Abstract
AbstractClimate is a strong determinant of tropical forest productivity; therefore, it is often assumed that Amazonian forest growing on the same local rainfall regime responds similarly to fluctuations in rainfall, independently of soil differences among them. We evaluated intra‐ and inter‐annual variation of net primary productivity (NPP) components, and forest dynamics during 2004–2012 yr in five forests on clay, clay‐loam, sandy‐clay‐loam, sandy‐loam and loamy‐sand soils, and the same local rainfall regime in northwestern Amazonia (Colombia). The questions were as follows: (1) Do NPP components and forest dynamics respond synchronously to temporal rainfall fluctuations? (2) Are the responses between above and belowground components and forest dynamics similar for different forest stands? A slight and complex synchronicity among different NPP components in their response to temporal rainfall fluctuations were found; few plots showed that aboveground biomass (AGB) and stem growth were susceptible to rainfall fluctuations, while belowground components (fine roots) showed correlation with one‐month lagged rainfall. Furthermore, despite that northwestern Amazonia is considered relatively aseasonal, litterfall showed high seasonality in the loam‐soil forest group, as well as the fine‐root mass, particularly during the 2005 drought. Litterfall correlation with rainfall of sandy‐loam terra‐firme forest was time lagged as well as fine‐root mass of the loamy‐sand forest. The correlation between mortality and rainfall was weak, except for the loamy‐sand forest (white‐sand forest, 77%). High mortality rates occurred in the non‐flooded forests for the censuses that included the dry years (2004–2005, 2005–2006). Interestingly, litterfall, AGB increment, and recruitment showed high correlation among forests, particularly within the loam‐soil forest group. Nonetheless, leaf area index (LAI) measured in the most contrasting forests (clay and loamy‐sand soil) was poorly correlated with rainfall, but highly correlated among them, which could be indicating a phenotypic response to the incident radiation in these sites; also, LAI did not reflect the differences in NPP components and their response to rainfall. Overall, the different temporal behavior of NPP components among forests in relation to rainfall fluctuations suggests the important role that soil exerts on the responses of plant species in each site, besides their effect on forest dynamics and community composition.
Highlights
Carbon dynamics in forest ecosystems are highly susceptible to weather extremes, with tree mortality and carbon allocation components being strongly affected by such events (Reichstein et al 2013)
We evaluated the intra- and interannual variation of net primary productivity (NPP) components and forest dynamics of five forest types in western Amazonia growing under the same local climate regime on different soils
We investigated the following research questions: (1) Do NPP components and forest dynamics respond synchronously to temporal rainfall fluctuations? (2) Are the responses between above and belowground components and forest dynamics similar for five old-growth forests growing on different soils? It is important to notice that the severe droughts of 2005 and 2010 are included in our eight-year period of observation, which should be crucial for understanding drought effects on the forest carbon balance in the Amazon basin
Summary
Carbon dynamics in forest ecosystems are highly susceptible to weather extremes, with tree mortality and carbon allocation components (biomass and fluxes) being strongly affected by such events (Reichstein et al 2013). A myriad of studies investigating the response of Amazon forests to drought have yield diverging and contrasting results (Saleska et al 2007, Malhi et al 2009, Phillips et al 2009, Brando et al 2010, Lewis et al 2011, Rammig et al 2010, Samanta et al 2012, Saatchi et al 2013). There is a paucity of studies conducted on contrasting soils investigating intra- and inter-annual fluctuations in processes such as mortality, recruitment, and the partitioning of NPP components (leaf, stem, and root growth), and how they respond to temporal rainfall variability
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