Extreme ecosystem engineering: The impact of marmots on vegetation cover and plant nitrogen and phosphorus content in a cold, extremely arid mountain environment

Abstract

We measured the content of nitrogen and phosphorus, as well as nitrogen stable isotopes in plant biomass and marmot faeces in a distance gradient up to 20 meters from marmot burrows in an extremely arid glacier valley in Eastern Pamir, Tajikistan. The goal of this study was to test well-known mechanisms of ecosystem engineering by burrowing animals in previously unstudied conditions. We captured aerial images of the area inhabited by marmots to study the spatial distribution of vegetation. There was no relationship between the presence of burrows and vegetation cover. Burrow mounds were not colonised by plants, as opposed to other ecosystems, where mounds are often microhabitats that enhance plant diversity. A significant increase in N and P in aboveground green plant biomass in the proximity of burrows was found in one out of six studied species. Stable N isotopes did not give further insight into N routing, contrary to our expectations. We assume that plant growth is strongly limited by water availability, which prevents them from utilizing the local increase in nutrients, certainly provided by marmot activity. The results are contrary to numerous studies which showed that the role of burrowing animals as ecosystem engineers increases with increasing abiotic stress, including aridity. This shows a lack of this type of study in the end of the gradient of abiotic factors.