Environmental landscape determinants of maximum forest canopy height of boreal forests

Aims Canopy height is a key driver of forest biodiversity and carbon cycling.Accurate estimates of canopy height are needed for assess-ing mechanisms relating to ecological patterns and processes of tree height limitations.At global scales forest canopy height patterns are largely controlled by climate,while local variation at fine scales is due to differences in disturbance history and local patterns in envir-onmental conditions.The relative effect of local environmental driv-ers on canopy height is poorly understood partly due to gaps in data on canopy height and methods for examining limiting factors.Here,we used airborne laser scanning(ALS)data on vegetation structure of boreal forests to examine the effects of environmental factors on potential maximum forest canopy height.Methods Relationships between maximum canopy height from ALS meas-ures and environmental variables were examined to assess factors limiting tree height.Specifically,we used quantile regression at the 0.90 quantile to relate maximum canopy height with environmental characteristics of climate(i.e.mean annual temperature[MAT]and mean annual precipitation),terrain(i.e.slope)and depth-to-water(DTW)across a 33000 km2 multiple use boreal forest landscape in northeast Alberta,Canada.Important Findings Maximum canopy height was positively associated with MAT,ter-rain slope and terrain-derived DTW,collectively explaining 33.2%of the variation in heights.The strongest explanatory variable was DTW explaining 26%of canopy height variation with peatland forests having naturally shorter maximum canopy heights,but also more sites currently at their maximum potential height.In con-trast,the most productive forests(i.e.mesic to xeric upland forests)had the fewest sites at their potential maximum height,illustrating the effects of long-term forest management,wildfires and general anthropogenic footprints on reducing the extent and abundance of older,taller forest habitat in Alberta’s boreal forest.

寒带森林中最大冠层高度与群落系统发育结构相关

了解最大冠层高度和森林群落构建的关系至关重要,但相关研究较少。最大冠层高度受到不同生态过程(如生态位分化和环境过滤),以及历史和随机因素的影响。然而,对影响冠层最大高度的生态过程的实证研究仍较少。本研究旨在揭示最大冠层高度与群落系统发育结构之间的关系。首先,我们从一项加拿大阿尔伯塔省东北部北方森林样方调查数据集(466个50 m×50 m的采样点)中调查了最大树冠高度。在此基础上,以净谱系亲缘关系指数(NRI)和净最近种间亲缘关系指数(NTI)表征样方中种子植物的系统发育结构,探讨了机载激光雷达测量的最大冠层高度与群落系统发育结构的关系。研究结果表明,最大冠层高度越高,主要进化分枝间的系统发育越聚集,这说明北方森林中存在非生物因子驱动的环境过滤。然而我们也发现,在每个主要演化分支内部,最大冠层高度更高的群落中系统发育结构更发散,这意味着其生态位分化更强烈。总之,最大冠层高度越高的群落可能经历了更强烈的历史非生物环境过滤和近期的生态位分化。这些发现将有助于森林生物多样性的监测和管理。