Abstract
Worldwide, forestry must face several challenges during the UN Decade on Ecosystem
Restoration. The decline of biodiversity and ecosystem services, ongoing deforestation,
climate change, and biological invasions must be mitigated with forest restoration and
by applying sustainable forest management. Experiences with the integration of nonnative
tree species into forest management in many parts of the world show benefits
but also trade-offs regarding sustainability. In Central Europe, Douglas fir [Pseudotsuga
menziesii (Mirbel) Franco], originating from Northern America, has been introduced by
forestry and managed for more than one and a half centuries. Growth characteristics,
drought tolerance, and timber quality are major reasons which make this tree species
attractive for forestry and wood industry. Whether Douglas fir might be invasive with
potential trade-offs regarding biodiversity, uncontrolled regeneration, and spread is not
yet fully understood and controversially debated. We investigated the regeneration of
Douglas fir in the Spessart mountains, a vast woodland in south-western Germany
which has a considerable cover of anthropogenic coniferous afforestations. We sampled
the regeneration of Douglas fir by differentiating height growth classes in various foreststand
types, taking the distance from mature mother trees, abiotic site conditions
(e.g., water balance and soil properties), light supply, forest-stand characteristics,
ground vegetation, and browsing pressure into account. Also integrating the individual
regeneration of the accompanying tree species, we applied multivariate analyses. Most
of our investigated variables did not show a significant correlation with Douglas fir
regeneration. However, results point to a positive relationship of spontaneous Douglas
fir regeneration at moist and light sites as well as in close distance to potential seed
trees. The analysis of the current invasion potential did not reveal a major risk under the
given site conditions in the study area.