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61.
Timo Kautz Ute Perkons Miriam Athmann Ralf Pude Ulrich Köpke 《Biology and Fertility of Soils》2013,49(7):959-963
Using the profile wall method, we determined the root-length density (RLD) of barley roots growing in large-sized biopores (diameter >2 mm) and in the bulk soil of a Haplic Luvisol down to 200 cm of soil depth. The maximum bulk density in the soil profile (1.52 g?cm?3) was recorded in the Bt horizon (41–115 cm of soil depth). The proportion of RLD in biopores over the total RLD increased with increasing soil depth down to the 45–75 or 75–105 cm of soil layer but then decreased again in deeper soil. In contrast to earlier investigations, the maximum percentage of RLD in biopores recorded in this study was only 25 %. Root sampling from individually dissected biopores confirmed that roots did not predominantly grow in biopores. Results suggest that roots can use biopores as preferred pathways for growth through rather compact soil layers, whereas they can possibly leave the biopore and re-enter the bulk soil in deeper, less compact layers. 相似文献
62.
Mohmoud Bayat Timo Pukkala Manouchehr Namiranian Mahmoud Zobeiri 《European Journal of Forest Research》2013,132(5-6):851-864
Hyrcania is a productive region near the southern coast of Caspian Sea. Her forests are mostly uneven-aged beach-dominated hardwood mixtures. There is increasing willingness to treat these forests without clear-felling, following the ideas of continuous cover management. However, lack of growth and yield models have delayed this endeavor, and no instructions for uneven-aged management have been issued so far. This study developed a set of models that enable the simulation of stand development in alternative management schedules. The models were used to optimize stand structure and the way in which various initial stands should be converted to the optimal uneven-aged structure. The model set consists of individual-tree diameter increment model, individual-tree height model, survival model, and a model for ingrowth. The models indicate that the sustainable yield of the forests ranges from 2.2 to 7 m3 ha?1 a?1 in uneven-aged management, depending on species composition. Better ingrowth would substantially enhance productivity. The optimal stand structure for maximum sustained yield has a wide descending diameter distribution, the largest trees of the post-cutting stand being 80–100 cm in dbh. If cuttings are conducted at 30- or 40-year intervals, they should remove 20–40 largest trees per hectare. Despite moderate growth rate, uneven-aged management produces high incomes, 850–1,000 UDS ha?1a?1, because the timber assortments that are obtained from the removed large trees have very high selling prices. Optimal conversion to uneven-aged structure showed that the steady-state stand structure depends on initial stand condition and discount rate when the length of the conversion period is fixed. Discount rates higher than 1 % lead to reduced wood production, heavy cuttings, and low basal areas of the steady-state forest. 相似文献
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Ekaterina Shorohova Timo Kuuluvainen Ahto Kangur Kalev Jõgiste 《Annals of Forest Science》2009,66(2):201-201
68.
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