Fahey Catherine, Choi Dennis, Wang Jianmin, Domke Grant M, Edwards Joseph D, Fei Songlin, Kivlin Stephanie N, LaRue Elizabeth A, McCormick Melissa K, McShea William J, Phillips Richard P, Pullen Jamie, Parker John D
Smithsonian Environmental Research Center, Edgewater, Maryland, USA.
Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana, USA.
Ecology. 2025 Jan;106(1):e4500. doi: 10.1002/ecy.4500.
Forest canopy complexity (i.e., the three-dimensional structure of the canopy) is often associated with increased species diversity as well as high primary productivity across natural forests. However, canopy complexity, tree diversity, and productivity are often confounded in natural forests, and the mechanisms of these relationships remain unclear. Here, we used two large tree diversity experiments in North America to assess three hypotheses: (1) increasing tree diversity leads to increased canopy complexity, (2) canopy complexity is positively related to tree productivity, and (3) the relationship between tree diversity and tree productivity is indirect and driven by the positive effects of canopy complexity. We found that increasing tree diversity from monocultures to mixtures of 12 species increases canopy complexity and productivity by up to 71% and 73%, respectively. Moreover, structural equation modeling indicates that the effects of tree diversity on productivity are indirect and mediated primarily by changes in internal canopy complexity. Ultimately, we suggest that increasing canopy complexity can be a major mechanism by which tree diversity enhances productivity in young forests.
林冠层复杂性（即冠层的三维结构）通常与天然林中物种多样性的增加以及高初级生产力相关。然而，在天然林中，冠层复杂性、树木多样性和生产力常常相互混淆，这些关系的机制仍不清楚。在此，我们利用北美两个大型树木多样性实验来评估三个假设：（1）树木多样性的增加会导致冠层复杂性增加，（2）冠层复杂性与树木生产力呈正相关，（3）树木多样性与树木生产力之间的关系是间接的，且由冠层复杂性的积极影响驱动。我们发现，将树木多样性从单一栽培增加到12种混合栽培，可分别使冠层复杂性和生产力提高多达71%和73%。此外，结构方程模型表明，树木多样性对生产力的影响是间接的，主要由内部冠层复杂性的变化介导。最终，我们认为增加冠层复杂性可能是树木多样性提高幼林生产力的一个主要机制。
