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At low elevation in Wallis, Scots pines have for a few decades experienced high mortality rates and are being progressively replaced by broadleaved trees, especially the downy oak. The driving factors involved in this pine decline and changing forest structure include changes in land use and climate. Using the structural changes, particularly within needles, as sensitive bioindications of environmental constrains, the main objectives in this project are to study the macro- and micro morphological reactions in foliage to low soil water availability.

Using different experimental settings, e.g. an irrigation experiment in the Pfyn forest near Leuk, a lower canopy removal assay in another forest stand close to Salgetsch and a mobile rainshelter facility located near Leuk/Susten, different morphological (needle/shoot length and biomass, male and female flower frequency, female cone biomass), histological (tissue area and relative area in needle cross-sections) and cytological (cuticula thickness, organelle structure, physiological responses) parameters are assessed in the foliage of trees with varying soil water availability. The results are being compared to those from other sub-projects assessing e.g. the nutrients in needles, foliage density, stem ecophysiology or mineralization processes in the soil.

The expected results should provide mechanistic insights on stress, tolerance and adaptation reactions in foliage and their consequences for tree growth and vitality. They should also deepen our understanding regarding the relative effects of abiotic constraints in a changing environment.