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Abstract
Introduction
Protected shelterbelts are biological engineering structures established for protecting against dust storms, wind and water erosion, land degradation, droughts, and desertification. Linear protective stands are the most vulnerable not only to the negative environmental impacts but also to anthropogenic pressure. In present, the vegetation of the majority of the landscapes has been radically transformed and remained unchanged only in partially transformed territories of agriculture-forest landscapes. The study of forest ecosystems in such landscapes will enable to trace changes in forest vegetation and its spatial patterns, as well as to study the impact of adverse factors on a forest ecosystem and the changes in its main properties as a result of chronic anthropogenic stresses, using ecological, floristic and forest mensuration techniques.
Materials and Methods
The object of research was the forest shelterbelt, which was an integral part of the system of field protective shelterbelts in Kharkiv National Agrarian University. The shelterbelt was established in the 1950s at a distance of 8.6 km from the city of Kharkiv. At the time of creation, shelterbelt was consisting of 9 rows formed by Quercus robur L. (60 %), Fraxinus lanceolata Borkh. (20 %) and Acer platanoides L. (20 %). Under the experiment, the shelterbelt was conditionally divided into two sections with different degrees of recreational loading. Forestry, inventory, pyrological and geobotanical techniques were used. The collected data were statistically processed using MS Excel 2016 and Statistica 10 (ANOVA, Tukey HSD) software.
Results
During a long period, the part of the shelterbelt in the first section (S-1) had been influenced by greater recreational pressure than the part in the second section (S-2). Accordingly, the stand density varied significantly: 801 stems per hectare for S-1 and 1,105 stems per hectare for S-2. Thus, originally homogeneous planting has undergone a significant transformation as a result of different recreational load. In the S-1 section, the stand density decreased by 27.5 %. The average diameter of the trees in the S-1 section was 16 % smaller compared to the S-2 section (Fst = 18.20; p = 0.05). The health condition of the stand in the S-1 section was slightly worse than at the S-2.
For the S-1 section, there was a significant proportion of weakened and severely weakened trees (2nd and 3rd health categories) amounted to 77 %, while in the S-2 section, their percentage was 39 %. At section S-1, mechanical damages of tree trunks (10 %), a significant compaction of soil, post-fire char at trunks (in 11 % of trees) and post-fire scars (in 34 % of trees) were registered. Such damage was found in more than 50 % of trees within the section. Post-fire scars covered up to 60 % of the trunk perimeter and reached up to 2.5 m in height. The height of the bark char ranged from 0.1 to 1.5 m.
The trees at the S-2 section showed no evidence of damage caused by a surface fire; the proportion of trunks with mechanical damage was insignificant, up to 5 %. The density of advance seedlings in the S-2 section was almost double that in the section S-1 and amounted to 13.5 thousand stems per hectare. The density of the undergrowth was 19.2 thousand stems per hectare, which was 73.4 % higher compared to the density of undergrowth in section S-1. Dense undergrowth was found under the canopy of the shelterbelt, 94.3% of the total. It practically did not spread in the direction of the shelterbelt edge where was detected only as clumps of trees. In the cenomorphic structure of the vegetation, ruderal species (24 species) dominated in both sections, which is specific for plantations in the last stages of recreational degradation.
Conclusions
Recreational impact on the health condition of trees in the shelterbelt depended on the intensity and duration of this factor. Common oak trees were found to be the most resistant to recreational stresses. Under the stress, the composition and structure of the planting shifted due to the green ash eliminated from the stand composition and the proportion of oak simultaneously increased. The strong recreational influence on the trees in the first section led to simplifying the species composition of the planting, to a significant stand density reduction, a decrease in mensuration values and to an abundant cereal vegetation and ruderal species under the shelterbelt canopy. Significant anthropogenic impact, including mechanical and pyrogenic damage, resulted in the group destruction of the understory and advanced seedlings, reduction of their density, uneven spacing, and change in the construction of the shelterbelt.
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