We estimated above- and belowground biomass and net primary production (NPP) of a 73-year-old Scots pine (Pinus sylvestris L.) forest stand in the Belgian Campine region. Total biomass for the stand was 176 Mg ha(-1), of which 74.4% was found in stems. The root system contained 12.6% of total biomass, most of it in coarse roots (> 5 mm). Fine roots (< 5 mm) comprised only about 1.7% of total biomass, and more than 50% of fine root biomass was retrieved in the litter layer and the upper 15 cm of the mineral soil. The ratio of belowground biomass to aboveground biomass was 0.14, which is lower than that of other Scots pine forests and other coniferous forests. Between 1995 and 2001, mean annual NPP was 11.2 Mg ha(-1) year(-1), of which 68.7% was allocated to aboveground compartments. Stems, needles and cones made relatively high contributions to total NPP compared with branches. However, branch NPP was possibly underestimated because litterfall of big branches was neglected. The proportion of total NPP in belowground components was 31.3%. Coarse root NPP (2% of total) was low compared with its biomass. Fine root NPP was 3.3 Mg ha(-1) year(-1), representing about 29.5% of total NPP; however, the estimate of fine root NPP is much more uncertain than NPP of aboveground compartments. The ratio NPP/GPP (gross primary production) was 0.32, which was low compared with other coniferous forests.
Litterfall is an important ecological process in forest ecosystem functioning. Some attempts have been made to develop spatially explicit models of litterfall, but wind influence has never been included. Therefore, we studied the effect of wind on litterfall in an intimately mixed birch-oak forest using tree diameter and position as input data. After testing a litterfall model that assumed isotropic leaf dispersal, an anisotropic dispersal module was developed to account for wind influence. Using leaf fall data of 104 litter traps, isotropic and anisotropic models were optimized for silver birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and red oak (Quercus rubra L.) and model quality was compared. The anisotropic leaf litterfall model proved to be relevant because (i) the estimated litterfall directions corresponded very well to prevailing wind directions during leaf fall and (ii) including directionality significantly increased the goodness of fit of the models for both oak species but not for birch. Consequently, prevailing wind directions during leaf fall affected leaf dispersal in a broad-leaved deciduous forest. Insight into the spatial variability of the litter layer in forest ecosystems can benefit from the improved understanding of small-scale litterfall processes.
In this study the direct method is considered to be the reference, giving the most accurate LAI-values. Both the hemispherical photography and the LAI-2000 PCA introduced an underestimation of LAI when the actual canopy leaf distribution in the crown layer deviates from a random distribution of leaf area in space as is found in the mixed oak/beech stand. However, when the condition of random leaf distribution is nearly fulfi lled (ash stand), the LAI-2000 PCA gave LAI-values which were close to the results obtained from the direct method. Regression curves with R 2 > 0.93 could be calculated for both indirect methods.
Abstract& Introduction To increase our understanding of litterfall dynamics in mixed-species forests, seasonal and annual variations in litterfall mass and nutrient concentrations were assessed for a 60-year-old spontaneously developed forest dominated by silver birch (Betula pendula Roth), pedunculate oak (Quercus robur L.), and northern red oak (Quercus rubra L.) in Belgium. & Results Total quantities and seasonal patterns of most litterfall fractions were similar over the 29-month study period, but the species differed in start and duration of their leaf shedding period. The spatial distribution of litterfall persisted over the years for leaves, but not for total litterfall because of the varying spatial pattern of fallen twigs and reproductive structures. Consequently, predicting humus build-up based on short-term litterfall measurements may be difficult in mixed forests. Nutrient concentrations in leaf litter differed considerably between the species and throughout the year, but the seasonal pattern did not depend on the species. Betula returned significantly more nutrients to the soil per mass unit than Quercus, except for sodium. & Conclusion As the present stand conditions only allow recruitment of Q. rubra, Betula is being outcompeted, which decreases the nutrient return to the soil and may negatively affect biogeochemical cycling.
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