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Glob Chang Biol. 2018 Dec;24(12):5867-5881. doi: 10.1111/gcb.14457. Epub 2018 Oct 21.

Windthrows control biomass patterns and functional composition of Amazon forests.

Author information

1
Biogeochemical Processes Department, Max-Planck-Institute for Biogeochemistry, Jena, Germany.
2
Laboratório de Manejo Florestal, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil.
3
AG Spezielle Botanik und Funktionelle Biodiversität, Universität Leipzig, Leipzig, Germany.
4
Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California.
5
Environmental Change Institute, University of Oxford, Oxford, UK.
6
Ciência e Tecnologia do Amazonas, Campus Manaus-Zona Leste, Herbário EAFM, Instituto Federal de Educação, Manaus, Brazil.
7
Geography Department, University of California, Berkeley, California.
8
German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany.
9
Functional Biogeography Fellow Group, Max-Planck-Institute for Biogeochemistry, Jena, Germany.

Abstract

Amazon forests account for ~25% of global land biomass and tropical tree species. In these forests, windthrows (i.e., snapped and uprooted trees) are a major natural disturbance, but the rates and mechanisms of recovery are not known. To provide a predictive framework for understanding the effects of windthrows on forest structure and functional composition (DBH ≥10 cm), we quantified biomass recovery as a function of windthrow severity (i.e., fraction of windthrow tree mortality on Landsat pixels, ranging from 0%-70%) and time since disturbance for terra-firme forests in the Central Amazon. Forest monitoring allowed insights into the processes and mechanisms driving the net biomass change (i.e., increment minus loss) and shifts in functional composition. Windthrown areas recovering for between 4-27 years had biomass stocks as low as 65.2-91.7 Mg/ha or 23%-38% of those in nearby undisturbed forests (~255.6 Mg/ha, all sites). Even low windthrow severities (4%-20% tree mortality) caused decadal changes in biomass stocks and structure. While rates of biomass increment in recovering vegetation were nearly double (6.3 ± 1.4 Mg ha- 1  year- 1 ) those of undisturbed forests (~3.7 Mg ha- 1  year- 1 ), biomass loss due to post-windthrow mortality was high (up to -7.5 ± 8.7 Mg ha- 1  year- 1 , 8.5 years since disturbance) and unpredictable. Consequently, recovery to 90% of "pre-disturbance" biomass takes up to 40 years. Resprouting trees contributed little to biomass recovery. Instead, light-demanding, low-density genera (e.g., Cecropia, Inga, Miconia, Pourouma, Tachigali, and Tapirira) were favored, resulting in substantial post-windthrow species turnover. Shifts in functional composition demonstrate that windthrows affect the resilience of live tree biomass by favoring soft-wooded species with shorter life spans that are more vulnerable to future disturbances. As the time required for forests to recover biomass is likely similar to the recurrence interval of windthrows triggering succession, windthrows have the potential to control landscape biomass/carbon dynamics and functional composition in Amazon forests.

KEYWORDS:

biodiversity; biomass/carbon dynamics and resilience; forest blowdowns; natural disturbances; recovery dynamics; tree mortality; tropical forest ecosystems

PMID:
30256494
DOI:
10.1111/gcb.14457
[Indexed for MEDLINE]

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