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Comparison of some growth characteristics between two different Douglas-fir ecosystems of the same age and site index Jaeger, Brigitte Maria

Abstract

This study compared growth characteristics of two naturally established, unmanaged, late-immature, Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stands. Both stands were very similar in regards to age, site index, relative density and history, but represented two different ecosystems. The objective was to determine and explain differences in major growth characteristics between the two stands. The ecosystems were identified at all levels of the biogeoclimatic ecosystem classification. The analysis of the ecosystems confirmed that the selected stands were considerably different in their ecotope. The stand in which Douglas-fir was moderately shade-tolerant had a warm and drier mesothermal climate. The other stand in which Douglas-fir was shade-intolerant had a cold and wetter mesothermal climate. Comparing edatopic differences, the site of the first stand was drier and had a poorer nutrient status than that of the second stand. The classification and site indices of Douglas-fir determined for the stands were in agreement with those predicted by Krajina (1969). The stand in which Douglas-fir was moderately shade-tolerant had a multilayered stand structure and the associated growth characteristics resembled those of an uneven-aged stand of shade-tolerant tree species. The stand in which Douglas-fir was shade-intolerant had a uniform canopy and the associated characteristics were typical for an even-aged stand of shade-intolerant tree species. Adjusting for a six year difference in age, there was a 15 percent difference in volume in favour of the stand in which Douglas-fir was shade-intolerant. The analysis of stand structure and relationship of density to a number of growth characteristics indicated consistent differences between the stands, which appeared to be correlated to shade tolerance of Douglas-fir. Despite the similar site index and relative density index, it was concluded that there was a disparity in stand structure and volume production, which was related to ecological differences. A small number of samples and unknown initial density levels however, limit the validity of conclusions reached. The described trends and relationships need to be verified by further integrated studies. If such studies can confirm the relationship between ecosystem taxa and growth characteristics as described in this study, the adoption of a selective ecosystem-specific approach to stand management and construction of yield tables for Douglas-fir should be recommended. This could help to fully utilize the production potential of a site and to accurately predict stand development.

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