Multi-site assessment of soil nitrogen stocks across temperate forests under different thinning intensities, recovery times, and site conditions.

Increasing research interests have been paid to understand the factors controlling soil nitrogen (N) stocks under diverse environmental conditions and forest thinning regimes. This study investigated soil N stocks across 13 temperate forests, each of which received three thinning intensities (unthinned control, 15-30 %, and 30-50 % basal area removals) under varying pre-treatment conditions (altitude, slope, soil pH, soil moisture, stand age, stand density, diameter at breast height, and tree height). The total N stored in the forest floor (L, F, and H layers) and mineral soils (0-10, 10-20, and 20-30 cm) was determined 1, 4, and 7 years after thinning. Given the various site conditions and thinning regimes, a standardized effect size was used to analyze the influences of thinning on N stocks. The N stocks (Mg N ha-1) of the forest floor and at 0-10, 10-20, and 20-30 cm mineral soil depths were 0.02-0.46, 0.32-3.21, 0.29-3.03, and 0.25-2.54 across all studied forests, respectively. The averaged effect sizes indicated decrease in forest floor N stocks and increase in mineral soil N stocks under thinning due to the reduced litterfall and eventual input of thinning residues. Thinning intensity negatively affected the effect sizes for the N stocks (P < 0.05), suggesting that excessively heavy thinning may be inappropriate for retaining forest soil N. However, multimodel inference showed that soil pH (relative importance = 1.00) and stand age (relative importance = 0.42) had the largest influence on the effect sizes for forest floor and mineral soil N stocks. This pattern suggests that the effects of thinning on soil N stocks might vary with pre-treatment conditions, even more than thinning intensities and recovery time; therefore, thinning to manage forest soil N should consider pre-treatment environmental conditions in addition to thinning regime.

No impact of nitrogen fertilization on carbon sequestration in a temperate Pinus densiflora forest.

Carbon (C) sequestration capacity in forest ecosystems is generally constrained by soil nitrogen (N) availability. Consequently, N fertilization is seen as a promising tool for enhancing ecosystem-level C sequestration in N-limited forests. We examined the responses of ecosystem C (vegetation and soil) and soil N dynamics to 3 years of annual nitrogen-phosphorus-potassium (N3P4K1 = 11.3 g N, 15.0 g P, 3.7 g K m-2 year-1) or PK fertilization (P4K1), observed over 4 years in a 40-year-old Pinus densiflora forest with poor N nutrition in South Korea. PK fertilization without N was performed to test for PK limitation other than N. Neither tree growth nor soil C fluxes responded to annual NPK or PK fertilization despite an increase in soil mineral N fluxes following NPK fertilization. NPK fertilization increased the rate of N immobilization and 80% of the added N was recovered from mineral soil in the 0-5 cm layer, suggesting that relatively little of the added N was available to trees. These results indicate that N fertilization does not always enhance C sequestration even in forests with poor N nutrition and should therefore be applied with caution.

Microbial biomass and enzymatic responses to temperate oak and larch forest thinning: Influential factors for the site-specific changes.

Microbial biomass and enzyme activity are essential for ecosystem function in managed forests; however, uncertainty remains because microbial biomass and enzymatic responses to thinning highly differ with case studies. This study addressed the drivers for the site-specific responses of microbial biomass and enzyme activity to thinning. Study sites included two oak and three larch forests; each had un-thinned control, intermediate thinning (15-23% basal area reduction), and heavy thinning treatments (30-44% basal area reduction). Soil properties (temperature, water content, pH, total and inorganic nitrogen, and total carbon/nitrogen ratio), microbial biomass, enzyme (ß-glucosidase, N-acetylglucosaminidase, leucyl aminopeptidase, acid phosphatase, and phenol oxidase) activity, and soil carbon storage were determined 6 years after thinning. Compared to the control, microbial biomass carbon and nitrogen were higher under the intermediate and the heavy thinning by 13.9 and 24.4% and 11.5 and 29.9% at one oak forests, respectively, and higher under the intermediate thinning by 53.7 and 70.7% at one larch forests. There were the post-thinning changes in leucyl aminopeptidase activity by -46.9% and by 150.0-210.0% at an oak and larch forest, respectively, acid phosphatase activity by 60.0% at one oak forest, and phenol oxidase activity by 355.0% at one oak forest. The effect sizes of thinning for soil properties explained 94% and 77% of variance of the effect sizes for microbial biomass and enzyme activity. Especially, the effect sizes for soil water content, NH4+, total carbon/nitrogen ratio, and temperature were the most influential. Furthermore, the effect size for soil carbon storage was parabolically related to the effect size for microbial biomass carbon (R2 = 0.66). These findings highlight that inconsistent thinning effects on soil properties varied microbial biomass and enzymatic responses to thinning, which differentiated the change in soil carbon storage across sites. Future studies should consider such inconsistencies when examining the effects of forest management.

Soil properties of cultivation sites for mountain-cultivated ginseng at local level.

BACKGROUND: Identifying suitable site for growing mountain-cultivated ginseng is a concern for ginseng producers. This study was conducted to evaluate the soil properties of cultivation sites for mountain-cultivated ginseng in Hamyang-gun, which is one of the most well-known areas for mountain-cultivated ginseng in Korea. METHODS: The sampling plots from 30 sites were randomly selected on or near the center of the ginseng growing sites in July and August 2009. Soil samples for the soil properties analysis were collected from the top 20 cm at five randomly selected points. RESULTS: Mountain-cultivated ginseng was grown in soils that varied greatly in soil properties on coniferous, mixed, and deciduous broad-leaved stand sites of elevations between > 200 m and < 1,000 m. The soil bulk density was higher in Pinus densiflora than in Larix leptolepis stand sites and higher in the < 700-m sites than in > 700-m sites. Soil pH was unaffected by the type of stand sites (pH 4.35-4.55), whereas the high-elevation sites of > 700 m were strongly acidified, with pH 4.19. The organic carbon and total nitrogen content were lower in the P. densiflora stand sites than in the deciduous broad-leaved stand sites. Available phosphorus was low in all of the stand sites. The exchangeable cation was generally higher in the mixed and low-elevation sites than in the P. densiflora and high-elevation sites, respectively. CONCLUSION: These results indicate that mountain-cultivated ginseng in Korea is able to grow in very acidic, nutrient-depleted forest soils.

Carbon storage and soil CO2 efflux rates at varying degrees of damage from pine wilt disease in red pine stands.

We evaluated the carbon (C) storage and soil CO2 efflux rates of red pine (Pinus densiflora S. et Z.) stands damaged by pine wilt disease (PWD) in Korea. Ten red pine plots at varying degrees of damage from PWD were established and grouped into five categories (very slightly, slightly, moderately, severely, and very severely damaged plots) based on differences in the tree density. The incidence of PWD was a major cause of C loss from forest ecosystems, but the magnitude of loss depended on the severity of disease damage. An exponential regression of the CO2 efflux rates against the corresponding soil temperature was highly significant (R(2)=0.82-0.95, P<0.01) for the varying degrees of damage from PWD. The rates of change in the CO2 efflux rates with temperature, as defined by the Q10 values, were generally lower in the slightly (2.94) versus the moderately (3.60) or severely (4.26) PWD-damaged stands. The cumulative soil CO2-C efflux rates for two years were significantly higher in the slightly (10.8 Mg Cha(-1) yr(-1)) or moderately (10.9 Mg Cha(-1) yr(-1)) versus the very severely (7.9 Mg Cha(-1) yr(-1)) PWD-damaged stands. The results indicate that the C storage and soil CO2 efflux rates in red pine stands can be impacted by the incidence of PWD, with a significant C reduction in the severely damaged stands.

Estimation of carbon storage based on individual tree detection in Pinus densiflora stands using a fusion of aerial photography and LiDAR data.

The objective of this study was to estimate the carbon storage capacity of Pinus densiflora stands using remotely sensed data by combining digital aerial photography with light detection and ranging (LiDAR) data. A digital canopy model (DCM), generated from the LiDAR data, was combined with aerial photography for segmenting crowns of individual trees. To eliminate errors in over and under-segmentation, the combined image was smoothed using a Gaussian filtering method. The processed image was then segmented into individual trees using a marker-controlled watershed segmentation method. After measuring the crown area from the segmented individual trees, the individual tree diameter at breast height (DBH) was estimated using a regression function developed from the relationship observed between the field-measured DBH and crown area. The above ground biomass of individual trees could be calculated by an image-derived DBH using a regression function developed by the Korea Forest Research Institute. The carbon storage, based on individual trees, was estimated by simple multiplication using the carbon conversion index (0.5), as suggested in guidelines from the Intergovernmental Panel on Climate Change. The mean carbon storage per individual tree was estimated and then compared with the field-measured value. This study suggested that the biomass and carbon storage in a large forest area can be effectively estimated using aerial photographs and LiDAR data.

Influence of stand density on soil CO2 efflux for a Pinus densiflora forest in Korea.

We investigated the influence of stand density [938 tree ha(-1) for high stand density (HD), 600 tree ha(-1) for medium stand density (MD), and 375 tree ha(-1) for low stand density (LD)] on soil CO(2) efflux (R (S)) in a 70-year-old natural Pinus densiflora S. et Z. forest in central Korea. Concurrent with R (S) measurements, we measured litterfall, total belowground carbon allocation (TBCA), leaf area index (LAI), soil temperature (ST), soil water content (SWC), and soil nitrogen (N) concentration over a 2-year period. The R (S) (t C ha(-1) year(-1)) and leaf litterfall (t C ha(-1) year(-1)) values varied with stand density: 6.21 and 2.03 for HD, 7.45 and 2.37 for MD, and 6.96 and 2.23 for LD, respectively. In addition, R (S) was correlated with ST (R (2) = 0.77-0.80, P < 0.001) and SWC (R (2) = 0.31-0.35, P < 0.001). It appeared that stand density influenced R (S) via changes in leaf litterfall, LAI and SWC. Leaf litterfall (R (2) = 0.71), TBCA (R (2) = 0.64-0.87), and total soil N contents in 2007 (R (2) = 0.94) explained a significant amount of the variance in R (S) (P < 0.01). The current study showed that stand density is one of the key factors influencing R (S) due to the changing biophysical and environmental factors in P. densiflora.

Carbon and nitrogen status of litterfall, litter decomposition and soil in even-aged larch, red pine and rigitaeda pine plantations.

The carbon (C) and nitrogen (N) status in forest ecosystems can change upon establishment of plantations because different tree species have different nutrient cycling mechanisms. This study was carried out to evaluate C and N status of litterfall, litter decomposition and soil in three adjacent plantations consisting of one deciduous (larch: Larix leptolepis) and two evergreen (red pine: Pinus densiflora; rigitaeda pine: P. rigida x P. taeda) species planted in the same year (1963). Both the pine plantations showed comparatively higher C input from needle litter but significantly lower N concentration and input than the larch plantation (P < 0.05). During the decomposition process, the deciduous larch needle litter showed low C concentration and C remaining in soil, but high N concentration and N remaining in soil compared to the two evergreen pine needle litters. However, the soil C and N concentration and their content at a soil depth of 0-10 cm were not affected significantly (P > 0.05) by the plantation type. These results demonstrate the existence of considerable variation in C and N status resulting from needle litter input and litter decomposition in these three plantations grown at sites with similar environmental conditions.