Regeneration der Fjellbirke (Betula pubescens ssp. czerepanovii) und Wurzelsysteme ihres Jungwuchses im Waldgrenzökoton, Finnische Subarktis

Ziel der Arbeit ist die Erfassung des Einflusses kleinräumig wechselnder Standortbedingungen auf die Verbreitung und die Entwicklung von Birkenjungwuchs (Betula pubescens ssp. czerepanovii) im Waldgrenzökoton des nördlichen Finnisch-Lappland. Jungwuchsdichte, Altersstruktur, Zuwachsraten und Ausprägung der Wurzelsysteme zeigen eine hohe Variabilität in Abhängigkeit von unterschiedlichen Boden-, Klima- und Konkurrenzbedingungen. Das Heranwachsen von Bäumen aus Jungwuchs wird jedoch auch an relativen Gunststandorten durch intensive Beweidung durch Rentiere verhindert. Ob es im Untersuchungsgebiet im Zuge von Klimaänderungen zu einem Waldgrenzanstieg kommt, hängt damit zunächst vom zukünftigen Weidemanagement ab. The aim of the study is to examine the influence of locally varying site conditions on distribution and development of mountain birch young growth (Betula pubescens ssp. czerepanovii) in the treeline ecotone in northern Finnish Lapland. Sapling density, age classes, growth rates and root system characteristics show a high variability depending on different soil conditions, microclimate and competition. However, tree growth from saplings is prevented by intensive reindeer grazing even on sites with otherwise relatively suitable conditions. Thus, it first of all depends on future pasture management whether the treeline in the investigated area will rise in connection with climate change

Functional traits shed new light on the nature of ecotones: a study across a bog-to-forest sequence

Ecotones have long been a focus of ecological research, and there is considerable current interest in functional traits in community ecology. Yet, surprisingly, the functional trait approach has not been applied to ecotones. A bog-forest sequence in southern New Zealand was sampled with a grid of quadrats, and eight traits related to leaf function were measured on the 54 species found. Two ecotones were identified using moving-window analysis: Ecotone I was the transition from bog to edge forest, and Ecotone II was the transition from edge forest to tall climax forest. No strict ecotonal species were present. In contrast to theoretical predictions, species richness was not higher or lower in either ecotone, rather, both ecotones represented a transition in richness from one community to the other. It has long been said that ecotones are mosaics, but species mosaicity was no higher in either ecotone than in the adjacent communities, in fact it was lower in Ecotone I. Functional trait diversity decreased along the sequence from bog to forest, with no deviation in either ecotone. However, examining mosaicity in terms of traits, there was a steady rise in Ecotone I and, in conformance with ecotone / functional trait theory, a clear peak in Ecotone II. We conclude that the features claimed for ecotones are often not present, and whether they are present is dependent on the components measured: species vs traits. Here, the clearest patterns were seen in trait mosaicity, but even this differed markedly between the two ecotones. Generalisations about ecotones should be avoided; they will vary from ecotone to ecotone, and probably depend on the type of ecotone: anthropogenic, environmental, switch, etc