Instituto Pirenaico de Ecología (IPE-CSIC), Zaragoza, Spain.
Departamento de Sistemas Físicos, Químicos y Naturales, Univ. Pablo de Olavide, Sevilla, Spain.
Ecol Appl. 2022 Jul;32(5):e2589. doi: 10.1002/eap.2589. Epub 2022 Apr 28.
Tree-ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree-ring growth chronologies and stand-level forest changes in basal area from two independent data sets to test if tree-ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree-ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981-2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree-ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought-prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought-induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought-prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought-induced growth reductions and their cumulative impacts have strong potential to be used as early-warning indicators of regional forest vulnerability.
树木年轮数据被广泛用于了解个体尺度上树木对干旱的生长响应，但对于树木对干旱的生长敏感性如何在尺度上上升从而驱动森林动态变化知之甚少。在这里，我们将两个独立数据集的树木年轮生长年表和林分水平的森林变化联系起来，以检验树木对干旱的响应是否与林分森林动态（林分基面积生长、新生长和死亡率）相匹配。我们评估了树木生长和森林基面积变化是否随空间尺度和树种（裸子植物或被子植物）而变化。为此，我们比较了一个树木年轮网络和西班牙国家森林清查的林分数据。我们关注的是 1981-2005 年间干旱对树木生长和种群动态的累积影响。干旱年份通过标准化降水蒸散指数确定，通过量化树木年轮宽度减少来确定干旱对树木生长的影响。我们假设，对树木生长有较大干旱影响的森林也将表现出较低的林分基面积生长、新生长和较高的死亡率。这预计将发生在干旱地区以裸子植物为主的森林中。在干旱年份，以裸子植物为主的森林的累积生长减少量较高，其幅度和空间自相关均大于被子植物。累积干旱引起的树木生长减少量与森林基面积变化相关，但初始林分密度和基面积是驱动基面积变化的主要因素。在干旱地区的裸子植物森林中，我们观察到生长减少量较大的地点林分基面积生长较低，死亡率较高。因此，受干旱影响较大地区的林分基面积、森林生长和新生长明显低于受干旱影响较小的地区。树木对干旱的生长敏感性可以作为预测树木生长和新生长的指标，但进一步的研究可能试图阐明初始林分密度如何调节这种关系。干旱引起的生长减少及其累积影响具有作为区域森林脆弱性早期预警指标的巨大潜力。
