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Abstract
Introduction
Now, during the search of the reasonable forest-breeding approaches to increase forest plantations productivity, trials of introduced coniferous species are relevant with a view to identifying high-productive, fast-growing wood species, resistant to diseases and pests and adversities of nature. From this perspective, Douglas fir (Pseudotsuga Menziesii (Mirb.) Franco) deserves closer consideration.
In Ukrainian Forest-Steppe zone, Douglas fir is mostly represented in arboretums, botanical gardens and forestry estates. However, the study of Douglas fir in this region is mainly fragmentary and there is a need to assess the prospects of using this non-native species for forestry.
Materials and Methods
We observed 10 plots of Douglas fir in arboretums, botanical gardens, tree nurseries and estates in five regions of the forest-steppe part of Ukraine, namely Khmelnitsky, Vinnitsa, Kyiv, Poltava and Kharkiv regions. For each tree, the diameter, Kraft class, and health condition were determined as well as the selection category and stem faults and damage. The average height was estimated by measuring 10–20 trees selected according to the thickness classes distribution and the height distribution curve.
Growth characteristics and state of surveyed introduced species are often compared with local species traditionally grown in the region in certain forest site conditions (i. e. with the species, instead which the introduced species can be used for forest growing under certain conditions). We used the tabular indices of the growth of planted pedunculate oak stands of the same age as a control for comparing the growth rates and the health condition of plantations of non-native species. A comprehensive score scale has been used for assessing the Douglas fir introduction prospects. To compare the climatic conditions of the regions, Walter's climatograms were constructed and Selyaninov’s hydrothermal coefficient was determined.
Results
The studied Douglas fir stands aged from 25 to 65 years, differing in growth rates and health conditions. On four plots, in Kharkiv and Poltava regions, the Douglas fir height was below the table values of pedunculate oak height. This may be explained by the arid climatic conditions, soil fertility and moisture, and human impact. At the same time, Douglas fir trees exceeded oaks by diameter in all the presented plots.
Most of the stands (9 out of 11) scored 19–24 points and fell in a promising group. The plot in the «old part» of the Danylivsky arboretum of Ukrainian Research Institute of forestry and Forest Melioration in the Kharkiv region got the minimum score with the total of 17 points. It can be classified as a relatively promising stand.
The climatic conditions of the investigated regions differed in their average annual rainfall, which was within the range of 527–681 mm; the average annual temperatures were quite close,
7.3–7.8°C. The hydrothermal coefficient of Selyaninov was ranged from 0.9 to 1.6.
The correlation between the average annual rainfall in different regions and the growth rate of the Douglas fir plantations was almost absent, whereas, between the amount of precipitation and height growth, the correlation was moderate (r = 0.49). The tendency to relationship was found for the Selyaninov’s hydrothermal coefficient and the reproductive capacity of Douglas fir trees (r = 0.28), for the Selyaninov’s hydrothermal coefficient and the height rate (r = 0.55), and for the Selyaninov’s hydrothermal coefficient and the health condition of Douglas fir (r = 0.41).
Conclusions
The Douglas fir trees grown in botanical gardens, arboretums and forest estates in the forest-steppe part of Ukraine had high growth rates and were healthy; they entered the stage of reproduction. Exceeding in height for Douglas firs was from 2.0 to 52.6 % over yield table values for pedunculate oak; the excess in diameter was in the range of 5.5–100.5 %.
According to the results of the integrated assessment of the plantations of different age, Douglas fir in most cases was noted a perspective species in the Ukrainian forest-steppe zone and can be used for the creation of forest plantations, protective stands, and landscaping.
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