Nam Jin Noh

Carbon and nitrogen storage in an age-sequence of Pinus densiflora stands in Korea

The carbon (C) and nitrogen (N) storage capabilities of Pinus densiflora in six different stand ages (10, 27, 30, 32, 44, and 71 years old) were investigated in Korea. Thirty sample trees were destructively harvested and 12 were excavated. Samples from the above and belowground tree components, coarse woody debris (CWD), forest floor, and mineral soil (0–30 cm) were collected. Tree biomass was highest in the 71-year-old stand (202.8 t ha−1) and lowest in the 10-year-old stand (18.4 t ha−1). C and N storage in the mineral soil was higher in the 71-year-old stand than in the other stands, mainly due to higher soil C and N concentrations. Consequently, the total ecosystem C and N storage (tree+forest floor+CWD+soil) was positively correlated with stand age: increasing from a minimum in the 10 year old stand (18.8 t C ha−1 and 1.3 t N ha−1) to a maximum in the 71-year-old stand (201.4 t C ha−1 and 8.5 t N ha−1). The total ecosystem C storage showed a similar sigmoidal pattern to that of tree C storage as a function of the age-sequence, while N storage in the CWD, forest floor and mineral soil showed no significant temporal trends. Our results provide important insights that will increase our understanding of C and N storage in P. densiflora stands and our ability to predict changes according to stand age in the region.

Responses of Soil, Heterotrophic, and Autotrophic Respiration to Experimental Open-Field Soil Warming in a Cool-Temperate Deciduous Forest

How global warming will affect soil respiration (RS) and its source components is poorly understood despite its importance for accurate prediction of global carbon (C) cycles. We examined the responses of RS, heterotrophic respiration (RH), autotrophic respiration (RA), nitrogen (N) availability, and fine-root biomass to increased temperature in an open-field soil warming experiment. The experiment was conducted in a cool-temperate deciduous forest ecosystem in northern Japan. As this forest is subjected to strong temporal variation in temperature, on scales ranging from daily to seasonal, we also investigated the temporal variation in the effects of soil warming on RS, RH, and RA. Soil temperature was continuously elevated by about 4.0°C from 2007 to 2014 using heating wires buried in the soil, and we measured soil respiratory processes in all four seasons from 2012 to 2014. Soil warming increased annual RS by 32–45%, but the magnitude of the increase was different between the components: RH and RA were also stimulated, and increased by 39–41 and 17–18%, respectively. Soil N availability during the growing season and fine-root biomass were not remarkably affected by the warming treatment. We found that the warming effects varied seasonally. RH increased significantly throughout the year, but the warming effect showed remarkable seasonal differences, with the maximum stimulation in the spring. This suggests that warmer spring temperature will produce a greater increase in CO2 release than warmer summer temperatures. In addition, we found that soil warming reduced the temperature sensitivity (Q10) of RS. Although the Q10 of both RH and RA tended to be reduced, the decrease in the Q10 of RS was caused mainly by a decrease in the response of RA to warming. These long-term results indicate that a balance between the rapid and large response of soil microbes and the acclimation of plant roots both play important roles in determining the response of RS to soil warming, and must be carefully considered to predict the responses of soil C dynamics under future temperature conditions.

Coarse woody debris mass dynamics in temperate natural forests of Mt. Jumbong, Korea

Coarse woody debris (CWD) mass dynamics in three temperate natural forests, dominated by Quercus mongolica, Ab- ies holophylla, and Pinus densiflora, were studied for 5 to 8 years in a Korea National Long-Term Ecological Research (KNLTER) site located in Mt. Jumbong, Korea. CWD mass (Mg/ha), input rate of CWD mass (Mg ha -1 y -1 ), and decay rate constant (1/y) were 20.6, 1.20, and 0.058 for Q. mongolica forest, 12.2, 0.44, 0.106 for A. holophylla forest, and 5.0, 0.00, and 0.086 for P. densiflora forest, respectively. CWD mass was classified into species, types (log, snag, and stump), and decay classes (I-V). The proportion of logs was higher than that of the other CWD types in Q. mongolica forest because of wind-related mortality, whereas the proportion of logs was similar to the proportion of snags in A. holophylla forest and P. densiflora forest. CWD mass, input rate, decay rate, and distribution reflected the status of forest regeneration and succession for three forests. Mass dynamics were affected interactively by a variety of factors including species, micro- climate, and topography, but these effects were hardly distinguishable in this study because of the limited number of comparable sites and pieces of CWD. Thus, further studies will require data regarding long-term microclimate and CWD mass dynamics in a variety of forest types, which could represent diverse environmental factors.

Utility of information in photographs taken upwards from the floor of closed-canopy deciduous broadleaved and closed-canopy evergreen coniferous forests for continuous observation of canopy phenology

Abstract Hemispherical photographs taken on forest floors are used to monitor seasonal changes in canopy openness or leaf area index in ecological studies. Those analyses usually use black and white images converted from the original colour images. Photographs taken by downwards-facing cameras installed on towers are used to provide detailed information on leaf expansion, maturation and senescence of various tree species through the analysis of red, green and blue ‘digital numbers’ (DNRGB) extracted from those images. To examine the usefulness of colour information encoded in upwards hemispherical photographs in monitoring canopy phenological characteristics, we examined the consistency of DNRGB values between downwards and upwards images in deciduous broadleaved and evergreen coniferous forests in Japan. In the deciduous broadleaved forest, the DNRGB values in the upwards images were able to detect canopy phenology almost as well as those in the downwards images. However, we found the effects on DNRGB of (1) the spatial heterogeneity among observed points, (2) low-vegetation (before the beginning of leaf-expansion and after the end of leaf-fall period) and (3) white balance settings. In the evergreen coniferous forest, in contrast, the DNRGB values in the upwards images did not capture canopy phenology. These different results may be attributable to the light attenuation characteristics in the canopies due to the geometries of leaves and branches. Thus, the DNRGB values obtained from upwards images are almost as good as those of downwards images for monitoring detailed canopy phenology in deciduous broadleaved forests with a closed canopy.

Biomass accumulations and the distribution of nitrogen and phosphorus within threeQuercus acutissima stands in central Korea

Above- and belowground biomass and nitrogen (N) and phosphorus (P) distribution within threeQuercus acutissima stands were investigated in central Korea. The average age (year) and diameter at breast height (DBH, cm) were 10.8 and 7.9 for Stand 1, 38.2 and 17.1 for Stand 2, and 44.0 and 20.7 for Stand 3, respectively. Fifteen trees were destructively harvested for dimension analysis of component biomass (stem wood, stem bark, foliage, branches, and roots) plus N and P concentrations. Total biomass (t ha-1) was 88.7 for Stand 1, 154.9 for Stand 2, and 278.1 for Stand 3 while N and P contents in all tree components (kg ha-1) were 483.3 and 52.2, 697.1 and 55.0, and 1113.9 and 83.7. Nitrogen concentrations were highest in the foliage, followed by the stem bark, branches or roots, and stem wood. In contrast, P concentrations were greatest in the roots, then foliage, branches, stem bark, and stem wood. In general, N and P concentrations in these components significantly decreased with tree age and DBH, while N and P contents significantly increased with age and size. These relationships were stronger for size than for age. Our current data could be utilized to estimate N and P budgets for silvicultural practices, including fertilization, thinning, and harvesting.

Influence of thinning on carbon storage in a Japanese larch (Larix kaempferi) plantation in Yangpyeong, central Korea.

This study was conducted to determine the carbon (C) contents in a Japanese larch (Larix kaempferi) plantation with four different thinning intensities over 12 years in Yangpyeong, central Korea. Thinning was applied in April of 1997 [control, no thinning (2250 trees/ha)], light thinning (T10, 10% thinning, 2000 trees/ha after thinning), moderate thinning (T20, 20%thinning, 1750 trees/ha after thinning), and heavy thinning (T40, 40% thinning, 1200 trees/ha after thinning)]. We measured individual tree DBH (cm) in November, 2009 and calculated biomass using the allometric regression equation. Forest floor (litter and coarse woody debris (CWD)) and soils, litter and soils up to 30 cm were collected and analyzed. Even though tree survival rate during 12 years was highest in the heavy thinning plot (T40), vegetation C content (Mg C/ha) was significantly higher in the light thinning plot (T10) than the other plots: 58.5 for control, 64.9 for T10, 60.4 for T20, and 55.8 for T40, respectively. Moreover, total soil C content (Mg C/ha) was higher in the moderate thinning plot (T20), however, there was no significant difference among the other plots; 56.2 for control, 57.8 for T10, 63.7 for T20, and 62.3 for T40. C contents of forest floor (litter plus CWD) were largest in the control plot, which might be influenced by the individual tree species competition; 11.9 for control, 10.2 for T10, 10.1 for T20, and 6.6 for T40, respectively. Total ecosystem C content was higher in the moderate thinning plot (T20) than those in other thinned and unthinned plots: 125.2 for control, 131.2 for T10, 132.4 for T20, and 125.9 for T40, respectively. Moderate thinning treatment (T20) seemed more effective to conserve total ecosystem C content while the individual tree growth (mean DBH and height) was higher in the heavy thinning plot (T40).

Preliminary study on estimating fine root growth in a natural Pinus densiflora forest using a minirhizotron technique

The minirhizotron technique was used to investigate the spatial (soil depth) and temporal (season) changes of fine roots (≤2 mm) in a mature Pinus densiflora forest. Length, production, and mortality of fine roots were measured at different depths on seven dates between March and October 2011. Average fine root length (mm cm−2), production, and mortality (μm cm−2) during the growing seasons were 2.54 ± 0.82, 84 ± 27, and 7 ± 4 at 0–20 cm depth, 0.85 ± 0.37, 39 ± 13, and 14 ± 9 at 20–40 cm depth, and 1.26 ± 0.92, 45 ± 28, and 34 ± 16 at 40–60 cm depth, respectively. There was no significant difference in length, production, or mortality of fine roots among the different seasons and depths (P > 0.05). The seasonal pattern in fine root length generally increased during the growing seasons. The fine root production was high in summer, whereas the mortality was high in autumn. This preliminary result using a minirhizotron technique can be used for quantifying and understanding the fine root dynamics in P. densiflora forests.

Small-scale spatial variability of soil properties in a Korean swamp

Wetland soils have distinctive biogeochemical processes and ecosystem functions. Therefore, knowledge of wetland soils is important for conserving and rehabilitating wetland ecosystems. We investigated soil properties and their spatial variability in a temperate swamp and compared them with those of an adjacent upland within a small-scale watershed in Korea. Soil water content and carbon and nitrogen concentrations were two- to four-times higher in wetland than in upland soils. Soil water content and organic matter, which represented a large proportion of the variability of wetland soil properties, could be considered primary soil quality indicators for wetland soils. Wetland soils were characterized as having high spatial variability and moderate to strong spatial autocorrelation within a 30- to 50-m range. Nutrient availability was mainly regulated by soil water content and organic matter, not by pH, which had low variability and showed an independent pattern. These findings imply that wetland soils should be surveyed using an appropriate sampling design to determine characteristics of spatial variability in soil quality indicators in wetlands. Reference values of wetland soil properties reported from this study are expected to contribute to wetland conservation and rehabilitation.

Effect of thinning on carbon storage in soil, forest floor and coarse woody debris of Pinus densiflora stands with different stand ages in Gangwon-do, central Korea

This study was conducted to investigate effects of thinning on carbon (C) storage of soil, forest floor and coarse woody debris (CWD) in Pinus densiflora stands, central Korea. Two study stands (25- and 55-year-old stands) were located in P. densiflora forests of Gangwon-do and thinned in 2008. Each stand was divided into three plots by different thinning intensities based on stand density: no thinning (control, 0%), moderate thinning (M, 30%), and heavy thinning (H, 50%) in the 25-year-old stand and no thinning (control, 0%), light thinning (L, 20%), and moderate thinning (M, 30%) in the 55-year-old stand. We measured C storage of 0–30 cm depth soil, forest floor and CWD in 2009. Total C storage (t C ha−1) of soil, forest floor and CWD in two thinned plots was significantly higher than that in the control plot only in the 55-year-old stand: 66.4 for control, <84.2 for L, <117.9 for M. On the other hand, total C storage in the 25-year-old stand did not show a consistent tendency among thinning intensities. We speculated that 1 year was too short to detect any consistent changes in total C storage of soil, forest floor and CWD by thinning, and long-term observation would be needed.

Carbon Storage of Pure and Mixed Pine-Deciduous Oak Forests in Gwangneung, Central Korea

This study was conducted to determine the carbon (C) contents in different mixed stands of P. densiflora and deciduous oak species in Gwangneung, central Korea. Five mixed stands with different ratios of P. densiflora and deciduous oak species were chosen based on the basal area of all trees ≥5 cm DBH: pure P. densiflora (P100D0), 70% P. densiflora+30% deciduous oak species (P70D30), 44% P. densiflora+56% deciduous oak species (P50D50), 37% P. densiflora+63% deciduous oak species (P40D60), and 10% P. densiflora+90% deciduous oak species (P10D90). Total C contents in the overstory (aboveground and belowground) vegetation were higher in the mixed stands (P70D30, P50D50, P40D60) than in the pure stands (P100D0, P10D90). Moreover, except for P40D60, C contents of forest floor (litter and coarse woody debris) were larger in the mixed stands (P70D30, P50D50) than in the pure stands. However, total soil C contents up to 30cm depth were highest in the pure deciduous oak stand than in the pure P. densiflora stand and mixed stands. Total ecosystem C contents (Mg/ha) were 163.3 for P100D0, 152.3 for P70D30, 188.8 for P50D50, 160.2 for P40D60, and 150.4 for P10D90, respectively. These differences in total ecosystem C contents among the different mixed stands for P. densiflora and deciduous oak species within the study stands were attributed by the differences in vegetation development and forest management practices. Among the five study stands, the total ecosystem C contents were maximized in the 1:1 mixed ratio of P. densiflora and deciduous oak species (P50D50).