Variations in vegetation are closely related to climate change, but understanding of their characteristics and causes remains limited. As a typical semi-humid and semi-arid cold plateau region, it is important to understand the knowledge of long term Normalized Difference Vegetation Index (NDVI) variations and find the potential causes in the source region of the Yangtze River. Based on four tree-ring width chronologies, the regional mean NDVI for July and August spanning the period 1665–2013 was reconstructed using a regression model, and it explained 43.9% of the total variance during the period 1981–2013. In decadal, the reconstructed NDVI showed eight growth stages (1754–1764, 1766–1783, 1794–1811, 1828–1838, 1843–1855, 1862–1873, 1897–1909, and 1932–1945) and four degradation stages (1679–1698, 1726–1753, 1910–1923, and 1988–2000). And based on wavelet analysis, significant cycles of 2–3 yr and 3–8 yr were identified. In additional, there was a significant positive correlation between the NDVI and the Palmer Drought Severity Index (PDSI) during the past 349 yr, and they were mainly in phase. However, according to the results of correlation analysis between different grades of drought/wet and NDVI, there was significant asymmetry in extreme drought years and extreme wet years. In extreme drought years, NDVI was positively correlated with PDSI, and in extreme wet years they were negatively correlated.

植被的变化与气候变化密切相关，但对其特征和成因的了解仍然有限。作为典型的半湿润半干旱寒冷高原地区，了解长江源区长期归一化植被指数（NDVI）变化的知识和寻找潜在原因很重要。基于四个年轮宽度年表，使用回归模型重建了跨越 1665-2013 年期间 7 月和 8 月的区域平均 NDVI，它解释了 1981-2013 年期间总方差的 43.9%。十年间重建的NDVI呈现8个生长阶段（1754-1764、1766-1783、1794-1811、1828-1838、1843-1855、1862-1873、1897-1909和1919-1919退化四个阶段）7 –1698、1726–1753、1910–1923 和 1988–2000）。并基于小波分析，确定了 2-3 年和 3-8 年的显着周期。此外，NDVI与过去349年的帕尔默干旱强度指数（PDSI）呈显着正相关，且以相位为主。但是，根据不同等级旱/湿与NDVI的相关分析结果，极端干旱年和极端湿润年存在显着的不对称性。在极端干旱年，NDVI与PDSI呈正相关，在极端湿润年呈负相关。不同等级旱/湿与NDVI的相关分析结果表明，极端干旱年和极端湿润年存在显着的不对称性。在极端干旱年，NDVI与PDSI呈正相关，在极端湿润年呈负相关。不同等级旱/湿与NDVI的相关分析结果表明，极端干旱年和极端湿润年存在显着的不对称性。在极端干旱年，NDVI与PDSI呈正相关，在极端湿润年呈负相关。