Long-term decline of Amazon carbon the sink
Brienen, R.J.W. ; Phillips, O.L. ; Feldpausch, T. ; Gloor, E. ; Baker, T.R. ; Arets, E.J.M.M. ; Pena Claros, M. ; Poorter, L. - \ 2015
Nature 519 (2015). - ISSN 0028-0836 - p. 344 - 348.
tropical rain-forests - experimental drought - wood productivity - tree mortality - turnover rates - sensitivity - biomass - growth - plots - co2
Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades1, 2, with a substantial fraction of this sink probably located in the tropics3, particularly in the Amazon4. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity5. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale1, 2, and is contrary to expectations based on models6.
Global variability in leaf respiration in relation to climate, plant functional types and leaf traits
Atkin, O. ; Bloomfield, K. ; Reich, P.B. ; Tjoelker, M.G. ; Asner, G. ; Bonal, D. ; Bönisch, G. ; Poorter, L. - \ 2015
New Phytologist 206 (2015)2. - ISSN 0028-646X - p. 614 - 636.
elevated atmospheric co2 - terrestrial carbon-cycle - tropical rain-forests - dark respiration - thermal-acclimation - temperature sensitivity - vegetation models - photosynthetic capacity - nitrogen concentration - scaling relationships
Leaf dark respiration (R-dark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of R-dark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in R-dark. Area-based R-dark at the prevailing average daily growth temperature (T) of each siteincreased only twofold from the Arctic to the tropics, despite a 20 degrees C increase in growing T (8-28 degrees C). By contrast, R-dark at a standard T (25 degrees C, R-dark(25)) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher R-dark(25) at a given photosynthetic capacity (V-cmax(25)) or leaf nitrogen concentration ([N]) than species at warmer sites. R-dark(25) values at any given V-cmax(25) or [N] were higher in herbs than in woody plants. The results highlight variation in R-dark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of R-dark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).
Integrating Stand and Soil Properties to Understand Foliar Nutrient Dynamics during Forest Succession Following Slash-and-Burn Agriculture in the Bolivian Amazon
Broadbent, E.N. ; Zambrano, A.M.A. ; Asner, G.P. ; Soriano, M. ; Field, C.B. ; Souza, H.R. de; Pena Claros, M. ; Adams, R.I. ; Dirzo, R. ; Giles, L. - \ 2014
PLoS ONE 9 (2014)2. - ISSN 1932-6203 - 23 p.
carbon-isotope discrimination - tropical rain-forests - n-15 natural-abundance - northeastern costa-rica - below-ground carbon - land-use change - n-p ratios - secondary forest - organic-matter - brazilian amazon
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 d13C 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 d13C dynamics were largely constrained by plant species composition. Foliar d15N 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 15N and 13C 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.
The Potential of Tree Rings for the Study of Forest Succession in Southern Mexico
Brienen, R.J.W. ; Lebrija Trejos, E.E. ; Breugel, M. van; Bongers, F. ; Meave, J. ; Martinez-Ramos, M. - \ 2009
Biotropica 41 (2009)2. - ISSN 0006-3606 - p. 186 - 195.
tropical rain-forests - deciduous forest - dry forest - growth - dynamics - chronosequence - disturbance - regeneration - diversity - history
Studies of tropical secondary forest succession face strong limitations due to the slow pace of succession and the time-consuming task of monitoring processes. The occurrence of tree rings in secondary forest trees may help expand our knowledge on succession in these systems and may be useful for fallow dating in chronosequence studies.We examine here the potential of tree rings to study forest succession by sampling 70 species along chronosequences of dry and wet forests in southernMexico. Based on wood anatomical features, we estimated that about 37 percent of the species presented distinct growth rings useful for ring studies.Overall, maximum number of rings matched well the interview-based fallow ages but, at some sites, trees had consistently higher numbers of rings, probably due to errors in fallow ages derived from interviews. Best fallow age estimations were obtained by examining rings in both pioneer and nonpioneer species. Reconstruction of species' establishment dates revealed that pioneer and nonpioneer species establish early during succession, and that species of both groups continue to recruit after many years. Our study clearly shows that tree ring analysis is a promising tool for studies on secondary forest succession in the tropics.
Species dynamics during early secondary forest succession: recruitment, mortality and species turnover.
Breugel, M. van; Bongers, F.J.J.M. ; Martínez-Ramos, M. - \ 2007
Biotropica 39 (2007)5. - ISSN 0006-3606 - p. 610 - 619.
tropical rain-forests - dispersal distance - plant succession - burn agriculture - moist forest - puerto-rico - growth - light - chronosequence - management
The "Initial Floristic Composition" hypothesis is applied to secondary tropical rain forest succession in abandoned agricultural fields with light previous land-use and close to seed sources. This hypothesis predicts that both pioneer and shade-tolerant species colonize a site directly after abandonment, and as the canopy closes, the recruitment of pioneers sharply declines, while recruitment of shade-tolerant species continues. It also predicts higher mortality among pioneers. Consequently, recruited and dead trees are expected to differ in species composition, with highest species richness for the recruits. During 18 mo, we monitored recruitment and mortality of trees with height ¿ 1.5 m in eight plots in abandoned cornfields with initial fallow age of 1¿5 yr, in SE Mexico. Shade-tolerant species established in the first years of succession, albeit in low numbers. As predicted, recruited and dead trees differed in species richness and composition, and in shade-tolerant frequency. In contrast to our expectations, over 50 percent of recruits were from pioneer species, as high stand-level mortality opened new opportunities for continued pioneer colonization. Species turnover starts very early in succession but is not always a gradual and continuous process, complicating prevailing succession models. The strong spatial and temporal variability of succession emphasizes the need to monitor these dynamics in permanent plots across a range of initial stand ages, with multiple plots in a given age class.