Jens Paulsen

Tree growth near treeline : abrupt or gradual reduction with altitude?

Natural climatic treelines are relatively discrete boundaries in the landscape established at a certain elevation within an otherwise continuous gradient of environmental change. By studying tree rings along elevational transects at and below the upper treeline in the European Alps, we (1) determine whether radial stem growth declines abruptly or gradually, and (2) test climatic influences on trees near treeline by investigating transects for climatically different historical periods. While tree height decreases gradually toward the treeline, there is no such general trend for radial tree growth. We found rather abrupt changes which imply threshold effects of temperature which moved upslope in a wave-like manner as temperatures increased over the past 150 yr. Currently radial tree growth at treeline in the Alps is the same magnitude as at several hundred meters below current treeline. Over short intervals, tree-ring width is more dependent on interannual climatic variability than on altitudinal distance to treeline. We conclude that (1) the elevational response of tree-rings includes a threshold component (a minimal seasonal temperature) and that (2) radial growth is more strongly correlated with year to year variation in climate than with treeline elevation as such. Our data indicate that the current treeline position reflects influences of past climates and not the current climate.

GIS-analysis of tree-line elevation in the Swiss Alps suggests no exposure effect

. Counter intuition, an analysis of tree-line position across the Swiss Alps based on a geographical information system (GIS) with a spatial resolution of 100 m (2.5 million points) revealed no difference in climatic tree-line altitude with slope exposure. Through step wise discrimination procedures our analysis accounts for anthropogenic tree-line depression. Any land cover bias affects the frequency of GIS-points corresponding to tree-line forests rather than the mean elevation of such points, captured by our analysis. We explain this phenomenon (1) by the absence of significant drought effects in the Alps (no disadvantages for southwest slopes), (2) by the fact that tree tops, unlike low stature vegetation, do not profit from greater radiation warming on south slopes during the growing season but are thermally coupled to free air circulation, and (3) by preliminary data for root zone temperatures during the growing season, which do not differ between south and north slopes, as long as the soil is screened by a closed forest canopy. The overall difference in season length and snow cover, often seen between south and north slopes, does not seem to affect tree-line position but explains greater natural forest fragmentation on north slopes. It is this greater fragmentation and patchiness (avalanche tracks, snow beds etc.) which seem to have nourished the idea of a generally lower limit of tree growth and tree lines at northern slopes. These results are in line with a recently developed theory, which suggests that tree-line elevations in humid climates correspond to similar isotherms, irrespective of latitude and thus, season length.

A greener Greenland? Climatic potential and long-term constraints on future expansions of trees and shrubs.

Warming-induced expansion of trees and shrubs into tundra vegetation will strongly impact Arctic ecosystems. Today, a small subset of the boreal woody flora found during certain Plio-Pleistocene warm periods inhabits Greenland. Whether the twenty-first century warming will induce a re-colonization of a rich woody flora depends on the roles of climate and migration limitations in shaping species ranges. Using potential treeline and climatic niche modelling, we project shifts in areas climatically suitable for tree growth and 56 Greenlandic, North American and European tree and shrub species from the Last Glacial Maximum through the present and into the future. In combination with observed tree plantings, our modelling highlights that a majority of the non-native species find climatically suitable conditions in certain parts of Greenland today, even in areas harbouring no native trees. Analyses of analogous climates indicate that these conditions are widespread outside Greenland, thus increasing the likelihood of woody invasions. Nonetheless, we find a substantial migration lag for Greenlands current and future woody flora. In conclusion, the projected climatic scope for future expansions is strongly limited by dispersal, soil development and other disequilibrium dynamics, with plantings and unintentional seed dispersal by humans having potentially large impacts on spread rates.

A bioclimatic characterisation of Europe's alpine areas

The natural high altitude treeline, the sole bio-reference for defining the alpine zone, integrates local thermal conditions in such a way that it occurs at equal temperatures, at both European and global scales (Korner 1998). This is seen by its occurrence at progressively lower elevations along a northward latitudinal gradient. Does this mean in practice that, for example, a Norwegian fellfield offers comparable life conditions to that of a Macedonian alpine heath? For our study, it was of interest if what in various localities in Europe has been referred to as alpine did indeed represent a quantitatively comparable environment.

A Geostatistical and Bioclimatological Comparison of the Central Great Caucasus and the Central Alps

Although almost 3000 km apart, the Great Caucasus at the eastern edge of Europe and the Alps in central Europe share a common young geological age, an approximative W-E orientation, they both belong to the Eurasian mountain chain that formed and is still forming as a result of southern continents pushing northwards. Using a 1000 m elevation minimum, the Great Caucasus is stretching from 41° 15′ N to 43° 45′ N (central part at 43°N) and the Alps from 44° 10′ N to 47° 40′ N (central part at 46° 30′N), with both chains belonging to the temperate zone (Fig. 1.1). In their central part, the Alps experience a stronger maritime and the Great Caucasus or more continental influence. Both ranges divide the weather systems into northern and southern climates, and both show strong precipitation gradients. In the Great Caucasus this is a NW-SE gradient, in the Alps (with some exceptions) a N-S gradient, ranging from around 2000 mm per year to less than 500 mm at places. Both mountain systems show a mass elevation effect (‘massenerhebungseffekt’), with a higher elevation of isotherms in the interior parts compared to front ranges, and a dry, step-type climate in parts of their deep central valleys. Yet, the Caucasus forms a single main divide with a series of side valleys on either side, whereas the Alps have several chains in parallel, permitting a more pronounced mass elevation effect to occur in its interior valleys. The maximum elevation is similar, with the highest peak of the Great Caucasus, Mount Elbrus 5642 m, and that of the Alps, Mont Blanc 4809 m. Yet, some of the highest peaks in the Caucasus are former volcanoes (Mount Kasbek with 5047 m, is one of them, in the core study region of this volume), whereas in the Alps, all summits are tectonic summits.

GMBA mountain inventory_V1.0

The GMBA mountain inventory is an inventory of the world’s mountains based on the GMBA mountain definition. Each of the 1003 entries corresponds to a polygon drawn around a mountain or a mountain range and includes the name of the delineated object, the area of mountainous terrain it covers stratified into different bioclimatic belts (all at 2.50 resolution), and demographic information.

Lässt sich das CO2-ProbIem biologisch managen?

„Mehr Arbeitsplatze oder weniger Kohlendioxid-Ausstoss“ — so sah ein Schweizer Vertreter an der Berliner Klimakonferenz die Management-Optionen fur die Zukunft. Abgesehen davon, dass es nicht nachvollziehbar ist, wieso bessere und mehr Warmeisolierung, effizientere Heizungen, mehr offentlicher und weniger Individual-Verkehr und bewussterer Umgang mit Energie im privaten Bereich Arbeitsplatze kosten sollen, anstatt Mittel fur privaten Konsum freizumachen, steht diese Aussage diametral zur Realitat. Trotz steigender Arbeitslosenzahlen steigen Energiekonsum und CO2-Ausstoss weltweit, was zu einem jahrlichen Anstieg der CO2-Konzentration der Luft von ca. 2 ppm fuhrt. Wahrend der Lebensspanne eines Waldbaumes hat sich somit seit etwa 1850 der CO2-Pegel in der Luft um 27 % erhoht. Der uberwiegende Teil dieses CO2-Ausstosses entfallt bekanntlich auf die Industrielander. Nach allen Befunden, die heute zur Verfugung stehen, gab es eine derartig rapide Zunahme des stofflichen Eckpfeilers des Lebens auf der Erde — das ist CO2 — bisher nicht (Abb. 1).