# Dual Roles of Water Availability in Forest Vigor:
## 5 Conclusions  
Water is an important climatic resource for vegetation. However, due to the complex spatio-temporal relationship among climatic factors and vegetation, water shows both positive and negative correlations with forest vigor, and the reasons for the negative impact are not well-known. In this study, we conducted a multiperspective analysis for the forests in China. Specifically, to reveal the underlying mechanism causing the positive and negative role of water availability, we considered the influences of multiple factors (i.e., temperature and water balance, forest types, season differences, and multiple time scales of water availability) by combining multiple data (e.g., satellite-derived _NDVI_ and the multiple time-scale _SPEI_s). The results indicated that the negative role of water availability in forest vigor mainly occurred in regions of \(T\leq T_{\text{threshold}}\) during the pregrowing season. In comparison, positive roles mainly occurred in warmer regions (\(T>T_{\text{threshold}}\)) during the pregrowing season and in better regions (\(WB>WB_{\text{threshold}}\)) during the growing season. The \(T_{\text{threshold}}\) and \(WB_{\text{threshold}}\) were vegetation type-dependent, with values ranging from 1.3 to 4.7 \({}^{\circ}\)C for \(T_{\text{threshold}}\) and 129.1 to 238.8 mm/month for \(WB_{\text{threshold}}\). These results revealed that both environmental climate and seasonality should be considered when monitoring or predicting the impacts of drought on the satellite-derived forest vigor (i.e., _NDVI_). Therefore, to explore the direct effects of drought on forests in the future, relevant research should focus on forests limited by water availability.  
The following are available online at [[https://www.mdpi.com/2072-4](https://www.mdpi.com/2072-4)]([https://www.mdpi.com/2072-4](https://www.mdpi.com/2072-4)) 292/13/1/91/s1, Table S1: The results of independent-samples \(t\)-test for temperature dependency, Table S2: The results of independent-samples \(t\)-test for water balance dependency, Table S3: The environmental climatic thresholds and their ranges for various time scales, Table S4: The environmental climatic thresholds and their ranges for a 0.1 statistically significant level, Figure S1: Spatial distribution of the strongest correlations (the \(r\) corresponds to \(|\,r|_{\text{max}}\)) of forest vigor with water availability in China, Figure S2: Comparisons between CRU data and the counterparts derived from meteorological stations.  
Conceptualization, H.L. and T.Z.; Data curation, H.L., T.Z., P.X., P.Y. and J.L.; Formal analysis, H.L., T.Z. and X.L.; Funding acquisition, T.Z. and P.S.; Investigation, H.L. and T.Z.; Methodology, H.L. and X.L.; Project administration, T.Z. and P.S.; Resources, H.L., T.Z., P.S., R.M. and X.Z.; Software, H.L., X.L. and P.X.; Supervision, T.Z. and P.S.; Validation, T.Z., X.L., P.S., R.M. and X.Z.; Visualization, H.L.; Writing--Original draft, H.L. and T.Z.; Writing--Review & editing, T.Z., X.L., P.S., R.M., X.Z., P.X., P.X., P.Y. and J.L. All of the authors contributed to the manuscript and approved the final version. All authors have read and agreed to the published version of the manuscript.  
We would like to thank the high-performance computing support from the Center for Geodata and Analysis, Faculty of Geographical Science, Beijing Normal University [[[https://gda.bnu.edu.cn/](https://gda.bnu.edu.cn/)]([https://gda.bnu.edu.cn/](https://gda.bnu.edu.cn/))]. This study was supported by the Major Project of Qinghai province (2019-SF-A12), the second Tibetan Plateau Scientific Expedition and Research Program (2019 QZKK0405), and the National Natural Science Foundation of China (41621061 and 41571185).  
**Infrared Consent Statement:** Not applicable.  
**Data Availability Statement:** Data is contained within the article or supplementary material.  
**Conflicts of Interest:** The authors declare no conflict of interest.