With the decrease of the groundwater level (Rybalova, Belan 2012) and the increase of the frequency and duration of droughts (Lyalko et al. 2015), a current state of shelterbelts in Kharkiv Region has recently deteriorated. The impact of shelterbelts with disrupted sub-optimal constructions on agricultural land still has not been thoroughly studied (Openko 2016).
The aim of the study is to analyze a modern state, growth and meliorative efficiency of the oak shelterbelts in Left-Bank Ukraine.
Materials and Methods
The research was conducted on 16 study plots (SP) which were laid according to the standard methods in forestry and agroforestry. When preparing the paternal list, several characteristics were registered, namely tree species, a diameter, a height, the Craft class and a health condition category of each tree. A number of rows, a width between rows of trees, a width of the crown edges and a protective height were recorded for each study plot. Furthermore, a width of the shelterbelts was defined according to the standard methods. It is a so-called organizational width of a shelterbelt (Bm) which is a length between marginal rows plus half the row spacing on each side of a shelterbelt. We separately counted a width of the shelterbelts according to the projections of the crowns in marginal rows (Вk). We also registered the advance growth in accordance with the URIFFM methodology (Pasternak 1990): 10 study plots were established in the periphery and central parts of the shelterbelts (10 m2) in order to assess both advance growth and undergrowth. The latter were divided by size categories.
Currently the construction of the shelterbelts varies from projected constructions (with a high porosity) to dense ones. Due to a lack of proper measures, the stand composition of the shelterbelts has considerably changed. Thus, a proportion of the oak decreased to 2-3 units in the forest. Moreover, it gets gradually replaced by the ash and maple. The results of the analysis show that the width of the shelterbelts according to the projection of the crowns within the research objects is 1.5-3.5 times larger than the projected width. Thus, the width of the shelterbelt increases due to the one-sided expansion of crown trees from the marginal rows. We also found out that the maximum length of the crown towards the field (Lkr) is characteristic for shelterbelts with predominance of the oak (from 7 to 10 units in stand composition). The intensity of tree growth in the shelterbelts depends essentially on their spatial placement in the planting, so the average diameter of trees that grow in the marginal rows was 10.2-20.9% higher compared to the average diameter of the planting. Furthermore, the study showed that the Acer platanoides trees were in the best health condition (1.0–2.7 points). It was revealed that the openness of the lower part of the profile depends on the presence and density of large and medium undergrowth (37%) in linear plantations.
Excessive growth of minor and shrub species leads to a decrease in the openness of the vertical profile to 0.5%. The stand сomposition has changed during the development and growth of plantings. Its transformation is caused by the decrease in the proportion of the oak in the stand (up to 2 units) and the increase in the proportion of accompanying species, namely Fraxinus excelsior L. and Acer platanoides. While no proper measures have been taken, there is an intensive asymmetrical crown proliferation in the marginal rows of the shelterbelts at 4.5 – 13.9 m. It, in turn, brings about the increase of the actual width of the shelterbelt from 1.5 to 3.5 times more compared to the projected width of shelterbelts. According to the multiple regression analysis, the openness of the lower part of the profile was determined by the density of the large and medium undergrowth and the number of rows in the shelterbelts by 47%.
7 Figs, 8 Tables, 39 Refs.