Alvar forest of Harjumaa district

Harjumaa loometsad Alvar forests in Harjumaa district, NW and N Estonia, were studied. Eight community types were established: (i) Inula salicina-Potentilla fruticosa-Pinus sylvestris , (ii) Carex panicea-C. cespitosa-Pinus sylvestris-Betula pubescens , (iii) Filipendula vulgaris-Brachypodium pinnatum-Pinus sylvestris , (iv) Brachypodium pinnatum-Calamagrostis arundinacea-Picea abies-Pinus sylvestris , (v) Hepatica nobilis-Brachypodium pinnatum-Picea abies-Pinus sylvestris , (vi) Paris quadrifolia-Anemone nemorosa-Fraxinus excelsior , (vii) Mercurialis perennis-Picea abies , and (viii) Pulmonaria obscura-Viola mirabilis-Betula pendula-Picea abies. The 2nd community type represents the Sesleria alvar forest site type (FST) habitats, while communities of the 1st, 3rd and 4th types belong to the Calamagrostis alvar FST. These communities grow mainly on medium thick or thin Calcaric Skeletic Regosols, less frequently on thin Renzic Leptosols or on other types of soil. Other communities qualified by forest inventory as alvar forests factually belong to the boreo-nemoral Hepatica FST (communities of 5th type) and Aegopodium FST (communities of 6th, 7th and 8th types). Alvar forests are characterized by remarkably high species diversity deriving first of all from the number of field and moss layer species. The number of species in all layers, except moss layer, depends significantly from the community type reflecting in integrated form effect of communities' structure. Diversity of field layer species is positively affected by the ratio of carbon and nitrogen content in soil humus horizon, whereas the higher abundance of pine trees has negative effect on the species number in moss layer.