Dissolved organic carbon and nitrogen leaching from Scots pine, Norway spruce and silver birch stands in southern Sweden

The effects of three common tree species - Scots pine, Norway spruce and silver birch - on leaching of dissolved organic carbon and dissolved nitrogen were studied in an experimental forest with podzolised soils in southern Sweden. We analyzed soil water collected with lysimeters and modeled water fluxes to estimate dissolved C and N fluxes. Specific UV absorbance (SUVA) was analyzed to get information about the quality of dissolved organic matter leached from the different stands. Under the O horizon, DOC concentrations and fluxes in the birch stands were lower than in the spruce and pine stands; annual fluxes were 21 g m⁻² y⁻¹ for birch and 38 g m⁻² y⁻¹ and 37 g C m⁻² y⁻¹ for spruce and pine, respectively. Under the B horizon, annual fluxes for all tree species ranged between 3 and 5 g C m⁻² y⁻¹, implying greater loss of DOC in the mineral soil in the coniferous stands than in the birch stands. We did not find any effect of tree species on the quality of the dissolved organic matter, as measured by SUVA, indicating that the chemical composition of the organic matter was similar in leachates from all three tree species. Substantial amounts of nitrogen was leached out of the soil profile at the bottom of the B horizon from the pine and birch stands, whereas the spruce stands seemed to retain most of the nitrogen in the soil. These differences in N leaching have implications for soil N budgets.     

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.     

The effect of land use type on net nitrogen mineralization on abandoned agricultural land: Silver birch stand versus grassland

The effect of land use type on the dynamics and annual rate of net nitrogen mineralization (NNM) in a naturally generated silver birch stand and in a grassland, both on abandoned agricultural land, was assessed in situ in the upper 0–20 cm soil layer using the method of buried polyethylene bags. Annual NNM rate in the birch stand (156 kg N ha⁻¹ year⁻¹) was higher than in the grassland (102 kg N ha⁻¹ year⁻¹); in both cases NNM covered a major part of the plants annual nitrogen demand. The rate of NNM in the upper 0–10 cm soil layer in the birch stand (99 kg N ha⁻¹ year⁻¹) exceeded the respective rate of NNM in the grassland (51 kg N ha⁻¹ year⁻¹) roughly two times. In the grassland the rates of NNM in the 0–10 and 10–20 cm layers were equal; in the birch stand NNM in the 0–10 cm layer was 1.7 times higher than in deeper 10–20 cm layer. The intensity of daily NNM in the upper 0–10 cm soil layer in the birch stand was the highest in June and in the grassland in May, 776 and 528 mg kg⁻¹ N day⁻¹, respectively. In our study no significant correlation was found between NNM and the environmental factors monthly mean soil temperature, soil moisture content and pH.     

Optimizing the joint production of timber and bilberries

Berries and mushrooms are increasingly appreciated products of Finnish forests. Therefore, there is a need to integrate them in silvicultural planning. Bilberry (Vaccinium myrtillus L.) is an economically important wild berry that is widely collected for household consumption and sale in North Karelia, Finland. In this study, bilberry yield models developed recently were included in a stand growth simulator and the joint production of timber and bilberry was optimized by maximizing soil expectation value (SEV) with 3% discounting rate, assuming that 75% of the bilberry yield is harvested. The effect of bilberry production on the optimal stand management increased with increasing bilberry price. With high bilberry prices (4–8 € kg⁻¹) it was optimal to manage the mixed stand of Scots pine, Norway spruce and birch, and the pure stand of Norway spruce so as to promote bilberry production. In the Scots pine stand, where bilberry yields are higher, bilberry production affected optimal stand management already with a price of 2 € kg⁻¹. Compared to timber production, joint production led to longer rotation lengths, higher thinning intensities, more frequent thinnings, and higher share of Scots pine in the mixed stand. The contribution of bilberries to the total SEV increased with increasing bilberry price and discounting rate. In the mixed stand and pine stand the SEV of bilberry production, calculated with 3% discounting rate, exceeded the SEV of timber production when bilberry price was 4 € kg⁻¹.With 4% discounting rate this happened already with bilberry price of 2 € kg⁻¹. It was concluded that forest management which promotes bilberry yields is the most profitable in pine stands where the potential bilberry yields are high.     

Aboveground biomass and nutrient accumulation dynamics in young black alder, silver birch and Scots pine plantations on reclaimed oil shale mining areas in Estonia

The growth, aboveground biomass production and nutrient accumulation in black alder (Alnus glutinosa (L.) Gaertn.), silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) plantations during 7 years after planting were investigated on reclaimed oil shale mining areas in Northeast Estonia with the aim to assess the suitability of the studied species for the reclamation of post-mining areas. The present study revealed changes in soil properties with increasing stand age. Soil pH and P concentration decreased and soil N concentration increased with stand age. The largest height and diameter of trees, aboveground biomass and current annual production occurred in the black alder stands. In the 7-year-old stands the aboveground biomass of black alder (2100 trees ha⁻¹) was 2563 kg ha⁻¹, in silver birch (1017 trees ha⁻¹) and Scots pine (3042 trees ha⁻¹) stands respective figures were 161 and 1899 kg ha⁻¹. The largest amounts of N, P, K accumulated in the aboveground part were in black alder stands. In the 7th year, the amount of N accumulated in the aboveground biomass of black alder stand was 36.1 kg ha⁻¹, the amounts of P and K were 3.0 and 8.8 kg ha⁻¹, respectively. The larger amounts of nutrients in black alder plantations are related to the larger biomass of stands. The studied species used N and P with different efficiency for the production of a unit of biomass. Black alder and silver birch needed more N and P for biomass production, and Scots pine used nutrients most efficiently. The present study showed that during 7 years after planting, the survival and productivity of black alder were high. Therefore black alder is a promising tree species for the reclamation of oil shale post-mining areas.     

Does tree species composition control soil organic carbon pools in Mediterranean mountain forests?

We compared soil organic carbon (SOC) stocks and stability under two widely distributed tree species in the Mediterranean region: Scots pine (Pinus sylvestris L.) and Pyrenean oak (Quercus pyrenaica Willd.) at their ecotone. We hypothesised that soils under Scots pine store more SOC and that tree species composition controls the amount and biochemical composition of organic matter inputs, but does not influence physico-chemical stabilization of SOC. At three locations in Central Spain, we assessed SOC stocks in the forest floor and down to 50 cm in the mineral in pure and mixed stands of Pyrenean oak and Scots pine, as well as litterfall inputs over approximately 3 years at two sites. The relative SOC stability in the topsoil (0-10 cm) was determined through size-fractionation (53 μm) into mineral-associated and particulate organic matter and through KMnO₄-reactive C and soil C:N ratio.Scots pine soils stored 95-140 Mg ha⁻¹ of C (forest floor plus 50 cm mineral soil), roughly the double than Pyrenean oak soils (40-80 Mg ha⁻¹ of C), with stocks closely correlated to litterfall rates. Differences were most pronounced in the forest floor and uppermost 10 cm of the mineral soil, but remained evident in the deeper layers. Biochemical indicators of soil organic matter suggested that biochemical recalcitrance of soil organic matter was higher under pine than under oak, contributing as well to a greater SOC storage under pine. Differences in SOC stocks between tree species were mainly due to the particulate organic matter (not associated to mineral particles). Forest conversion from Pyrenean oak to Scots pine may contribute to enhance soil C sequestration, but only in form of mineral-unprotected soil organic matter.     

Development of bioavailable pools of base cations and P after afforestation of volcanic soils in Iceland

Few long-term studies have been conducted on changes in soil nutrients after afforestation in Iceland, a country with a young history of forest management. While fertilization was shown to improve survival of seedlings in the first years after planting on the nutrient limited soils, knowledge about the nutrients status of the soils that develop under maturing forest stands is still scarce. In a chronosequence study, the development of base cations and Olsen-phosphorus (Olsen-P) in the mineral soil was followed in six forest stands of two different tree species of increasing age (14–97 years): native birch (Betula pubescens) and introduced Siberian larch (Larix sibirica). A treeless heathland was included to present soil conditions prior to forest establishment. The sites are part of the largest forest area in Iceland, located in the east of the country. Results revealed an effect of stand age on all soil nutrients investigated except for potassium (K). Olsen-P increased in 0–10 cm depth of the mineral soil, indicating a better availability and thus improved P supply in maturing forest stands. Calcium (Ca) and magnesium (Mg) concentrations decreased with stand age in 0–10 and 10–20 cm soil depth, while sodium (Na) decreased only in the upper soil layer. Only Olsen-P and K concentrations were higher in the upper soil layer as compared to 10–20 cm depth. This indicates a higher biotic control as opposed to the geochemical control of the other base cations.     

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.     

The effects of burning and dead-wood creation on the diversity of pioneer wood-inhabiting fungi in managed boreal spruce forests

The loss of natural forest habitats due to forestry is the main reason for the decline in boreal forest biodiversity of the Nordic countries of Europe. Ecological rehabilitation may provide means to recover and sustain biodiversity. We analyzed the effects of controlled burning and dead-wood creation (DWC) on the diversity of pioneer wood-inhabiting fungi in managed Norway spruce (Picea abies) forests in southern Finland. Altogether 18 stands were first subjected to a partial cutting with ordinary logging residues in form of cut stumps and treetops left on site. The subsequent rehabilitation treatments consisted of a controlled burning applied in half of the stands and three levels of dead-wood creation (5, 30 and 60 m³ ha⁻¹). The DWC involved creation of logs; felling of whole trees to mimic downed logs formed by natural disturbance processes. Each treatment was replicated three times. Inside each stand, substrates were sampled in two different biotopes; one on mineral soil and one on mineral soil with a thin peat layer. We surveyed the fungal flora on the logs (n = 364) and the ordinary residue stumps (n = 1767) and tops (n = 845) five years after the treatments.When comparing different stands, controlled burning had a significant effect on species composition; certain species were significantly more frequent on substrates in burned stands than in unburned stands, indicating that these species were favored by controlled burning. By contrast, we found no significant effects of DWC levels or biotope on species composition or richness. When comparing different substrates, 99% of the logs hosted at least one species and the occurrence probability of certain species was significantly higher on logs than on ordinary residue stumps and tops. Yet, volume-based rarefaction analyses showed that residues were more species dense than the logs, indicating that ordinary logging residues constitute important resources for many pioneer species.We conclude that controlled burning combined with DWC have strong effects on biodiversity; it modifies the composition of the pioneer wood-inhabiting fungal species found in managed forests and may thereby also influence the further succession and diversity of the secondary fungal flora.     

Soil changes induced by Acacia mangium plantation establishment: Comparison with secondary forest and Imperata cylindrica grassland soils in South Sumatra,Indonesia

Acacia plantation establishment might cause soil acidification in strongly weathered soils in the wet tropics because the base cations in the soil are translocated rapidly to plant biomass during Acacia growth. We examined whether soils under an Acacia plantation were acidified, as well as the factors causing soil acidification. We compared soils from 10 stands of 8-year-old Acacia mangium plantations with soils from 10 secondary forests and eight Imperata cylindrica grasslands, which were transformed into Acacia plantations. Soil samples were collected every 5–30 cm in depth, and pH and related soil properties were analyzed. Soil pH was significantly lower in Acacia plantations and secondary forests than in Imperata grasslands at every soil depth. The difference was about 1.0 pH unit at 0–5 cm and 0.5 pH unit at 25–30 cm. A significant positive correlation between pH and base saturation at 0–20 cm depth indicated that the low pH under forest vegetation was associated with exchangeable cation status. Using analysis of covariance (ANCOVA), with clay content as the covariate, exchangeable Ca (Ex-Ca) and Mg (Ex-Mg) stocks were significantly lower in forested areas than in Imperata grasslands at any clay content which was strongly related to exchangeable cation stock. The adjusted average Ex-Ca stock calculated by ANCOVA was 249 kg ha⁻¹ in Acacia plantations, 200 kg ha⁻¹ in secondary forests, and 756 kg ha⁻¹ in Imperata grasslands at 0–30 cm. Based on a comparison of estimated nutrient stocks in biomass and soil among the vegetation types, the translocation of base cations from soil to plant biomass might cause a decrease in exchangeable cations and soil acidification in Acacia plantations.     

Effects of thinning on growth of six tree species in north-temperate forests of Lithuania

This paper summarises the results from 35 years-observed thinning experiments on 256 permanent sample plots in 10–60 year-old stands of ash, aspen, birch, oak, pine and spruce in Lithuania. Thinning enhanced crown projection area increment of residual trees. The largest effect was observed in stands of aspen and birch (growth increase by 200%), followed by ash and oak (over 100%), and spruce and pine (about 80%). Thinning also promoted dbh increment, especially in younger stands, and the increase of dbh increment was positively correlated with the thinning intensity. The strongest reaction was exhibited by oak and aspen, while ash, birch and conifers reacted to a lower extent. Low and moderate intensities of thinning stimulated volume production in younger stands while the opposite was observed in older stands with increasing removals. Spruce stands exhibited relatively strongest increase of volume increment and pine, –the weakest, while the effect on deciduous species was intermediate. The results demonstrate that significant increase in volume increment is achievable with thinning of only young forest stands, e.g. 10–20 year-old pine, birch and ash, or 10–30 year-old oak, aspen and spruce.     

Forest thinning and subsequent bark beetle-caused mortality in Northeastern California

The Warner Mountains of northeastern California on the Modoc National Forest experienced a high incidence of tree mortality (2001–2007) that was associated with drought and bark beetle (Coleoptera: Curculionidae, Scolytinae) attack. Various silvicultural thinning treatments were implemented prior to this period of tree mortality to reduce stand density and increase residual tree growth and vigor. Our study: (1) compared bark beetle-caused conifer mortality in forested areas thinned from 1985 to 1998 to similar, non-thinned areas and (2) identified site, stand and individual tree characteristics associated with conifer mortality. We sampled ponderosa pine (Pinus ponderosa var ponderosa Dougl. ex Laws.) and Jeffrey pine (Pinus jeffreyi Grev. and Balf.) trees in pre-commercially thinned and non-thinned plantations and ponderosa pine and white fir (Abies concolor var lowiana Gordon) in mixed conifer forests that were commercially thinned, salvage-thinned, and non-thinned. Clusters of five plots (1/50th ha) and four transects (20.1 × 100.6 m) were sampled to estimate stand, site and tree mortality characteristics. A total of 20 pre-commercially thinned and 13 non-thinned plantation plot clusters as well as 20 commercially thinned, 20 salvage-thinned and 20 non-thinned mixed conifer plot clusters were established. Plantation and mixed conifer data were analyzed separately. In ponderosa pine plantations, mountain pine beetle (Dendroctonus ponderosae Hopkins) (MPB) caused greater density of mortality (trees ha⁻¹ killed) in non-thinned (median 16.1 trees ha⁻¹) compared to the pre-commercially thinned (1.2 trees ha⁻¹) stands. Percent mortality (trees ha⁻¹ killed/trees ha⁻¹ host available) was less in the pre-commercially thinned (median 0.5%) compared to the non-thinned (5.0%) plantation stands. In mixed conifer areas, fir engraver beetles (Scolytus ventralis LeConte) (FEN) caused greater density of white fir mortality in non-thinned (least square mean 44.5 trees ha⁻¹) compared to the commercially thinned (23.8 trees ha⁻¹) and salvage-thinned stands (16.4 trees ha⁻¹). Percent mortality did not differ between commercially thinned (least square mean 12.6%), salvage-thinned (11.0%), and non-thinned (13.1%) mixed conifer stands. Thus, FEN-caused mortality occurred in direct proportion to the density of available white fir. In plantations, density of MPB-caused mortality was associated with treatment and tree density of all species. In mixed conifer areas, density of FEN-caused mortality had a positive association with white fir density and a curvilinear association with elevation.     

Influences of forest tending works on carbon distribution and cycling in a Pinus densiflora S. et Z. stand in Korea

This study was conducted to determine carbon (C) dynamics following forest tending works (FTW) which are one of the most important forest management activities conducted by Korean forest police and managers. We measured organic C storage (above- and below-ground biomass C, forest floor C, and soil C at 50 cm depth), soil environmental factors (soil CO₂ efflux, soil temperature, soil water content, soil pH, and soil organic C concentration), and organic C input and output (litterfall and litter decomposition rates) for one year in FTW and non-FTW (control) stands of approximately 40-year-old red pine (Pinus densiflora S. et Z.) forests in the Hwangmaesan Soopkakkugi model forest in Sancheonggun, Gyeongsangnam-do, Korea. This forest was thinned in 2005 as a representative FTW practice. The total C stored in tree biomass was significantly lower (P < 0.05) in the FTW stand (40.17 Mg C ha⁻¹) than in the control stand (64.52 Mg C ha⁻¹). However, C storage of forest floor and soil layers measured at four different depths was not changed by FTW, except for that at the surface soil depth (0–10 cm). The organic C input due to litterfall and output due to needle litter decomposition were both significantly lower in the FTW stand than in the control stand (2.02 Mg C ha⁻¹ year⁻¹ vs. 2.80 Mg C ha⁻¹ year⁻¹ and 308 g C kg⁻¹ year⁻¹ vs. 364 g C kg⁻¹ year⁻¹, respectively, both P < 0.05). Soil environmental factors were significantly affected (P < 0.05) by FTW, except for soil CO₂ efflux rates and organic C concentration at soil depth of 0–20 cm. The mean annual soil CO₂ efflux rates were the same in the FTW (0.24 g CO₂ m⁻² h⁻¹) and control (0.24 g CO₂ m⁻² h⁻¹) stands despite monthly variations of soil CO₂ efflux over the one-year study period. The mean soil organic C concentration at a soil depth of 0–20 cm was lower in the FTW stand (81.3 g kg⁻¹) than in the control stand (86.4 g kg⁻¹) but the difference was not significant (P > 0.05). In contrast, the mean soil temperature was significantly higher, the mean soil water content was significantly lower, and the soil pH was significantly higher in the FTW stand than in the control stand (10.34 °C vs. 8.98 °C, 48.2% vs. 56.4%, and pH 4.83 vs. pH 4.60, respectively, all P < 0.05). These results indicated that FTW can influence tree biomass C dynamics, organic C input and output, and soil environmental factors such as soil temperature, soil water content and soil pH, while soil C dynamics such as soil CO₂ efflux rates and soil organic C concentration were little affected by FTW in a red pine stand.     

Rapid,non-destructive carbon analysis of forest soils using neutron-induced gamma-ray spectroscopy

Forest soils are pivotal to understanding global carbon (C) cycling and evaluating policies for mitigating global change. However, they are very difficult to monitor because of the heterogeneity of soil characteristics, the difficulty of representative sampling, and the slow time scale of response to environmental change. Here we demonstrate that use of gamma-ray spectroscopy facilitates in situ non-destructive analysis of C and other elements in forest soils. In this approach the element-specific gamma-rays are induced by fast and thermal neutrons interacting with the nuclei of the elements present in the soil. Background gamma-rays emanating from naturally occurring radionuclides in the forest are recorded as well. We applied this approach in a mature northern hardwood forest on glacial till soils at the Bartlett Experimental Forest in New Hampshire, USA. The inelastic neutron scattering (INS) system yielded strong signals in gamma-ray counts/h, from C and other elements present in the soil matrix that included silicon, oxygen, hydrogen, iron, aluminum, manganese and potassium. The INS sensitivity for carbon was 20.656 counts h⁻¹ kg⁻¹ C m⁻² based on current net C gamma-ray counts and the data for the O horizon and mineral soil to a depth of 30 cm obtained from a nearby quantitative soil pit (7.35 kg C m⁻²). We estimate the minimum detectable change to be ∼0.34 kg C m⁻², which is ∼5% of the current soil C content, and the minimum detectable limit to be ∼0.23 kg C m⁻². Eight % reproducibility from 11 measurements was limited, in part, by the large variability in the system counting geometry due to the uneven forest microtopography. The INS approach has the potential to revolutionize belowground monitoring of C and other elements, because the possibility of detecting a 5% change in forest soils has not been possible with destructive sampling methods.     

Forest structure,habitat and carbon benefits from thinning floodplain forests: Managing early stand density makes a difference

Forest ecosystems are increasingly expected to produce multiple goods and services, such as timber, biodiversity, water flows, and sequestered carbon. While many of these are not mutually exclusive, they cannot all be simultaneously maximised so that management compromise is inevitable. We used a 42-year dataset from a naturally regenerating floodplain forest of the river red gum (Eucalyptus camaldulensis) to investigate the effects of pre-commercial thinning on long-term patterns in habitat quality, forest structure and rates of carbon storage (i.e. standing aboveground carbon). Estimates of habitat quality were based on the density of hollow-bearing trees because hollows are ecologically important to many species of vertebrates and invertebrates in these forests. Thinning improved habitat value by producing 20 (±8) hollow-bearing trees per ha after 42 years, while the unthinned treatment produced none. Unthinned (highest density) stands were dominated by many slender trees, mostly <25 cm in diameter, whereas thinned stands produced negatively skewed size distributions with higher median and maximum stem diameters. Moderately thinned stands (560 trees ha⁻¹) had the highest aboveground carbon storage rate (4.1 t C year⁻¹) and the highest aboveground carbon stocks (200.2 ± 9.6 t C ha⁻¹) after 42 years, while the unthinned treatment had the lowest carbon storage rate (1.6 t C year⁻¹) and an intermediate level of aboveground standing carbon (165.1 ± 31.1 t C ha⁻¹). Our results highlight the importance of early stand density as a determinant of long-term forest structure, habitat quality and carbon storage rates. We recommend that thinning be considered as one component of a broader strategy for enhancing the structure, habitat value and aboveground carbon storage of developing floodplain forests.     

Recovery of carbon and nutrient pools in a northern forested wetland 11 years after harvesting and site preparation

We measured the change in above- and below-ground carbon and nutrient pools 11 years after the harvesting and site preparation of a histic-mineral soil wetland forest in the Upper Peninsula of Michigan. The original stand of black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) was whole-tree harvested, and three post-harvest treatments (disk trenching, bedding, and none) were randomly assigned to three Latin square blocks (n = 9). Nine control plots were also established in an adjoining uncut stand. Carbon and nutrients were measured in three strata of above-ground vegetation, woody debris, roots, forest floor, and mineral soil to a depth of 1.5 m. Eleven years following harvesting, soil C, N, Ca, Mg, and K pools were similar among the three site preparation treatments and the uncut stand. However, there were differences in ecosystem-level nutrient pools because of differences in live biomass. Coarse roots comprised approximately 30% of the tree biomass C in the regenerated stands and 18% in the uncut stand. Nutrient sequestration, in the vegetation since harvesting yielded an average net ecosystem gain of 332 kg N ha⁻¹, 110 kg Ca ha⁻¹, 18 kg Mg ha⁻¹, and 65 kg K ha⁻¹. The likely source for the cations and N is uptake from shallow groundwater, but N additions could also come from non-symbiotic N-fixation and N deposition. These are the only reported findings on long-term effects of harvesting and site preparation on a histic-mineral soil wetland and the results illustrate the importance of understanding the ecohydrology and nutrient dynamics of the wetland forest. This wetland type appears less sensitive to disturbance than upland sites, and is capable of sustained productivity under these silvicultural treatments.     

Transpiration and hydraulic traits of old and regrowth eucalypt forest in southwestern Australia

We tested the hypothesis that overstorey of eucalypt forest dominated by tall, large diameter trees uses less water than regrowth stands in the high rainfall zone (>1100 mm year⁻¹) of the northern jarrah (Eucalyptus marginata) forest in southwestern Australia. We measured leaf area, cover, sapwood area and sapwood density at three paired old and regrowth stands. We also measured sapflow velocity at one paired stand (Dwellingup) from June 2007 to October 2008. Old stands had more basal area but less foliage cover, less leaf area and slightly thinner sapwood. The ratio of sapwood area to basal area decreased markedly as tree size increased. Sapwood area of the regrowth forest stands (6.6 ± 0.30 m² ha⁻¹) was nearly double that of the old stands (3.4 ± 0.17 m² ha⁻¹), despite larger basal area at the old stands. Leaf area index of the regrowth stands (2.1 ± 0.26) was only one-third larger than that at the old stands (1.5 ± 0.15); hence, the ratio of leaf area to sapwood area was larger in old stands than in regrowth stands (0.45 ± 0.022 m² cm⁻² versus 0.32 ± 0.045 m² cm⁻²). Our results are consistent with theories that trees have evolved to optimize carbon gain rather than maintain stomatal conductance. Neither sapwood density (540–650 kg m⁻³) nor sap velocity differed greatly between regrowth and old stands. At the old forest site, daily transpiration rose from 0.5 mm day⁻¹ in winter to 0.9 mm day⁻¹ in spring–summer, compared to 0.9 mm day⁻¹ and 1.8 mm day⁻¹ at the regrowth site. Annual water use by the overstorey trees was estimated to be ∼230 mm year⁻¹ for the old stand and ∼500 mm year⁻¹ at the regrowth stand, or 20% and 44% of annual rainfall. The overwhelming role of stand sapwood area in determining stand water use, combined with the marked changes in the ratio of sapwood area to basal area with tree age and size, suggest that stand overstorey structure can be managed to alter overstorey water use and catchment water yield. Silviculture to promote old-forest-like attributes may be a viable means of delivering multiple water and conservation benefits.     

Concentrations and fluxes of dissolved organic carbon and nitrogen in a Picea abies chronosequence on former arable land in Sweden

Shifting land use from agriculture to forestry induces major changes in the carbon (C) and nitrogen (N) cycles, including fluxes of dissolved organic carbon (DOC) and nitrogen (DON). This study investigated the long-term effects of afforestation on ecosystem DOC and DON dynamics using a chronosequence approach comprising four arable fields and nine differently aged (10–92 years) Norway spruce stands growing on similar former arable soils in the same area. Along the chronosequence, concentrations and fluxes of DOC and DON were determined in bulk precipitation, throughfall, O horizon leachate and mineral soil solution during a 2–3-year period. Soil water fluxes were calculated using a soil hydrological model (SWAP). Results showed that DOC concentrations and fluxes with throughfall were strongly positively correlated with tree height (r² = 0.95; P < 0.05 for both conc. and flux) and stand age, while DON showed no such trends, suggesting different origins of DOC and DON in throughfall. The highest concentrations and fluxes of DOC and DON occurred in soil leachate from the O horizon. Here, DOC flux was 250–310 kg C ha⁻¹ yr⁻¹ and DON flux 8–9 kg N ha⁻¹ yr⁻¹ in stands afforested between 65 and 92 years ago. Concentrations and fluxes of DOC and DON in the mineral subsoil were consistently low. Flux calculations suggest that there was a net loss of >90% (230–280 kg ha⁻¹ yr⁻¹) of DOC leached from the O horizon within 0–60 cm of the mineral soil. There was no significant effect of land use or forest age on DOC concentrations in solution from the lower part of the A horizon. The effect of time since afforestation was masked by soil properties that influence DOM retention in the mineral soil. Our data indicate that DOC concentrations in the A horizon of the sites studied were primarily related to the oxalate-extractable Al and Fe amounts in the same horizon. Afforestation of arable land induced a gradual qualitative change in soil organic matter (SOM) and dissolved organic matter (DOM), with significantly increasing C:N ratios in soil and soil solution over time. The development of an O horizon and the subsequent leaching of DOC and DON to the underlying mineral soil are important drivers of a changing soil C and N turnover following afforestation.     

Can we use shelterwoods in Mediterranean pine forests to promote oak seedling development?

The use of shelterwoods to favour the development of natural or underplanted seedlings is common in temperate forests but rare in the pine forests of the Mediterranean area. Our aim was to assess the use of shelterwoods in Aleppo pine (Pinus halepensis) woodlands in southern France to promote the survival and growth of two co-occurring oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex.Twelve Aleppo pine stands were selected and differentially thinned to create a light shelterwood (basal area = 10 m²/ha, irradiance 52%), a medium shelterwood (basal area = 19 m²/ha, irradiance 33%) and a dense shelterwood (basal area = 32 m²/ha, irradiance 13%). A total of 1248 sowing points, half composed of Q. pubescens and half of Q. ilex, were then set up in these three conditions. Seedling survival and growth were monitored for 3 years. Plant stress was assessed by measuring predawn leaf potential and photosynthetic performance through the F_v/F_m ratio. Soil moisture was also recorded at two depths during two growing seasons.Survival was high for both species in all three conditions due to three consecutive wet years. The lowest survival was recorded for Q. pubescens in the dense shelterwoods. Growth in diameter and height increased from the dense to the light shelterwoods. Shrubs developed more strongly in the light shelterwood, and increasing shrub cover enhanced height growth. Photosynthetic performance was lowest for Q. pubescens in dense shelterwoods and highest in light shelterwoods, whereas the reverse was true for Q. ilex. The lowest predawn potentials were recorded in the dense shelterwoods even though higher soil water content values were measured in this treatment during the summer drought.We show that light shelterwoods were more beneficial to growth than denser ones, indicating control mainly by light availability during the 3 years of the study. However, as lower soil moisture at 30-50 cm depth and faster understorey development were also recorded in this condition, more extended observation is needed to determine whether this benefit persists in subsequent years.     

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.