Community composition | Species extinction | Endemic species | Neophytes

Two different trends regarding species diversity in the alpine can be observed. On the one hand, upward shifts of species result in an increase in species richness at the local scale in many regions, especially in summit regions where usually a relatively high amount of open space is available. On the other hand, in some areas a reduction of species numbers has been observed, e.g. in many Mediterranean mountains, where warming is accompanied by increasing desiccation.
The expansion of generalist species leads to a homogenisation and a loss of beta-diversity (fig. 1).

Community composition

Typical winners of climate change are shrubs and graminoids, whereas mosses and lichens usually decline in abundance (fig. 2).

In mid-species ranges and at wetter sites shrubs will probably considerably expand also in future. This will entail changes in ecosystem characteristics like soil temperature, soil-atmosphere exchange of water, carbon and nutrient cycling, and species composition. The increasing dominance of a few competitive species that profit from climate change will probably lead to a declining species diversity in the long run.

Species extinction

Species may go extinct locally, especially were elevated temperature is accompanied by drought or increased disturbance, e.g. due to permafrost melt. In contrast, widespread extinctions seem unlikely, but there is the danger of genetic losses due to local extinction, but also as a result of fragmentation of habitats due to more intensive land use.

As migration between mountain systems and even between neighbouring summits is naturally constrained, species with restricted local distributions run a higher risk of (local) extinction (table 1), among these many endemic species.

Table 1 - Likely loosers and winners of climate change (from Körner 2009)

3 - Pika (Ochotona princeps)

Different taxonomic groups seem to be threatened unequal, with butterflies and spiders being less threatened than vascular plants and beetles probably due to their higher colonization ability.

Generally, low competitive species will suffer from increased competition by newly arriving species. But for mountain ranges reaching into the nival life zone, with increasing altitude areas with low plant cover expand, so most species will be able to reach suitable microsites at least in the medium term.
Yet, it is easier to recognize changes in species richness than declins in species abundance, which may lead to species extinction in the long run.

Endemic species

In many temperate mountain ranges, the diversity of endemic species is highest in peripheral or isolated mountain chains with relatively low summits at or above the tree line, where glaciations were less severe. These endemits are at risk of extinction when treeline is shifting upward. But also other endemic species are threatened. Whereas plant diversity usually decreases with increasing altitude, the diversity and number of endemic species standardized for area are often quite high at high altitudes (fig. 4). Therefore, the observed upward shift of lower elevation species may be a threat to overall alpine biodiversity in the long run.

4 - Altitudinal variation in land area (top), plant taxon richness and species endemism (centre) and plant taxon density (bottom) in the Central Mountain Range of Taiwan (from Jump 2012)

Neophytes

Neophytes (plant species which are non-native to a geographical region, and were introduced in recent history; often, neophytes are defined as plant species that were introduced after 1492) represent an increasing problem for many habitats. Yet, at present, the occurrence of alien invasive species in alpine regions is usually low as alien species richness decreases with elevation (fig 5). Almost only generalist species reach high elevations and often they are restricted to disturbed sites like roadsides.

Nevertheless, some non-native invasive species have established in undisturbed alpine plant communities with negative effects on native species. For example, Taraxacum officinale is an invasive neophte in the Andes of Central Chile (fig. 6). Whereas single individuals of this plant can have facilitative effects on pollinator service or seed output in surrounding native species, the presence of five individuals of T. officinale negatively affected these reproductive variables.

The few alien species that have caused environmental damage in mountains have established relatively recently. Hence, an increased invasion risk and management challenge can be expected in the future because of climate change and a more intense anthropogenic land use (fig. 7).

6 - Taraxacum officinale in the Andes of Central Chile (photo: Anibal Pauchard). Whereas single individuals of T. officinale can have facilitative effects on pollinator service or seed output in surrounding native species, the presence of five individuals of T. officinale negatively affected these reproductive variables (Munoz and Cavieres 2008).

7 - Factors affecting mountain plant invasions (from Pauchard et al. 2009)

Historically, introductions took place mainly at lower elevations. With increasing altitude, human disturbance and propagule pressure decreased, whereas climatic severity increased. Therefore, only climatic generalists with high dispersal ability, phenotypic plasticity or rapid evolution were able to reach the alpine.
Aspects of global change will reduce climatic barriers at higher elevations, increasing the chances of an upward movement of lowland invasive plants. Invasion pathways will also be directly affected through increased commerce/agriculture and the introduction of non-native species directly to high-altitude areas (e.g. via agriculture, tourist infrastructure or ornamental species). These alien mountain specialists are pre-adapted to high-elevation climates and are expected to pose a greater invasion risk.

Mountain Invasion Research Network

Biochange Genetic diversity, contemporary evolution and the maintenance of biodiversity in changing alpine environments

13 August 2018
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