Climate variations affect the growth period of young Tectona grandis Linn F. in the Amazon

ABSTRACT Climate change is expected to increase the occurrence of severe droughts in the tropics, and little is known about its influence on tree dynamics. Tree-ring width and remote sensing tools can help understand the impacts of climate change on tree growth. We evaluated the applicability of NDVI to obtain phenological metrics (e.g., start, peak, end, and length of growth season) and explored its relationship with tree-ring width of Tectona grandis (teak). The phenological metrics and tree-ring width were correlated with each other, and with both local (temperature, precipitation, solar insolation, Standardized Precipitation Evapotranspiration Index - SPEI) and large-scale (El Niño) climatic variables. The length of season and tree-ring width of teak were positively correlated with precipitation and negatively correlated with temperature in the initial months of the growth period. Tree-ring width was negatively correlated with El Niño events. Climate variables and length of season from the prior period were correlated with the tree-ring width of the current growing period. This study demonstrated that rather than directly affecting productivity, climate might also affect the length of the growing season, which would affect tree growth in the next season.摘要 气候变化预计将加剧热带地区极端干旱的发生频次，目前学界对其对树木动态的影响尚知之甚少。树木年轮宽度与遥感技术有助于阐释气候变化对树木生长的影响。本研究评估了归一化差异植被指数（NDVI）用于提取物候参数（如生长季始期、峰值期、末期及生长季长度）的适用性，并探讨了其与柚木（Tectona grandis）年轮宽度的关联。物候参数与树木年轮宽度之间存在相关性，二者均与局地气候变量（气温、降水、太阳辐射、标准化降水蒸散指数（SPEI））及大尺度气候变量（厄尔尼诺（El Niño））相关。在生长初期的数月内，柚木的生长季长度与年轮宽度均与降水呈正相关，与气温呈负相关。柚树木轮宽度与厄尔尼诺事件呈负相关。前期的气候变量与生长季长度与当前生长季的树木年轮宽度存在关联。本研究表明，气候变化可能并非直接影响树木生产力，而是通过调控生长季长度，进而影响下一季节的树木生长。