Methodological comparison and time series analyses on ungulate browsing on tree regeneration in Switzerland

Tree regeneration is a complex process that is strongly influenced by abiotic and biotic factors, such as browsing by wild ungulates. In recent years, ungulates have spread in different numerical and spatial terms in Switzerland. Using the data of the Swiss National Forest Inventory (NFI) this project shall provide information on the temporal evolution of the influence of wild ungulates on the regeneration structures in Swiss forest. This is not easily possible since the sampling method of the tree regeneration has been changed several times between NFI 1 and NFI 4. Thus, first a detailed analytical and simulation-based method comparison of the four NFI surveys will be carried out. Meanwhile, various estimates of the density of wild ungulates will be generated. Together, this allows estimations of the long-term development of the biodiversity of the forest trees under different ungulate densities.

The ultimate goal is to provide information on the spatial and temporal evolution of the influence of deer, chamois and red deer on tree regeneration in the Swiss forest.

Concrete goals of the modular project are:

1.    Detailed analytical and simulation-based comparison of the methods used in the first to the fourth NFI as the basis for a method-adjusted Swiss-wide comparison of the browsing intensity on tree regeneration.
2.    Search for the lowest possible level of stratification of the NFI regeneration surveys, i.e., can statements on the level of wildlife management units be made?
3.    Processing of various regional density estimates of wild ungulates for a Swiss-wide analysis (culling data, density estimates based on spotlight counting, vehicle collisions, etc.).
4.    Estimation of the spatial and temporal influence of wild ungulates on tree regeneration including these regional ungulate densities.
5.    Eventually estimating the cascading effects of predators (lynx and wolf) via ungulates on tree regeneration in Swiss forests.

The NFI is the only nationwide unified dataset about tree regeneration and ungulate browsing in Switzerland. Thus, a correct method-adjusted data preparation is very important for a assessing temporal effects; such as the temporal variations in the densities of wild ungulates, the spread of the red deer and the reintroduction of large carnivores (lynx and wolf).