como al final del estudio, el stock de biomasa fue >50% más grande en la colina que en el valle mientras que el crecimiento y la mortalidad relativa fueron mayores en el valle. La media de la gravedad específica de la madera (GEM) fue menor a mayor clase diamétrica; en el bosque maduro, el cambio en la GEM fue insignificante y no contribuyó al aumento en stocks de biomasa. El bosque incrementó la biomasa aérea pero mucho menos que el promedio reportado para otros bosques amazónicos (i.e. 0.30 vs. 0.98 Mg ha−1/año). No se encontró evidencia que apoye la noción de que el bosque se está recuperando de un disturbio de gran escala ocurrido en el pasado. En su lugar, se cree que el bosque cambió en respuesta a fluctuaciones naturales del ambiente (e.g. cambios en precipitación, mayor concentración de CO2), vendavales u otro tipo de eventos más recientes. La diferencia significativa en los stocks de biomasa encontrada entre el valle y la colina sugiere que la tierra firme es un mosaico de hábitats naturales y que este mosaico podría explicar en parte la variación encontrada en los stocks de biomasa de bosques amazónicos de tierra firme.
11 - Seed dispersal of woody plants in tropical forests: concepts, examples and future directions
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- By Helene C. Muller-Landau, University of Minnesota, Britta Denise Hardesty, University of Georgia
- Edited by David Burslem, University of Aberdeen, Michelle Pinard, University of Aberdeen, Sue Hartley, University of Sussex
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- Book:
- Biotic Interactions in the Tropics
- Published online:
- 25 August 2009
- Print publication:
- 08 September 2005, pp 267-309
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Summary
Introduction
Understanding seed dispersal is critical to understanding plant population and community dynamics (Nathan & Muller-Landau 2000), especially in tropical forests where seed rain of virtually all plant species is sparse and patchy (Hubbell et al. 1999; Muller-Landau et al. 2002). Seed rain determines potential population growth rates and spatial patterns, as well as the relative influences of post-dispersal processes such as seed predation (e.g. Wright et al. 2000), microhabitat requirements for establishment (e.g. Svenning 1999) and density-dependent survival (e.g. Harms et al. 2000). Despite its importance, we know very little about seed dispersal of tropical trees, because it has been studied in only a tiny proportion of the many tropical tree species and seed dispersers, and because the patterns that have been observed have largely eluded easy generalization.
Just as there is a greater diversity of plant species and animal species in the tropics than in other regions, there is also a greater diversity of seed-dispersal strategies and patterns. Seed dispersal by animals predominates – it is the main strategy of 70%–90% of tropical forest plant species (Willson et al. 1989) – and involves a tremendous diversity of animal species and behaviours. Birds, bats, arboreal and terrestrial mammals (everything from mice to elephants), ants, dung beetles, even fish can disperse seeds (Levey et al. 1994). Animals may consume fruit and drop, spit or defecate the seeds, carry seeds in their coats or scatter-hoard seeds for later consumption.