Elevation and latitude drives structure and tree species composition in Andean forests: Results from a large-scale plot network

Our knowledge about the structure and function of Andean forests at regional scales remains limited. Current initiatives to study forests over continental or global scales still have important geographical gaps, particularly in regions such as the tropical and subtropical Andes. In this study, we assessed patterns of structure and tree species diversity along ~ 4000 km of latitude and ~ 4000 m of elevation range in Andean forests. We used the Andean Forest Network (Red de Bosques Andinos, https://redbosques.condesan.org/) database which, at present, includes 491 forest plots (totaling 156.3 ha, ranging from 0.01 to 6 ha) representing a total of 86,964 identified tree stems ≥ 10 cm diameter at breast height belonging to 2341 identified species, 584 genera and 133 botanical families. Tree stem density and basal area increases with elevation while species richness decreases. Stem density and species richness both decrease with latitude. Subtropical forests have distinct tree species composition compared to those in the tropical region. In addition, floristic similarity of subtropical plots is between 13 to 16% while similarity between tropical forest plots is between 3% to 9%. Overall, plots ~ 0.5-ha or larger may be preferred for describing patterns at regional scales in order to avoid plot size effects. We highlight the need to promote collaboration and capacity building among researchers in the Andean region (i.e., South-South cooperation) in order to generate and synthesize information at regional scale.

目前学界对区域尺度安第斯森林的结构与功能认知仍存在明显不足。当前针对大陆或全球尺度森林开展的研究计划，仍存在重要的地理空白，尤以热带及亚热带安第斯地区为甚。本研究沿安第斯森林带约4000千米的纬度梯度与4000米的海拔梯度，对其结构与树木物种多样性的分布格局展开了评估。本研究使用了安第斯森林网络（Andean Forest Network，Red de Bosques Andinos，https://redbosques.condesan.org/）的数据库，该数据库目前收录了491块森林样地，总面积达156.3公顷，单块样地面积介于0.01至6公顷之间；共包含86964株经鉴定的胸径（diameter at breast height）≥10厘米的树木茎干，隶属于2341个物种、584个属以及133个植物科。研究结果显示，树木茎干密度与胸高断面积随海拔升高而增加，而物种丰富度则随海拔升高呈下降趋势；茎干密度与物种丰富度均随纬度升高而降低。亚热带安第斯森林与热带安第斯森林的树木物种组成存在显著差异。此外，亚热带样地的区系相似性介于13%至16%之间，而热带森林样地的区系相似性则介于3%至9%之间。总体而言，为避免样地面积效应的干扰，在描述区域尺度的分布格局时，优先选用面积≥0.5公顷的样地。本研究强调，需推动安第斯地区科研人员间的合作与能力建设（即南南合作），以生成并整合区域尺度的相关研究数据。