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Saturday, 4 August 2012

Patterns and processes in pasture woodlands of the Swiss Jura mountains

 Pasture woodland with spruce (Picea abies) 
in the Swiss Jura mountains at 1350 m a.s.l. 
(Combe des Amburnex, Marchairuz VD,  46°31’ N, 6°11’ E)


Many European mountain wooded pasture landscapes are threatened by a dichotomous evolution: tree overgrowth in insufficiently productive zones, which tend to get abandoned by farmers, and loss of trees and shrubs as well as a deficient re-growth in more favourable areas that permit a more intensive use. This is also observed in wooded pastures of the Swiss Jura Mountains. As a consequence, there is a loss of biodiversity and landscape attractiveness. The use of these semi-natural ecosystems is critical since their existence and survival depend on a subtle management equilibrium, which aims at providing various ecological goods and services, including grass and wood production and recreational areas. This question becomes even more important considering the present changes in agricultural practices in mountain regions, as a result of the transformation of this sector of the economy, and also in relation to the climate change issue.

In a large scale survey, one sixth of the Swiss vascular flora (about 3000 species) was observed in the wooded pastures of the Swiss Jura Mountains. Plant biodiversity is also very high at fine scale. The origin of this multi-scale high plant species richness is multiple. First, soil spatial variability is important, ranging from shallow calcareous to deep, acidic and silty soils. Secondly, a complex mosaic of trees, shrubs and open grasslands creates various microclimates favouring different plant species. For example, a species richness optimum at 30% of tree cover has been demonstrated. Thirdly, cattle activities can change plant species composition. Finally, plant species richness is related to topographic complexity described by elevation variability and its spatial configuration. Wooded pastures are therefore a good example of a landscape where high biodiversity can coexist with extensive land use. Many transitional zones and boundaries occurring in a highly heterogeneous and fluctuating environment, including various tree densities, create optimal conditions for biodiversity.

Pasture woodland with beech (Fagus sylvatica)  
in the Swiss Jura mountains  at 1200 m a.s.l. 
(Métairie d’Évilard, Orvin BE, 47°09’ N, 7°10’ E) 
Livestock activity is an important factor in structuring vegetation in silvopastoral ecosystems. Large herbivores may influence vegetation in three ways: (1) herbage removal and tree-shrub browsing, (2) trampling, (3) dung and urine deposition. Differences in spatial distribution of cattle effects at the landscape level may have important ecosystem implications. In particular, the spatial segregation of feeding and excretion should lead to a transfer of nutrients from feeding places to resting places, with trampling effects concentrated in intermediate situations such as along paths. At fine scale, pastured areas can be considered as a patchwork of various levels of disturbances (trampling and grazing) and resources (nutrients from dung and urine), which can change from year to year. Thus, herbaceous plant communities undergo change in resource availability and disturbance regime at various temporal and spatial scales, leading to a sort of shifting mosaic of species and plant communities. These observations explain the coexistence of a high number of species in these grasslands.
Trees are key organisms in silvopastoral ecosystems and interactions with cattle and herbaceous vegetation are critical to understand patterns and processes in these highly heterogeneous landscapes. The regeneration of trees is also crucial for the long-term sustainability of wooded pastures. In the wooded pastures of the Swiss Jura Mountains, one conifer species (Picea abies L.) and two deciduous species (Acer pseudoplatanus L. and Fagus sylvatica L.) can dominate, Picea being the most abundant. Their different life stages show various sensitivities with respect to cattle activities.

In wooded pastures, spatio-temporal scales are critical. Three spatial scales seem to be important. At large scale, the human (e.g., fences, water points) and natural (e.g., slope, openness) landscape structures of the paddock will induce the first general patterns of cattle activity. At medium scale (few square meters), among plant communities, cattle choose communities with the best forage availability. At fine scale, within a given plant community, cattle avoid dung pats and unpalatable plants. Each entity or process considered in a silvopastoral ecosystem has a characteristic spatial and temporal scale and processes occurring at a certain scale may impact on entities at another scale. For example, a cattle foraging behaviour of few minutes can have an impact during decades on the tree pattern, or, as an example of what can happen at a higher integration level, some political decision in relation to agriculture policy can have a long-lasting effect on the entire landscape. The integration of all these spatial and temporal scales has to be taken into account for sustainable management. The complex interactions between cattle activities, vegetation and landscape structure, shifting mosaic in the herb layer and tree regeneration can be modelled in a spatially explicit mosaic compartment model of the dynamics of silvopastoral ecosystems which then can be used as a decision tool in management projects.

Considering the high cultural, socio-economic, ecological and landscape values of these ecosystems, there is an increasing need to develop conservation tools. Integrated management planning of wooded pastures requires an intensive collaboration between agronomists, foresters, ecologists and socio-economists. The ecological work has been extended in this direction in the framework of the French-Swiss cross border program Interreg IIIA and in some other important projects such as MOUNTLAND of the Competence Center Environment and Sustainability of the ETH-Domain.

References

Barbezat, V., Boquet, J.-F. (Eds.) 2008. Gestion intégrée des  paysages sylvo-pastoraux de l'Arc jurassien – Manuel (Handbook). Conférence  TransJurassienne, La Chaux-de-Fonds, Besançon. 160 p et 1 CD-ROM (Programme Interreg IIIA).
Buttler, A., Kohler, F., Gillet, F. 2009. The Swiss mountain wooded pastures: patterns and processes. In : Agroforestry in Europe, Current Status and Future Prospects, Eds A. Rigueiro-Rodrigues et al. Springer Science, Advances in Agroforestry  vol. 6 : 377-396, 450 p. ISBN 978-1402082719.
Gallandat, J.-D., Gillet, F., Havlicek, E., Perrenoud, A. 1995. Pâtubois: typologie et systémique phyto-écologiques des pâturages boisés du Jura suisse. Laboratoire d'écologie végétale, Université de Neuchâtel, Neuchâtel, Suisse.
Gillet F., 2008. Modelling vegetation dynamics in heterogeneous pasture-woodland landscapes. Ecological Modelling 217 (1-2), 1-18.
MOUNTLAND Sustainable land-use practices in mountain regions: Integrative analysis of ecosystem dynamics under global change, socio-economic impacts and policy implications. CCES-Competence Center Environment and Sustainability (http://www.cces.ethz.ch/projects/sulu/MOUNTLAND).


Professeur Alexandre Buttler

Laboratoire des Systèmes écologiques - ECOS
Ecole polytechnique fédérale de Lausanne (EPFL),
School of Architecture, Civil and Environmental Engineering (ENAC),
and Institut fédéral de recherches WSL, Site de Lausanne
Station 2
CH - 1015 Lausanne (Switzerland)
E-Mail: alexandre.buttler@epfl.ch
Web page : http://ecos.epfl.ch/page-7569-en.html

1 comment:

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