Fadrique, B; Gann, D; Nelson, BW; Saatchi, S; Feeley, KJ (2020). Bamboo phenology and life cycle drive seasonal and long-term functioning of Amazonian bamboo-dominated forests. JOURNAL OF ECOLOGY.

1. 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. 2. 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 (similar to 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. 3. 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. 4. 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. 5. 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.