Effects of Christmas-tree plantations on phytodiversity: implications for conservation

Abstract

Perennial crops such as Christmas trees have increasingly been cultivated throughout Europe. However, knowledge on the influence of Christmas-tree plantations (CTP) on biodiversity is still scarce. We examined phytodiversity and soil and habitat-structure characteristics within young (CTP-YOUNG, tree age ≤ 6 years) and old (CTP-OLD, tree age > 6 years) conventionally managed CTP in comparison with the three most dominant habitat types within the study area: (1) intensively managed grasslands (GRASS), (2) windthrows (WIND) and (3) non-native spruce forests (FOREST) (nper sample type = 18). Our study revealed clear differences in soil characteristics, habitat structure and plant-species richness between the five sample types. These differences were most pronounced between three groups of habitats: (1) CTP, (2) GRASS and (3) WIND/FOREST. CTP were characterized by a typical habitat structure composed of a distinct shrub layer, an intermediate herb layer and a low litter cover. In contrast to the other sample types CTP had a comparably high cover of bare ground and stones/gravel. Due to the practiced management CTP were characterized by a unique plant species community composed of a high number of ruderal species and some neophytes. The differences between CTP-YOUNG and CTP-OLD were generally small. Next to management, phytodiversity in CTP was influenced by the size of CTP. Small-scale CTP generally had a higher phytodiversity. For the cultivation of Christmas trees, we recommend the reduction of herbicide use as far as possible. New plantations should be implemented preferentially within homogeneous landscapes composed of habitats with low importance for biodiversity.