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Abstract
Introduction
Among the biological ways of the development of disturbed lands, forest recultivation is second only to agricultural reclamation in the area. By economic profitability, forest recultivation is 18.6 % higher than the agricultural one: 58.4 % vs 39.8 %. One of the methods of intensifying the growth and development of forest plantations on recultivated lands is the use of nitrogen-gathering plants. Forest plantations on recultivated lands, created near settlements and in the sparsely forested parts of the southern and eastern regions of Ukraine, are the subject to intense uncontrolled recreation and often suffer from forest fires.
The aim of the study was to identify the peculiarities of the growth and development of planted Scots pine stands in conditions of intense uncontrolled recreation and to investigate the effect of common alder (Alnus glutinosa (L.) Gaertn.) and perennial lupine (Lupinus perenne L.) on pine growth.
Materials and Methods
We studied 19-year-old forest plantations of Scots pine (Pinus sylvestris L.), created at spoil heap of stripping soils of Novoselivsky Mining and Processing Enterprise in the Kharkiv region. The plantations were established using nitrogen-gathering plants Alnus glutinosa (L.) Gaertn. and Lupinus perenne L. The study was conducted on three sample plots. The first sample plot (SP 1) was established in a pure pine plantation and served as control. The second sample plot (SP 2) was laid out in the pine stand with common alder and the third (SP 3) was established in pine plantation with lupine sowing. Forest mensuration characteristics of the stands were determined by Kraft classes and health condition index. Core samples of wood were taken by Pressler increment borer in different variants of the experiment and the dynamics of tree radial increment for Scots pine and common alder was analyzed in the variants.
Results
In all sample plots, plantations were “severely weakened” on the sanitary condition scale. The health condition indices for planted pine stands were as follows: 3.14 for the control, 2.95 for pine with alder, and 2.92 in the variant with lupine sowing. Only a part of 1st Kraft class trees belonged to healthy ones in all sample plots: their share was 3.3 % on the control (SP 1), 3.2 % on SP 2 and 1.4 % on SP 3. In general, planted pines with lupine were 26.6 % higher than pure pine plantations (9.4 m vs 6.9 m), they had 35.0 % larger diameter (9.7 cm vs 6.4 cm) and 25.2 % higher stock volume (100.2 m3·ha-1 vs 74.9 m3·ha-1). A positive effect of common alder has resulted in slight increase in mean diameter and height as compared with the control. On SP 2, mean height was 7.7 m and diameter at breast height amounted to 7.3 cm while at SP 1 the values were 6.9 m and 6.3 cm respectively. The volume of the average pine tree was 20.6 dm3 in the plantation with alder and 15.2 dm3 without alder. Actually, alder itself died, only 35 stems per ha were left. The proportions of stock of target (promising) trees (I, II and partly III Kraft class) were different in different plots. On SP 1, the total stock of trees of I and II Kraft class was 49.0 m3·ha-1 or 65.4 % of the total; it was 47.4 m3·ha-1 or 82.1 % of the total on SP 2 and 83.5 m3·ha-1 or 83.3 % of the total on SP 3. On SP 1, trees of the first three growth classes had a stock of 67.4 m3·ha-1, which was 90.0 % of the total; on SP 2 the value was 56.2 m3·ha-1 or 97.4 % of the total and on PP 3, 95.3 m3·ha-1 or 95.1 % of the total.
Due to the ability of alder and lupine to fix nitrogen and the enrichment of soils with nitrogen, there was an increase in the radial increment of the pine trees in the variant with alder (SP 2), beginning on 6th year from the plantation creation, and with lupine (SP 3), from 5th year, compared to the control (SP 1).
Conclusions
In the forest-steppe zone, on dumps of overburden grounds on soils of the 1st and 2nd classes of forest-growing ability, 20-years-old forest plantations of Scots pine grow as in dry and fresh poor or fresh relatively poor forest site conditions. The use of nitrogen-fixing plants in forest plantation contributes to an increase in the nutrient status of the edatope, which is reflected in the growth of the stands. In the plantations of Scots pine on reclaimed lands, the trees of the lower Kraft classes and the plants having smaller diameter are most vulnerable. As a result of thinning and sanitary felling, the health condition index decreases but the stands are still weakened.
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