In our study of colonisation of abandoned farmland byJuniperus thuriferaL., environmental and geographic distances were stronger drivers of functional differentiation among trees than genetic distance and tree intrinsic features. However, these effects varied both along the colonisation gradient and across predictors’ values, highlighting the complexity of the conditions under which functional diversity of forests is maximised. Forest expansion after land abandonment is changing Mediterranean landscapes, but the underlying ecological and evolutionary processes remain poorly understood. We evaluated whether forest expansion reduces within-stand tree functional distances and whether its environmental, geographical and genetic drivers vary along the expansion gradient. We sampled Juniperus thurifera in mature, transition and expanding stands along a colonisation gradient in Spain. We measured functional traits, genetic relatedness, surrounding vegetation cover and intrinsic features (size, phytosanitary status) on trees. We calculated within-stand pairwise functional distances and quantified the effects of genetic relatedness, geographic distance, vegetation cover and intrinsic tree features. Functional and genetic distances showed no consistent patterns along the expansion gradient. Functional distance was unrelated with genetic distance and strongly driven by geographic distance, likely representing unmeasured environmental factors. Vegetation cover and intrinsic tree features affected functional traits in transition and expanding stands. The effects on functional distance changed across predictors’ values. The role of environmental and geographic factors on tree functional divergence varied along the farmland colonisation gradient, while we did not detect effects of genetic distance. Accounting for this context-dependence and for non-linear effects on functional traits can improve our understanding and management of forest expansions.

中文翻译：

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在 Juniperus thurifera L. 扩大林分中，环境因素比遗传相关性更强烈地驱动功能距离

在我们对杜松对废弃农田定殖的研究中，环境和地理距离比遗传距离和树木内在特征更能驱动树木之间的功能分化。然而，这些影响随着殖民梯度和预测值的变化而变化，突出了森林功能多样性最大化的条件的复杂性。土地废弃后的森林扩张正在改变地中海景观，但潜在的生态和进化过程仍然知之甚少。我们评估了森林扩张是否会减少林分内树木功能距离，以及其环境、地理和遗传驱动因素是否随扩张梯度而变化。我们采样了成熟的杜松，转型和扩张沿着西班牙的殖民梯度发展。我们测量了树木的功能性状、遗传相关性、周围植被覆盖和内在特征（大小、植物检疫状态）。我们计算了林间成对功能距离并量化了遗传相关性、地理距离、植被覆盖和内在树木特征的影响。沿着扩展梯度，功能和遗传距离没有显示出一致的模式。功能距离与遗传距离无关，受地理距离的强烈驱动，可能代表未测量的环境因素。植被覆盖和树的内在特征影响了过渡和扩展林分的功能特征。对功能距离的影响随预测变量的值而变化。环境和地理因素对树木功能差异的作用沿着农田定植梯度而变化，而我们没有检测到遗传距离的影响。考虑到这种环境依赖性和对功能特性的非线性影响，可以提高我们对森林扩张的理解和管理。