The invasion of squat elm into postagrogenic phytocenoses south of Middle Siberia
M.A. MARTYNOVA
Research Institute of Agricultural Problems of Khakassia, vil. Zelenoe, Russia
Keywords: invader, deposit, life condition, succession, natural renewal, field-protective forest belts
Abstract
Presented are the results from studying the invasion of squat elm (Ulmus pumila L.) into vegetation cover of fallow lands provided with elm shelterbelts. It was found that because of abundant fruiting at a young age and in the presence of a healthy state of individuals, Ulmus pumila L. could become a transformer. But this does not happen because a number of biotic and abiotic factors negatively affect the vital state of woody plants and their ability to bear fruit: the existence of animal grazing, a strong degree of soil degradation, climatic conditions (insufficient moisture, frost weathering and drying of the soil), and strong grass cover. As part of the research it was established that on moderately degraded soils, the Ulmus pumila L. spread to all interstrip fields of the system of shelterbelts; in the first layer of phytocenoses, woody plants withstood the winter period quite well. Within seven years, a tendency for a decrease of the number of undergrowth by a factor of 19.9 was observed. The crown density of the tree and shrub canopy was 0.1-0.7. On slightly degraded soils in the presence of grazing, Ulmus pumila L. occupied 33 % of the study area, and 73 % within eight years. Plants of the first layer were few and weakened. The maximum crown density of 0.5-1.0 was observed near field-protective forest belts. The intensive distribution of Ulmus pumila L. was restrained by grazing and a thick layer of dead litter, reaching 4.2-7.5 q/ha of air-dry matter. It was established that on heavily degraded soils, the density of individuals influenced the vital state of undergrowth. In phytocenoses with a sparse undergrowth, the state of life was assessed as “healthy”, “weakened” or “drying out”, and where the undergrowth was thick, as “drying out”. Identification of patterns of formation and development of facies with the participation of Ulmus pumila L. will help to predict a further course of development of successional processes and landscape dynamics in the south of Middle Siberia.
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