FraDiv Transplant
In this subproject, we investigate to what extent the stand of origin of ash seedlings and habitat quality affect the regeneration potential of ash stands. In addition, experimental approaches are used to study the role of density-dependent plant mortality for the establishment of young ash trees.
Site selection and experimental design
Between the Flensburg Fjord and Ahrensburg (eastern hill country), a total of ten forest stands of the Schleswig-Holstein State Forests were selected to be used for a reciprocal transplant experiment. The ten stands are comparable in terms of their hydrological and edaphic conditions and represent medium (i.e. slightly alternating moist to waterlogged) sites along the gradient sampled by FraDiv. The plots are geographically widely distributed and, at the time of establishment in 2019, comprise five pairs of stands, one moderately damaged by ash dieback and one severely damaged. The systematic sampling of five stands each that are already severely affected by ash dieback and those that have so far only shown moderate damage should make it possible to assess the extent to which the previous damage to the original stands has an influence on the regeneration potential and the establishment success of young ash trees.
All transplant sites were provided with a wildlife protection fence. Two different approaches were used with natural ash offspring of different life stages sampled from the mature stands. While young ash saplings aged 1 to 3 years were sampled in each of the ten stands in 2019, the seedlings that had just emerged this year were explicitly sampled in 2020.
- For the first approach, six subplots (blocks) were set up in each area, into each of which individuals from all ten source populations were transplanted once. To manipulate the light conditions, shading roofs were also randomly assigned to half of all blocks. Standardised volumetric soil samples were taken for each block of all planting sites in order to characterise the site conditions (carbon and nitrogen content in the topsoil; pH value). This also included recording the light conditions for each of the blocks.
- In the second approach with seedlings, the role of density-dependent mortality is also investigated. This also involves the establishment of a total of four density levels on a base area of 30×30 cm each, which was repeatedly established for each of the origins per experimental site.
The seedlings and saplings for all approaches were recruited in the stands, cleaned and cultivated in a shaded open area under standardised conditions before being reciprocally replanted across all sites. A total of more than 10,000 seedlings and young plants were transplanted in both experimental approaches.
Preparation of the transplant experiment
Variables analysed
An initial measurement of the individuals (basal diameter and shoot length) was carried out immediately after planting in October 2019. Since May 2020, all individuals have been measured several times, possible fungal damage has been assessed and functional traits, such as the specific leaf area, have been recorded. After completion of the assessment and measurement in October 2021, the individuals of the first approach have already been fully harvested and the above- and below-ground biomass determined. In addition, in collaboration with the Northwest German Forest Research Centre (Nordwestdeutsche Forstliche Versuchsanstalt), plants from each plot were examined for possible pathogen communities.
In addition to the above-mentioned recordings of the planted young ash trees and the analysis of the chemical soil properties, all stands were analysed with regard to the composition of the herb and tree layer at the level of the planting areas, and ash tree damage in the immediate vicinity of the planting areas was also documented.
- To what extent are foreign origins superior to local origins for establishment at different locations?
- Does the damage already experienced by the adult stands affect the vitality of the juveniles?
- Does the constant (re-)infection with H. fraxineus act as a selection filter for the adaptation of young growth?
- What is the role of light conditions for the establishment and performance of young ash trees?
This project is funded by the Federal Agency for Nature Conservation with resources from the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection.