Patterns and drivers of deadwood quantity and variation in mid-latitude deciduous forests

Deadwood is a fundamental forest habitat component and highly important for biodiversity conservation. Its availability, composition, size, categories and distribution depend on various structural and environmental factors (e.g., forest age, management, tree mortality, climate, decomposition). We analysed deadwood patterns along altitudinal gradients of managed (three) and unmanaged (one) deciduous forests in Western Romania. A total of 153 plots (119 managed, 34 unmanaged) of four pre-classified forest types dominated by Fagus sylvatica, Quercus petraea, Quercus frainetto with Quercus cerris, and Tilia tomentosa were evaluated, the former two both in managed and unmanaged stands. The managed forest types displayed an average deadwood volume of 47 m(3) ha(-1) with lying deadwood accounting for over 70%. About 40% of deadwood objects occurred in the early to intermediate decomposition stage. Deadwood volumes in unmanaged forest types exceeded those of managed forests two-to threefold although the deadwood amounts observed in managed forests were similar to low-intervention or recently abandoned forests, lying within critical threshold values considered important for the long-term preservation of biodiversity. Linear-mixed-effects models confirmed the positive impact of non-management and the negative effect of annual mean temperature on deadwood volume. Prediction models suggested that management and annual mean temperature showed additive effects, indicating that a combination of environmental and structural parameters determines the amount of deadwood in the studied forest types. As climatic variables strongly influence tree species composition and thus forest type, management involving deadwood retention or accumulation should consider forest-type specific characteristics and thresholds.