The main forest forming species of the Eastern Polissya of Ukraine is Scots pine (Pinus sylvestris L.). However, the share of natural pine stands in the region as of December 31, 2012, was only 19.1 % (55.7 thousand hectares).
In Eastern Polissya, successful natural regeneration of Scots pine on felled areas after final harvesting occurs usually only under favorable climatic and soil conditions as follows: sufficient moisture and illumination of the soil, the absence of sod formation with abundant weeds and shrubs in the first years after the felling, optimal thermal conditions at the plot, etc. Therefore, in practice, the natural regeneration of felled areas occasionally takes place.
The wider use of natural regeneration of felled areas has important economic and environmental significance.
Taking into account the low intensity of natural regeneration of forests in Polissya zone of Ukraine, a gradual transition to a comprehensive forest renewal with the fullest possible use of the natural regeneration of valuable species is necessary.
The aim of the research was to study the condition of Scot pine natural regeneration grown after felling in the most common types of forests and soils in the Eastern Polissya, and its conservation dynamics in the subsequent years after the cutting. The study was carried out in the plots of narrow and medium-coupes clear felling of pine forests.
Materials and Methods
On cut areas left under natural regeneration, the accounting of pine self-seeding and advance growth was carried out by the selectively-computational method using accounting strips of 20 m length and of 2.0–2.5 m width (between centers of adjacent furrows). Experimental accounting strips (on the sides and center) were laid according to cardinal points in the direction of the furrows (9 strips per test area).
When recording forest regeneration (for furrows and between furrows separately), its specific composition, age, origin (seed or vegetative), density, viability (viable or dead), a total accounted area and its share in the total area of the plot were determined.
The evaluation of the Scot pine regeneration success in the felled areas was carried out according to the scale of the assessment of the natural regeneration success, developed in URIFFM. On the felled areas, all types of grass cover and its compactness were determined by the scale of G. M. Vysotsky.
Planted mature pine stands with silver birch (Betula pendula Roth), English oak (Quercus robur L.), Norway spruce (Picea abies L.), Norway maple (Acer platanoides L.) in composition were designated for clear felling in Svesske and Seredino-Budske Forestry Enterprises of Sumy Regional Department of Forestry and Hunting. The felling was conducted in the autumn-winter period. Before the felling, the studied stands had the stocking of 0.4-0.8 and were highly productive (Ia–I site classes).
During 2015–2016, there was a natural regeneration of 23 felled areas with a total area of 42.7 hectares in the forestry fund of two forest enterprises.
In 9 plots (39.1 %), the width of felling area did not exceed 50 m (strip-coupe felling); 6 felled areas (26.1 %) were in the range of 51–70 m width (middle-coupe felling) and in the 8 remaining plots (34.8 %), the width of coupe ranged from 76 to 138 m. The felling area was from 0.1 to 4.0 hectares.
In 9 plots (39.1 %), the direction of the felling strips was meridian, in 9 plots (39.1 %) latitudinal and at 5 remaining (24.0%), the strips were arranged at an angle to the meridian and latitudinal directions.
By the accounting of seed production of pine trees using the seed trap method, it was found that the number of pine seeds that got into the soil ranged from 588.4 thousand pcs. per ha to 1 million 256 thousand pcs. per ha in 2015 and from 258.7 thousand pcs. per ha to 864.2 thousand pcs. per ha in 2016.
The experience to left cut areas after clear felling under the natural regeneration of Scot pine in the Olinske forestry of the Svesske Forestry Enterprise during 2009–2016 was mostly positive. Scots pine reforestation at 14 (77.8 %) of the 18 plots in the Olinske forestry, which were accounted for in 2015–2016, was assessed as "good"; at another 3 plots (15.0 %) it was "satisfactory" and only at 1 (5.0 %), "insufficient".
Two of the 3 plots left for natural pine regeneration in 2015 in Golubivske forestry of Seredino-Budske Forestry Enterprise were restored naturally in 2 years by the category "good" (more than 12.0 thousand of 2–3-year-old pine trees per ha); one plot had "satisfactory" category of regeneration (from 7.0 to 12.0 thousand of 2–3-year-old pine trees per ha). Two felled areas left under the natural regeneration in 2016 in the Znob-Novgorodske forestry of Seredino-Budske Forestry Enterprise had relatively poor natural regeneration of the Scots pine, "insufficient" and "satisfactory", which may be due to lower pine seed production in 2016 compared with the previous year, 2015.
The most influential factors to ensure the success of the Scot pine natural regeneration on clear felled areas in the conditions of Eastern Polissya in dominant forest types are the follows:
- The felled areas should be surrounded by Scot pine forests of reproductive age from three or four sides;
- Seed year for Scots pine before the final harvesting;
- The direction of felling should be opposite to dominant winds (from east to west or from north-east to the south-west) for better sowing of felled areas by Scot pine seeds;
- Cutting plowed furrows 10–20 cm depth through 2–2.5 m in autumn or early spring;
- Conducting timely tending (within furrows and cutting off unwanted vegetation and sprouts between furrows) for self-sowing of pine during the first 3–4 years after the final harvesting.
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