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Der heute vielerorts angestrebte naturnahe Waldbau setzt in hohem Maße auf biologische Automation (vgl. Gauer 2009). Grundlegend für eine solche Forstwirtschaft ist unter anderem die räumlich-differenzierte Erfassung und Bewertung wasserhaushaltsbezogener Standortsmerkmale. Denn erst die Kenntnis der Dynamik des pflanzenverfügbaren Bodenwasserangebotes oder auch eines möglichen Überschusses in Form von Stauwasser erlaubt eine standortsgerechte Baumartenwahl als Voraussetzung für eine nachhaltige Waldbewirtschaftung.
The promotion and extension of continuous cover mixed stands with a simultaneous reduction of conifer-monocultures play a major role in current silvicultural practices in Central Europe. It is assumed that the admixture of the natural dominant beech (Fagus sylvatica) in pure non site-specific conifer stands automatically indicates better conditions in terms of nature conservation and forest management. To test this hypothesis three different conifer-beech-comparisons of pure and mixed stands in Lower Saxony are studied, analyzing plant species diversity and naturalness of understory vegetation as one important indicator for the ecological status of forests. Each comparison includes pure coniferous stands (Picea abies, Pinus sylvestris, Pseudotsuga menziesii), mixed coniferous-beech-stands, and pure beech stands on similar acidic mineral soils where the potential natural vegetation will be an oligotrophic beech forest (L u z u l o - Fa g e t um). The age of stands varies between 50 and 150 years. To specify tree species influence on site conditions and vegetation, the study also includes light climate and soil data of the stands. It is observed that, with regard to all comparisons, the admixture of beech reduces plant species diversity but increases naturalness of the stands. The intensity of beech admixture effects differs. While in Scots pine stands the impact of admixed beech is very noticeable, with the mixed stands being nearly identical with pure beech stands, the species change in Douglas-fir and Norway spruce stands proceeds more slowly. Assuming that the status in nature conservation and forest management is improving with increasing plant species diversity and increasing naturalness, the results of this study show a contrary development on a stand scale, as the potential natural vegetation of the L u z u l o - F a g e t u m is in its self very species poor on vascular plants.
Mountains, with their isolated position and altitudinal belts, are hotspots of biodiversity. Their flora and fauna have been observed worldwide since the days of Alexander von Humboldt, which has led to basic knowledge and understanding of species composition and the most important driving forces of ecosystem differentiation in such altitudinal gradients. Systematically designed analyses of changes in species composition with increasing elevation have been increasingly implemented since the 1990s. Since global climate change is one of the most important problems facing the world this century, a focus on such ecosystem studies is urgently needed. To identify the main future needs of such research we analyze the studies dealing with species changes of diverse taxonomical groups along altitudinal gradients (0 to 6,400 m a.s. l.) on all continents, published during the past one to two decades. From our study we can conclude that although mountains are powerful for climate change research most studies have to face the challenge of separating confounding effects driving species assemblages along altitudinal gradients. Our study therefore supports the view of the need of a global altitudinal concept including that (1) not only one or a few taxonomical groups should be analyzed, but rather different taxonomical groups covering all ecosystem functions simultaneously; (2) relevant site conditions should be registered to reveal direct environmental variables responsible for species distribution patterns and to resolve inconsistent effects along the altitudinal gradients; (3) transect design is appropriate for analyzing ecosystem changes in site gradients and over time; (4) both the study design and the individual methods should be standardized to compare the data collected worldwide; and (5) a long-term perspective is important to quantify the degree and direction of species changes and to validate species distribution models. (6) Finally we suggest to develop experimental altitudinal approaches to overcome the addressed problems of biodiversity surveys.