Alpine biodiversity in a climate of change
Volume 6 Number 2 - October 2009
French: La biodiversité alpine dans un climat de changements
Spanish: La biodiversidad alpina y el cambio climático
High alpine ecosystems are expected to react sensitively not only to climate change but also to changes in land use. The 21st century is predicted to be facing a significant increase in temperature that will bring about drastic changes in biodiversity on summit areas. Living between the timberline and the mountain top is naturally limited, but temperature change is already causing a rapid advance of the tree line. On the other hand, many farmers are ceasing to cultivate mountain pastures and that also leads to a loss of open space in these regions. Situated in the centre of the Alps, the Botanical Gardens at Innsbruck is dedicating its 2010 activities to call public attention to the many tiny species living in the alpine region (above 2000m). The focus is on the various adaptation mechanisms these dwarf plants have developed to tolerate extreme environmental conditions.
The effects of climatic warming and changes in land use have left clear fingerprints on the vegetation. Trees at the climatic tree line have never grown so fast as they do today, showing that they are not feeling the constraints of colder conditions. The reason trees reach the edge of their range at a lower altitude than shrubs, grasses or herbs has to do with their tall, aerodynamic open canopy structure and their ambient air conditions, which means they closely track air temperature, and they are now following the current trends of warming. In contrast, shrubs, grassland and fellfield vegetation engineer their own microclimate by means of small stature and compact growth forms. For these plants any warming of the climate will have less effect and the mosaic of microhabitats will mean local rearrangement rather than an upslope migration (Körner, 2009). There is evidence that some alpine /nival plant species respond by spreading upslope, but others do not (Erschbamer, 2009).
Looking closely at the historic tree line one has to distinguish carefully between true elevational advances and infilling of the open terrain due to land use change. In the valleys, the ecological impact of more and more land taken for settlement and transport purposes affects both soil function and the preservation of natural habitats as a basis of biodiversity, but at higher mountain regions we observe the opposite to be true. Here, many farmers are no longer interested in alpine pasture farming, which is leading to infill of the open space by shrubs and trees and a loss of grassland habitat.
While the overall biodiversity of the whole alpine region may not be affected dramatically by climate and land use changes, we anticipate that the regional diversity will be. Lower mountain areas especially are expected to face a reduction of diversity due to the locally increasing competition caused by tree line elevation (Grabherr, 1994) and it is here, particularly, that endemic species may go extinct.
Dwarf alpine project
At the heart of the Alps, the Botanical Gardens at Innsbruck, Austria, is planning its 2010 activities to direct public interest towards all those tiny species of the alpine region. We will take a close look at grassland and fellfield vegetation and we will introduce the public to the various adaptation mechanisms these dwarf plants have developed living in a harsh alpine habitat (Körner, 1999). Activity programmes will lead children and family groups through our garden to see, touch, taste and smell how alpine plants grow in an environment that humans usually only visit for a short time.
A rucksack takes centre stage
A hiking tour up a mountain top is an adventure for all of us and in preparation we pack our rucksacks with some essential items to help us to endure this harsh environment. Children are invited to think about what they would take for a hiking tour, such as a water bottle, lunch box, sun lotion and sunglasses, a rope, maybe a wind jacket and gloves in case the weather turns nasty. All these things go into the rucksacks and as we walk through the alpine garden we can link our choices to the adaptation mechanisms shown by alpine plants.
Looking at the effects of sun lotion, for example, we compare plants which have a tough epidermis and are covered in thin hairs on their leaves (pubescence) and stems. Furrowed leaves reflect sunlight and protect plants against harmful UV radiation. Pubescence also helps plants to limit transpiration so that they do not lose water too quickly. Other plants have red-tipped leaves and the red colour comes from anthocyanin, a chemical that protects against UV radiation, as does sun lotion.
Some alpine plants have particularly thick leaves in which they are able to store water – very useful on rocky terrain where there is hardly any soil to hold the moisture. These thick leaves belonging to succulent plants can be likened to the water bottle we carry with us in case we become thirsty and there are no springs nearby.
To see how plants protect themselves against wind and cold weather, we compare our wind jacket and gloves to the typical dwarf habit and the cushion plant structure alpine plants often show. Nestling low on the ground and growing in a compact structure helps plants to keep their microclimate untouched by temperature changes on the outside. We use a thermometer to measure the temperature inside and on the surface of a cushion plant like Silene acaulis which shows how these plants keep their core temperature low even when the surface temperature is soaring on a hot day. On the other hand, the centre of the plant remains warm compared to its extremities on a freezing cold day. Keeping most of its biomass underground is another method of helping the plant to protect itself against low temperatures which could lead to frostbite. The underground parts can also be linked to the children’s lunchboxes, because alpine plants often make use of their roots for storage.
Finally, the piece of rope is a useful analogy to show how cushion plants fix themselves between rocks on a steep mountain slope. Many alpine plants have thick, strong roots and the cushion shape of the structure helps to balance the weight. One root does not have to bear the weight of the whole plant. There is a nice group activity to demonstrate this: the children gather around a loop made with one end of the rope. One person takes hold of the other end. As long as all the children are evenly distributed around the loop it is easy for the single person at the other end to hold steady. But if everyone pulls on one side, it is much more difficult for the single person to stand his/her ground.
Körner, C., 1999. Alpine Plant Life, Springer, Berlin, Germany.
Körner, C., 2009. Mountain Vegetation under Environmental Change, in Jandl, R., Borsdorf, A., VanMiegroet, H., Lackner, R. & Psenner,R. (eds) Global Change and Sustainable Development in Mountain Regions, Innsbruck University Press, Innsbruck, Austria.
Erschbamer, B., Kiebacher, T., Mallaun, M., & Unterluggauer, P., 2009. Short-term Signals of Climate Change along an Altitudinal Gradient in the South Alps, Plant Ecology 202: 79–89.
Grabherr, G., Gottfried, M. & Pauli, H., 1994. Climate Effects on Mountain Plants, Nature 369: 448.
Les écosystèmes alpins sont sensibles non seulement aux changements climatiques mais également aux changements d’utilisation des terres. Des augmentations de température considérables sont prévues au cours du XXIe siècle, ce qui engendrera d’importants changements dans la composition de la biodiversité en zones alpines. La surface située entre la limite forestière et le sommet d’une montagne est restreinte, laissant peu de place aux variations altitudinales. Avec les changements de température, les espèces végétales avancent vers le haut de la montagne. De nombreux agriculteurs cessent également l’entretien des pâturages en montagne, menant à la diminution d’espaces ouverts dans ces régions. Situé au cœur des Alpes, le jardin botanique d’Innsbruck a choisi de dédier ses activités de 2010 à la sensibilisation du public à toutes ces minuscules espèces qui vivent dans la région des montagnes alpines. Elles s’attacheront aux différents mécanismes d’adaptation que ces pantes ont développés afin de faire face à des conditions environnementales extrêmes.
Los ecosistemas alpinos son muy sensibles tanto al cambio climático como al cambio del uso del suelo. Las predicciones de incremento significativo en la temperatura para el siglo XXI producirán cambios muy drásticos en la composición de la biodiversidad principalmente en las regiones alpinas. El área entre la zona arbórea y la cima de las montañas es limitada, dejando muy poco espacio para un desplazamiento altitudinal. Con el cambio de temperatura las especies vegetales avanzaran montaña arriba. Muchos granjeros están deteniendo el cultivo de zonas de pastoreo de montaña y esto induce la reducción de espacios abiertos en las zonas alpinas.
El jardín Botánico de Innsbruck se localiza en el centro de los Alpes y ha decidido que este 2010 sea el año de actividades para crear conciencia publica acerca de todas las especies de pequeña talla que viene en la región montañosa alpina. El enfoque es en cuanto a los diversos mecanismos adaptativos que estas plantas han desarrollado para enfrentarse a las condiciones extremas del medio ambiente.