Andmebaasi logo

3. Doktoritööd

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/7081

Sirvi

Sirvi 3. Doktoritööd Autor "Becker, Hardo" järgi

Nüüd näidatakse 1 - 1 1
  • Pisipilt
    Kirje
    The Effect of Forest Management on the Carbon and Nitrogen Fluxes and Storages in Different Forest Ecosystems
    (Eesti Maaülikool, 2016) Becker, Hardo; Uri, Veiko
    In the light of increased CO2 concentration in the atmosphere, which evokes global climate change, the importance of woody biomass for energy production is increasing. On the other hand, the role of forest ecosystems is highly important for C accumulation reducing thereby the effect of global warming. The present thesis considers the production and yield of grey alder stands, the effect of alders on the soil C status and the effect of the clear-cut of matured grey alder stand on N cycling. Also the biomass of harvested stumps and the environmental effects of stump harvesting on nutrient cycling were studied. The main aims of the study: 1. To estimate the above-ground biomass production and carbon accumulation in grey alder chronosequence stands; 2. To compile a new yield table for natural grey alder stands in Estonia; 3. To assess the effect of clear-cut of mature grey alder stand on nitrogen fluxes; 4. To establish the potential of Norway spruce stumps as a source of bioenergy in Estonia; 5. To evaluate nutrient and carbon loss from the soil due to stump removal; 6. To assess the effect of stump harvesting on NNM intensity and nutrient leaching in Norway spruce clear-cut area. Grey alder is a highly productive and prospective tree species for short rotation forestry in the conditions of Estonia. The average yearly biomass production of grey alders varied between 3-15 m3 ha-1 yr-1, however, the biomass production could also reach 19-35 m3 ha-1 yr-1. The bulk maturity in grey alder stands is reached within 12-13 years, yet the production stays at high level also for the next five years. Optimal harvesting age for grey alder stands should be around 20-25 years according to the estimated bulk maturity and growth dynamics of grey alder stands. However, the data of stand volume presented in the new yield table do not exceed the respective values of the earlier yield table for Estonia, which could be explained through the smaller stand density nowadays. Land use history affects C accumulation in the soil of grey alder stands. Soil C accumulation increased in the first generation grey alder stands growing on previously non-forested lands. Apparently the soil C storage reaches its optimal level in the rotation length of grey alder and will not increase in the next forest generation. Management of grey alder stands by traditional silvicultural methods, i.e. clear-cut, did not increase hazardous N losses: after the clear-cut the annual net nitrogen mineralization (NNM) flux, N leaching and N2O emissions remained on the same level. Stumps of Norway spruce appear to be a potential bioenergy resource in Estonia, the estimated biomass of the harvested stumps can reach even up to 130 m3 ha-1. Stump harvesting did not cause any environmental hazards through nutrient depletion. As the study sites were on highly fertile soils the share of nutrients carried away via stumps were minor compared to the soil nutrient storages. However, in less fertile sites nutrient depletion could be significant. The effect of stump harvesting on the annual NNM flux was highly soil specific. After stump harvesting, the annual NNM flux decreased in the Oxalis site type (Endogleyic Arenosol), remained the same in Hepatica site type (Endogleyic Cambisol) and increased in the Myrtillus site type (Endogleyic Albic Podzol). Stump harvesting effect on N leaching was weak or practically missing. P leaching was negligible on all study areas.