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Ekaterina Shorohova Timo Kuuluvainen Ahto Kangur Kalev Jõgiste 《Annals of Forest Science》2009,66(2):201-201
66.
Litter quality and environmental effects on Scots pine (Pinus sylvestris L.) fine woody debris (FWD) decomposition were examined in three forestry-drained peatlands representing different site types along a climatic gradient from the north boreal (Northern Finland) to south (Southern Finland) and hemiboreal (Central Estonia) conditions. Decomposition (percent mass loss) of FWD with diameter ≤10 mm (twigs) and FWD with diameter >10 mm (branches) was measured using the litter bag method over 1–4-year periods. Overall, decomposition rates increased from north to south, the rate constants (k values) varying from 0.128 to 0.188 year−1 and from 0.066 to 0.127 year−1 for twigs and branches, respectively. On average, twigs had lost 34%, 19% and 19%, and branches 25%, 17% and 11% of their initial mass after 2 years of decomposition at the hemiboreal, south boreal and north boreal sites, respectively. After 4 years at the south boreal site the values were 48% for twigs and 42% for branches. Based on earlier studies, we suggest that the decomposition rates that we determined may be used for estimating Scots pine FWD decomposition in the boreal zone, also in upland forests. Explanatory models accounted for 50.4% and 71.2% of the total variation in FWD decomposition rates when the first two and all years were considered, respectively. The variables most related to FWD decomposition included the initial ash, water extractives and Klason lignin content of litter, and cumulative site precipitation minus potential evapotranspiration. Simulations of inputs and decomposition of Scots pine FWD and needle litter in south boreal conditions over a 60-year period showed that 72 g m−2 of organic matter from FWD vs. 365 g m−2 from needles accumulated in the forest floor. The annual inputs varied from 5.7 to 15.6 g m−2 and from 92 to 152 g m−2 for FWD and needles, respectively. Each thinning caused an increase in FWD inputs, up to 510 g m−2, while the needle inputs did not change dramatically. Because the annual FWD inputs were lowered following the thinnings, the overall effect of thinnings on C accumulation from FWD was slightly negative. The contribution of FWD to soil C accumulation, relative to needle litter, seems to be rather minor in boreal Scots pine forests. 相似文献
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Jari Vauhkonen Timo Tokola Matti Maltamo Petteri Packalén 《European Journal of Forest Research》2010,129(5):803-811
Airborne laser scanning (ALS) data are not usually considered to be very informative with respect to tree species, and this
information is often obtained by combining such data with spectral image material. The aim was to test the ability of height,
density, intensity and applied 2D and 3D texture variables derived solely from a very high-density ALS point cloud to describe
the crown shape and structure characteristics required for tree species discrimination. Linear discriminant analysis was used
to find optimal combinations of variables within the predictor groups, and classifications based on variables from different
groups were compared. The third power of the tree diameter was used as a stem volume approximate, and rather than examining
species alone, the classification was evaluated with respect to the volume approximates assigned to the predicted species.
The sensitivity of pulse density to the methodology presented here was determined by simulating thinned data sets by reducing
the initial pulse density. The reliability of the estimates was analysed both with functions generated using the original
data and with new functions for each thinning level. Alpha shape metrics developed for describing tree crowns constructed
from the 3D point clouds proved capable of discriminating between all three species groups evaluated, and several height distribution
and textural variables were found to discriminate between the coniferous tree species. The results demonstrate the importance
of species interpretation in forest inventories based on allometric modelling, but then indicate that species-specific estimation
could be carried out using ALS-derived variables alone. 相似文献
69.
Sanna Härkönen Antti Mäkinen Timo Tokola Jussi Rasinmäki Jouni Kalliovirta 《Forest Ecology and Management》2010
Tree-level and stand-level forest growth simulators and their combination were evaluated using data from a large network of permanent sample plots of the National Forest Inventory covering the whole of Southern Finland. The simulators were built up with the SIMO framework. The evaluation was carried out both at the stand-level and separately for Scots pine (Pinus sylvestris), Norway spruce (Picea abies), silver birch (Betula pendula) and white birch (Betula pubescens) strata within the plots. Effects of different factors, e.g. age, soil type, stand density and geographical location on the results were also analysed. 相似文献
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Greenhouse gas emissions from managed peatlands are annually reported to the UNFCCC. For the estimation of greenhouse gas (GHG) balances on a country-wide basis, it is necessary to know how soil–atmosphere fluxes are associated with variables that are available for spatial upscaling. We measured momentary soil–atmosphere CO2 (heterotrophic and total soil respiration), CH4 and N2O fluxes at 68 forestry-drained peatland sites in Finland over two growing seasons. We estimated annual CO2 effluxes for the sites using site-specific temperature regressions and simulations in half-hourly time steps. Annual CH4 and N2O fluxes were interpolated from the measurements. We then tested how well climate and site variables derived from forest inventory results and weather statistics could be used to explain between-site variation in the annual fluxes. The estimated annual CO2 effluxes ranged from 1165 to 4437 g m−2 year−1 (total soil respiration) and from 534 to 2455 g m−2 year−1 (heterotrophic soil respiration). Means of 95% confidence intervals were ±12% of total and ±22% of heterotrophic soil respiration. Estimated annual CO2 efflux was strongly correlated with soil respiration at the reference temperature (10 °C) and with summer mean air temperature. Temperature sensitivity had little effect on the estimated annual fluxes. Models with tree stand stem volume, site type and summer mean air temperature as independent variables explained 56% of total and 57% of heterotrophic annual CO2 effluxes. Adding summer mean water table depth to the models raised the explanatory power to 66% and 64% respectively. Most of the sites were small CH4 sinks and N2O sources. The interpolated annual CH4 flux (range: −0.97 to 12.50 g m−2 year−1) was best explained by summer mean water table depth (r2 = 64%) and rather weakly by tree stand stem volume (r2 = 22%) and mire vegetation cover (r2 = 15%). N2O flux (range: −0.03 to 0.92 g m−2 year−1) was best explained by peat CN ratio (r2 = 35%). Site type explained 13% of annual N2O flux. We suggest that water table depth should be measured in national land-use inventories for improving the estimation of country-level GHG fluxes for peatlands. 相似文献