Data from: Tree-growth is more sensitive than species distributions to recent changes in climate and acidic deposition in the northeastern United States

Tree-growth responses to environmental change could provide early detection of shifts in forest composition and help facilitate ecosystem management and conservation.
We studied forest tree responses to recent trends in climate and acidic deposition using analyses of tree rings and long-term climate, deposition and forest plot data along an elevational climatic gradient in the northeastern United States. We analyzed how (a) individual growth of dominant species (Picea rubens, Abies balsamea), and (b) spatial distributions of all species, changed with elevation over time due to changing environment.
We observed a mean 220 m upslope shift of temperature envelopes since the 1960s, consistent with regional climate warming, but found no evidence of synchronous upslope shifts in species abundance. Species’ ranges were stable although some leaned upslope or downslope, suggesting species-specific migration lags or controls on species’ ranges.
Compared to species distributions, the growth of dominant species was more responsive to environmental change. Although the basal area of P. rubens declined within its range since the 1960s, its growth has increased recently with increasing precipitation pH and to a lesser extent with warming climate. Abies balsamea has gradually increased in both basal area and density since the 1960s, with its growth responding to precipitation pH but not climate. Historically, P. rubens grew better at lower and A. balsamea at higher elevations, but these elevation effects appeared to be mediated primarily by moisture, and have disappeared over time.
Synthesis and applications. Mean tree-growth responses to changing climate (temperature, moisture) and precipitation chemistry were more consistent and more clearly detectable than shifts in tree species’ ranges, suggesting that monitoring tree growth across climatically-controlled species’ ranges (e.g. along elevational or latitudinal gradients) may provide a powerful tool for early detection of potential future changes in forest composition in a changing environment.

树木生长对环境变化的响应，可为森林群落组成转变的早期侦测提供支撑，并助力生态系统管理与保护工作的开展。
本研究依托美国东北部沿气候海拔梯度的树轮（tree rings）分析数据、长期气候与酸性沉降（acidic deposition）监测数据，以及森林样地数据，探究了林木对近期气候与酸性沉降变化趋势的响应。我们分析了两类要素随环境变化沿海拔梯度的时间演变特征：(a) 优势树种红云杉（Picea rubens）、香脂冷杉（Abies balsamea）的单木生长情况；(b) 所有树种的空间分布格局。
自20世纪60年代以来，我们观测到物种适宜温度生态幅（temperature envelopes）平均向海拔上方移动了220米，这与区域气候变暖的趋势相符，但未发现物种丰度同步发生海拔上移的证据。尽管部分物种存在向高海拔或低海拔偏移的倾向，但整体物种分布范围保持稳定，这暗示存在物种特异性的迁移滞后效应，或是物种分布范围受到特定调控因素的限制。
相较于物种分布格局，优势树种的生长对环境变化的响应更为显著。自20世纪60年代以来，尽管红云杉（Picea rubens）分布范围内的胸高断面积（basal area）有所下降，但其近期生长量随降水pH值升高而增加，同时也受气候变暖的小幅促进。香脂冷杉（Abies balsamea）的胸高断面积与种群密度自60年代以来均呈逐步上升趋势，其生长仅受降水pH值调控，与气候因素无关。历史上，红云杉多在低海拔区域生长更佳，而香脂冷杉则更适宜高海拔生境，但这类海拔驱动的生长差异主要由水分条件介导，且随时间推移已逐渐消失。
综合分析与应用启示：相较于树种分布范围的转变，林木生长对气候变化（温度、水分）与降水化学性质的响应更为一致，也更易被观测到。这表明，在受气候调控的物种分布范围内（例如沿海拔或纬度梯度）开展林木生长监测，可为未来环境变化下森林群落组成的潜在转变提供早期侦测的有效手段。