Jörg Löffler

Complex climate controls on 20th century oak growth in Central-West Germany

We analyze interannual to multi-decadal growth variations of 555 oak trees from Central-West Germany. A network of 13 pedunculate oak (Quercus robur L.) and 33 sessile oak (Quercus petraea (Matt.) Liebl.) site chronologies is compared with gridded temperature, precipitation, cloud-cover, vapor pressure and drought (i.e., Palmer Drought Severity Index, PDSI) fluctuations. A hierarchic cluster analysis identifies three groups for each oak species differentiated by ecologic settings. When high precipitation is primarily a characteristic for one Q. robur and one Q. petraea cluster, the other clusters are more differentiated by prevailing temperature conditions. Correlation analysis with precipitation and vapor pressure reveals statistically significant (P < or = 0.05) correlations for June (r = 0.51) and annual (r = 0.43) means. Growth of both species at dry sites correlates strongly with PDSI (r = 0.39, P < or = 0.05), and weakly with temperature and cloud-cover. In natural stands, Q. robur responds more strongly to water depletion than Q. petraea. Twenty-one-year moving correlations show positive significant growth response to both PDSI and precipitation throughout the 20th century, except for the 1940s - an anomalously warm decade during which all oak sites are characterized by an increased growth and an enhanced association with vapor pressure and temperature. We suggest that the wider oak rings that are exhibited during this period may be indicative of a nonlinear or threshold-induced growth response to drought and vapor pressure, and run counter to the general response of oak to drought and precipitation that normally would result in suppressed growth in a warmer and drier environment. As the wide rings are formed during the severe drought period of the 20th century, a complex model seems to be required to fully explain the widespread oak growth. Our results indicate uncertainty in estimates of future growth trends of Central European oak forests in a warming and drying world.

Climate Change, Land Use Conflicts, Predation and Ecological Degradation as Challenges for Reindeer Husbandry in Northern Europe: What do We Really Know After Half a Century of Research?

Reindeer grazing has been entitled as ecological keystone in arctic–alpine landscapes. In addition, reindeer husbandry is tightly connected to the identity of the indigenous Sámi people in northern Europe. Nowadays, reindeer husbandry is challenged in several ways, of which pasture degradation, climate change, conflicting land uses and predation are the most important. Research on reindeer-related topics has been conducted for more than half a century and this review illuminates whether or not research is capable to match these challenges. Despite its high quality, traditional reindeer-related research is functionally isolated within the various disciplines. The meshwork of ecology, socio-economy, culture and politics, however, in which reindeer husbandry is embedded by various interactions, will remain unclear and difficult to manage, if actors and relationships are kept separate. We propose some targets for new integrative research approaches that incorporate traditional knowledge and focus on the entire human-ecological system ‘reindeer husbandry’ to develop solutions for its challenges.

High-resolution spatial analysis of mountain landscapes using a low-altitude remote sensing approach

Mountain landscapes are characterized by great spatial diversity. One basic problem is that there are few high‐resolution data for secluded mountain areas. We present a new approach towards topographic mapping and vegetation monitoring: low‐altitude remote sensing using Kite Aerial Photography (KAP). The study was conducted in the Norwegian mountains above the treeline. We assessed this approach under specific alpine circumstances. Following the collection of data, we derived a digital elevation model (DEM) from two overlapping images. The model was evaluated by the statistical correlation of 265 random field points and extracted heights from (i) linear contour line interpolation of a topographic map of scale 1 : 50 000, (ii) photogrammetric analysis of kite aerial photographs, and (iii) kriging interpolation of approximately 1000 measured field points. Finally, the vegetation was classified, using both supervised and unsupervised methods. The accuracy of the classification results was evaluated by comparing 265 random points, derived from terrestrial mappings, to classified vegetation types by an error matrix. The generation of derived data compared well with data obtained from high‐resolution field surveys and was better than data derived from public‐domain government cartography and moderate‐scale satellite remote sensing data. Our results demonstrate the economic and logistic advantages of this new KAP‐based methodology. The flexibility and outstanding high resolution of our new low‐altitude remote sensing approach proved to be particularly suitable for closing the gap between terrestrial investigations and high‐altitude remote sensing. Hence, our KAP approach addresses the challenge of multiscale research in mountain landscapes.

Alpine Soil Temperature Variability at Multiple Scales

Abstract The functioning of ecosystems is strongly correlated to soil temperature dynamics. Because only a few studies so far have investigated the spatio-temporal variability of alpine soil temperatures, we proceeded to analyze soil temperatures in a heterogeneous alpine landscape by means of a multi-scale approach. We combined vertical soil temperature gradients from surface to 15 cm depth, microspatial variability within small catchments, and altitudinal changes of a continental mountain system. We analyzed differences at single sites and at multiple spatial scales. We found that microtopographic site conditions dominated thermal changes along altitudinal gradients. The adiabatic lapse rate did not show high correlations with local soil temperature gradients. We used isopleth diagrams of soil temperature gradients and corresponding scatterplots of soil temperature gradients between each pair of sites and low alpine–middle alpine mountain couples to quantify these overlying phenomena. This enabled us to quantify the significance of soil temperature gradients across vertical soil profiles, topography, and altitude in order to facilitate future microclimate extrapolation and modeling in high mountain (alpine) landscapes. Such procedures are crucial for describing expected responses of alpine ecosystems to global climatic change.

Ring-Width Chronologies of the Alpine Dwarf Shrub Empetrum Hermaphroditum FROM THE NORWEGIAN MOUNTAINS

In this study, we present the first ring-width chronologies of the dwarf shrub species Empetrum hermaphroditum. For a proper synchronization of the growth rings, serial sectioning was applied in order to deal with the high intern al growth variability and the high proportion of discontinuous rings. The plants were collected from three micro-sites in the middle alpine belt of the Norwegian Scandes wh ich differed regarding solar insolation, snow accumulation and wind exposure. The constructed ringwidth chronologies cover aperiod of max. 80 years. Irrespective of microclimatic differences, the chronologies are highly correlated among each other and with temperatures during the growth period (June-August). However, ecological differences between the micro-sites are reflected by the mean annual growth increments of the plants. We compared the Empetrum chronologies with a ring-width chronology of Betula pubescens trees from the local tree line. Despite the differences in life form and local site conditions, the growth patterns are very similar, an observation which underscores the dominant influence of temperature on growthring formation. Due to the strong climatic signal recorded in the growth curves of E. hermaphroditum, this dwarf shrub provides a significant potential for climate-growth studies in arctic and alpine regions beyond the tree line.

Diversity Patterns in Relation to the Environment in Alpine Tundra Ecosystems of Northern Norway

ABSTRACT We analyzed diversity patterns of alpine tundra ecosystems along environmental gradients. We hypothesized that alpine diversity is affected by climate at local and regional scales, nutrient availability, soil moisture, and disturbance related to herbivory. In all, 232 samples in 11 study areas in Troms and Finnmark counties were analyzed with regard to α- and β-diversity of vascular plants and lichens. Relationships between α-diversity and environmental variables were analyzed by regression trees. β-diversity defined as species turnover was investigated using indirect ordination methods. Sites with non-acidic soil parent material showed highest species densities. Lowest species numbers were typical for extreme topographic positions. Heavily grazed samples showed less species numbers and coverage percentage of vegetation. The number of graminoid species was found to be highest in areas of high grazing pressure. We concluded that α-diversity was controlled by growing season, snow cover, pH, soil moisture, disturbance, temperature, and precipitation, stressing the importance of multi-factorial approaches in diversity studies. Determinants of β-diversity were predominantly local environmental conditions, whereas regional conditions were less important.

Deepened winter snow increases stem growth and alters stem δ13C and δ15N in evergreen dwarf shrub Cassiope tetragona in high-arctic Svalbard tundra

Deeper winter snow is hypothesized to favor shrub growth and may partly explain the shrub expansion observed in many parts of the arctic during the last decades, potentially triggering biophysical feedbacks including regional warming and permafrost thawing. We experimentally tested the effects of winter snow depth on shrub growth and ecophysiology by measuring stem length and stem hydrogen (δ2H), carbon (δ13C), nitrogen (δ15N) and oxygen (δ18O) isotopic composition of the circumarctic evergreen dwarf shrub Cassiope tetragona growing in high-arctic Svalbard, Norway. Measurements were carried out on C. tetragona individuals sampled from three tundra sites, each representing a distinct moisture regime (dry heath, meadow, moist meadow). Individuals were sampled along gradients of experimentally manipulated winter snow depths in a six-year old snow fence experiment: in ambient (c. 20 cm), medium (c. 100 cm), and deep snow (c. 150 cm) plots. The deep-snow treatment consistently and significantly increased C. tetragona growth during the 2008-2011 manipulation period compared to growth in ambient-snow plots. Stem δ15N and stem N concentration values were significantly higher in deep-snow individuals compared to individuals growing in ambient-snow plots during the course of the experiment, suggesting that soil N-availability was increased in deep-snow plots as a result of increased soil winter N mineralization. Although inter-annual growing season-precipitation δ2H and stem δ2H records closely matched, snow depth did not change stem δ2H or δ18O, suggesting that water source usage by C. tetragona was unaltered. Instead, the deep insulating snowpack may have protected C. tetragona shrubs against frost damage, potentially compensating the detrimental effects of a shortened growing season and associated phenological delay on growth. Our findings suggest that an increase in winter precipitation in the High Arctic, as predicted by climate models, has the potential to alter the growth and ecophysiology of evergreen shrub C. tetragona through changes in plant mineral nutrition and frost damage protection. (Less)

Indicators of species richness at the local scale in an alpine region: a comparative approach between plant and invertebrate taxa

Studies investigating congruent variations in species richness patterns in alpine habitats are scarce. We investigated the potential of using the indicator taxa approach for species richness in alpine habitats of the Scandes (Norway). In four areas, we investigated seven functional and taxonomic terrestrial groups of organisms and evaluated their contribution to the species diversity. The function of each group as a surrogate for the overall species diversity or for the diversity of another taxon was analysed. Three groups of invertebrates (spiders without Lycosids, Lycosids only, and ground beetles), three groups of plants (shrubs, graminoids, and herbs), and lichens were used for a cross-taxon analysis of species diversity. Congruence in species richness was restricted to several significant results, with vascular plants and spiders (Araneae) being best suited as surrogate taxa in alpine habitats of the Scandes. In the cross-taxon analyses they showed strongest significant positive correlations, covering the total species richness of the alpine habitats best. Species counts in one group account for up to 70% of the variation in total species richness. We found only limited evidence for an ideal, efficient biodiversity indicator taxon that could be applied without restrictions at different alpine habitats in low and middle alpine areas. Thus, our results suggest that it is very important to use more than one taxon as indicator for species richness in terrestrial alpine habitats. This should facilitate future conservation planning in alpine areas.

Spatio-temporal Gradients between High Mountain Ecosystems of Central Norway

Abstract Spatio-temporal gradients between ecosystems of the central Norwegian high mountains are analyzed. Complex landscape ecological site analyses combined with intensive pitfall trapping are carried out in four investigation areas in two regions. Key questions are addressed for the differences among ecosystems along a broad-scaled oceanic-continental gradient. The answers are based on ecological process analysis and mapping of zoocoenoses in small catchments of two alpine altitudinal belts. A comparison of four ridge sites is presented by analyzing water and temperature balance and activity of arthropods during the driest summer month. The results do not implicate summer drought and heat as limiting factors; summer wetness and cooling are most decisive. Landscape ecological processes, like the accumulation of snow during winter, snow melting, freeze-thaw action, percolation, soil moisture variation, and temperature regimes are exemplified by long-term measurements throughout the year in a small catchment in continental eastern Norway—the driest mountain region in Scandinavia. To learn about the organization and diversity of zoocoenoses, epigeic arthropods (Araneae, Carabidae) are investigated along spatial gradients. Interrelations between distribution patterns of animals and spatio-temporal dynamics of the environmental conditions are presented. The results are framed by gradient theory in landscape ecology. Finally, the complexity of spatio-temporal gradient determination between ecosystems is discussed and summarized by a scheme of gradient principles for the Norwegian mountains.

High Mountain Ecosystems and Landscape Degradation in Northern Norway

Abstract The influence of reindeer pasturing on high mountain ecosystems in northern Norway was investigated using a landscape-ecological analysis. The most visible impacts of overgrazing are on the vegetation. In addition, soils and humus have been changed due to morphodynamic processes induced to a large extent by reindeer pasturing. Degradation of the high mountain landscapes within the last 30 years is described on 3 spatial levels: large-scale effects at specific localities, linear effects along reindeer fences, and small-scale effects on the altitudinal zonation of entire mountain systems. The structure of the ecosystem has changed completely due to reindeer pasturing, which has resulted in landscape degradation under great pasturing pressure. The processes that influence the ecosystem as a function of different pasture intensities are described and show a complex correlation and interaction between the ecofactors. These include destruction of vegetation cover, reduction of root density, erosion of humus and mineral soil horizons, reduction of soil moisture and soil stability, and changes in plant species composition. On the whole, degradation leads to a depression of the altitudinal belts, indicated by the new organization of the ecosystems. It can be concluded that reindeer herding at current levels is a destructive form of land use in the northern Norwegian high mountains and hence is not sustainable. The author believes that destruction of the natural environment could be reversed, although this is not to be expected.