From seeds to saplings

Abstract/Description

Protection forests in the European Alps are frequently overaged and lack sufficient advanced regeneration. Accelerating disturbance regimes, particularly on steep, sun-exposed slopes with shallow soils, cause challenging conditions for the restoration of forest functions. In the present study we analyse the performance of artificially regenerated trees at four disturbed sites in the mixed spruce-beech-fir vegetation belt of the Northern Calcareous Alps over 14 years. We established the experiment with pioneering and late successional species. We excluded the effect of ungulate herbivory via fencing. Overall, soil and microsite conditions as well as competition/facilitation by grass, shrubs and herbs explain only a minor proportion of the variance of survival time (r²=0.03 to 0,17; Picea abies < Fagus sylvatica < Abies alba <Larix decidua < Pinus sylvestris < Sorbus aucuparia < S. aria < Alnus incana < Acer pseudoplatanus). Biotic and abiotic factors caused severe mortality already in the first year after planting. Delayed planting at a site already covered by ground vegetation leads to overall higher survival compared to immediate planting after disturbance. There is a species-specific substrate effect on survival and growth. After 14 years, average height of the surviving trees is lowest on dolomite (1.1 m) and does not differ significantly between sites on limestone (2.6 to 3.0 m). Larix is partly outgrowing the resources – a prolonged drought period in 2018 caused desiccation of several well growing trees. On the other end Abies alba grows slow. Foliar analyses show severe deficiencies of phosphorus at all sites and of potassium, sulfur, manganese and partly nitrogen at Tyrolian sites with a history of intensive forest grazing. The results confirm the complex interaction of biotic and site factors for the performance of regeneration and the limited possibilities of post disturbance establishment of Fagus in drought prone mixed mountain forests. Natural regeneration of Acer, Popolus, Salix, Sorbus, Ulmus, Fraxinus etc. additionally contribute to canopy cover and species diversity, demonstrating the importance of pioneer species in post-disturbance forest regeneration. This work was co-funded by the European Union (INTERREG Bavaria-Austria Projects SicAlp (J00183), StratAlp (J00316) and WINALP 21 (BA0100020).

Abstract/Description

Fertilization is a common practice in forestry nurseries to promote seedling growth and enhance future survival in the field, particularly as climate change-induced droughts increasingly threaten forest ecosystems. However, the interplay between nutrient availability and drought stress on hydraulics and growth of young trees is not well understood. We investigated the combined effects of fertilization and drought on seedlings of three European tree species (Pinus sylvestris, Fagus sylvatica, and Quercus robur) focusing on hydraulic traits, gas exchange, and growth. Our findings revealed that fertilized seedlings exhibited reduced water transport capacity (specific stem conductivity, root conductance), lower stomatal conductance and net photosynthesis, and stunted growth, especially under severe drought, with species-specific variation. Stem embolism resistance and leaf drought tolerance remained unchanged. However, in fertilized P. sylvestris and F. sylvatica, low root biomass combined with reduced water transport capacity is likely to have impaired survival under severe drought, leading to 30–40% mortality. In contrast, fertilized Q. robur demonstrated higher drought resilience and no mortality, possibly due to greater water-use efficiency. These results highlight species-specific risks associated with fertilization under drought, posing potential threats to F. sylvatica and P. sylvestris, while potentially benefiting Q. robur. Our study highlights the importance of tailored fertilization strategies for sustainable forest management in the face of climate change.

Abstract/Description

The Swiss Rhone valley is one of the driest regions of the European Alps, surrounded by high mountain ranges which intercept precipitations. For more than 100 years, the forests on the steep slopes between Hohtenn and Brig have successfully protected the BLS railway line from natural hazards thanks to careful management and continuous irrigation. However, water is becoming increasingly scarce and the climate in these extreme locations hotter and drier. Questions are increasingly being asked about the future tree species composition and management of these forest areas. As part of an afforestation experiment, nine possible future tree species have been tested since 2011, Acer opalus, Fraxinus excelsior, Fraxinus ornus, Pseudotsuga menziesii, Pinus nigra, Pinus sylvestris, Quercus ilex, Quercus pubescens and Sorbus aria. Half of the more than 2’000 plants were irrigated while the other half was exposed to natural weather conditions.

The results of this experiment show that after more than ten years, Fraxinus ornus and Quercus pubescens had both a high survival rate as well as rapid height and diameter growth under both treatments. While Pseudotsuga menziesii had a high mortality under dry conditions, these didn’t affect the growth of the surviving plants, making this species a valuable option for forest management at dry sites. Pinus sylvestris didn’t reach the high survival of the first two species, nor quite the impressive growth of Pseudotsuga menziesii. Nevertheless, it still proved a valuable addition and as an important native tree species, deserves to be included in the management of these protection forests. These results are not only relevant for the Swiss Rhone valley, but also for other dry alpine valleys, as well as an early response area to climate change, indicating what future conditions and challenges might look like at less extreme sites in central Europe in the future.