Václav Treml

Woody biomass production lags stem-girth increase by over one month in coniferous forests

Wood is the main terrestrial biotic reservoir for long-term carbon sequestration(1), and its formation in trees consumes around 15% of anthropogenic carbon dioxide emissions each year(2). However, the seasonal dynamics of woody biomass production cannot be quantified from eddy covariance or satellite observations. As such, our understanding of this key carbon cycle component, and its sensitivity to climate, remains limited. Here, we present high-resolution cellular based measurements of wood formation dynamics in three coniferous forest sites in northeastern France, performed over a period of 3 years. We show that stem woody biomass production lags behind stem-girth increase by over 1 month. We also analyse more general phenological observations of xylem tissue formation in Northern Hemisphere forests and find similar time lags in boreal, temperate, subalpine and Mediterranean forests. These time lags question the extension of the equivalence between stem size increase and woody biomass production to intra-annual time scales(3, 4, 5, 6). They also suggest that these two growth processes exhibit differential sensitivities to local environmental conditions. Indeed, in the well-watered French sites the seasonal dynamics of stem-girth increase matched the photoperiod cycle, whereas those of woody biomass production closely followed the seasonal course of temperature. We suggest that forecasted changes in the annual cycle of climatic factors(7) may shift the phase timing of stem size increase and woody biomass production in the future.

Late-Holocene human-induced changes to the extent of alpine areas in the East Sudetes, Central Europe

The easternmost parts of the Hercynian mid-mountains of Central Europe, namely Hrubý Jeseník and Králický Sněžník, are characterised by extensive alpine areas at altitudes above approximately 1300 m a.s.l. In order to determine the contribution of human activities to the extent of these summit grasslands we analysed charcoal assemblages and pollen profiles taken from high elevation sites. The first burn was dated to the Iron Age (about the first to second centuries BC), with successive fire events recorded in the early Mediaeval epoch from about AD 670. Significant human influence as recorded in pollen diagrams was detected as late as during the High Middle Ages (about the twelfth to thirteenth centuries AD). Charcoal assemblages reveal similar trends in species composition. The oldest and/or deepest samples are represented by charcoal fragments of Picea abies and various broadleaf trees and shrubs such as Betula sp., Sorbus sp., Juniperus sp. and Salix sp. Towards the surface, Picea abies gradually becomes dominant and then Vaccinium charcoal particles dominate the charcoal pool. Radiocarbon data of individual charcoal fragments did not, however, confirm a stratification of charcoal in the soil. According to anthracomass, pollen and macrofossils, the pattern of forest-free areas was originally determined by terrain morphology. While forest-free patches occurred on exposed summits and the convex edges of summit plateaus, open canopy tree growths dominated high elevation summit flats, and closed canopy forests occurred on adjacent slopes.

Holocene dynamics of the alpine timberline in the High Sudetes

The study focuses on the High Sudetes that represent the most distinctive islands of alpine forest-free area among hercynian mid-mountains of Central Europe. Based on data from newly taken cores and previously published pollen profiles, comparison of the development of the alpine timberline position is carried out. The first of the analysed pollen profiles — the Labský důl core in the Krkonoše Mts spans the whole period of the Holocene, the Keprník and Mezikotlí profiles in the Hrubý Jeseník Mts bring information from the Subboreal/older Subatlanticum turn to the present. An exceptional position of the Krkonoše Mts in terms of permanent presence of the alpine belt throughout the Holocene was confirmed. Three oscillations of the alpine timberline during the Lower Holocene were detected in the profile from the Labský důl site. In the Hrubý Jeseník Mts a temperature dependent forest-free area existed at least since Subboreal to the present.

The Effect of Exposure on Alpine Treeline Position: a Case Study from the High Sudetes, Czech Republic

Using the High Sudetes as an example, we examined whether the position of the alpine treeline is in fact related to the heat load of the site, and whether the temperatures of the air and soil change along slopes with differing exposure to solar radiation. We hypothesized that if there are really strong exposure effects they must be expressed both in significant correlations between treeline elevation and heat load of respective sites and in distinct differences in root zone and tree top temperatures. We found that the highest positions of the alpine treeline were situated in places with the potentially highest heat load. Nevertheless, only weak exposure effects on the soil temperatures during the growing season were detected, both in the closed forest and in the tree groups. Further, air temperatures near the terminal shoots varied significantly less than soil temperatures; however, the margins of the closed forest were especially more favorable at the south-facing slopes. Winter soil temperatures did not seem to be generally more advantageous on sites with high heat load. Direct temperature measurements thus indicated that established positions of the alpine treeline are just slightly influenced by differences in heat load.

Ecotonal dynamics of the altitudinal forest limit are affected by terrain and vegetation structure variables: an example from the Sudetes Mountains in Central Europe

Abstract At the landscape scale, the response of alpine treelines to increasing temperatures often varies due to second-order factors such as terrain properties, vegetation structure, and land use. In this study, we examined the influence of topographic and vegetation-structure variables on spatial patterns of treeline ecotone shifts in the Sudetes Mountains (Czech Republic). The changing positions of the alpine timberline and alpine treeline were determined from orthogonal aerial images allowing comparisons between 1936 and 2005. Our results showed that the alpine timberline advanced upward at an overall rate between 0.30 m yr-1 in the Hrubý Jeseník Mountains (eastern part of the Sudetes) and 0.43 m yr-1 in the Giant Mountains (western part of the Sudetes). Forest infilling was substantially greater than advances above original alpine treeline positions. Forest upward shifts occurred mostly on sites with already established, well-dispersed trees and low levels of prostrate dwarf pine cover. Topographic variables such as altitude and heat load affected forest advance if initial tree cover was low. The occurrence of competitive prostrate shrubs and the presence of climatically extreme convex parts of slopes appear to be important second-order factors affecting treeline ecotone shifts, particularly at wind-affected treelines.

Growth trends and climate responses of Norway spruce along elevational gradients in East-Central Europe

Key messageDecadal growth variability of Norway spruce increases with elevation. Recent temperature sensitivity and growth enhancement are limited to trees growing in the zone adjacent to timberline.AbstractGrowth trends and climate responses of forest trees along elevational gradients are not fully understood. A deeper insight is, however, fundamental for predicting ecosystem functioning and productivity under future climate change. Supplementary to the effects of elevation and regional provenance on tree growth are sample depth, uneven representation of sample age and varying site conditions. Furthermore, there is only a limited number of studies addressing growth changes along elevational gradients, while at the same time applying tree-ring standardization methods that are sensitive to trend preservation. Here, we introduce 12 novel tree-ring width chronologies of Norway spruce (Picea abies[L.] Karst.) from four elevational belts encompassing montane forests and the local timberline in three regions in East-Central Europe between 15° and 19°E. Each chronology is characterized by sufficient sample replication and a comparable age structure between 1906 and 2010. Tree growth near timberline revealed substantial medium-frequency variability and sharply increasing ring widths since the 1980s. Medium-frequency growth variability of lower elevation trees was, however, relatively small, and growth rates over the last decade were either stable or even decreased. During the last four decades, Norway spruce from higher elevations exhibited a reduced response to autumn temperatures preceding ring formation. In contrast, trees from the lower-montane zone increased their sensitivity to drought during the same time. Our results emphasize not only different but also instable growth trends and climate responses of forest trees along altitudinal gradients, which should be considered in future forest management strategies.

Effects of Prostrate Dwarf Pine on Norway Spruce Clonal Groups in the Treeline Ecotone of the Hrubý Jeseník Mountains, Czech Republic

Abstract Global temperature increase would seem likely to result in general upwards shifts of altitudinal margins of tree stands. However, range expansion of trees could be significantly affected by both negative and positive interactions with alpine shrubs in existing treeline ecotones. We examined the effects of dwarf pine (Pinus mugo) shrubs on the vegetative propagation and height growth of Norway spruce (Picea abies) trees in the treeline ecotone of the Hrubý Jeseník Mountains, Czech Republic. Here, the non-native dwarf pine was planted above timberline during the 19th and 20th centuries. In the treeline ecotone, vegetative propagation is important both for generation of clonal groups from seed-originated individuals and for persistence of such stands. We found that increasing density of dwarf pine stands strongly reduced vegetative propagation of spruce, as shown by the spruce clonal groups surrounded by dense pine having fewer layering branches and ramets than such groups outside pine stands. This has likely resulted from competitive pressure of pine causing decreased spruce layering mainly through mechanical damage and shading. In contrast, dense pine stands increased spruce height growth, presumably by providing shelter against wind and/or browsing. Our results indicate that interactions of prostrate dwarf pine and Norway spruce clonal groups include both competitive and facilitative components, which probably change in importance along climatic stress gradients.

SNOWPATCH HOLLOWS AND PRONIVAL RAMPARTS IN THE KRKONOŠE MOUNTAINS, CZECH REPUBLIC: DISTRIBUTION, MORPHOLOGY AND CHRONOLOGY OF FORMATION

Margold, M., Treml, V., Petr, L. and Nyplová, P., 2011. Snowpatch hollows and pronival ramparts in the Krkonoše Mountains, Czech Republic: distribution, morphology and chronology of formation. Geografiska Annaler: Series A, Physical Geography, 93, 137–150. DOI: 10.1111/j.1468‐0459.2011.00422.x Abstract Two types of landforms attributed to the geomorphological effects of long‐lasting snow accumulations, snowpatch hollows and pronival ramparts, were studied in the Krkonoše Mountains, Czech Republic. Factors influencing the distribution and morphology of snowpatch hollows were examined using statistical analysis of field‐measured and DEM‐modelled snowpatch hollow characteristics. Snowpatch hollows were classified into two groups. The first group comprises hollows developed mainly in erosional incisions from streams on low‐relief summit planation surfaces. The hollows of this group are relatively small and display signs of recent activity, with development during the Holocene. The second group consists of larger snowpatch hollows developed in debris‐covered slopes of the highest summits, closely related to the cryoplanation terraces occurring in the area. The hollows of this group are suggested to have developed in the periglacial environment of the glacial periods. The age and degree of activity of pronival ramparts, occurring only at two sites in the study area, were determined using several methods (Schmidt hammer, lichenometry, pollen analysis, and radiocarbon dating). The appearance of these pronival ramparts differs between the two sites as a result of the different geological setting. Both the ramparts in the Harrachova jáma cirque, consisting of coarse granite debris, and the rampart in the Úpská jáma cirque, developed of mica‐schist clasts, have been active during the late Holocene and are considered to be active even today.

Assessing the Change in Cover of Non-Indigenous Dwarf-Pine Using Aerial Photographs, a Case Study from the Hrubý Jeseník Mts., the Sudetes

Assessing the Change in Cover of Non-Indigenous Dwarf-Pine Using Aerial Photographs, a Case Study from the Hrubý Jeseník Mts., the Sudetes In addition to ongoing climate change, alpine ecosystems are also threatened by the expansion of non-indigenous species. Expansion of dwarf pine (Pinus mugo Turra) in the Hrubý Jeseník Mts. is an excellent example of the interactions between a planted alpine shrub and alpine ecosystems dominated by grassland species. Based on a comparison of aerial photographs taken in two different periods (1971/73 and 2003) we analyzed spatial changes in the dwarf pine cover. We focused on an evaluation of the current proportion of dwarf pine stands above the upper forest limit, as well as on the effects of stand texture and environmental variables on dwarf pine expansion over this 30 year period. During this time, dwarf pine stands increased their extent by 63%. Small forest-free areas above the upper forest limit in the northern part of the Hrubý Jeseník ridge are currently covered by dwarf pine on more than 30% of their surface. Expansion of dwarf pine was fastest in open, fine-grained stands, often situated in lower altitudes and on north- to east-facing slopes. The dwarf pine expansion was more intense than predicted by simple model of vegetative growth, especially within open stands with short polycormon margins in low altitudes. This might be explained by more intensive growth in less extreme environment and/or by higher generative reproduction on these sites. Finally, we suggest that expanding dwarf pine shrubs and recessing grassland patches negatively affects the abundance of heliophilous alpine plants and insects. We believe that the results of this study could be relevant to ongoing discussions on the management of summit forest-free areas in the Hrubý Jeseník Mts.

Meta-analysis of dendrochronological dating of mass movements

Absolute dating of mass movements is crucial for disentangling possible release factors and determining the frequency of events. Here, we present an overview of a recent approach to dendrochronological dating of rockfalls, flows, landslides and avalanches. The results, based on 69 casestudies, show that methodological approaches to sampling and material processing differ considerably for different types of mass movements. Landslides are usually detected through abrupt growth changes and changes in stem eccentricity, whereas high-energy events as avalanches and flows are mostly identified by the formation of traumatic resin ducts, reaction wood, growth injuries and eccentricity changes. Cross-dating of dead wood is applicable as well. The dating of most mass movements except landslides is common, even with sub-annual resolution. In comparison to other methods of absolute dating, the main benefit of dendrochronology still lies in the high temporal resolution of the results. If living material is accessible, on-going research progress makes absolute dating of most mass-wasting events possible with sub-annual precision.