Establishment success of 19 different tree species on afforestations -: Results of a biodiversity experiment

Afforestations of arable land are a challenge for forestry. Their success may be jeopardised by abiotic factors like summer drought, spring frost or biotic factors like damages by rabbit and vole. Moreover, the treatment of the seedlings and their quality are major factors that determine the establishment success of the trees. 19 different tree species on 70 ha afforestations in Thuringia/Germany have been investigated during the first 3 years after planting as part the of BIOTREE biodiversity project. The tree species showed significant differences in their sensitivity towards these factors. 19-61 % of the oak seedlings (Quercus petrea) did not survive. For up to 1/3 of the dead seedlings, damage by vole was found as death cause. Also beech (Fagus sylvatica) had high losses (up to 79%) amoung the planted seedlings. About 25% of the terminal shoots were damaged by frost or drought that led to negative growth rates during the first 2 vegetation periods. Not only late successional deciduous trees were difficult to establish. Aspen (Populus tremula) as pioneer species had losses up to, 34% and Douglas fir (Pseudotsuga menziesii) as coniferous species was especially sensitive towards treatment before planting. Afforestations have to be done by professional personal to minimize the risk of failure. Additionally, the establishment success of Douglas fir was dependent on the seedling quality. The survivership could be increased from 32 to 95% with high quality planting material. Broadleaves of high value like elm (Ulmus glabra), lime (Tilia cordata), ash (Fraxinus excelsior), mountain ash (Sorbus aucuparia) and three maple species (Acer campestre, Acer platanoides, Acer pseudoplatanus) had high establishment successes. These tree species cover less than 6% of the forests in Germany at the moment and form a potential species pool to increase biodiversity in forests. Soil quality seems to be another important factor for the establishment success of the seedlings. A gradient of soil quality within one site did party explain the establishment success of some tree species. However, for oak and beech, the two species with the lowest grow on rate, no correlation between soil quality and establishment success could be found. Beach, oak and cherry trees (Prunus avium) were particularly damaged by voles and rabbits. However, the degree of damage was depending on the species number in a I ha plot. Plots with high biodiversity level (6 tree species) showed significant less biotic damages than plots with low biodiversity. The causes of this effect may be the different susceptability of the tree species towards vole damage. Almost no vole damage could be found for coniferous trees and lime. Our results are in line with experience in afforestations of 2000 ha afforested land in Thuringia since 1991. Our study showed that the planting of species rich afforestations, including less abundant broadleaves, may increase the establishment success of the trees and minimizes the risk of biotic damages by voles and rabbits.