Dual function of Potentilla (Rosaceae) in the life history of the rare boreoalpine osmiine bee Hoplitis (Formicapis) robusta (Hymenoptera, Megachilidae)

Hoplitisrobusta (Nylander) is a rare and poorly known osmiine bee species occurring in the subalpine zone of the Alps. The discovery of two nests of H.robusta in a thin branch of a dead fallen spruce on a sunny clearing of a subalpine spruce forest allowed the investigation of the nest architecture, the analysis of the larval diet and the assessment of the nest building material. X-raying, computed tomography and subsequent dissection of the nest branch revealed that the nests were built in L-shaped pupation tunnels of cerambycid beetles, which were probably cleaned from wood debris by the female bees with the aid of their large and powerful mandibles after nest site selection. The two nests contained five and six linearly arranged brood cells separated from each other by thin partitions built from masticated green leaves (“leaf pulp”). They were sealed at their opening by a thick plug consisting of several successive layers of leaf pulp constructed immediately behind each other. Microscopical analysis of the larval provisions of eight brood cells and of 41 pollen loads of females from museum and private collections showed that H.robusta exhibits a strong preference for the pollen of Potentilla (Rosaceae). Based on field observations, DNA metabarcoding of one nest plug and stereomicroscopic analysis of the leaf pulp matrix, Potentilla was also identified as an important source for the leaf pulp needed for nest construction, rendering H.robusta one of the few bee species known to collect floral resources and nest building material from the very same plant.

NEP of a Swiss subalpine forest is significantly driven not only by current but also by previous year's weather

Understanding the response of forest net ecosystem productivity (NEP) to environmental drivers under climate change is highly relevant for predictions of annual forest carbon (C) flux budgets. Modeling annual forest NEP with soil–vegetation–atmosphere transfer models (SVATs), however, remains challenging due to unknown delayed responses to weather of the previous year. In this study, we addressed the influence of previous year's weather on the interannual variability of NEP for a subalpine spruce forest in Switzerland. Analysis of long-term (1997–2011) eddy covariance measurements showed that the Norway spruce forest Davos Seehornwald was a consistent sink for atmospheric CO2, sequestering 210 ± 88 g C m−2 yr−1 on average. Previous year's weather strongly affected interannual variability of NEP, increasing the explained variance in linear models to 53% compared to 20% without accounting for previous year's weather. Thus, our results highlight the need to consider previous year's weather in modeling annual C budgets of forests. Furthermore, soil temperature in the current year's spring played a major role controlling annual NEP, mainly by influencing gross primary productivity early in the year, with spring NEP accounting for 56% of annual NEP. Consequently, we expect an increase in net CO2 uptake with future climate warming, as long as no other resources become limiting.

Rozpad drzewostanu i odnowienie świerka a struktura i dynamika karpackiego boru górnoreglowego [Breakdown of tree stand and spruce regeneration versus structure and dynamics of a Carpathian subalpine spruce forest]

Structure and dynamics of the Carpathian subalpine spruce forest was a subject of research conducted in Babia Góra National Park, protecting the highest massif in the whole West Beskids. The mosaic structure was simultaneously treated as a background for and a result of breakdown of spruce stand and spruce regeneration. The forest texture, dead trees, gaps, synusia of herb layer and spruce saplings were mapped over the area of 14,4 ha. Simultaneous mapping over the same and large area madę it possible to analyse the spatial relationships between all these phenomena and to reveal strong dependence between most of them. Particular attention was focused on spruce regeneration. It was stated that young spruces arę closely linked to microsites created by death of trees: windthrow mounds, logs and stumps in advanced stage of decay, and gaps larger than 200 m². Seedlings and saplings were also relatively more abundant in patches dominated in herb layer by <em>Vaccinium myrtillus</em> or <em>Dryopteris dilatata</em> than in others. The conclusion was achieved that coarse-grained type of mosaic structure in subalpine spruce forest and large-scale disturbances not only arę the result of low resistance of congeneric and one-layered tree stands against wind, snów, glaze and insects. To large degree they are also shaped by condition of spruce regeneration. As a light-demanding species, spruce at high elevation needs large gaps for successfull regeneration. It leads to excessive thinning of stands and expose them to disruptive action of harsh climat in the subalpine forest belt.

Forest NEP is significantly driven by previous year's weather

Understanding the response of forest net ecosystem productivity (NEP) to environmental drivers under climate change is highly relevant for predictions of annual forest carbon (C) flux budgets. Modeling annual forest NEP with soil–vegetation–atmosphere transfer models (SVATs), however, remains challenging due to unknown responses of forests to weather of the previous year. In this study, we addressed the influence of previous year's weather on the inter-annual variability of NEP for a subalpine spruce forest in Switzerland. Analysis of long-term (1997–2011) eddy covariance measurements showed that the Norway spruce forest Davos Seehornwald was a consistent sink for atmospheric CO2, sequestering 210 ± 88 g C m−2 per year on average. Previous year's weather strongly affected inter-annual variability of NEP, increasing the explained variance in linear models to 53% compared to 20% without previous year's weather. Thus, our results highlight the need to consider previous year's weather in modeling annual C budgets of forests. Furthermore, soil temperature in the current year's spring played a major role controlling annual NEP, mainly by influencing gross primary productivity early in the year, with spring NEP accounting for 56% of annual NEP. Consequently, we expect an increase in net CO2 uptake with future climate warming, as long as no other resources become limiting.