Disentangling the impacts of herbivory and climate on ecological dynamics

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2017

End date

12/31/2021

Budget

762,054 EUR

Fundings

Abstract

Climate change is one of today's biggest environmental challenges. However, in many parts of the world, ecosystems are changing because of variation in grazing and browsing by large herbivores. Densities of large herbivores are affected by human management and land-use and are also linked to climate. This is particularly relevant in tundra and boreal parts of the world. Since herbivory and climate can interact to affect ecosystem dynamics, it may be possible to manage large herbivores to counteract the effects of climate change. In this project we investigated how climate and herbivory together affect ecological processes in northern ecosystems. These processes were researched at scales from individual plants to whole biomes. At the smallest scale, we developed a network of boreal and tundra sites in the North Atlantic region to investigate how the growth of woody plants in northern ecosystems responds to climate and herbivory and to highlight ecosystems that are vulnerable to changes in climate or herbivore density. Our results have shown that both red deer and moose can cool down the warming response of trees in multiple contexts including the Scottish Highlands and the boreal forests of Canada and Norway. However, the magnitude of the cooling effects of herbivores depends on the relationships between herbivores and vegetation, and other factors such as snow cover. In the Arctic tundra, the effect of herbivory on shrub growth was moderate, but peaked at intermediate temperatures. At larger scales, we investigated the impact of herbivores on plant species distributions, as well as how climate affects the interactions between plants and herbivores. Across Norway we have shown that herbivore communities have become wilder as livestock are replaced by increasing populations of cervids. The change has been particularly evident in the lowland forested regions of Norway. In these ecosystems, we have found that rare plants have wide ranging responses to wild herbivore densities; with some rare plants responding positively, others negatively and a third group with a hump-backed response with peak habitat suitability at intermediate herbivore densities. We have identified that epiphytic lichen species are particularly sensitive to herbivore densities, most likely due to herbivore impacts on tree composition. Finally, in order to identify regions that are susceptible to future environmental change due to changes in herbivore species composition, we have mapped patterns of herbivore diversity and community composition across global arctic and boreal biomes in terms of species richness, evolutionary relatedness and functional diversity finding lower phylogenetic diversity and functional diversity than expected in the Arctic. This shows that herbivore communities in northern ecosystems are under strong environmental constraints. Furthermore, threshold changes in the composition of herbivore communities was observed across the biome boundary between the boreal forest and Arctic tundra. Herbivore communities were directly affected by temperature, rather than through vegetation. This indicates that herbivore communities will respond to warming in northern ecosystems, with limited opportunities for trophic interactions to preserve current dynamics. Through the DISENTANGLE project, we have started to understand how the interactions between herbivores and climate jointly affect ecological dynamics in northern ecosystems. While herbivory can often counter warming climates, there are additional interacting factors that shape the overall ecological responses.