Abstract
The potential utilisation of natural regeneration of European beech (Fagus sylvatica L.) for forest conversion has received little attention to date. Ecological knowledge is necessary to understand and predict successful natural regeneration of beech. The objective of this study was to improve understanding of what drives the occurrence of beech regeneration and, once regeneration is present, what drives its density. In the study, we utilised a forest inventory dataset provided by Sachsenforst, the state forestry service of Saxony, Germany. The dataset was derived from 8725 permanent plots. Zero-altered negative binomial models (ZANB) with spatial random effects were used to analyse factors influencing occurrence and density simultaneously. The results provided by the spatial ZANB models revealed that the probability of the occurrence of beech regeneration is highly dependent on seed availability, i.e. dependent on source trees in close proximity to a plot. The probability of beech regeneration rises with the increasing diameter of a potential seed tree and decreases with increasing distance to the nearest potential seed source. The occurrence of regeneration is affected by overstorey composition and competition exerted by spruce regeneration. Where sites are affected by groundwater or temporary waterlogging, the impact on the occurrence of regeneration is negative. Although distance to the nearest potential seed source has an influence on occurrence, this variable exerts no influence on density. A high regeneration density arises in conjunction with a high beech basal area in the overstorey. Beech regeneration density, but not occurrence, is negatively affected by browsing intensity. These variables can be used to predict the occurrence and density of beech regeneration in space to a high level of precision. The established statistical tool can be used for decision-making when planning forest conversion using natural regeneration.
Highlights
European beech (Fagus sylvatica L.) is the most abundant broadleaf tree species in central Europe
Natural regeneration can play an important role in the process of converting pure coniferous stands to mixed stands by increasing the proportion of broadleaf trees (Felton et al 2016), contributing to the restoration of forests
Maximum likelihood methods and Bayesian methods with weakly informative priors provide the same results for fixed effect models (Rue et al 2009; Zuur et al 2018), the great advantage of using Bayesian methods in R-integrated nested Laplace approximation (INLA) is the userfriendly integration of spatial random effects
Summary
European beech (Fagus sylvatica L.) is the most abundant broadleaf tree species in central Europe. Natural regeneration can play an important role in the process of converting pure coniferous stands to mixed stands by increasing the proportion of broadleaf trees (Felton et al 2016), contributing to the restoration of forests. The. European Journal of Forest Research (2021) 140:947–968 regeneration phase is the best opportunity to influence tree species composition and forest ecosystem structures (Fischer et al 2016; Löf et al 2018). With natural regeneration playing an expanding role in silviculture in central Europe, the monitoring of the success of regeneration in stands is an important issue for forest management. Predicting natural regeneration in mixed stands is difficult (Löf et al 2018)
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