Scuola di Scienze Agrarie, Forestali, Alimentari e Ambientali, Università della Basilicata, Viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
Dipartimento di Agraria, Università di Napoli Federico II, via Università 100, IT-80055 Portici, (Napoli), Italy.
Sci Total Environ. 2022 Mar 20;813:152666. doi: 10.1016/j.scitotenv.2021.152666. Epub 2021 Dec 27.
Several dieback episodes triggered by droughts are revealing the high vulnerability of Mediterranean forests, manifested as declines in growth, increased defoliation, and rising mortality rates. Understanding forest responses to such climate extreme events is of high priority for predicting their future vegetation dynamics. We examined how remotely sensed measures of vegetation activity (NDVI, Normalized Difference Vegetation Index) and radial growth (BAI, basal area increment) responded to climate extreme events. We considered tree (Pinus sylvestris, Quercus pubescens, Quercus frainetto) and shrub (Juniperus phoenicea) populations from Italy and Spain showing recent dieback phenomena. Two components of drought, namely elevated atmospheric demand (VPD, vapor pressure deficit) and low soil moisture were analyzed in nearby stands showing or not showing dieback symptoms. Dieback stands exhibited lower NDVI values than non-dieback stands. NDVI and BAI were positively related in all sites except for the dieback stand of Q. frainetto that was negatively related. Such NDVI-BAI linkages were related to specific time windows, which could be useful for identifying when climatic conditions have the greatest influence on vegetation. Growth decline occurred in response to increasing VPD, but responses differed among species. J. phoenicea was the most negatively impacted by higher VPD, whereas oaks responded to soil moisture. A high VPD was related to stronger growth reduction in dieback P. sylvestris trees regardless of soil moisture changes. We highlighted that coupling between proxies of forest productivity (NDVI, BAI) allows better understanding and forecasting of drought-induced dieback phenomena in forests and shrublands. Scaling up from tree to stand levels might be feasible when using the maximum growing season NDVI, which can be applied for retrospective modeling of the impact of drought stress on forest productivity and tree growth.
多次由干旱引发的枯梢事件揭示了地中海森林的高度脆弱性，表现为生长下降、落叶增加和死亡率上升。了解森林对这种气候极端事件的反应对于预测其未来的植被动态至关重要。我们研究了植被活动（NDVI，归一化差异植被指数）和径向生长（BAI，基面积增量）的遥感测量如何对气候极端事件做出响应。我们考虑了来自意大利和西班牙的表现出近期枯梢现象的树木（Pinus sylvestris、Quercus pubescens、Quercus frainetto）和灌木（Juniperus phoenicea）种群。在表现出或未表现出枯梢症状的附近林分中，分析了导致干旱的两个组成部分，即升高的大气需求（VPD，蒸气压亏缺）和低土壤水分。枯梢林分的 NDVI 值低于非枯梢林分。除了 Q. frainetto 的枯梢林分外，NDVI 和 BAI 在所有站点均呈正相关。这种 NDVI-BAI 联系与特定的时间窗口有关，这对于确定气候条件对植被影响最大的时间可能很有用。生长下降是对 VPD 增加的响应，但不同物种的响应不同。J. phoenicea 受较高 VPD 的影响最大，而橡树则对土壤水分做出响应。高 VPD 与枯梢 P. sylvestris 树木的生长减少密切相关，而与土壤水分变化无关。我们强调，森林生产力（NDVI、BAI）代理之间的耦合可以更好地理解和预测森林和灌丛中的干旱引起的枯梢现象。当使用最大生长季节 NDVI 时，从树木到林分水平的扩展可能是可行的，这可以应用于对干旱胁迫对森林生产力和树木生长影响的回溯建模。
