Forest tree seedlings may suffer from predicted future winters

201

Winter in a changing climate affecting the survival of Scots pine seedlings

Poster

Impact of Large-Scale Fire and Habitat Type on Ant Nest Density and Species Abundance in Biebrza National Park, Poland

Fire can have negative effects on the ant community by reducing species abundance through direct mortality, changes in resource availability, or foraging activity. Fire can also have positive effects, especially for opportunistic species preferring open or disturbed habitats. We assessed the direct effects of a large-scale fire on ant communities in open habitats (grassland and Carex) and moist forested peatland (birch and alder) sites in Biebrza National Park, testing three hypotheses: (i) the large-scale fire had more significant effects on ant nest density in forests than in open habitats, (ii) the post-fire ant diversity changes within sites are stronger in forests than open habitats, and (iii) ant species preferring disturbed habitats are favoured by the fire event. The fire had negative effects on ant nest density only in the Carex and grassland sites but not in the birch and alder sites, suggesting that fire had a stronger impact in open habitats than in forests. Temporal post-fire ant diversity changes within sites were stronger in forests than in open habitats. We observed higher beta diversity changes between the first and second year of the study in the burned forest sites due to colonisation, indicating a greater fire impact on species community composition followed by a higher recolonisation rate. Ant species preferring disturbed habitats were favoured by the fire. The seed-eating ant species Tetramorium caespitum, a thermophilous and opportunistic species, dominated the burned grassland site. This contrasts with other species, e.g., Lasius alienus, for which nest density decreased after fire, underlining the importance of food resource availability as a major driver of community changes after fire. Our study also underlines the importance of periodic biodiversity monitoring in conservation areas for assessing the recovery of the original status after disturbances and revealing possible habitat changes endangering the survival of local biotic communities

Tree species richness affecting fine root biomass in European forests

201

Is tree species diversity or tree species identity the most important driver of European forest soil carbon stocks?

201

Effects of snow condition on microbial respiration of Scots pine needle litter in a boreal forest

201

Soil frost affects stem diameter growth of Norway spruce with delay

Soil temperature and soil frost intensity are affected by the depth of insulating snow cover and the timing of snowmelt which are predicted to change by climate warming. This may increase tree growth if there is less soil freezing or decrease growth if there is no insulating snow cover, but frost temperatures still exist. Previously, we showed that the changes in soil frost by snow manipulations in a ~50-year-old stand of Norway spruce (Picea abies (L.) Karst.) in eastern Finland in two winters (2005/2006 and 2006/2007) led to short-term changes in physiology, morphology, and the growth of the shoots and roots. The treatments were: (i) control with natural insulating snow accumulation and melting; (ii) snow removal during winter; and (iii) snow removal in winter and insulation at the top of the forest floor in late winter to delay soil thawing. In this study, we examined lagged effects of those treatments by radial trunk increment cores during the nine-year recovery period after the termination of the treatments. Annual ring width index (AWI) was calculated for each year by normalization of the ring width in the respective year in proportion to the ring width in the last year (2005) before the treatments. No differences in AWI were found between the treatments before or during the snow manipulation period. However, differences started to appear one year after the treatments were finished, became significant four years later in 2011 and lasted for three years. The radial increment was lower in the treatment with snow removed than in the control and in the treatment with insulation to delay soil thawing, but there were no differences between the latter two treatments. The results indicate that a lack of snow cover may not only have short-term impacts but longer-lasting consequences on the radial growth of trees. The positive effects of prolonged growing season by the increasing summer temperatures on forest growth predicted for the boreal region may therefore not be fully realised due to the negative effects of decreased snow cover and increasing soil freezing

Interactive effects of moose browsing and stand composition on the development of mixed species seedling stands

The moose (Alces alces L.), a common large herbivore in the boreal region, impairs forest regeneration by browsing on tree seedlings and saplings. Moose prefer deciduous species, but during winter more coniferous seedlings are used. We used meta-analyses, separately for deciduous and coniferous seedlings, for evaluating whether excluding moose browsing affected seedling density and height. In addition, we compared (1) deciduous seedling proportion, (2) stand density, (3) elapsed time from fencing and (4) estimated moose density with moose exclusion effect sizes. Fencing had a positive effect on coniferous seedling height. With more deciduous trees in a seedling stand, the fencing effect for both seedling height and density of coniferous seedlings decreased. On the other hand, the fencing effects increased with denser stands. At some point effect sizes turned to negative, and conifer species varied in their response to browsing. This implies that deciduous seedlings can protect conifers from browsing by moose up to some mixing ratio, but when deciduous seedling densities are too high, their negative effect increases, presumably through increased competition. Our results suggest that a moderate deciduous admixture in conifer-dominated mixed seedling stands can decrease moose damage but also underline the significance of timely silvicultural measures to minimize the negative effects of excessive deciduous seedlings and too dense stands. Due to differences in coniferous and deciduous species, as well as their compositions and amounts in studied experiments, more studies adjusted to local conditions are still needed to give exact measures for silvicultural recommendations