Di Maurizio Vanessa, Searle Eric, Paquette Alain
Centre d'Étude de la Forêt, Faculté des Sciences, Département des Sciences Biologiques Université du Québec à Montréal Montreal Quebec Canada.
Ontario Ministry of Natural Resources and Forestry Ontario Forest Research Institute Sault Ste. Marie Ontario Canada.
Ecol Evol. 2023 Dec 21;13(12):e10804. doi: 10.1002/ece3.10804. eCollection 2023 Dec.
Scientific consensus is that diverse tree species positively impact forest productivity, especially when species are functionally dissimilar. Under the complementarity hypothesis, differences in species traits reduce competition among neighboring tree species. However, while this relationship has been extensively studied at the community level, there is a lack of understanding regarding how individuals of different species specifically respond to a functionally dissimilar neighborhood. In this study, we used permanent plots from Quebec, Canada, and 19 focal tree species to test whether: (1) tree growth response to neighborhood dissimilarity varies with their identity and competition intensity, and (2) focal tree species' traits explain their response to neighborhood dissimilarity. We demonstrate that: tree growth is primarily influenced by competition, species identity, and their interactions, but that dissimilarity, alone and in interaction with the main drivers of tree growth, explains an additional 1.8% of the variation in species growth. Within this context, (1) most species' respond positively to neighborhood dissimilarity, with magnitude being species and competition dependent, and (2) focal tree traits partly explain these dependencies, with shade-intolerant species benefiting most from dissimilar neighbors under high competition. Our study provides empirical support for the complementarity hypothesis, emphasizing the small but consistent positive effect of functional dissimilarity on tree growth in local neighborhoods. Our findings identify the species with the highest potential of benefiting from dissimilar neighbors but also demonstrate that the positive effect of neighborhood dissimilarity is not limited to a select few species with specific traits; rather, it is observed across a diverse range of species. The cumulative growth responses of individuals to functionally dissimilar neighbors may help explain the commonly observed higher productivity in more diverse communities.
科学共识是，多样的树种对森林生产力有积极影响，尤其是当树种在功能上不同时。根据互补性假说，物种特征的差异会减少相邻树种之间的竞争。然而，虽然这种关系在群落层面已得到广泛研究，但对于不同物种的个体如何具体响应功能不同的邻域，人们还缺乏了解。在本研究中，我们使用了来自加拿大魁北克的永久样地和19种目标树种，以测试：（1）树木生长对邻域差异的响应是否随其身份和竞争强度而变化，以及（2）目标树种的特征是否能解释它们对邻域差异的响应。我们证明：树木生长主要受竞争、物种身份及其相互作用的影响，但差异，单独以及与树木生长的主要驱动因素相互作用时，能解释物种生长变异的另外1.8%。在此背景下，（1）大多数物种对邻域差异有积极响应，其程度取决于物种和竞争，并且（2）目标树特征部分解释了这些依赖性，在高竞争下，不耐阴的物种从不同的邻居中受益最大。我们的研究为互补性假说提供了实证支持，强调了功能差异对局部邻域树木生长的微小但一致的积极影响。我们的发现确定了最有可能从不同邻居中受益的物种，但也表明邻域差异的积极影响并不局限于少数具有特定特征的物种；相反，在各种各样的物种中都能观察到。个体对功能不同的邻居的累积生长响应可能有助于解释在更多样化群落中普遍观察到的更高生产力。
