Production forestry is known to reduce the naturally variable microhabitat pools in live trees and their biodiversity by tree removal and broad indirect effects of silviculture. However, the tree-scale processes are not known well enough for microhabitat management for the future. This study investigates how tree age affects the microhabitat occurrence in live trees, its effect modifiers, and explanatory value compared with tree diameter. We inventoried tree-related microhabitats on 879 live aspens (Populus tremula) and Norway spruces (Picea abies) of known age in 141 forests representing contrasting productive site conditions in Estonia. We analysed microhabitat incidence using logistic mixed models for significant tree-scale and stand-scale factors. Most microhabitat types appeared rare even in old trees, and the age effects had various patterns. Only 2% of trees bore five or more microhabitat types. Aspens and spruces had a similar microhabitat diversity before 80 years of age. Stand-level effects varied among microhabitat types but were less significant than tree-level effects; interactions were even rarer. Most effects found could be interpreted through known ecological processes; for example, humidity-dependent epiphytic growth; bark stripping by herbivores; pathogen effects in forests with distinct histories. In contrast, a reliable tree-scale prediction of microhabitat occurrence appears rarely possible; and depending on microhabitat type, either tree age or diameter can be a better predictor. We suggest that managing for tree-related microhabitats in production forests should combine facilitating ecological conditions for microhabitat formation, and early detection and retention of the trees with high microhabitat potential.

众所周知，生产林业会通过砍伐树木和造林的广泛间接影响来减少活树中自然可变的微生境库及其生物多样性。然而，对于未来的微生境管理，树尺度的过程还不够了解。本研究调查了树龄如何影响活树中微生境的发生、其影响修饰符以及与树直径相比的解释值。我们盘点了 879 棵活白杨（Populus tremula）和挪威云杉（Picea abies）上与树木相关的微生境) 的 141 座森林中的已知年龄，代表了爱沙尼亚不同的生产场地条件。我们使用逻辑混合模型分析了微生境发生率的重要树木规模和林分规模因素。大多数微生境类型即使在老树中也很少见，并且年龄效应具有多种模式。只有 2% 的树木有五种或更多的微生境类型。白杨和云杉在 80 岁之前具有相似的微生境多样性。林分效应因微生境类型而异，但不如树级效应显着；互动更是少之又少。发现的大多数影响可以通过已知的生态过程来解释；例如，依赖湿度的附生生长；食草动物剥皮；具有不同历史的森林中的病原体效应。相比之下，对微生境发生的可靠的树尺度预测似乎不太可能；并且根据微生境类型，树龄或直径可以是更好的预测指标。我们建议对生产林中与树木相关的微生境进行管理，应结合促进微生境形成的生态条件，以及早期发现和保留具有高微生境潜力的树木。