Viscum album subsp. austriacum (Santalaceae R. Br.) in Volyn Polissia and Zhytomyr Polissia (Ukraine): current distribution, ecology and prediction of future spread

Abstract

Background. One of the subspecies of the European mistletoe, the so called pine mistletoe (Viscum album subsp. austriacum (Wiesb.) Vollm.) is a hemiparasitic, evergreen, epiphytic phanerophyte that parazitizes predominantely on the Scots pine (Pinus sylvestris L.) in Ukraine. The pine trees infested with V. album subsp. austriacum lack moisture for transpiration and photosynthesis, which reduces their primary productivity, viability and health. The purpose of this study was: 1) to determine the current distribution of V. album subsp. austriacum in Volyn and Zhytomyr Polissia regions using GIS-technology; 2) study the main taxation parameters of pine stands infested with V. album subsp. austriacum; 3) predict the possible further spread of V. album subsp. austriacum in the studied Region. Materials and Methods. The grid mapping method based on GIS technology, with a grid size of 10×10 km and 20×20 km, was used to create the map of the species distribution. The spatial distribution of soil moisture in the forest soils of Drevlyanskyi Nature Reserve was determined using satellite images and data on soil moisture from the Earth Engine Data Catalog. The taxation parameters of the mistletoe-infested pine stand (i.e., participation of the Scots pine in the stand composition, area distribution of pine stands by age, relative completeness, stand quality class, trophotope, and hygrotope) were obtained from standard taxation descriptions. Results and Discussion. The study found that V. album subsp. austriacum is more widespread in Volyn Polissia than in Zhytomyr Polissya – 87 and 20 localities respectively. It was shown that the forest plantations colonized by V. album subsp. austriacum in Drevlyansky Nature Reserve are located in areas with the lowest moisture content, with a moisture reserve of 16–70 mm in the 0–100 cm soil layer, which corresponds to dry and fresh hygrotopes. Conclusions. V. album subsp. austriacum is more widely distributed in such nature reserves of the region as Shatskyi National Nature Park and Drevlianskyi Nature Reserve, and less so in Rivne, Cheremskyi, Polissia Nature Reserves and Pripyat-Stokhid National Nature Park. In the region under study, V. album subsp. austriacum mostly affects pure pine forests aged 80‒140 years, of medium completeness (0.5‒0.7), and relatively high and high stand quality classes – Ic–II, in fresh hygrotopes – 67.3 % of the area and in fairly infertile pine site type (trophotope B) – 51.5 %. Based on the distribution of forest site types in the region and their susceptibility to V. album subsp. austriacum, the possibility of its further intensive spread in the study region can be predicted.