Browsing Lawns in a Landscape of Fear - The impact of wolves on browsing lawn structure in the Białowieża Primeval Forest, Poland

Abstract

The Białowieża forest is one of Europe’s only remaining lowland broadleaved forests still containing a complete contemporary assemblage of browsing ungulates and predators. The presence of gray wolves (Canis lupus) causes behavioural responses in browsing ungulates, the result of which has an impact on lower trophic levels. The impact of this top-down control on browsing lawns (areas of trees maintained in hedge-like states by browsing) is investigated here, through examining browsing lawns across a gradient of wolf presence. The results of this investigation show that the morphology of trees within browsing lawns varies with a gradient of wolf presence, with trees in wolf-core areas showing reduced signs of herbivore control. Reduced numbers of browsing lawns were observed within the core area of the wolfpack territory, and whilst species diversity within these lawns showed no statistically significant change, species not seen in areas of intense browsing could be observed growing in lawns closer to the wolf activity centre. The findings of this investigation demonstrate that herbivore top-down control has tangible effects on browsing lawns, and that this control varies in accordance with a landscape of fear in the Białowieża forest.

Popular Abstract

Browsing Lawns in a Landscape of Fear

When we say the word ‘ecosystem’, we generally think of a large, interconnected web of different species, each in their own unique niche. The question of how such an ecosystem forms, and how it maintains its particular characteristics has fascinated ecologists since the birth of ecology as a discipline. In the past three decades two key hypotheses have formed as to how ecosystems maintain their diversity. The first to be developed was the ‘bottom-up’ hypothesis, this is a rather common-sense approach to ecology; environmental factors such as soil type, water availability and light availability dictate what plants grow where. This plant life then dictates which herbivores can inhabit an area, which in turn creates a food source for certain predators. Thus the diversity of an ecosystem is dictated from its lowest levels.

However, a less intuitive model for the maintenance of diversity has been developed; that of ‘top-down’ control. In this model apex predators control numbers and behaviour of prey species. The presence/absence of these herbivores or their altered behaviour causes different niches for plants to exist in. The Białowieża forest in the far East of Poland, on the border with Belarus, provides evidence in support of this hypothesis.

The Białowieża forest is unique as Europe’s sole remaining lowland broadleaved forest containing its original species assemblage. Here bison, moose and deer roam free, largely safe from humans but at risk from their natural predators; wolves and lynx. However, the risk from wolves is not constant, and varies across the forest. As shy animals, wolves tend to avoid areas of human habitation, thus for a deer; the closer to human habitation they are, the safer they are from wolves, and vice versa.

The trickle-down effects of this gradient are substantial; and are particularly obvious when ‘browsing lawns’ are considered. Browsing lawns are peculiar natural hedge formations brought about by a feedback loop. In this feedback loop browsing by deer leads trees to branch and take on a bushy morphology. However, across the ‘landscape of fear’ in the Białowieża forest, these lawns show a telling level of variation. Far from human habitation ‘delicate’ plants such as oak and maple are able to grow where wolves provide them with protection from deer. Conversely, more hardy, browsing tolerant species, in particular hornbeam, are able to dominate where browsing pressure is greatest. The ‘bushiness’ of these hedges clearly changes with the presence of wolves. In areas closer to villages browsing lawns are dense, homogenous and well maintained. In areas with high densities of wolves the browsing lawns are less frequent, and generally poorly maintained, as a result trees have a greater chance to ‘escape’ and grow out of the reach of browsing deer.

Clearly, wolves exert a top-down control on the browsing lawns in the Białowieża forest. We can see from this that deer behaviour in response to danger is what dictates many of the attributes of browsing lawns.

Master’s Degree Project in Biology 30 credits 2018
Department of Biology, Lund University

Supervisors: Dries Kuijper, Marcin Churski
Mammal Research Institute, Polish Academy of Sciences, Białowieża
Joris Cromsigt
Dept. Wildlife, Fish & Environmental Sciences, SLU, Umeå

• author: Whitehead, James
• supervisor: Dries Kuijper
• organization: Degree Projects in Biology
• course: BIOM01 20171
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8947975
• date added to LUP: 2018-06-12 08:41:39
• date last changed: 2018-06-12 08:41:39