A Critical Comparison of Typologies of Small-Scale Forestry in Baden-Württemberg Derived Using Single and Multiple Criteria

The paper presents a typology of small-scale forest owners in Baden-Württemberg based on multiple criteria and derived using multivariate cluster analysis of long-term accountancy network data. Four distinct types of landholders are identified based on a combination of structural, financial and biophysical data. These groups fit well with the present knowledge on small-scale forest owners in Baden-Württemberg. In addition, the members of each group display clear differences in attitudes towards forestry, giving further support for the validity of the grouping. A comparison is made of this typology and typologies derived using the single criteria of forestry region, forest size class, cutting volume, proportion of coniferous trees, forest income and main source of income. This comparison demonstrates the advantages of using cluster analysis to identify types of small-scale forest owners in south-west Germany. No matter whether structural, natural or financial data are assessed, the multiple criteria typology produced by cluster analysis provides the highest percentage of statistically significant distinctions between the medians of the groups identified. A typology based on the single criterion of ‘regions’ provides the second best fit and has the advantage of being simple to develop. A more detailed comparison between these two typologies, whereby the differences between groups were analysed based on the links between individual groups in respect to individual variables, also indicated that the multiple criteria typology was superior.

Abundance, niche breadth, and niche occupation of Central European tree species in the centre and at the margin of their distribution range

How abundance, niche breadth and niche occupation of species change within the distribution range remains unresolved for tree floras. We compared populations of three common and three rare European tree species in the distribution centre and at the eastern margin with respect to abundance, niche breadth, and preferential occurrence along several soil-related niche axes. We hypothesised: (i) that abundance is higher, and niche breadth greater, in the distribution centre than at the margin, (ii) that the occupied niche differs between central and marginal populations with species being restricted to more favourable soils at the margin, and (iii) that common and rare species show different patterns.We characterised the occupied niche and niche breadth in a semi-quantitative way and discuss the role of human impact on tree abundance in the light of evidence from paleoecology and forest dynamics research.Five of the six species are more abundant in the centre than at the margin, at least in the natural vegetation prior to human intervention. In contrast to soil niche breadth, the preference for soil chemical and hydrological properties differed between centre and margin. Contrary to expectation, a shift to less fertile and partly also drier sites at the margin was observed, although bedrocks which give rise to the development of fertile soils were more frequent in Slovakia (ca. 49% of the total area compared to 20% in Central Germany) and bedrock types which produce infertile soils were more abundant in Central Germany (about 23% vs. 2% in Slovakia).While the abundant-centre-distribution hypothesis is supported by our data, we found no conclusive evidence of competitive displacement of weaker competitors and of a niche shift of superior competitors to more favourable sites at the range margin. Factors other than competition must be responsible for the observed niche shifts. Higher drought stress does not seem to be a limiting factor at the eastern margin, where dry sites were occupied more frequently compared to the centre.     

Dendroecological assessment of the complex causes of decline and recovery of the growth of silver fir (Abies alba Mill.) in Southern Germany

Causes of decline and silver fir (Abies alba Mill.) mortality in Central Europe have been controversially discussed for a long time. This contribution details a comprehensive dendroecological investigation of two basic and alternative hypotheses that explain the decline by either climatic influences or by SO₂ pollution as the primary factors. Growth reduction between the 1960s and 1980s as well as the recovery of growth during recent decades have be seen as a response to complex interactions of multiple factors. Herein, we undertake a multidisciplinary evaluation of a broad database, representing the long-term growth of 1010 firs from 51 sites, long-term climate records as well as data assessing the long-term pollution situation in Southern Germany. The results provide clear evidence that SO₂-immissions play a key role in decline and that tree growth corresponds with the regional and temporal pattern of SO₂ pollution. Calculations with a new complex growth model indicate that tree-ring widths of fir at many sites were more influenced by SO₂ than by any other growth-determining factor during the second half of the last century. Strongest coherence between measured and modelled ring widths are found if – in addition to temperature, available soil water content, heavy frost events and long-term growth trends – the site-specific trend of SO₂ pollution is included. Both the immediate response to SO₂ pollution and the quick recovery of fir since the beginning of the 1980s after the decrease of SO₂ emissions indicate a direct impact of SO₂ in gaseous form and not via the soil in terms of soil acidification. Tree-ring widths document that radial growth response occurs at air concentrations above 10 μg SO₂ m⁻³ (annual average), which can be thought of as a critical threshold for silver fir health. Since the beginning of the 1980s, increasing growth trends have been observed which predominantly result from decreased SO₂ pollution in most parts of Central Europe, although climate change, fertilization by nitrogen deposition and a reduced tree-to-tree competition are also relevant factors. The drastic reduction of SO₂ emission during the recent decades significantly improved the environmental conditions for fir. Consequently, an increased cultivation of silver fir on suitable sites is recommended.     

Climate change impact predictions on Pinus patula and Pinus tecunumanii populations in Mexico and Central America

Climate change is likely to have a negative impact on natural populations of Pinus patula and Pinus tecunumanii, two globally important tree species in plantation forestry. The objective of this work was to evaluate the impact of climate change on the persistence of the natural populations of these species at their actual locations in order to take appropriate conservation measurements. A common approach to assess the impact of climate change on species natural distributions is climate envelope modeling (CEM). CEMs suggest significant impacts of climate change on the natural distribution of the two pine species, but their predictions contain considerable uncertainty related to the adaptive ability of tree populations to withstand future climate conditions. We assessed the adaptive ability of the two pine species based on the evaluations of provenance trials and used the results of these field trials to validate CEM impact assessment studies on provenance collection sites in the wild. The two pine species performed well in a wide range of climates, including conditions that were recorded by CEM as unsuitable for natural pine occurrence. The climate conditions where the two pine species naturally occur are predicted to become in the future more similar to the present climate of some areas where they are successfully established in field trials. These findings suggest that these pine species are in their natural habitat better adapted to climate change than CEM predicts. For the most vulnerable species, P. tecunumanii, human disturbances such as fragmentation from urbanization and conversion to agriculture that are occurring today are more urgent threats requiring action compared to the threat from climate change.     

Growth of European beech (Fagus sylvatica L.) saplings is limited by elevated atmospheric vapour pressure deficits

There is an ongoing debate about how European beech might be affected by a future drier climate. While numerous studies have examined the effects of soil drought on beech growth and development, studies investigating the effects of elevated atmospheric water vapour pressure deficit (VPD) are lacking. By increasing VPD in climate and open-top chamber experiments, with moisture in the rooting medium near optimum, we tested the hypothesis that increased VPD negatively affects the growth and development of European beech saplings. In the climate chambers, a reduction in relative air humidity by 40% resulted in a 68% reduction in productivity. Similarly, in the open-top chamber experiment conducted on the forest floor, biomass declined by 30% when relative air humidity was 15% lower. The reduction in biomass was mainly a consequence of a dramatically reduced leaf growth of beech in the elevated VPD treatments. Our results show that growth and development of beech saplings strongly depend not only on soil moisture but also on the prevailing VPD level. We conclude that the vapour pressure deficit is a widely ignored factor which influences the growth and vitality, and possibly also the distribution of European beech. Future forest management schemes under an altered climate should take this factor into account.     

Effects of experimental drought on the fine root system of mature Norway spruce

Norway spruce (Picea abies (L.) Karst.) is an economically important, but relatively drought-sensitive tree species that might suffer from increasing drought intensities and frequencies, which are predicted to occur in parts of central Europe under future climatic change. In a throughfall exclusion experiment using sub-canopy roofs, we tested the hypothesis that enhanced drought leads to an increase in fine root mortality, and also to a higher, subsequent fine root growth. Fine root production and mortality were assessed using two independent approaches, sequential soil coring (organic layer) and direct observations in minirhizotrons (organic layer plus upper mineral soil). Six weeks of throughfall exclusion resulted in mild drought stress, i.e. a reduction in average soil moisture from 20 to 12 vol.% during the treatment. Based on the sequential coring data, experimental drought did not result in significant changes in fine root biomass during the 6-week treatment period, but caused an increase in fine root mortality by 61% in the 6 weeks following the drought treatment. Remarkably, fine root production showed a synchronous increase in this period, which more than compensated for the loss due to increased mortality. The minirhizotron data confirmed that the drought treatment increased fine root loss in the organic layer. Based on this method, however, root loss occurred during the drought period and was not compensated by increased root production. The mild drought stress was mainly restricted to the organic layer and did not significantly influence fine root dynamics in the mineral soil. We calculated that the drought event resulted in an extra input of about 28 g C m⁻² and 1.1 g N m⁻² to the soil due to increased fine root mortality. We conclude that even periods of mild drought significantly increase fine root mortality and the associated input of root-derived C to the soil organic matter pool in temperate Norway spruce forests.     

The potential of SilviScan’s X-ray diffractometry method for the rapid assessment of spiral grain in softwood, evaluated by goniometric measurements

The orientation of the tracheid cells with respect to the stem axis (grain angle, spiral grain) exerts a strong influence on numerous material properties. Therefore, several methods have been developed to assess this wood anatomical feature. The current study compares SilviScan spiral grain measurements, which uses X-ray diffractometry, with direct goniometer readings. The correlation between these two methods yielded an r² of 0.874 and a root mean square error of prediction (RMSEP) of 1.21 clearly demonstrating that X-ray diffractometry can provide accurate and rapid information on the grain orientation in Norway spruce (Picea abies (L.) Karst.) or similar structured softwoods.     

Hydrochars derived from sewage sludge: effects of pre-treatment with water on char properties,phytotoxicity and chemical structure

Large amounts of labile compounds are adsorbed to the surface of chars produced by hydrothermal carbonization (HTC). The aim of this study was to characterize the core and adsorbed fractions of hydrochars and to gain knowledge about the possibility to remove phytotoxic compounds by washings with water. Chars were produced by HTC of sewage sludge at different temperatures (180 – 200 °C) and over different periods of time (4 – 8 h). For comparison one pyrolysis char produced by thermocatalytic low temperature conversion (LTC) at 400 °C for 1 h was included in the study. The chars and their feedstocks were treated varying the duration (1 x 15, 1 × 30 and 1 × 60 min) and number (2 x 60 and 3 × 60 min) of washings. Physicochemical properties, including the molecular structure of the test materials, and their effects on germination and plant growth were analysed. Element concentrations and phytotoxic effects were reduced and the number of washings had a stronger effect than their length of time. Intensive washings with water reduced the hydrochars’ portion of biodegradable compounds significantly. However, also plant available nutrients were lost by washing with water, decreasing the value of hydrochars as a soil amendment.     

River damming drives population fragmentation and habitat loss of the threatened Danube streber (Zingel streber): Implications for conservation

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