Impact of browsing on tree regeneration

Background

Tree regeneration is part of the normal diet of ungulates species such as roe and red deer and chamois. Silver fir and sycamore maple are particularly preferred tree species for ungulate browsing, but also silvicultural important tree species. Analyses of data from long-term surveys in indicator areas are used to determine whether and how ungulate browsing affect the structure of regeneration in the long term, i.e. the size distribution of the tree species.

Project objectives

The project seeks to demonstrate the extent or in which cases high browsing intensities can cause problems in the tree regeneration (low regeneration densities, slow growth of the regeneration, segregation). Furthermore, this project will contribute to the objective quantification of the influence of ungulates on the regeneration under different light availability. Since light availability is affected by silvicultural measures, this project provide an important basis for decision-making, do which extent silvicultural measures contribute to improve the situation.

Research questions

1. How does the browsing intensity affect the structures of regeneration, and the succession of these structures, individually for silver fir and sycamore, and overall in the representation of these species.
2. Are there any differences between forest stands (beech, fir-beech forests) and along the light gradient from windthrow areas to closed forest stands?

Method

Data from long-term surveys of ungulate browsing in indicator areas with each 20-50 sample plots of about 12.6 or 78.5 m² (2 – 5 m radius) serve as a base (method Rüegg 2008, English description in Berwert-Lopes 1996). Since the analysis focus on silver fir and sycamore, a substantial regeneration of these species must be present in the indicator areas. Using the following criteria the 38 indicator areas were selected: recording period at least 10 years, presence of silver fir in a minimum of 10 sample plots, and current recording available (2011 or 2010).

In 2012, additional surveys were made in 660 sample plots with fir presence in order to quantify (i) the light conditions (canopy openness, basal area, gap size), ii) the site conditions, iii) the rejuvenation that has outgrown the reach of ungulate browsing, iv) the ground vegetation as alternative food and competition for tree regeneration, as well as v) the intensity and frequency of browsing on silver fir saplings compared to other damage such as fungi, fraying, mechanical damage, insects and frost.<br/>Analyzes are based on the comparison of regeneration densities per size class and tree species in the sample plots.

Literature

Rüegg, D., 2008. Verjüngungskontrolle: Methoden Stichproben in Indikatorflächen. Dani Rüegg, Kaltbrunn.

Berwert-Lopes, R., 1996. Assessment of tolerable browsing by Eiberle's method: Limitations and future prospects. Forest Ecology and Management 88, 87-91.