Семенное возобновление самшита колхидского (Buxus colchica Pojark.) в условиях эпифитотии самшитников

Abstract

In response to expansion of Cydalima perspectalis Walker, 1859, mass scale drying of Buxus colchica Pojark. resulted in succession of forest communities of the Western Caucasus in 2014–2017. Changes in illumination of the forest low storeys were conducive to intensive growth of such herbaceous plants as Symphytum grandiflorum DC., Asarum intermedium (C. A. Mey. ex Ledeb.) Grossh., Festuca drymeja Mert. & W.D.J. Koch, Allium ursinum L., etc. and Ruscus colchicus Yeo, Geranium robertianum L., Rubus anatolicus Focke, Hedera colchica (K. Koch) K. Koch in the undergrowth. The ground vegetation with total projective cover up to 100 % was formed. Under current conditions the total number of B. colchica seedlings 2–15 cm high is only 10–320 pcs/ha on the southern macroslope and 5–87 pcs/ha on the northern macroslope. It is hundreds and thousands of times less as it was before boxwood forests extinction. The research purpose was to determine the factors effecting seed regeneration of B. colchica in the Western Caucasus under the conditions of succession caused by C. perspectalis expansion and further epiphytotics of boxwood forests. We carried out the studies on the southern and northern macroslopes of the Western Caucasus in the basins of the Khosta, Kurdzhips, and Tsitsa rivers in 2018–2019. The number of B. colchica seedlings was determined by their complete enumeration within 66 sampling plots; the area of each plot comprised 400 m2. When revealing the factors which effect seed regeneration of B. colchica, we analyzed 17 landscape and phytocenotic parameters: altitude above sea level; exposure and slope inclination; crown density of upper storey; parameters of undergrowth, main species stands, and dead boxwood; total projective cover of undergrowth and herbage. The principal factor preventing development of B. colchica seedlings is growthinhibition due to the herb-shrub storey. The total projective cover of undergrowth and herbage are the most important predictors for the number of B. colchica seedlings on the sampling plots. For the mentioned parameters we revealed the maximum regression coefficients b* at the significance level p < 0.05: –0.589 and –0.478 for the southern macroslope, and – 0.667 and –0.954 for the northern macroslope. The maximum projective cover of undergrowth in forest areas with boxwood regeneration is 50 % for both macroslopes. The maximum acceptable herbage cover is 15 % in the basin of the Khosta river, and 40 % in the basins of the Tsitsa and Kurdzhips rivers. Shading from the side of the forest upper storey suppresses growth of ground vegetation, and also prevents the development of B. colchica seedlings. Therefore the crown density, within the complex of factors, has no direct effect on the parameters of seed regeneration of B. colchica. In case of further intensive growth of the herb-shrub storey in forest phytocenoses, natural boxwood forests regeneration is highly improbable in the Western Caucasus. Artificial removal of undergrowth and herbage in forest areas will facilitate seed regeneration of the species. The research results are the basis for further monitoring of the regeneration processes of boxwood forests or their possible aboriginal change in the region.