Alpine Ecosystems and Global Change

'Global change' includes changes in atmospheric chemistry (CO2, CH4, NjOj), the climatic consequences of these changes, and the manifold direct influences of humans on landscapes. All three global change complexes affect alpine biota, either directly or indirectly.

Elevated atmospheric carbondioxide (CO2) concentrations affect plant photosynthesis directly, although late-successional alpine grassland in the Alps was found to be carbon saturated at ambient CO2 concentrations of the early 1990s. The effect of doubling CO2 concentrations

Cushion Plants Kilimandscharo

Figure 5 The four major life-forms of flowering plants in alpine ecosystems: cushion plants (Azorella compacta, Sileneexscapa), herbs (small: Chrysanthemum alpinum, tall: Gentiana puncata), dwarf shrubs (Loiseleuria procumbens, Salix herbacea), and tussock-forming graminoids (Carex curvula, diverse tall grass tussock).

Figure 5 The four major life-forms of flowering plants in alpine ecosystems: cushion plants (Azorella compacta, Sileneexscapa), herbs (small: Chrysanthemum alpinum, tall: Gentiana puncata), dwarf shrubs (Loiseleuria procumbens, Salix herbacea), and tussock-forming graminoids (Carex curvula, diverse tall grass tussock).

over four consecutive seasons on net productivity was zero. However, not all species within that sedge-grass-herb community responded identically, hence there is a possibility of gradual shifts in species compositition in the long run, with some species getting suppressed and others gaining.

In contrast, even very moderate additions of soluble nitrogen fertilizer at rates of those received today by mountain forelands in Central Europe with rains (40— 50kgNha~ a~ ) doubled biomass in only 2 years. Even 25 kgha_1a_1 had immediate effects on biomass (+27%), again favoring some species more than others. Atmospheric nitrogen deposition is thus far more important for alpine ecosystems than elevated CO2. Just for comparison, in intense agriculture, cereals are fertilized with >200 kgNha-1 a~\

Consequences of climatic change for alpine ecosystems are hard to predict because of the interplay of climatic warming with precipitation. A warmer atmosphere can carry more moisture; hence increasing precipitation had been predicted for temperate mountain areas. Greater snowpack can shorten the growing season at otherwise higher temperatures. While the temperate zone has seen more late winter snow in recent years, the uppermost reaches ofhigher plants seem to have profited from climatic warming over the twentieth century. Several authors documented a clear enrichment of summit floras, accelerated in recent decades.

Treeline trees respond to warmer climates by faster growth, but whether and how fast this would cause the treelines of the world to advance upward depends on tree establishment, which is a slow process. Hence treelines always lagged behind climatic warming during the Holocene by centuries, as evidenced by pollen records. Current trends are largely showing an infilling of gaps in the treeline ecotone, but upward trends await larger-scale confirmation. Eventually any persistent warming will induce upward migration of all biota. By contrast, recent climatic warming has caused the tropical upper montane/ alpine climate on Kilimanjaro to become drier, facilitating devastating fires, which depressed the montane forest by several hundred meters with a downslope advance (expansion) of alpine vegetation following.

Land use is still the most important factor for changes in alpine ecosystems. Around the globe, alpine vegetation is used for herding or uncontrolled grazing by lifestock. Much of the treeline ecotone has been converted into pasture land, with both overutilization and erosion (mainly in developing countries) and abandonment of many centuries old, high-elevation cultural landscapes (mainly industrialized countries) causing problems. The question is not whether there should be pasturing, but how it should be done. Sustainable grazing requires shepherding and observation oftraditional practices, which largely prevent soil damage and erosion.

Traditional alpine land use has a several thousand years history and was optimized for maintaining an intact landscape for future generations as opposed to land-hungry newcomers faced with the need of feeding a family today, rather than thinking of sustained livelihood in a given area. All other forms of land use (except mining), as dramatic their negative effects at certain places may look, are less important, because their impact is rather local (e.g., tourism, road projects). Agriculture is by far the most significant factor in terms of affected land area.

Mismanagement of alpine ecosystems has severe consequences (e.g., soil destruction, sediment loading of rivers) not only for the local population, but for people living in large mountain forelands, which depend on steady supplies of clean water from high-altitude catchments. Almost 50% of mankind consumes mountain resources, largely water and hydrolectric energy, hence there is an often overlooked teleconnection between alpine ecosystems and highly populated lowlands. Highland poverty is thus affecting the conditions and the economic value of catchments, which goes far beyond the actual agricultural benefits. This insight should lead to better linkages between lowland and highland communities and also include economic benefit sharing with those that perform sustainable land care in alpine ecosystem.

See also: Alpine Forest; Land-Use Modeling. Further Reading

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