Ecological effects of ungulate grazing

Summary of the aims of the project

The project will study the impact of grazing by red deer and sheep, and by red deer alone, in coastal pine forest over ten years. In 2000 the Institute of Zoology at the University of Bergen, the Department of Natural Sciences at Sogn & Fjordane University College and the Norwegian Red Deer Centre established twelve 100-m2 exclosures on Svan&0slash;y island on the west coast of Norway in order to protect from grazing by red deer (Cervus elaphus) and sheep (Ovies aries). A review of the literature reveals that few long-term exclosure studies have tested the impact of ungulate grazing in coastal pine-forest. In this project the following will be compared between grazed and ungrazed areas: i) analyses of species richness and species diversity of bryophytes, lichens and vascular plants, ii) records of flowering intensity, iii) analyses of interspecific plant relationships, iv) analyses of successional changes in areas of different productivity, v) analyses of demographic and population dynamics of bilberry (Vaccinium myrtillus) and cowberry (Vaccinium myrtillus), vi) analyses of trade-offs between vegetative growth, sexual reproduction (berry production) and the production of grazing-induced chemical defence compounds in bilberry, vii) comparison of growth and survival of individually tagged young rowan (Sorbus aucuparia) trees and bilberry-shoots, iix) analyses of microbial activity, nutrient turnover and diversity of soil organisms, ix) quantification of grazing intensity of vertebrates and herbivorous insects on bill-berry, and x) counts of fecal pellets of red deer and sheep; an indirect method for variation in area use between study sites.

Methodology and approach

Ten 100 m2 exclosures (10x10 m) were established in the bilberry-pine forest on the island Svanøy on the west coast of Norway in order to exclude grazing by red deer and sheep. Another two exclosures were established in the bilberry-pine forest on the Norwegian Red Deer Centre farm. Although there is a very high grazing intensity by red deer within the farm, its impact alone can be quantified. Thus, the project can test the responses of the vegetation, key plant species, the allocation of resources in bilberry, and the impact on the soil community at three grazing intensities: i) in ungrazed areas within the exclosures (0), ii) in areas moderately grazed by red deer and sheep (+) and iii) in areas grazed intensively by red deer alone (++). The twelve exclosures are distributed within an 11-km2 area of coastal pine-forest. Within and outside each exclosure, seven permanent 1 m2 sample plots have been established, a total of 168 permanent plots. Each 1 m2 sample plot is subdivided into one hundred 10x10 cm subplots. Thus the responses of bryophytes, lichens, and vascular plants to variation in grazing intensity can be examined in detail. The analyses of chemical defence compounds and soil parameters are performed at the 100- m2 scale.

Scientific benefits

Large vertebrate herbivores are supposed to be an important structuring agent in terrestrial food chains through their impact on plant diversity and plant nutritional value. In low productive systems in the north, sustained heavy grazing by large vertebrates may change interplant relationships, e.g. inter-specific plant competition for light and nutrients, and disturb important ecological processes such as the soil-plant nutrient cycle. Vertebrate grazing or browsing therefore has the potential to change biodiversity. In more productive systems, grazing may increase plant species richness by removing strong competitors, thus giving space for the growth of less competitive species. In contrast, in low productive systems such as many alpine areas and on the arctic tundra, intense grazing can reduce plant species richness and species diversity. The ecological impact of ungulate grazing is not only determined by the productivity of the system, but also of the type of grazer, the degree of herbivory and the grazing history. Over most of northwest Europe the population density of wild ungulates such as moose, red deer and roe deer has increased several-fold over the past 30-40 years. The population growth of wild ungulates in Norway has been especially strong since the 1980`s, mainly due to modern management procedures. The aim of the current project is to improve our understanding of how sustained selective grazing by ungulates affects succession rates of vegetation, interspecific plant competition, grazing induced plant chemical defence, soil processes and the nutrient flow through terrestrial food chains (vegetation, herbivores and predators). Studies from North-America, Great Britain and Fennoscandia give equivocal information on how ungulate grazing affects biodiversity and ecosystem functioning. Our project encompasses analyses of vegetation dynamics (i.e. successional changes over ten years), resource allocation of a functional important food plant such as bilberry, demography and population dynamics of bilberry and cowberry, and analyses of the soil-plant nutrient cycle. We use red deer as model species and bilberry-pine forest as model system in order to add more information to the current knowledge of how ungulate grazing affects the pine-forest ecosystem. Understanding the impact of ungulate grazing or browsing on the functioning of terrestrial food chains is crucial for the conservation of biodiversity and for ecosystem management.