The Alpine Life Zone

Explore Some Characteristics

In this introduction you will find some general information about alpine regions of the world, altitudinal zonation, the main climatic zones and a course overview.

The Fragile Alpine Environment

Hard rocks, a solid basement (Veit & Jenny)

Rocks form an essential part of alpine ecosystems. Their variable composition and resistance against erosion have important effects on relief, geomorphologic processes and soils and consequently on many ecosystem characteristics. The occurrence of certain rock types is related to the tectonic history of a mountain. Corresponding to the characteristics and regional patterns of plate tectonics and types of plate margins, the tectonic style, landscape dynamics (e.g. volcanism, earthquakes), rock types and relief of mountains differ broadly. Despite the complex tectonic evolution of the mountains worldwide, there are certain common features, allowing a general classification, which can be related to other ecosystem parameters.

Dynamic mountain climate (Körner)

The climate reported from weather stations is not the climate plants, animals and microbes experience in the alpine. It will be demonstrated how relief, exposure and type of ground cover (plant life form) modify the actual life conditions. These modifications control plant distribution, plant functioning and ecosystem stability. Special reference is made to thermal regimes, snow distribution, wind effects and local stress gradients. Students will also learn some basic rules and techniques of how to obtain climatic data with simple devices. Students find links to actual weather stations and "visits" to alpine field sites.

Snow and perennial ice (Hölzle, Haeberli & Stöckli)

Glacial ice, permafrost soil and a seasonally changing snow cover are dominant environmental aspects especially in the higher alpine habitat. Alpine snow is an intermediate to cold and deep snow cover, composed of layers and crusts. Its temporal and spatial variability as well as its physical and chemical characteristics largely determine both variability of permafrost and glaciers and performance of organisms in the alpine habitat.

Slope processes and alpine soils (Veit, Hölzle, Haeberli & Jenny)

Due to the high elevation, steep relief, debris covered slopes and intense frost action, alpine landscapes are characterized by the wide occurrence of mass movements like e.g. rock falls, landslides, debris flows, solifluction and permafrost creep. Theses processes strongly influence soil development, vegetation patterns and the life of human beings and animals (natural hazards). Alpine soils are highly variable and have different characteristics, compared to lowland soils. Beside climatic factors and their variation with altitude, soils depend very much on the relief and the characteristics of the parent material, which is related not only to geology but also to landscape history and geomorphology. Future climate change will have severe consequences on these landscape dynamics and soil development.

Disturbance as an ecological factor (Dietz, Dietz, Edwards & Wildi)

The disturbance regime is an important determinant of the structure and composition of an ecological community. Mountain habitats are particularly unstable due to the wide range of disturbance processes operating over a range of spatial and temporal scales. These include small scale freeze-thaw processes, rock falls, extreme rainfall events, mudflows/debris flows, avalanches and damage by strong winds and fire. Variation in the relative importance of these processes leads to different disturbance regimes in different topographical situations and has major consequences for the structure and functioning of ecosystems. The aim of this section is to describe how various types of disturbance affect the stability and biological diversity of alpine ecosystems. In each case we will consider what was the natural regime of disturbance, and how humans have altered these regimes. We will also consider how plants and animals are adapted to particular patterns of disturbance.

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Plants & Life Processes

Alpine plant biodiversity (Kammer)

In mountain massifs, the richness of vascular plant species is regularly greater than in the surrounding lowlands. This unit shows the causes leading to this phenomenon. It further explains the formation of endemic species as well as the nature of plant communities. Moreover, an introduction to the most frequent plant communities above treeline in the European Alps, including their habitat characteristics and floristic composition, is given in form of a virtual excursion. Finally, the impact of human activities and global climate warming on vascular plant species richness in the alpine life zone are discussed.

Patterns and processes in alpine vegetation (Dietz, Dietz, Edwards & Wildi)

In alpine environments vegetation patterns (species composition, relative dominance of the species and vegetation structure) often change dramatically, even over short distances. This pronounced heterogeneity results from steep gradients in environmental conditions, e.g. small-scale variability in the topography. In addition, environmental conditions may vary widely over time due to frequent disturbance events. In some areas, particularly where highly variable abiotic conditions interact with frequent disturbance events on a small scale, there are pronounced spatio-temporal dynamics in the alpine vegetation. Other areas show remarkably stable communities with very long-lived dominants.
The aim of this section is to demonstrate how vegetation develops in primary and secondary succession in the alpine environment and, particularly, under what circumstances small-scale or temporary mosaics in vegetation pattern develop as opposed to more homogeneous or long-lived communities. For an understanding of the mechanisms underlying these patterns we consider biotic factors such as turnover, competition, facilitation, regeneration and dispersal as well as refer to and synthesize the effects of abiotic factors presented in other lessons.

Why treelines? (Körner)

The lower boundary of the alpine life zone is commonly termed the treeline. Often this is not a line, but at some point neither closed forests nor isolated trees can exist, hence, the more adequate term is treeline ecotone. The biological, i.e. physiological and life form related, bioclimatological causes of this most prominent vegetation boundary are discussed. Examples from various parts of the world highlight global commonness and local peculiarities of this phenomenon. It is demonstrated by new research data that the natural, climatic, high elevation treeline is largely caused by developmental constraints and not by a shortage of photo-assimilates. A central theme is the differentiation between local phenomena and global patterns.

Dynamics of subalpine forests (Burga & Holzhauser)

The subalpine zone is the highest altitudinal range where closed coniferous forests may establish. In contrast to lower elevations, the subalpine environment allows only limited growth, survival and regeneration. Environmental conditions typical for the timberline ecotone as cold climate, snow and an increased frequency of natural hazards influence tree growth and forest dynamics.

Plants and climatic stress (Körner)

Alpine plants experience a multitude of physical conditions which for most other plants would be fatal. How do they cope with these commonly and misleadingly termed 'stress'-conditions? The surprising observation is that if one relieves alpine plants from the presumed 'stress' (from an anthropocentric point of view), most will rapidly die or become overgrown by others. You will see how alpine plants cope with thermal extremes (low and high temperatures), UV-B radiation, long lasting snow cover and mechanical impacts (unstable substrate) as the most important factors.

Alpine plants and water (Körner)

Globally, water relations are second in importance only to temperature in shaping vegetation. To what extent does periodic shortage or overabundance of moisture availability affect alpine plants? This topic will be developed by first reconsidering the ecosystem water balance as it changes with elevation. After a short introduction to principles, the alpine plants' moisture availability will be illustrated. Responses discussed will be both physiological and anatomical. They will include stomatal responses, water potential, syndromes such as succulence and CAM, desiccation tolerance, rooting strategies and carbon isotope signals.

Alpine plant nutrition (Körner)

Nutrient limitation is a universal theme, though with doubtful relevance to ecology unless treated with care. It is demonstrated that early as well as late successional alpine vegetation respond with dramatic growth stimulation when nutrients are added, but this leads to a complete removal of the original plant community, hence nutrients can not be considered “limiting” if the removal of limitation is fatal. This insight will help understand both natural as well as anthropogenically influenced nutrient regimes. Aspects of litter decomposition, nutrient uptake, the role of legumes and nutrient consumption strategies are also discussed.

Alpine plants' carbon relations and growth (Körner)

Constraints of plant primary production at high elevation are discussed both at the level of primary metabolism and growth phenomena. A comparison of photosynthesis and respiration of alpine plants with their growth responses to temperature illustrates that growth constraints are largely a matter of sink activity, i.e. formative processes (development). The formation of carbon reserves and the annual carbon acquisition, through growth per unit of available time (snow free period), underline that alpine productivity equals that of tropical forests. This is possible the best evidence, that physiology hardly constrains alpine plants, hence the doubtful meaning of stress as discussed in the teaching unit on stress.

Atmospheric influences (Körner)

Global change has many facets. The two major areas are changes imposed by land use and changes related to atmospheric change. The first largely relate to alpine farming and tourism, the second relates to aspects like soluble nitrogen deposition, elevated CO2 and the multitude of consequences associated with climatic warming. This teaching unit will familiarize you with potential effects of the physical and chemical changes imposed to alpine vegetation by global change. Actual Changes of the environment are documented and experimental case studies are used to illustrate possible effects.

Sex at high altitudes: plant reproduction (Stöcklin)

Alpine plants developed a large variety of life history tactics providing a maximum of flexibility and reproductive success in a frequently hostile environment. Constraints to sexual reproduction at high altitudes include the short vegetation time, pollinator limitation and high risks of early frosts limiting seed set. What are the flower visiting animals at high altitudes? What are the particularities of seed dispersal, germination and establishment between ice, stones and sand? Early flowering vs. a larger seed set is an unavoidable contradiction when the favourable growth period is short. Breeding systems and incompatibility systems determine the rate of selfing vs. outcrossing. Case studies of reproduction in alpine habitats and alpine species demonstrate what is similar and what is different in the sexual life of plants at high altitudes.

Clonal growth and longevity in alpine plants (Stöcklin)

Clonal growth strategies are abundant in alpine habitats. Nevertheless, long-lived giant rosette plants with a single big bang reproduction are common in tropical regions at high altitude. The complex life cycle of clonal pioneer species will be used to illustrate the diversity of clonal growth. The advantages of clonal growth include a high persistence in time and space, physiological integration and high tolerance to stress, spreading and foraging, as well as division of labour among parts of a clone. Important trade-offs (sex vs. clones, early vs. late flowering, persistence vs. dispersal), patterns of genetic diversity and factors important for species distribution in a naturally fragmented landscape will be explored.

Aquatic life: selection under extreme conditions (Hanselmann)

Ecological determinants such as solar radiation and wind influence the life conditions in aquatic ecosystems. See how a combination of water mixing, atmospheric depositions and other processes have generated specialised aquatic life forms in high mountain lakes and ponds with their richness of habitats.

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Alpine fauna: habitats and adaptations (Müller & Briner)

It is hard to define what an alpine animal is. An approach is given by introducing the different mountain habitats the animal live in, and by showing adaptations to peculiar difficulties an animal has to deal with in the alpine environment. A special focus is put on the comparison between the European Alps, the Ethiopian Highlands and the Snowy Mountains of Australia.

Alpine fauna: origin of species composition (Müller & Briner)

Mountains play an important role in species evolution. The great variety of different habitats and isolated, island like biotopes supports a high biodiversity. Speciation processes and endemism are discussed with focus on peculiar situations in different mountain ranges over the world. Besides evolutionary processes, also the colonisation history plays an important role in the species composition of a mountain range and species composition is never static but only a momentary situation.

Alpine fauna: food ecology (Müller & Briner)

The chapter deals with the interactions between animals and their environment. The classical "plant-herbivore-predator" relationships are discussed but also characteristics of high mountains concerning incomplete food-chains and the source-sink phenomenon. The single components of food webs, from herbivores to carnivores and destruents, will be discussed in detail.

Herbivory (Dietz, Dietz, Edwards & Wildi)

The activities of herbivores can have a major influence on the species composition and functioning of ecosystems. Herbivory represents a particular type of disturbance which is very important in high mountain ecosystems because growth and biomass production of alpine plants is often severely limited. Alpine plants may be adapted to deter herbivory and their attractiveness to herbivores varies widely. This variation may be matched by high selectivity of alpine herbivores. We cover the influence of native herbivores (from small invertebrates such as bark beetles and molluscs to large vertebrates such as deer and chamois) upon vegetation structure and species composition and plant population dynamics in alpine ecosystems. This includes nutrient cycling, alterations of competitive relationships between co-occurring plants and long term influence of herbivores on vegetation dynamics. The problems associated with managing populations of native herbivores, and the implications for bio-diversity and conservation, are also considered.

Impact of domestic livestock (Dietz, Dietz, Edwards & Wildi)

Many alpine regions have been used for livestock production for centuries. However, alpine pastures, although often very rich in species and important for the conservation of biodiversity, are not natural habitats. A range of traditional alpine livestock systems has produced a wide diversity of different plant communities which reflect gradients in nutrient enrichment and grazing/mowing intensity. The plant species they contain, although derived from many habitats, possess species traits which enable them to persist under agricultural management. Today many of these communities are threatened, both from intensification and from the abandonment of traditional agriculture. In this section we will also consider the management problems associated with the high density of domestic animals in some places of the Alpine environment. These include effects of intense grazing and trampling on a landscape scale and changed spatial patterns of nutrient loss and nutrient enrichment (Lägerflur).

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Landscape Evolution

Quaternary paleoenvironments - archives (Veit, Jenny & Holzhauser)

The field evidence for past variations in the Earth’s climate and landscapes has been used by scientists for predicting future climate change. So-called climate archives (e.g. lakes, soils) “collect” data often continuously over long periods of time and provide ideal records of past climate conditions. Therefore, investigations of climate archives, preferably with a high time resolution, in different areas of the world show global and regional differences in previous environmental conditions.

Quaternary paleoenvironments - methods (Veit, Jenny & Holzhauser)

Overall, terrestrial as well as marine archives are of great value in the study of climate and its vulnerability to sudden changes and to establish future climate scenarios. In order to investigate climate archives, a huge set of methods is available. Most methods are suitable for different archives and mostly, several methods are applied in one archive in order to reconstruct climate and previous landscapes. In the lesson Quaternary paleoenvironments - methods, a small selection of widely used methods is given.

Quaternary paleoenvironments - results (Veit, Burga, Jenny & Holzhauser)

For a better understanding of modern alpine landscapes as well as their long and short-term dynamics, the knowledge of the past evolution of landscapes is essential. Almost all ecosystems are influenced by pleistocene climatic changes and the strong impact of alternating ice ages and warm periods. Even "minor" climatic variations, which occurred during the postglacial period, play an important role in the evolution and characteristics of modern landscapes. Studies of long-term records of these geo-ecological changes are the basis for understanding possible future impacts of global warming.

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