Mats Varik

Towards complete and harmonized assessment of soil carbon stocks and balance in forests: The ability of the Yasso07 model across a wide gradient of climatic and forest conditions in Europe

Accurate carbon-balance accounting in forest soils is necessary for the development of climate change policy. However, changes in soil organic carbon (SOC) occur slowly and these changes may not be captured through repeated soil inventories. Simulation models may be used as alternatives to SOC measurement. The Yasso07 model presents a suitable alternative because most of the data required for the application are readily available in countries with common forest surveys. In this study, we test the suitability of Yasso07 for simulating SOC stocks and stock changes in a variety of European forests affected by different climatic, land use and forest management conditions and we address country-specific cases with differing resources and data availability. The simulated SOC stocks differed only slightly from measured data, providing realistic, reasonable mean SOC estimations per region or forest type. The change in the soil carbon pool over time, which is the target parameter for SOC reporting, was generally found to be plausible although not in the case of Mediterranean forest soils. As expected under stable forest management conditions, both land cover and climate play major roles in determining the SOC stock in forest soils. Greater mean SOC stocks were observed in northern latitudes (or at higher altitude) than in southern latitudes (or plains) and conifer forests were found to store a notably higher amount of SOC than broadleaf forests. Furthermore, as regards change in SOC, an inter-annual sink effect was identified for most of the European forest types studied. Our findings corroborate the suitability of Yasso07 to assess the impact of forest management and land use change on the SOC balance of forests soils, as well as to accurately simulate SOC in dead organic matter (DOM) and mineral soil pools separately. The obstacles encountered when applying the Yasso07 model reflect a lack of available input data. Future research should focus on improving our knowledge of C inputs from compartments such as shrubs, herbs, coarse woody debris and fine roots. This should include turnover rates and quality of the litter in all forest compartments from a wider variety of tree species and sites. Despite the limitations identified, the SOC balance estimations provided by the Yasso07 model are sufficiently complete, accurate and transparent to make it suitable for reporting purposes such as those required under the UNFCCC (United Nations Framework Convention on Climate Change) and KP (Kyoto Protocol) for a wide range of forest conditions in Europe.

The growth and production of some fast growing deciduous tree species stands on abandoned agricultural land

Mõningate kiirekasvuliste lehtpuupuistute kasv ja produktsioonivõime endisel põllumaal Several studies about stands growing on abandoned agricultural lands are induced by extensive afforestation of agricultural lands and more intensive use of biomass. Overview of above-ground biomass production of grey alder, hybrid alder and silver birch young stands growing on former agricultural areas are presented in current paper. The results of 16- and 6-year period of alders and silver birch stands, respectively, are reported. Above-ground biomass and biomass production of stands were estimated. The growing stock and current annual increment (CAI) of 16-years-old grey alder stand were 250 m3 ha-1 and 35.6 m3 ha-1, respectively. Due to fast growth and high biomass production capacity grey alder is promising tree species for short-rotation forestry in Estonia. Hybrid alder is productive tree although not exceeding the productivity of grey alders. Stem volume and CAI of the 16-years-old hybrid alder stand were 155 m3 ha-1 and 21 m3 ha-1, respectively. Our results supported earlier data reported in literature: rotation period of hybrid alder is longer than for grey alder and CAI of hybrid alder stands culminate later. The productivity of young silver birch stands on abandoned agricultural land is varying in a broad range. One young silver birch stand growing on abandoned agricultural land was involved into study. Growing stock and CAI in 13-years old stand were 118 m3 ha-1 and 15 m3 ha-1, respectively. These values are exceeding respective values of several yield tables of silver birch and biomass production capability of silver birch stands in favourable conditions is high. The growth and production of some fast growing deciduous tree species stands on abandoned agricultural land In the middle of 1990s considerable amount of abandoned agricultural land came into existence in Estonia. Such areas are often characterized by rapid occupation by pioneer tree species (alders, silver birch, willows) which has led to an increase of woodland area. During the last decade several studies about afforestation of former agricultural areas are published. From the point of view of biomass production and afforestation of abandoned agricultural areas fast growing deciduous tree species (alders, birches, aspens, willows) are most prospective. Current paper presents the overview of above-ground biomass production of grey alder, hybrid alder and silver birch stands growing on abandoned agricultural lands. In case of alders and silver birch the results of the periods of 16- and 6-years, respectively, are reported. In all cases the stand above-ground biomass and biomass production were estimated on the bases of model trees. Growing stock of 16-years-old grey alder stand was 250 m3 ha-1 and CAI 35.6 m3 ha-1 which are high values for Estonian conditions and also compared to results reported from Nordic and Baltic countries. Due to fast growth and high biomass production capacity grey alder is promising tree species for short-rotation forestry in Estonia. Young grey alder stands in Estonia have a potential to grow faster than published yield tables are reflecting. Hybrid alder is also proved to be productive tree species, although not exceeding the respective values of grey alders. Stem volume and CAI of the 16-year-old hybrid alder stand was 155 m3 ha-1 and 21 m3 ha-1, respectively. Our studies have supported earlier results in literature. Rotation period for hybrid alder is longer than for grey alder and the peak of CAI will occur later. Data reflecting growth and yield of hybrid alder are very scarce in the literature. According to earlier results and literature data, the productivity of young silver birch stands on abandoned agricultural areas is very variable, depending mainly on soil conditions and stand density. One productive 13-year-old silver birch stand, growing on abandoned agricultural land has been studied. Growing stock in the stand was 118 m3 ha-1 and CAI 15 m3 ha-1, which exceeded respective values of several birch yield tables. Biomass production capability of silver birch stands in favourable conditions can be high. Taking into account silvicultural properties and economical value of timber, probably the most suitable tree species for afforestation abandoned agricultural lands is silver birch.

Long-term dynamics of leaf and root decomposition and nitrogen release in a grey alder (Alnus incana (L.) Moench) and silver birch (Betula pendula Roth.) stands

ABSTRACT The decomposition of the leaf litter, fine roots (d < 2 mm) and coarser roots (2 ≤ d < 5 mm) of grey alder and silver birch, as well as of α-cellulose sheets using the litterbag method was studied in two experimental stands on Podzoluvisol soils in Southern Estonia. For both tree species, the coarser roots decomposed faster than the fine roots, (p < .05), tree species did not affect the decomposition rate of the roots (p > .5). The nitrogen (N) input to soil from aboveground litter was multiple times higher than the N flux from roots. The remaining relative ash-free mass of the leaves of grey alder and silver birch after three and a half years was similar. After 11 years the remaining relative ash-free mass of the fine and coarser roots of grey alder still accounted for around 10% of the initial value. For silver birch the remaining value was around 20% after 9 years. The litterbag method to underestimates in fertile soils the decomposition of organic matter and thus did not reflect the actual dynamics of decomposition.

Biomass production and carbon accumulation in silver birch stands in Oxalis site type

Biomassi produktsioon jänesekapsa kasvukohatüübi arukaasikutes Present study was carried out in three silver birch (Betula pendula Roth.) stands in the Oxalis site type in South-Estonia. The above-ground biomass, above-ground biomass production and foliar characteristics of 14-, 32- and 45-year-old silver birch natural stands were studied. The above-ground biomass and production of the stand was estimated in August 2008 using dimension analysis (model tree method). The above-ground biomasses in the 14-, 32- and 45-year-old silver birch stands growing on forest land were 39.9; 140.3 and 224.3 t ha-1 respectively. All results are given in dry mass (DM). Current annual production (CAP) of stem mass ranged 4.7-7.5 t ha-1. Leaf area index (LAI) ranged 2.5-4.4 m2 m-2 in the studied stands. Based on these results, stands of silver birch growing in Oxalis site type are very productive and may exceed the respective values presented in yield tables used in Estonian forestry. Biomass production and carbon accumulation in silver birch stands in Oxalis site type The main aim of the present study was to investigate above-ground biomass, production and foliar characteristics of three different-aged silver birch (Betula pendula Roth.) stands growing on forestland, in Oxalis site type. This study is based on three experimental sites, located in Tartu and Põlva county, Southern-Estonia. The above-ground biomass was estimated in August 2008 by the method of model trees (dimension analysis). Above-ground biomasses in the 14-, 32- and 45-year-old silver birch stands were 39.9; 140.3 and 224.3 t ha-1 respectively. Current annual increment (CAI) of stem mass varied from 4.7-7.5 t ha-1. The leaf area index (LAI) ranged 2.5-4.4 m2 m-2 in the studied stands. Biomass production capacity and stem masses were high in cases of all studied sites, comparing to previously worked out yield tables (Henno, Tjurin, Vargas de Bedemar). Biomass production in silver birch stands can be considered as an actual issue in relation of carbon sequestration and mitigation of climate changes and needs future investigations.