Наукові праці Лісівничої академії наук України (Dec 2020)
Pseudotsuga menziesii (Mirb.) Franco as a promising tree species for forest plantations in the western region of Ukraine
Abstract
Douglas-fir is an introduced species with a pronounced specific character of growth - it grows relatively slowly at a young age, but with a subsequent acceleration of the growth rate and maintaining its high intensity for a long period of time - one hundred or more years. Due to the variability of soil conditions in which Douglas fir of various provenances are cultivated, as well as due to different technologies of establishing and cultivating plantations of this species, the biometric indexes of forest stands with the participation of this coniferous species vary widely. Particularly favorable for the growth of Pseudotsuga menziesii are moist fertile beech forest types and spruce forests of the Pre-Carpathian region, where already, starting from the age of 20, Douglas fir exceeds spruce in height and diameter, and the growth retardation from larch is much less than in the conditions of the Western Forest-steppe (within 10-15%). The density of Douglas fir in both young and middle-aged and mature stands plays a significant role in the stem wood accumulation by the species. The most productive plantations are characterized by the uniform distribution of trees over the area and high crown density. The participation of Pseudotsuga menziesii in the composition that provides the maximum amount of wood accumulated by the species depends on the age of the plantations. In young plantations, the high share of Douglas fir in the tree composition is not accompanied by high stocks of wood, while in plantationss older than 40 years, the highest stock of wood of this species is formed in pure stands. At the same time, the highest indexes of the height and diameter of Douglas fir are characteristic of plantations, where its share is on average 30%. For mixed plantations of 35 years of age, with a 60% share of Douglas fir in the stand composition, a close to the optimal spacing of the species can be considered as 4 × 3 m; in such a case, there is a good cleaning of trunks from branches (natural pruning), the compact crown formation with an average area of 12-15 m2. After 35 years of age and with the participation in the stand composition of more than 60%, Douglas fir significantly increases the intensity of growth, its density increases in all the studied stands, as a result of which the stock of stem wood increases. When growing Douglas fir in plantations, you should not expect to obtain significant volumes of wood of this species until the age of 30 to 40 years old. The task is to grow plantations in the optimal density mode, which will provide a very significant increase in the growth intensity of the species after the indicated age, and by the age of 50-60, wood standing volume will reach 700 m3∙ha-1 and more. Douglas fir forest plantations should be grown pure in composition, which will eliminate the negative impact on the species at a young age of other faster-growing tree species, this will realize the potential for rapid growth and facilitate the crop tending. In order to protect Douglas fir from winter frosts, it is advisable to introduce an auxiliary tree species, for example, Norway spruce, into its plantations. Douglas fir reaches the highest classes of quality in plantations at the age of 40 to 60 years old at various initial schemes of spacing of planting spots – 2.0-6.0 × 0.8-2.0 m. In pure plantations of Pseudotsuga menziesii, under conditions of fresh fertile site type, when creating plantations of the species, the initial density should be taken as 1.5-2.0 thousand pcs / ha (taking into account the auxiliary species, the total density will be 6.6 thousand pcs / ha). In moist fertile site types, the growth rate of Pseudotsuga menziesii is slightly higher, so the initial density of the species should be slightly less (1.0-1.5 thousand pieces / ha), and taking into account the auxiliary species - 4.5-5.0 thousand pcs / ha.
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