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Woody or treeless pastures? Effects of EU tree density limitations on biodiversity in woody pastures
Stockholm University, Faculty of Science, Department of Physical Geography. (Biogeography and Geomatics)
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The high biological and cultural values of traditionally managed rural landscapes are threatened by habitat change and degradation due to homogenisation through modern agricultural practices and abandonment. Woody pastures are important for many different taxa, and hence crucial for biodiversity conservation in these agricultural landscapes. To mitigate biodiversity loss, agricultural policy recommendations and subsidies are important tools, but if not implemented properly they may have the opposite effect. To keep agricultural landscapes open and to preserve biodiversity, the Common Agricultural Policy (CAP) of the European Union (EU) regulates how many trees farmers are allowed to have on their pastures to receive subsidies from the EU. A seemingly arbitrary limit was set to 50 trees/ha in 2003, which changed recently to 100 trees/ha. However, woody pastures are environments where high nature values often arise from the trees themselves, whereas there is little evidence on how biodiversity is directly affected by tree density in woody pastures. In this study, the tree density limit is targeted to investigate the effects on plant and bird diversity in 64 Swedish woody pastures along a gradient from 0 to 200 trees/ha. The results show that tree density is one of the major drivers of plant diversity, by favouring shade tolerant species without having a negative effect on less shade tolerant grassland specialists. Tree density positively affect bird diversity, an effect saturating at medium dense pastures but large species turnover rates along the gradient point at a variety of species found within woody pastures. Woody pastures with high tree densities in this study contribute substantially to biodiversity as heterogeneous environment enables high species richness. This thesis demonstrates a mismatch between subsidy systems and biological values that need to be further scrutinised to preserve biodiversity of agricultural landscapes.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University , 2015. , 31 p.
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-121799OAI: oai:DiVA.org:su-121799DiVA: diva2:861476
Presentation
2015-11-06, Högbomsalen, Geovetenskapens hus, Svante Arrhenius väg 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2016-01-25 Created: 2015-10-16 Last updated: 2016-01-25Bibliographically approved
List of papers
1. Governing nature by numbers - EU subsidy regulations do not capture the unique values of woody pastures
Open this publication in new window or tab >>Governing nature by numbers - EU subsidy regulations do not capture the unique values of woody pastures
2015 (English)In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 191, 1-9 p.Article in journal (Refereed) Published
Abstract [en]

A vast majority of European farmers are dependent on EU subsidies, which makes subsidy regulations through the Common Agricultural Policy (CAP) powerful tools in shaping agricultural landscapes. Unfortunately, steering recommendations are sometimes arbitrary, like in the case of pasture management, where 50 trees per hectare constitute an upper limit to qualify for subsidies. Although pasture biodiversity is well studied and the core of many CAP conservation programmes, it is seldom studied as direct effects of subsidy systems. In this paper, we examine plant diversity in relation to the impact of subsidy systems in Swedish woody pastures along a gradient from 3 to 214 trees per hectare. We selected 64 sites where we recorded vascular plants, soil properties and canopy cover. We found a general increase in γ- and β-diversity along the gradient, whereas α-diversity and the number of grassland specialists remained indifferent along the gradient. Additionally, tree density, organic content and C:N-ratio were the strongest predictors of species composition. Hence, when CAP regulations encourage tree cutting for pastures to qualify for subsidies there is risk of homogenisation of EU grasslands, leading to decreased γ- and β-diversity. If a general target for the subsidies is to increase biodiversity, there is need to scrutinise these regulation details to preserve the high values of woody pastures. We argue that habitat variation, species diversity and low intensity management, rather than a specific number of trees, should be the main incentives for financial support to preserve biodiversity.

Keyword
CAP, Diversity, European Union, Plant, Tree Density
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-121797 (URN)10.1016/j.biocon.2015.06.007 (DOI)000364257100001 ()
Available from: 2015-10-16 Created: 2015-10-16 Last updated: 2016-01-25Bibliographically approved
2. Tree density limitations within EU overlook woody pasture bird diversity
Open this publication in new window or tab >>Tree density limitations within EU overlook woody pasture bird diversity
(English)Manuscript (preprint) (Other academic)
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-121798 (URN)
Available from: 2015-10-16 Created: 2015-10-16 Last updated: 2016-01-28Bibliographically approved

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