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4. Residual analysis of the linear mixed-effect model (LME) without climate variables and without the values from trees 48 and 55. Neither the TukeyAnscombe plot nor the QQ plot show unwanted structures.
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http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:91-diss-20130219-1121109-0-3
Citations
... Land-use and climate change are the main processes predicted to have major effects on biodiversity and the functioning of terrestrial ecosystems [1,2]. In montane and subalpine grasslands, below the treeline, land abandonment is the main driver of shrub and tree colonization [3]. In Europe, semi-natural grasslands, mainly used for foraging purposes, have been prevalent on south-facing slopes and managed to prevent tree establishment [4][5][6]. ...
Woody species encroachment on grassland ecosystems is occurring worldwide with both negative and positive consequences for biodiversity conservation and ecosystem services. Remote sensing and image analysis represent useful tools for the monitoring of this process. In this paper, we aimed at evaluating quantitatively the potential of using high-resolution UAV imagery to monitor the encroachment process during its early development and at comparing the performance of manual and semi-automatic classification methods. The RGB images of an abandoned subalpine grassland on the Western Italian Alps were acquired by drone and then classified through manual photo-interpretation, with both pixel-and object-based semi-automatic models, using machine-learning algorithms. The classification techniques were applied at different resolution levels and tested for their accuracy against reference data including measurements of tree dimensions collected in the field. Results showed that the most accurate method was the photo-interpretation (≈99%), followed by the pixel-based approach (≈86%) that was faster than the manual technique and more accurate than the object-based one (≈78%). The dimensional threshold for juvenile tree detection was lower for the photo-interpretation but comparable to the pixel-based one. Therefore, for the encroachment mapping at its early stages, the pixel-based approach proved to be a promising and pragmatic choice.
... However, to the best of our knowledge there is no clear trend at the landscape scale of trees moving upslope (Holtmeier & Broll 2005). As land use is the key driver of tree colonization into man-made grasslands below the tree line (Rickebusch 2006), it is difficult to distinguish climate-related signals from a response to land-use change, beyond land-use legacies (Didier 2001) and atmospheric CO 2 concentration (Körner 2003). Tree colonization into grasslands is also influenced by dispersal and biotic processes (competition and facilitation) (Li & Wilson 1998; Dullinger et al . ...
In many places in Europe, trees are currently far below their theoretical altitudinal limit because of past land use. However, under the current crisis affecting mountain agriculture, trees are likely to recolonize the subalpine belt. Addressing the societal issues associated with such landscape change requires predictive tools to assess vegetation dynamics in relation to management strategies. This study aims to analyse the factors determining tree dynamics at the subalpine ecotone and to evaluate the impact of land‐use change on landscape vegetation patterns.
We developed a hierarchical scaling approach and applied it to a European larch ( Larix decidua Mill.) colonization in the French Alps. Our landscape case study focused on subalpine south‐facing grasslands of Villar d’Arêne (France). First, we used a habitat‐suitability model to delineate the climatic suitability habitats of larch in the French Alps. Then we used a landscape model (LaMoS) to determine whether larch is able to colonize these grasslands predicted to be climatically suitable, considering land use and local vegetation. The sensitivity of landscape colonization patterns to land‐use scenarios (abandonment, delayed mowing or traditional mowing) and biological attributes of larch were analysed with a factorial simulation experiment.
The accuracy of the habitat‐suitability model at the French Alps scale allowed for the prediction that the grasslands of Villar d’Arêne were highly suitable for larch.
Simulations highlighted the effect of land use on larch establishment at the local but not at the landscape scale. On the other hand, larch attributes such as dispersal capacity, juvenile tolerance to light interaction (competition and facilitation) and its capacity to survive on infertile soil were shown as essential for tree spatial dynamics.
Synthesis and applications . Combining a habitat‐suitability model with a spatially and temporally explicit landscape model enhances the capacity to account for environmental factors acting at different overlapping scales. This modelling strategy increases the robustness and accuracy of predictions, a prerequisite for landscape management in a global change context. We conclude that ongoing and future agri‐environmental policies have to be quickly adapted to protect biodiversity and ecosystem services provided by subalpine grasslands.
