Halli lepa, hübriidlepa ja arukase biomassi produktsioon endistel p llumaadel

Due to the high prices and lack of fossil fuels in the world, it is necessary to look for new, alternative fuel sources. In Estonia one of the possibilities for renewable energy would be growing deciduous tree species on abandoned agricultural land. Usually silver birch (Betula pendula) and grey alder (Alnus incana) are the most common tree species to occupy agricultural lands which are left out of use. Also the hybrid alder (Alnus hybrida) may be considered a fast-growing species in our conditions. The main aim was to investigate the above-ground biomass production and the dynamics of young stands of fast-growing deciduous tree species on former agricultural land. This study is based on four experimental sites, located in South-Estonia: grey alder and hybrid alder plantations in P lvamaa, established in 1995 and 1996 respectively, and two silver birch natural stands in Tartumaa, Haaslava and Kambja, established in 2001 and 2004 respectively. The basal density of experimental sites was very different. In Haaslava it was the highest (36 200 trees per ha) and in hybrid alder stand it was the lowest (6700 trees per ha). In Kambja it was 11 600 and in grey alder stand 15750 trees per hectare. The soil conditions were very similar in all sites. Mean diameter at breast height and mean height of the stands were measured annually. The above-ground biomass of the stands was estimated during 2003-2007, by the method of model trees. It was not done in every stand every year due to its labor-intensity. 8-year old stands were compared, because the above-ground biomass of all four experimental sites was determined at that age. Mean height and diameter growth of grey alder at young age were higher and faster than in hybrid alder stand, but at the age of 14 these parameters were practically equal. When comparing the above-ground biomasses of the alder stands, it can be noted, that at the age of 8 grey alder overcomes the hybrid alder stand (biomasses respectively 26.8 t ha-1 and 9.76 t ha-1), but later, at the age of 13 the difference between the two sites diminishes (76.1 t ha-1 and 51.5 t ha-1). The average dry mass of grey alder stems in 8-year old stand was bigger than that of hybrid alders (2.87 and 2.01 kg). The annual increment of above ground-biomass was almost at the same level in Kambja birch stand and in grey alder stand (11.9 and 14.0 t ha -1 y respectively). Although the dimensions of trees are smaller in Kambja stand, the large number of trees and the wood density makes the biomass accumulation high per hectare. Mean height, diameter, average tree stem mass, and above-ground biomass was bigger in Kambja than in Haaslava stand. In 8-year old stands, the average dry mass of stem of alders is bigger than that of birches, the highest is grey alders (2.87 kg) and the lowest is in very dense Haaslava stand (0.44 kg).