Skip to main content

Effects of climate-induced habitat fragmentation on high alpine biodiversity

Final Report Summary - ALPINEFRAGMENTATION (Effects of climate-induced habitat fragmentation on high alpine biodiversity)

Climate change has caused altitudinal shifts in mountain vegetation zones. In the future, continued climate warming is likely to reduce the size of key high-alpine habitats (above c. 2000m) and increase effects of fragmentation due to these shifts. This project considered such impacts on alpine faunal communities by determining factors affecting distributions along altitudinal gradients in the Western Italian Alps, including size and isolation of suitable habitat patches, in order to assess effects of climate-induced vegetation shifts on high-alpine animal communities. The project was addressed through four objectives.

1 Collect biodiversity data in high-alpine grassland habitat patches.

Fieldwork was carried out from April – September in 2010 and 2011. Birds, carabid beetles, orthoptera, spiders and dung beetles were sampled along altitudinal gradients (altitudinal range 1726m-3030m). For birds, the sampling consisted of a series of point counts along each transect. In total, a total of 414 point counts were made on 261 points (so some, but not all, had two visits) over 33 transects. Invertebrate sampling (which was much more labour-intensive) was carried out on 9 transects, each transect having four sampling stations and each station having 6-16 traps. Habitat data was recorded for each point count location and each invertebrate sampling station. In addition, remote-sensed data were obtained describing habitat, climate and topography. Invertebrate samples were stored and later identified in the laboratory. This time-consuming process was completed for carabids and dung beetles. The identification of spiders and orthopera is ongoing.

2 Develop models linking animal distributions and environmental factors

Animal distribution patterns were modelled in relation to a range of environmental variables. In many cases, there was evidence that both local climate and habitat composition dictated the distribution of species along the altitudinal gradients. Open habitat specialists (grassland birds and carabid beetles) seemed particularly linked to climate, or proxy measures, in addition to broad habitat cover. Therefore, future climate changes may affect species distributions by gross changes to habitat structure (such as treeline shifts) or via more subtle effects within alpine grasslands. There was no evidence that current animal distributions are affected by patch size or isolation.

The diversity of each group varied systematically along the gradient. Bird and dung beetle diversity decreased with increasing altitude, and this was strongly linked to habitat (tree and scrub presence), which is a typical pattern in many animal and plant groups. Carabid beetles on the other hand showed a peak in diversity in open habitats at relatively high altitude (c. 2500m), suggesting that this is a high alpine specialist group.

For alpine grassland birds, models were constructed with remotely-sensed land cover variables, in addition to climatic and topographic variables. The models were used to predict the probability of occurrence of each species at high altitudes (above 1700m) in the Western Italian Alps. These models were then used to predict distributions of grassland birds under different future scenarios of climate and habitat change using data from the literature review (see below) and expert opinion. This included different scenarios of climate change, different rates of advance of the treeline (incorporating climate effects, and climate-independent effects of agricultural land use) and different response rates of soil formation at higher altitudes. For widespread species that were not alpine specialists (e. g. Skylark, Black Redstart), there was predicted to be little detrimental impact on the species distribution in the region. However, there were potential serious consequences of future change for two alpine specialists, Wheatear and Water Pipit. Under a scenario of moderate climate change where all vegetati9on zones respond to warming at the same rate, a loss of range of 5 % for Wheatear and 10 % for Water Pipit was predicted. However, due to slow soil development and loss of snow cover, it is unlikely that the upper limit of the grassland zone will respond, resulting in advancing treelines at lower altitudes, but no concomitant change at the upper limit. Such a scenario of habitat'squeeze'would result in a loss in range of 35 % for Wheatear and 43 % for Water Pipit by the end of this century.

3 Literature review

A database of relevant publications was built during the course of the project. Published estimates of shifts in vegetation zones (particularly treeline shift) were used in the predictive models (see above). In collating the literature on animal distributions at high altitudes, for the focal groups it was evident that: (i) there were very few studies on distributional changes at high altitude; (ii) there were few detailed autecological studies at high altitude; and (iii) there were very few examples of predictive models. These factors precluded a full quantitative review. However, the key concepts developed, and the main research gaps identified, during the course of the literature review were published as a paper in the journal Ibis.

4 Make conservation recommendations

The high alpine grassland habitat is likely to be threatened under future climate change, as habitat loss due to treeline shifts at lower altitudes are unlikely to be compensated by expansion of the upper grassland limit at higher altitudes. This is likely to have detrimental effects on some specialist alpine grassland birds, and on the carabid community as a whole. Management to ameliorate these effects could include active clearance of advancing trees and scrub, or encouragement of traditional grazing practices in alpine grasslands in order to maintain as large an area of alpine grassland as possible. The efficacy of habitat management will depend on the extent to which species are limited by climatic variation within grasslands, which was implied by the models for several species. The next research step should therefore be to understand the mechanisms that underpin animal distributions in alpine habitats through intensive studies on demographic traits (productivity, survival, dispersal).