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Stephan Getzin

The Doktorhut of Stephan immediately after successfully defending the PhD.

Analysis of hierarchical structures in forest stands using detailed spatial statistics

Stephan attempted in his thesis to contribute to selected topics in forest ecological research to better understand essential processes that lead to small- and large-scale forest structures. His topics were centered on point pattern analysis of fully mapped forest stands to analyze their spatial structure and to reveal which processes and factors may determined the structure of these forest communities. Comparative analyses were done by comparing chronosequences of stands of different age and stands with homogeneous and heterogeneous environmental conditions. He also analyzed asymmetric tree growth at the stand level by comparing the stem pattern and the crown patterns and used recent remote sensing techniques to assess competition at the stand level from field-measured and photo-derived crown extent.

In Getzin et al. 2006 we  investigated four hypotheses on the fine-scale spatial structure of the forest on Vancouver Island. Our primary purpose is to understand how the three dominant species, Douglas-fir, western hemlock and western redcedar, coexist and partition space along a chronosequence comprising of three stands of immature, mature and old-growth. We used the O-ring statistic and Ripley’s L-function to quantify the change in spatial distribution and association of the species along the chronosequence. Evidence on intra- and inter-specific competition was also inferred from correlations between nearest-neighbor distances and tree size. Our results showed that (1) variation in local site characteristics was highly important for the unexpected aggregated pattern of Douglas-fir in old-growth, (2) surviving trees of the species were less aggregated than their pre-mortality patterns, thus rejecting the random mortality hypothesis and being strong evidence for intra-specific competition, (3) tree death was a random process among larger overstorey trees in the plots, and (4) inter-specific competition declined with increasing plot age as a result of spatial resource partitioning. We highlighted the importance of spatial heterogeneity for the long-term coexistence of shade-intolerant pioneer Douglas-fir and shade-tolerant colonizer species during forest succession.