The article focuses on vegetation diversity in the black alder Alnus glutinosa (L.) Gaertn. woodland key habitats in Zemgale, Latvia. Together nine sample plots were established on these habitat types, where next stand South – South West (S-SW) side at the age 1-10; 20-30 and 40-50 years. The vegetation survey has been made in vegetation period of 2010 and 2011. Braun – Blanque method has been used to estimate the projective coverage (%) of tree layer (E3), shrub layer (E2), herb layer (E1) and moss layer (E0) in order to assess the edge effect impact on vegetation diversity according to different ages classes in a next stands of sample plots. The analysis of edge effect verifies that there is a significant influence from the edge in 1st and 3rd zones of sample plots, which lies at S-SW side at the ages 1-10 and 20-30. In sample plots several indicator species of black alder woodland key habitats have been found: Vaccinium myrtillus L., Lycopus europaeus L., Iris pseudacorus L., Comarum palustre L., Plagiomnium ellipticum (Brid.)T.kop. Ordination confirmed that composition of species are relatively close, which demonstrate that species are able to live in similar type growing conditions. Protective species Circaea lutetiana L. and Plagiothecium undulatum (Hedw.) B., S. et G were found on the study sites. Also, adventive species Impatiens parviflora DC was found. Comparing the analysis by zones and sample plots and different age classes, the impact on edge effect has been distinguished in black alder woodland key habitats.

Main factors raised interest about biomass as the source of energy increase renewable resource demand in the context of Green house gases emissions decrease and the problem of environmentally friendly and efficient waste utilization. Legislation of waste water sewage sludge use is becoming stricter now. After cutting away top peat layer of peat quarry, the owners have two alternatives: the first, to flood the fields and transform them into bogs, the second, to carry out some economic activities - one of which must be field afforestation with traditional or fast growing tree species. Before planting trees it is necessary to fertilize the fields, and waste water sewage sludge will be one of potential fertilizers. Aims of research were to determine the impact of waste water sewage sludge fertilization 10 t haE-1 on tree growth and soil properties. Concentration changes of N, P, K, and Ca, Mg in different depth and concentration of S and total C and heavy metal in soil top layer during the year 2006 were determined. The effect of fertilization on tree growth and stock was determined by the non-destructive method, data were calculated by height and root core diameter of trees. Fertilization stimulates tree growth as weed growth too. On peat areas observed soil acidity decreasing. Despite of sufficient amount of nutrients willows were not suitable for peat fields. To avoid increasing of heavy metals content in soils, only qualitative waste water sewage sludge or waste water sewage sludge composts is acceptable for fertilization.