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Abstract Bamboo‐dominated forests (BDF) extend over large areas in the drought‐prone Southwestern Amazon, yet little is known about the dynamics of these ecosystems. Here, we investigate the hypothesis that bamboo modulates large‐scale ecosystem dynamics through competition with coexisting trees for water.
We examined spatio‐temporal patterns of remotely sensed metrics (Enhanced Vegetation Index [EVI], Normalized Difference Moisture Index [NDMI]) in >300 Landsat images as proxies for canopy leaf phenology and water content at two time scales: (1) a complete bamboo life cycle (~28 years), and (2) the seasonal cycle; and at two spatial scales: (a) comparing adjacent areas of BDF vs.
Terra‐firme forests (TFF) to investigate regional dynamics, and (b) comparing the vegetation classes of bamboo, trees in BDF, and trees in TFF to investigate the effects of bamboo on coexisting trees.At the regional scale, BDF showed higher EVI (leaf area density) and lower NDMI (water content) than nearby TFF but these differences disappeared as bamboo died, suggesting a strong influence of bamboo life stage in the functioning of these forests. BDF seasonal cycle showed a bimodal EVI pattern as trees and bamboos had asynchronized leaf production peaks.
At the scale of vegetation classes, trees in BDF showed lower NDMI (i.e. water content) than trees in TFF except after bamboo mortality, indicating a release from competition with bamboo for water. Canopy water content of trees in BDF was also reduced during bamboo dry‐season greening (increased EVI ~ leaf production) due to increased water demands. Nevertheless, long‐term and seasonal phenology of trees in BDF did not differ from that of trees in TFF suggesting a potential selection for drought‐tolerant trees in BDF.
Synthesis . Bamboo‐dominated forests have received less attention than other Amazonian forests and their functional dynamics are commonly ignored or misinterpreted. Using remote sensing to characterize forest phenology and water content, we show the distinctive seasonal and long‐term dynamics of BDF and coexisting trees and the importance of bamboo competition for water in shaping this ecosystem. Our results suggest a potential selection for drought‐tolerant trees in BDF since they maintain the same EVI as trees in bamboo‐free forests but with lower water content. A better characterization of BDF and their cyclical dynamics is crucial for accurately interpreting Amazonian forests' responses to extreme climatic events such as high temperatures and droughts. -
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Abstract The “hierarchy of factors” hypothesis states that decomposition rates are controlled primarily by climatic, followed by biological and soil variables. Tropical montane forests (TMF) are globally important ecosystems, yet there have been limited efforts to provide a biome‐scale characterization of litter decomposition. We designed a common litter decomposition experiment replicated in 23 tropical montane sites across the Americas, Asia, and Africa and combined these results with a previous study of 23 sites in tropical lowland forests (TLF). Specifically, we investigated (1) spatial heterogeneity in decomposition, (2) the relative importance of biological factors that affect leaf and wood decomposition in TMF, and (3) the role of climate in determining leaf litter decomposition rates within and across the TMF and TLF biomes. Litterbags of two mesh sizes containing
Laurus nobilis leaves or birchwood popsicle sticks were spatially dispersed and incubated in TMF sites, for 3 and 7 months on the soil surface and at 10–15 cm depth. The within‐site replication demonstrated spatial variability in mass loss. Within TMF, litter type was the predominant biological factor influencing decomposition (leaves > wood), with mesh and burial effects playing a minor role. When comparing across TMF and TLF, climate was the predominant control over decomposition, but the Yasso07 global model (based on mean annual temperature and precipitation) only modestly predicted decomposition rate. Differences in controlling factors between biomes suggest that TMF, with their high rates of carbon storage, must be explicitly considered when developing theory and models to elucidate carbon cycling rates in the tropics.Abstract in Spanish is available with online material.
