Logging residue removal after thinning in Nordic boreal forests: Long-term impact on tree growth

The aim of this study was to determine the effect of whole-tree harvesting (WTH) on the growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as compared to conventional stem harvesting (CH) over 10 and 20 years. Compensatory (WTH + CoF) and normal nitrogen-based (CH + F or WTH + F) fertilisation were also studied. A series of 22 field experiments were established during 1977-1987, representing a range of site types and climatic conditions in Finland, Norway and Sweden. The treatments were performed at the time of establishment and were repeated after 10-13 years at 11 experimental sites. Seven experiments were followed for 25 years.Volume increment was on average significantly lower after WTH than after CH in both 10-year periods in the spruce stands. In the pine stands thinned only once, the WTH induced growth reduction was significant during the second 10-year period, indicating a long-term response.Volume increment of pine stands was 4 and 8% and that of spruce stands 5 and 13% lower on the WTH plots than on CH during the first and the second 10-year period, respectively. For the second 10-year period the relative volume increment of the whole-tree harvested plots tended to be negatively correlated with the amount of logging residue. Accordingly, the relative volume increment decreased more, the more logging residue was harvested, stressing the importance of developing methods for leaving the nutrient-rich needles on site.If nutrient (N, P, K) losses with the removed logging residues were compensated with fertiliser (WTH + CoF), the volume increment was equal to that in the CH plots. Nitrogen (150-180 kg ha⁻¹) or N + P fertilisation increased tree growth in all experiments except in one very productive spruce stand. Pine stands fertilised only once had a normal positive growth response during the first 10-year period, on average 13 m³ ha⁻¹, followed by a negative response of 5 m³ ha⁻¹ during the second 10-year period. The fertilisation effect of WTH + F and WTH + CoF on basal area increment was both smaller and shorter than with CH + F.     

Soil solution,foliar concentrations and tree growth response to 3-year of ammonium-nitrate addition in two boreal forests of Québec,Canada

Ammonium nitrate (NH₄NO₃) was applied monthly (from June to October) for 3 years in a balsam fir (Abies balsamea (Linné) Miller) and a black spruce (Picea mariana (Mill.) BSP) boreal forest in Québec (Canada). The design was composed of nine experimental units of 10 m × 10 m for each site. Application rates were 3 and 10 times the atmospheric N deposition measured at each site which was 6 and 3 kg ha⁻¹ year⁻¹ for the fir and the spruce sites, respectively. Soil solution composition (30 and 60 cm), tree growth, and foliar concentrations were analysed. The inorganic N in the soil solution of the control plots of both sites was low, particularly at the spruce site indicating that these forests are actively accumulating the atmospheric deposited N. Nitrogen additions regularly caused sudden and large inorganic N increases in the soil solution at both sites, both treatments and both sampling depths. However, these increases were transitory in nature and no persistent changes in inorganic N were observed. It was estimated that more than 95% of the added N was retained above the rooting zone at both sites. Nitrogen addition increased N, Ca, Mg and Mn foliar concentrations at the black spruce site but had no effects at the balsam fir site. After 3 years of N application, tree growth was similar in the control and the treated plots at both sites. Our results show that slow growing black spruce boreal forests with low ambient N deposition are responsive (in term of foliar N, Ca, Mg and Mn concentrations) to even small increases in N inputs, compared to higher growth balsam fir boreal forests with higher N deposition.     

Photosynthetic characteristics of Fagus sylvatica and Quercus robur established for stand conversion from Picea abies

Efforts in Europe to convert Norway spruce (Picea abies) plantations to broadleaf or mixed broadleaf-conifer forests could be bolstered by an increased understanding of how artificial regeneration acclimates and functions under a range of Norway spruce stand conditions. We studied foliage characteristics and leaf-level photosynthesis on 7-year-old European beech (Fagus sylvatica) and pedunculate oak (Quercus robur) regeneration established in open patches and shelterwoods of a partially harvested Norway spruce plantation in southwestern Sweden. Both species exhibited morphological plasticity at the leaf level by developing leaf blades in patches with an average mass per unit area (LMA) 54% greater than of those in shelterwoods, and at the plant level by maintaining a leaf area ratio (LAR) in shelterwoods that was 78% greater than in patches. However, we observed interspecific differences in photosynthetic capacity relative to spruce canopy openness. Photosynthetic capacity (A₁₆₀₀, net photosynthesis at a photosynthetic photon flux density of 1600 μmol photons m⁻² s⁻¹) of beech in respect to the canopy gradient was best related to leaf mass, and declined substantially with increasing canopy openness primarily because leaf nitrogen (N) in this species decreased about 0.9 mg g⁻¹ with each 10% rise in canopy openness. In contrast, A₁₆₀₀ of oak showed a weak response to mass-based N, and furthermore the percentage of N remained constant in oak leaf tissues across the canopy gradient. Therefore, oak photosynthetic capacity along the canopy gradient was best related to leaf area, and increased as the spruce canopy thinned primarily because LMA rose 8.6 g m⁻² for each 10% increase in canopy openness. These findings support the premise that spruce stand structure regulates photosynthetic capacity of beech through processes that determine N status of this species; leaf N (mass basis) was greatest under relatively closed spruce canopies where leaves apparently acclimate by enhancing light harvesting mechanisms. Spruce stand structure regulates photosynthetic capacity of oak through processes that control LMA; LMA was greatest under open spruce canopies of high light availability where leaves apparently acclimate by enhancing CO₂ fixation mechanisms.     

Thirteen-year monitoring of liming and PK fertilization effects on tree vitality in Norway spruce and European beech stands

The chemical fertility of the forest soils in the Belgian Ardenne is threatened by acidifying and eutrophying deposition and by the nutrient removal due to timber harvesting. Experiments were launched to evaluate the ability of liming and fertilization to improve foliar nutrition, maintain or restore crown condition and promote tree growth. In 1995, 10 liming and fertilization trials were installed in even-aged stands of European beech (5) and Norway spruce (5) distributed throughout the Ardenne. In each stand, two treatments were tested: liming with 3,000 kg ha⁻¹ of dolomitic limestone and liming plus fertilization with 0 to 800 kg ha⁻¹ of rock phosphate and 0 to 350 kg ha⁻¹ of K₂SO₄. Between 1995 and 2006, the foliar Ca and Mg status of spruce and beech trees improved in the limed stands, which limited significantly but did not prevent the decline in crown condition triggered by the summer drought in 2003. For spruce, liming also increased the increment in basal area. The additional fertilization increased the foliar nutrition in P but had no significant effects on soil chemistry and tree vitality.     

Regeneration growth in different light environments of mixed species, multiaged, mountainous forests of Romania

Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL<20–35%; BA>30 m²/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35–70%; BA=15–35 m²/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL>80–90%; BA<15–20 m²/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech.     

Stand characteristics and downed woody debris accumulations associated with a mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak in Colorado

Lodgepole pine (Pinus contorta Dougl. ex Loud.)-dominated ecosystems in north-central Colorado are undergoing rapid and drastic changes associated with overstory tree mortality from a current mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak. To characterize stand characteristics and downed woody debris loads during the first 7 years of the outbreak, 221 plots (0.02 ha) were randomly established in infested and uninfested stands distributed across the Arapaho National Forest, Colorado. Mountain pine beetle initially attacked stands with higher lodgepole pine basal area, and lower density and basal area of Engelmann spruce (Picea engelmannii [Parry]), and subalpine fir (Abies lasiocarpa (Hook.) Nutt. var. lasiocarpa) compared to uninfested plots. Mountain pine beetle-affected stands had reduced total and lodgepole pine stocking and quadratic mean diameter. The density and basal area of live overstory lodgepole declined by 62% and 71% in infested plots, respectively. The mean diameter of live lodgepole pine was 53% lower than pre-outbreak in infested plots. Downed woody debris loads did not differ between uninfested plots and plots currently infested at the time of sampling to 3 or 4–7 years after initial infestation, but the projected downed coarse wood accumulations when 80% of the mountain pine beetle-killed trees fall indicated a fourfold increase. Depth of the litter layer and maximum height of grass and herbaceous vegetation were greater 4–7 years after initial infestation compared to uninfested plots, though understory plant percent cover was not different. Seedling and sapling density of all species combined was higher in uninfested plots but there was no difference between infested and uninfested plots for lodgepole pine alone. For trees ≥2.5 cm in diameter at breast height, the density of live lodgepole pine trees in mountain pine beetle-affected stands was higher than Engelmann spruce, subalpine fir, and aspen, (Populus tremuloides Michx.), in diameter classes comprised of trees from 2.5 cm to 30 cm in diameter, suggesting that lodgepole pine will remain as a dominant overstory tree after the bark beetle outbreak.     

Litterfall and nutrient return in five tree species in a common garden experiment

Canopy litterfall is a significant pathway for return of nutrients and carbon (C) to the soil in forest ecosystems. Litterfall was studied in five even-aged stands of Norway spruce, Sitka spruce, Douglas-fir, European beech and common oak at three different locations in Denmark; two sandy sites, Ulborg and Lindet in Jutland, and one loamy site, Frederiksborg on Zealand. Litterfall was collected during three years from 1994 to 1996 in all five species and during six years from 1994 to 1999 in Norway spruce, Sitka spruce and European beech. The average total litterfall was in the range of 3200–3700 kg ha⁻¹ yr⁻¹ and did not differ significantly among tree species. There were no significant differences in total litterfall among sites during the short period, but during the longer period the richer site Frederiksborg had significantly higher total and foliar litterfall amounts compared to the more nutrient-poor sites Lindet and Ulborg. There were close relationships between foliar and total litterfall suggesting that foliar litterfall can be reliably estimated from total litterfall. Beech and oak bud scale litter was significantly related to foliar litterfall. The amount of branch and twig litter was significantly higher in oak than in other tree species. The average foliar litterfall was well related to the annual volume increment. The relationship differed markedly from previously reported relationships based on global litterfall data suggesting that such relationships are better evaluated at the regional level. Nutrient concentrations and fluxes in foliar litterfall were not significantly different among the five tree species. However, there was a significant effect of site on most nutrient concentrations of the three litterfall fractions, and foliar fluxes of P, Ca and Mn were all significantly highest at Frederiksborg and lowest at Ulborg. The similarity in litterfall inputs to the forest floor under these five tree species suggested that previous reports of large variability in forest floor accumulation should primarily be attributed to differences in litter decomposition.     

Growth and productivity of black spruce in even- and uneven-aged stands at the limit of the closed boreal forest

The increasing commercial interest and advancing exploitation of new remote territories of the boreal forest require deeper knowledge of the productivity of these ecosystems. Canadian boreal forests are commonly assumed to be evenly aged, but recent studies show that frequent small-scale disturbances can lead to uneven-aged class distributions. However, how age distribution affects tree growth and stand productivity at high latitudes remains an unanswered question. Dynamics of tree growth in even- and uneven-aged stands at the limit of the closed black spruce (Picea mariana) forest in Quebec (Canada) were assessed on 18 plots with ages ranging from 77 to 340 years. Height, diameter and age of all trees were measured. Stem analysis was performed on the 10 dominant trees of each plot by measuring tree-ring widths on discs collected each meter from the stem, and the growth dynamics in height, diameter and volume were estimated according to tree age. Although growth followed a sigmoid pattern with similar shapes and asymptotes in even- and uneven-aged stands, trees in the latter showed curves more flattened and with increases delayed in time. Growth rates in even-aged plots were at least twice those of uneven-aged plots. The vigorous growth rates occurred earlier in trees of even-aged plots with a culmination of the mean annual increment in height, diameter and volume estimated at 40–80 years, 90–110 years earlier than in uneven-aged plots. Stand volume ranged between 30 and 238 m³ ha⁻¹ with 75% of stands showing values lower than 120 m³ ha⁻¹ and higher volumes occurring at greater dominant heights and stand densities. Results demonstrated the different growth dynamics of black spruce in single- and multi-cohort stands and suggested the need for information on the stand structure when estimating the effective or potential growth performance for forest management of this species.     

Medicinal plants in old-growth, degraded and re-growth forests of NW Pakistan

Many old-growth forest stands in northwest Pakistan have been structurally transformed as a consequence of logging and livestock grazing, some of which are thereafter left to secondary succession. These forests represent an important resource for local inhabitants who gather and sell medicinal plants as part of their livelihood. With this in mind, the main objectives of our study were: (1) to assess differences in the structure of the tree layer and the abundance of medicinal plants among differently transformed forests, (2) to evaluate the recovery potential of medicinal plants under re-growth forests, and (3) to assess relationships between tree stand structural characteristics and the occurrence of medicinal plants.The first step of the study involved creating an approximate map covering an area of 90 km² for five forest-use types (old-growth forest, forest degraded by logging, derived woodland, agroforest and re-growth forest). Fifteen plots per forest-use type were randomly allocated at altitudes ranging from 2200 m to 2400 m asl, within which the abundance of 10 locally important medicinal herb species was assessed.The study stands differed greatly in tree basal area, which was highest in old-growth forest (48 m² ha⁻¹), lowest in agroforest areas (6 m² ha⁻¹) and intermediate in re-growth forest (20 m² ha⁻¹). All ten medicinal plant species were encountered in old-growth and in re-growth forests, but only five of these species also occurred on agroforest plots. The mean coverage of study medicinal plants was highest in old-growth forest (7%), low in forest degraded by logging, derived woodland and agroforest (0.3-2%), and intermediate in re-growth forest (4%). The Jaccard abundance based similarity index indicates a considerable similarity (0.6) between re-growth and old growth forest for both trees and medicinal plants. The overall abundance of medicinal plants increased with increasing tree basal area and canopy cover. The abundance of some particular species decreased; however, the most sought-after medicinal species Bergenia ciliata, Valeriana jatamansi and Viola cancescens increased with tree basal area within specific forest-use type and also across forest-use types. In conclusion, our data suggest that anthropogenic forest degradation leads to a reduction in the abundance of economically viable medicinal plants for the study region. It is further indicated that this can be reversed if degraded forests are allowed to regenerate.     

Species mixing effect on Norway spruce response to elevated CO2 and climatic variables: root and radial growth response

A 7-year study was conducted to examine the growth (diameter and root) response of Norway spruce (Picea abies (L.) Karst.) seedlings to elevated CO₂ (CO_2ELV, 770 μmol (CO₂) mol^?1) in different mixture types (monospecific (M): a Norway spruce seedling surrounded by six spruce seedlings, group-admixture (G): a spruce seedling surrounded by three spruce and three European beech seedlings, single-admixture (S): a spruce seedling surrounded by six beech seedlings). After seven years of treatments, no significant effect from elevated CO₂ was found on the root dry mass (p?=?0.90) and radial growth (p?=?0.98) of Norway spruce. Neither did we find a significant interaction between [CO₂]?×?mixing treatments (p?=?0.56), i.e. there was not a significant effect of CO₂ concentrations [CO₂] in all the admixture types. On the contrary, spruce responses to admixture treatments were significant under CO_2AMB (p?=?0.05), which demonstrated that spruce mainly increased its growth (diameter and root) in M and neighbouring with beech was not favourable for spruce seedlings. In particular, spruce growth diminished when growing beside high proportions/numbers of European beech (S). Here, we also evaluated the association between tree-ring formation and climatic variables (precipitation and air temperature) in different admixture types under elevated and ambient CO₂ (CO_2AMB, 385 μmol (CO₂) mol^?1). Overall, our result suggests that spruce responses to climate factors can be affected by tree species mixing and CO₂ concentrations, i.e. the interaction between climatic variables?×?admixture types?×?[CO₂] could alter the response of spruce to climatic variables.

     

Dynamics of seedling establishment and survival in uneven-aged boreal forests

The aim of this study was to describe the dynamics of seedling establishment and development in spruce-dominated uneven-aged boreal forests. The study was based on empirical data from 15 stands with permanent plots, which had been intensively monitored for 10 years in southern Finland. All trees (height > 1.3 m) were measured every fifth year. Regeneration was measured on 64 permanent sample plots (4 m²) in each stand. The establishment of first-year seedlings was analysed on a yearly basis. The survival and development of older Norway spruce (Picea abies (L.) H. Karst.) seedlings were analysed based on observations made every five years. The establishment of spruce seedlings was closely correlated with the abundance of seed crops. Seedling cohorts originating from abundant seed crops were clearly detectable in the development of seedling height distributions over time. It took about 15 years for spruce seedlings to reach a height level of 15-30 cm. Local basal area had hardly any effect on the emergence or survival of small spruce seedlings, while the number of higher spruce seedlings decreased with increasing local basal area.     

Modeling individual-tree growth in stands under forest conversion in East Germany

One major result of forest conversion in Saxony, East Germany, is the increasing importance of two-storied stands composed of a conifer canopy and a deciduous-tree understory. To enhance the applicability of the growth and yield simulator BWINPro under these conditions, three of its major sub-models were adapted to the regional growing conditions and to the relatively high level of diversity in spatial structure, mixture of species, and age variability typical for forests in conversion: (1) A new module for simulating single-tree juvenile growth was developed for European beech and Common oak under canopies of Norway spruce and Scots pine. Predictions in this sub-model are derived from individual height, diameter at breast height (dbh), and the influences of horizontal and vertical competition; (2) An alternative distance-dependent competition index was introduced to estimate individual basal area increment according to tree-specific growing conditions; (3) A modified logistic mortality model was parameterized for the most important Saxon species based on tree dimensions and basal area increment. Data came from permanent sample plots distributed throughout the region and from three chronosequence plot series established specifically for obtaining model input data. The new components were included into the existing structure of BWINPro. As a result of the adaption, the regional version BWINPro-S provides enhanced opportunities of planning and management for forest conversion and for multi-storied stands.     

Effect of species and spacing of fast-growing nurse trees on growth of an indigenous tree, Hopea odorata Roxb., in northeast Thailand

We tested the effects of species and spacing of nurse trees on the growth of Hopea odorata, a dipterocarp tree indigenous to Southeast Asia, in a two-storied forest management system in northeast Thailand. Eucalyptus camaldulensis, Acacia auriculiformis, and Senna siamea were planted as nurse trees in 1987 at spacings of 4 m × 8 m, 2 m × 8 m, 4 m × 4 m, and 2 m × 4 m in the Sakaerat Silvicultural Research Station of the Royal Forest Department, Thailand. Seedlings of H. odorata were planted in the nurse tree stands at a uniform spacing of 4 m × 4 m and in control plots (no nurse trees) in 1990. Stem numbers of some nurse trees were thinned by half in 1994. The stem diameter and height of all trees were measured annually until 1995 and again in 2007. The mean annual increment (MAI) in volume was estimated as 8.2–10.1 m³ ha⁻¹ year⁻¹ for E. camaldulensis and 0.9–1.2 m³ ha⁻¹ year⁻¹ for S. siamea, smaller than reported elsewhere. This suggests that the site properties were not suitable for them. The MAI of A. auriculiformis was 7.9–9.8 m³ ha⁻¹ year⁻¹, within the reported range. Survival rates of H. odorata in the S. siamea stands and the control plots decreased rapidly during the first 2 years but then stayed constant from 1992. In contrast, survival rates of H. odorata in the E. camaldulensis and A. auriculiformis stands were initially high (>70%), but then decreased after 1995. Stem diameter, tree height, and stand basal area of H. odorata were large in both the S. siamea stands and the control plots from then. The growth of H. odorata was largest in the 2 m × 8 m S. siamea stands. In contrast, it was restricted in the E. camaldulensis and A. auriculiformis stands owing to strong shading by their canopies. Thinning by 50% tended to facilitate the growth of H. odorata temporarily in the E. camaldulensis and A. auriculiformis stands. The stand basal areas of nurse trees and of H. odorata showed a trade-off. These results suggest that the growth of H. odorata was maximized in the S. siamea stands. We assume, however, that the growth of H. odorata could be improved even in the E. camaldulensis and A. auriculiformis stands by frequent or heavy thinning.     

Modelling and economic evaluation of forest biome shifts under climate change in Southwest Germany

We evaluated the economic effects of a predicted shift from Norway spruce (Picea abies (Karst) to European beech (Fagus sylvatica (L) for a forest area of 1.3 million ha in southwest Germany. The shift was modelled with a generalised linear model (GLM) by using presence/absence data from the National Forest Inventory in Baden-Württemberg, a digital elevation model, and regionalised climate parameters from the period 1970 to 2000. Two scenarios from the International Panel on Climate Change (IPCC) (B1, A2) for three different time scales (2030, 2065, and 2100) were investigated. The GLM predicted a decrease of the suitable area for growing Norway spruce between 21% (B1, 2030) and 93% (A2, 2100) in comparison to 2000. This corresponds to a reduction in the potential area of Norway spruce from between 190,000 and 860,000 ha. The financial effect of this reduction in area was then evaluated by using a classical Faustmann approach, namely the land expectation value (LEV) as an economic parameter for forests of Norway spruce versus European beech. Underlying cash flows were derived from a distance dependent, single-tree growth simulator (SILVA) based on data for prices and costs of the year 2004. With an interest rate of r = 2%, the predicted loss in the potential area of Norway spruce is related to a decrease of the LEV between 690 million and 3.1 billion Euro. We discuss the sensitivity of these results to changing interest rates, risk levels, and rotation lengths. Results suggest that managing forestland for profitability will be increasingly difficult under both climate scenarios.     

Growth recovery of mature Norway spruce and European beech from chronic O<Subscript>3</Subscript> stress

Elevated O₃ levels can strongly impair the health and vitality of forest ecosystems. Free-air exposure systems reveal that forest tree and stand growth can be reduced strongly under chronic O₃ stress. Detailed knowledge of the effect of O₃ exposure on photosynthesis, carbon sequestration, allometry and growth during chronic stress is available. However, knowledge of growth response after O₃ reduction is scarce. Here, we analyse the growth of mature Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in the free-air O₃ fumigation experiment at Kranzberg Forest. We compare tree growth over a 9-year period (2008–2016) after exposure to O₃ (2000–2007). During 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech decreased by 24 and 32%, respectively. After cessation of 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech not only recovered but exceeded the growth of the trees in the control condition by 14 and 24%, respectively. The growth resilience and resistance of trees previously exposed to 2?×?O₃ towards drought stress and late frost was hardly lower than that of the trees in the control condition. The capacity for growth recovery even after long-term chronic O₃ stress emphasizes the strong beneficial effect of air pollution control on the health of forest ecosystems and on the global land carbon sink.     

Whole tree harvesting can reduce second rotation forest productivity

The practice of harvesting forest residues is rapidly increasing due to rising demand for renewable energy. However, major concerns have been raised about the sustainability of this practice and its net impact on productivity, in particular through negative effects on the growth of subsequent tree crops. We measured height, diameter at breast height (DBH) and tree spacing density on 23-year-old second rotation stands of Sitka spruce (Picea sitchensis), following whole tree harvesting (WTH—of all above ground biomass, by cable crane) or conventional stem-only harvesting (CH) of the first rotation crop. Overall, WTH reduced tree DBH by 10.3% (p = 0.017), with weaker evidence that it may have reduced height (by 8.2%, p = 0.164) and stand basal area (by 15.3%, p = 0.101). However, treatment effects differed greatly between individual blocks and, analysed separately by block, significant differences (WTH plot trees smaller than CH plot trees) were most notable in the two more exposed south-facing blocks (where, in both cases, p < 0.01 for height and p < 0.05 for basal area). Variation in productivity between the experimental plots cannot simply be attributed to preharvesting site environment – no correlation was found between first rotation and second rotation productivity – nor was treatment effect explained by differences in tree spacing density. Treatment effects can be attributed to the removal of three to four times larger quantities of N, P and K in the tree biomass by WTH than by CH of the first rotation crop, combined with greater competition with tree natural regeneration and other vegetation in WTH plots during the early stages of the second rotation. Soil moisture was higher in WTH plots but there was no evidence that WTH increased soil acidity or aluminium mobility nor that it decreased soil organic matter. The results also highlight the complexities of predicting the effect of harvesting treatment on future productivity, even within single-age, single-species forests. The study demonstrates the risk that WTH can reduce second rotation productivity of conifer forests in acidic upland sites, and that this practice will only be sustainable with appropriate interventions to overcome shortage of nutrients and high levels of vegetation competition.     

Comparison of direct and indirect genetic methods for estimating seed and pollen dispersal in Fagus sylvatica and Fagus crenata

The comparison between estimates of historical gene flow, using variance in allelic frequencies, and estimates of contemporary gene flow, using parentage assignment, is expected to provide insights into ecological and evolutionary processes at work within and among populations. Genetic variation at microsatellite loci was used to quantify genetic structure in two wind pollinated, gravity and animal-dispersed tree species (Fagus sylvatica L. and Fagus crenata Blum.) and to derive historical estimates of gene flow. The gene dispersal distances estimated assuming effective population density to be 1/4 of the observed density were ∼77 m in European beech and ∼40 m in Japanese beech. Parentage analyses and a neighbourhood model approach were used to estimate contemporary patterns of seed and pollen dispersal. Our results suggest restricted seed dispersal abilities in both European beech (δ_s = 10.5 m) and Japanese beech (δ_s = 12.4 m), with an exponential shaped seed dispersal kernel. A non-negligible rate of seed immigration (m_s = 27%) was detected in European beech sites but not in Japanese beech site. Pollen dispersal within studied sites also appeared limited (δ_p = 41.63 m in European beech and δ_p = 79.4 m in Japanese beech), despite high rate of pollen immigration (m_p = 68% in European beech and m_p = 40% m in Japanese beech). Interestingly, contemporary and historical estimates of gene flow were within the same order of magnitude (a few tens of meters).     

Effect of climate change and nitrogen deposition on central-European forests: Regional-scale simulation for South Bohemia

The simulation of forest production until 2100 under different environmental scenarios and current management practices was performed using a process-based model BIOME-BGC previously parameterized for the main Central-European tree species: spruce, pine, beech and oak and adapted to include forest management practices. Climatic scenario HadCM3 used in the simulations was taken from the IPCC database created within the 3rd Assessment Report. It was combined with a scenario of CO₂ concentration development and a scenario of N deposition. The control scenario considered no changes of climatic characteristics, CO₂ concentration and N deposition. Simulation experiment was performed for the test region - South Bohemia - using a 1 km × 1 km grid. The actual data on the regional forest cover were aggregated for each grid cell in such a way that each cell represented an even-aged single-dominant species stand or non-forested area, and a standard management scenario depending on the stand age and species was applied to each cell. The effect of environmental variables was estimated as the difference of simulated carbon pools and fluxes in 2050 under environmental changes and under control scenario.The model simulation for the period to 2050 with only climate change under constant CO₂ concentration and N deposition indicated a small decrease of NPP (median values by species reached −0.9 to −1.7% for different species), NBP (−0.3 to −1.7%) and vegetation carbon (−0.3 to −0.7%), whereas soil C slightly increased. Separate increase of N deposition gave small positive effect on carbon pools (0.8-2.9% for wood C and about 0.5% for soil C) and more expressed effect on carbon fluxes (1.8-4.3% for NPP and 1.0-9.7% for NBP). Separate increase of CO₂ concentration lead to 0.6-2.4% increase of wood C pool and 0.1-0.5% increase of soil C. The positive effects of CO₂ concentration and N deposition were more pronounced for coniferous than for deciduous stands.Replacement of 0.5% of coniferous plantations every year by natural broadleaved stands evoked 10.5% of increase of wood carbon pool due to higher wood density of beech and oak compared to spruce and pine, but slightly decreased soil and litter carbon pools.     

Modelling self-pruning and branch attributes for young Quercus robur L. and Fagus sylvatica L. trees

The aim of this study was to develop statistical models for first order branchiness in young planted forest stands of pedunculate oak (Quercus robur L.) and European beech (Fagus sylvatica L.), and to give an ecological and silvicultural interpretation to these models. The reported models focus on the lower most-valuable stem part (i.e. until 6 m height), and cover different tree development classes to capture the development of branchiness over time. For each species 30 study plots were selected spread over two nearby forests in Flanders (northern Belgium), minimising site and genetic variability. Branches were counted on a total of 399 oak and 376 beech trees. On a subsample of 30 trees per species (one tree per plot), detailed non-destructive branch measurements were performed, yielding data for 555 oak and 438 beech branches. For both species, models for tree self-pruning (i.e. total branch number and dead branch portion), branch mortality and branch architecture (i.e. branch diameter and branch insertion angle) were built. A generalised linear mixed modelling approach was adopted. The models for total branch number and dead branch portion may be interpreted in terms of four processes contributing to self-pruning: (1) stand and tree development, (2) tree competitive status, (3) stand density and (4) site humidity. The reported models reveal similar self-pruning rates in oak and beech, but with different driving factors: early branch dying and slow shedding for oak and the other way around for beech. Mortality of individual branches is further determined by branch position and branch dimension. Branch diameter and branch insertion angle of both species are mainly related to branch cord length and relative branch position. All modelled effects are consistent with known ecological and ecophysiological processes. Silvicultural implications for stand establishment and early tree selection are discussed. The reported models can be used to fine-tune operational silvicultural choices for quality timber production. This is a first step towards the integration of branchiness models for oak and beech into forest growth simulators.