Current issue: 53(4)
Considering the increasing use of wood biomass for energy and the related intensification of forest management, the impacts of different intensities of biomass harvesting on nutrient leaching risks must be better understood. Different nitrogen forms in the soil solution were monitored for 3 to 6 years after harvesting in hemiboreal forests in Latvia to evaluate the impacts of different biomass harvesting regimes on local nitrogen leaching risks, which potentially increase eutrophication in surface waters. In forestland dominated by Scots pine Pinus sylvestris L. or Norway spruce Picea abies L. (Karst.), the soil solution was sampled in: (i) stem-only harvesting (SOH), (ii) whole‐tree harvesting, with only slash removed (WTH), and (iii) whole‐tree harvesting, with both slash and stumps harvested (WTH + SB), subplots. In agricultural land, sampling was performed in an initially fertilised hybrid aspen (Populus tremula L.× P. tremuloides Michx.) short-rotation coppice (SRC), where above-ground biomass was harvested. In forestland, soil solution N (nitrogen) concentrations were highest in the second and third year after harvesting. Mean annual values in WTH subplots of medium to high fertility sites exceeded the mean values in SOH subplots and control subplots (mature stand where no harvesting was performed) for the entire study period; the opposite trend was observed for the low-fertility site. Biomass harvesting in the hybrid aspen SRC only slightly affected NO3–-N (nitrate nitrogen) and NH4+-N (ammonium nitrogen) concentrations in the soil solution within 3 years after harvesting, but a significant decrease in the TN (total nitrogen) concentration in the soil solution was found in plots with additional N fertilisation performed once initially.
The aim was to investigate relative susceptibility of stumps of spruce and pine to airborne infections by Heterobasidion following pre-commercial thinnings. The proportions of infected stumps and colonized stump surface areas were analysed in 16 forest stands. In total, 746 spruce and 1063 pine stumps were sampled, and 184 and 105 infected stumps, respectively, were analysed. In conclusion, the present study demonstrated that in the investigated area: i) both Heterobasidion infection frequency and the extent of surface colonization correlated positively with stump diameter of both spruce and pine; ii) spruce stumps were significantly more often subjected to primary infections than pine stumps; iii) the pathogen exhibited more extensive surface colonization of spruce stumps than of pine stumps.
The objective of this study was to investigate basic density and its within-stem variation by studying 84 European aspen stems from 28 forest stands in Latvia. The studied forest stands covered all age classes from young stands to matured forests in representative growth conditions of European aspen. The densities of 2722 wood and 1022 bark specimens were measured from the sampled trees. Only the knot-free wood specimens without obvious wood defects were chosen for analyses. A map of basic density summarizing its radial and axial variations was constructed to show species-specific, within-stem variability and the relationships between density and tree and stand variables were examined. Stem wood and bark of the European aspen show different patterns of basic density variation along the tree stem. Wood density increases from pith to bark up to certain dimensions and shows a slight decrease afterwards. The weighted basic density of bark (446 ± 39.6 kg m–3) was higher than stem wood density (393 ± 30.4 kg m–3). Our results suggest that wood and bark density measurements obtained at breast height can be used for reliable estimation of the densities of whole-tree stem components, while tree parameters such as diameter at breast height (DBH), tree height and social status or stand parameters, including number of trees, basal area and age, are weak predictors in this context.