Tree death is not always preceded by a visible decline in vigor (canopy dieback) or a progressive loss in crown volume. Identifying early-warning signals of incipient decline can help to implement the necessary measures to prevent tree death. The aim of this work is to understand what functional alterations preceded the massive drought-induced death of adult Pinus canariensis trees in an arid stand, located in the Canary Islands. To this aim, we analyzed interannual variations in earlywood and latewood width, wood density and anatomy, and carbon isotope composition, and the relationships among these variables, in dead and living trees from 1980 to 2013. Dead trees grew less since the 1990′s, produced fewer parenchyma rays and resin canals, and exhibited a trend of decreasing latewood density and a marked shift in carbon isotope discrimination over the last 34 years that were reversed in living trees. Higher wood density in living trees resulted from thicker tracheid cell walls rather than narrower lumens. The intrinsic water use efficiency shifted from higher to lower values in dead trees after the 2000s. These results suggest a carbon limitation to maintain hydraulic safety under xylem tension, as well as to maintain storage and defense capacity, which can render trees more vulnerable to severe drought episodes. A long-term trend of decreasing tree-ring density and a reduced intrinsic water use efficiency in the short-term can be early-warning signals of carbon limitation and tree decline in drought-stressed P. canariensis. The analysis of these variables can be used to assess tree decline risks in similarly vulnerable conifer populations inhabiting drought-prone regions.

树木死亡之前并不总是出现明显的活力下降（树冠枯死）或树冠体积逐渐减少。识别初期衰退的早期预警信号有助于采取必要措施防止树木死亡。这项工作的目的是了解在成年加那利松因干旱导致大规模死亡之前发生了哪些功能改变位于加那利群岛的干旱林地中的树木。为此，我们分析了 1980 年至 2013 年间死树和活树中早材和晚材宽度、木材密度和解剖结构以及碳同位素组成的年际变化，以及这些变量之间的关系。自 1990 年代以来，死树的生长量减少了，产生较少的薄壁组织射线和树脂通道，并且在过去的 34 年中表现出晚材密度降低的趋势和碳同位素识别的显着变化，而这在活树中发生逆转。活树中较高的木材密度是由于管胞细胞壁较厚，而不是管腔较窄。2000 年代以后枯死树的内在水分利用效率从较高值变为较低值。这些结果表明在木质部张力下维持液压安全的碳限制，以及保持储存和防御能力，这会使树木更容易受到严重干旱的影响。树木年轮密度下降和短期内内在水分利用效率降低的长期趋势可以成为干旱胁迫下碳限制和树木衰退的预警信号P. canariensis。对这些变量的分析可用于评估居住在干旱易发地区的类似脆弱针叶树种群的树木衰退风险。