Phytodiversity in Christmas-tree plantations under different management regimes

Abstract

Christmas trees are increasingly being cultivated throughout Europe. Christmas-tree plantations (CTP) are characterised by intensive vegetation management, which is essential for ensuring tree quality. Within conventional CTP, herbicides are applied extensively, whereas in organic plantations, alternative methods for vegetation management, such as grazing, are implemented. A further characteristic of organic CTP is the application of organic fertiliser. We compared soil conditions, habitat structure and phytodiversity of differently managed CTP for deriving management recommendations for promoting plant species diversity in CTP. We focused on four different plantation types, representing a gradient of land-use intensity: conventional CTP in open landscapes (CTP-OPEN) and on former windthrows (CTP-WIND), organic CTP (CTP-ORG) and fir-greenery plantations (FIR) as a baseline for lowest land-use intensity. Our study discovered clear differences in soil characteristics, habitat structure and phytodiversity among the different plantation types. However, former land use had only little impact, as the differences between the two conventional CTP (CTP-OPEN/-WIND) were small. Soil conditions were similar among the three types of CTP compared to FIR. In contrast, habitat structure and phytodiversity differed between the two conventional CTP and the less intensively managed CTP-ORG and FIR. Conventional CTP were characterised by open vegetation with relatively low plant species richness and a low number of stress-tolerant species, but some neophytes. In contrast, CTP-ORG and FIR had a high cover of grasses, the highest overall species richness and the highest number of stress-tolerant species. For promoting plant species diversity in CTP, we recommend a reduction in management intensity, especially herbicide application.