竞争调控沙地天然樟子松树木生长动态及其气候适应性的树轮生态学研究

Global warming may increase the frequency and intensity of climatic drought. It is concerned how to adapt to the climate warming and drying for the sandy natural Mongolia pine(Pinus sylvestris var. mongolica) forest in Hulunbuir sandland. However, how tree-to-tree competition's influence on adaptation mechanism to climate remains to be studied. Our previous works showed that the tree radial growth of sandy natural Mongolia pine forest decreased significantly over the past 30 years. Based on these previous works, the project will resolve the following two questions: 1) How will the competition modulate the tree radial-growth sensitivity to climate in the stand and individual-tree scales? and what is its mechanism? and 2) Could the mixed forests enhance the adaptability to drought for the Mongolia pine? Therefore, based on the dendrochronological method and tree-ring stable isotope techniques, the project will investigate the trees' competition and radial-growth of Mongolia pine, and analyze the tree radial-growth response to climate and their recovery ability to the extreme drought under the different modes and intensities of competition. And then, combined with the tree-ring stable isotope composition (delta 13C and delta 18O) changes and their sensitivities to climate, it will be determined quantitatively the relationships between the competition and the tree radial-growth or their climate sensitivities. Finally, we will clarify the mechanism that competition modulates the tree radial-growths and their climate sensitivities and verify whether multi-species mixed forest can enhance their adaptability to the drought. The program will be important significances for the adaptive management and regulation of the natural Mongolian pine forests and desertification control under the context of climate warming and drying.

全球变暖可能增加干旱的频率与强度，沙地天然樟子松林如何适应未来暖干化的气候备受关注。然而，树间竞争如何影响树木对气候的适应性还有待深入研究。我们前期工作表明近30多年来沙地天然樟子松树木生长量显著下降，本项目在此基础上重点解决：1)在林分与树木个体尺度上竞争如何调控樟子松树木生长对气候的响应？其调控机制是什么？2)混交林是否增强樟子松树木的干旱适应性？为此，本项目基于树木年代学方法与稳定同位素技术，在调查不同竞争模式与强度下樟子松树木竞争格局及其径向生长动态基础上，分析不同竞争条件下树木生长对气候的敏感性及其对极端干旱的适应性，并结合树轮稳定同位素δ13C和δ18O变化及其气候敏感性分析，揭示竞争与树木生长及其气候敏感性关系，阐明竞争调控樟子松树木生长及其气候敏感性机制，验证树种混交能否增强其对干旱的适应性，它将对气候暖干化背景下沙地天然樟子松林的适应性管理与调控、防治荒漠化具有重要意义。

沙地天然樟子松(Pinus sylvestris var. mongolica )林主要分布于东北呼伦贝尔沙地，发挥着重要生态服务功能。全球变暖可能增加干旱的频率与强度，沙地天然樟子松林如何适应未来暖干化的气候备受关注。树间竞争是调控树木的气候适应性的重要因素。为揭示竞争影响树木生长及其气候响应的关系，本项目组在呼伦贝尔建立了20个50×50m2的样地，调查了11000多棵樟子松树木，取样树木1600多棵，3200多个树芯，研究发现：沙地樟子松树轮宽度与各月气温、日温差和太阳辐射多呈负相关关系，特别是生长季（5-9月），多达到显著或极显著水平；与当年生长旺盛期的降水量、相对湿度和PDSI呈正相关关系，特别是夏季（6-8月）及生长季（5-9月），多达到显著或极显著水平。在林分尺度上，林分密度对树木生长及其气候敏感性的影响不显著；在单木尺度上，树木径向生长随竞争压力的增加而显著逐渐降低，特别是在极端干旱条件下更加显著。竞争能力弱的树木对生长季气候响应相对更加强烈，而竞争能力强的树木则对冬春季气候响应更加敏感；竞争对气候敏感性的影响在干旱年时不明显，但在湿润年时，竞争对树木气候敏感性的影响非常明显。随着竞争压力增加，湿润年的树木干旱敏感性逐渐增强，而在干旱年则减弱。在较低竞争指数时，干旱年份较湿润年份的干旱敏感性更强，但在较高竞争指数时，湿润年份较干旱年份的干旱敏感性更强。在林分尺度上，沙地樟子松对极端干旱的抵抗力、恢复力和弹性力随着林分密度增加而逐渐增强；在单木尺度，随着竞争压力的增加，树木对极端干旱的抵抗力呈不显著的趋势降低，而恢复力和弹性力则逐渐增强。沙地樟子松树木径向生长与研究区域的NDVI变化具有很好的一致性，即树木径向生长与4-10月NDVI的相关性均较好，特别是夏季月份（6和8月）。本研究对于预测未来气候变化情景下沙地樟子松应对气候变化的能力，增强其适应性管理与合理调控具有重要意义。