Saerom Han

Experimental warming studies on tree species and forest ecosystems: a literature review

Temperature affects a cascade of ecological processes and functions of forests. With future higher global temperatures being inevitable it is critical to understand and predict how forest ecosystems and tree species will respond. This paper reviews experimental warming studies in boreal and temperate forests or tree species beyond the direct effects of higher temperature on plant ecophysiology by scaling up to forest level responses and considering the indirect effects of higher temperature. In direct response to higher temperature (1) leaves emerged earlier and senesced later, resulting in a longer growing season (2) the abundance of herbivorous insects increased and their performance was enhanced and (3) soil nitrogen mineralization and leaf litter decomposition were accelerated. Besides these generalizations across species, plant ecophysiological traits were highly species-specific. Moreover, we showed that the effect of temperature on photosynthesis is strongly dependent on the position of the leaf or plant within the forest (canopy or understory) and the time of the year. Indirect effects of higher temperature included among others higher carbon storage in trees due to increased soil nitrogen availability and changes in insect performance due to alterations in plant ecophysiological traits. Unfortunately only a few studies extrapolated results to forest ecosystem level and considered the indirect effects of higher temperature. Thus more intensive, long-term studies are needed to further confirm the emerging trends shown in this review. Experimental warming studies provide us with a useful tool to examine the cascade of ecological processes in forest ecosystems that will change with future higher temperature.

Initial effects of thinning on soil carbon storage and base cations in a naturally regenerated Quercus spp. forest in Hongcheon, Korea

Thinning can affect soil carbon (C) and base cation balances by reducing tree density and altering microclimate and organic matter budget; however, the subsequent changes in soil C and base cation contents after thinning are not well elucidated. Thus, this study investigated the effects of thinning on C storages in soil (at 0–10 cm, 10–20 cm, and 20–30 cm depths) and forest floor and concentrations of soil exchangeable base cations (Ca2+, Mg2+, K+, and Na+). Thinning treatments of different intensities based on the removed basal area (no thinning: control, 15% thinning: T15, and 30% thinning: T30) were applied to a naturally regenerated 31 to 40-year-old Quercus spp. forest. Soil C concentrations at 10–20 cm and 20–30 cm depths were significantly higher in T15 and T30 than in the control after 39 months, but not after 4 months. T15 and T30 treatments seemed to increase soil C storage at 0–30 cm after 39 months, but did not significantly change forest floor C storage after 4 and 39 months. Concentrations of exchangeable K+ of T15 and exchangeable base cations except for Ca2+ of T30 depth were significantly lower than those of the control at 0–10 cm after 4 months, but not after 39 months. This study shows that thinning treatments on a naturally regenerated Quercus spp. forest could increase soil C concentration after a few years but temporally decrease concentrations of soil exchangeable base cations.

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.

Differences in soil aggregate, microbial biomass carbon concentration, and soil carbon between Pinus rigida and Larix kaempferi plantations in Yangpyeong, central Korea

This study was conducted to examine the soil aggregate distributions and their relationship with microbial biomass carbon (C) concentration and soil C in Pinus rigida and Larix kaempferi plantations. Soil samples of 0–10 cm, 10–20 cm, and 20–30 cm depth were collected and the microbial biomass C concentration was measured. The soils were then classified into four aggregate size classes by wet-sieving procedure [large macroaggregate (>2000 μm), small macroaggregate (250–2000 μm), microaggregate (53–250 μm), and silt-plus-clay (<53 μm)] and the C content of each aggregate size class was analyzed. The L. kaempferi plantation contained more macroaggregate over 250 μm than the P. rigida plantation did. The mean weight diameter (MWD) of the soil aggregate up to 30 cm depth was 1.26 mm and 1.45 mm in the P. rigida and L. kaempferi plantations, respectively, and it decreased with soil depth. The microbial biomass C concentration up to 30 cm depth was 510 μg C g soil−1 for the P. rigida plantation and 764μg C g soil−1 for the L. kaempferi plantation, and it was greatest in the surface soil in both plantations. The mean soil C concentration up to 30 cm depth was 2.00% for the P. rigida plantation and 2.88% for the L. kaempferi plantation. In both plantations, the soil C concentration was higher in the surface soil than in the deep soil. However, there was no significant difference of C concentration among the soil aggregate size classes. The soil C content up to 30 cm depth in the P. rigida and L. kaempferi plantations were 47.69 Mg ha−1 and 61.49 Mg ha−1, respectively, and were also higher in the surface soil than in the deep soil. In both plantations, macroaggregate contained more Ccontent than microaggregate did. The microbial biomass C and soil C concentrations were significantly higher (P < 0.05) in the L. kaempferi plantation than in the P. rigida plantation due to the effect of species difference. The MWD and C content tended to be greater in the L. kaempferi plantation than in the P. rigida plantation, but the differences were not significant. In this study, the soil aggregate size, microbial biomass C and soil C concentrations were positively correlated with one another.

Early fertilization and absorbent treatments continuously enhanced windbreak tree growth and soil properties in the Hetao Plain of Inner Mongolia, China

Intensive and continuous management has rarely been applied in forestation designed to combat desertification, except for a few instances of fertilization and irrigation in the early stage in northern China. We hypothesized that early and discontinuous fertilization and absorbent treatments would continuously increase tree growth and improve soil properties in an arid region. In 2003 and 2004, treatments of nitrogen fertilization and absorbents were applied to Populus alba var. pyramidalis trees in an experimental windbreak site in the Hetao Plain of Inner Mongolia, China. Nevertheless, the current study results have demonstrated that early and discontinuous nitrogen fertilization and absorbent treatments continuously increased tree growth (2003–2009) without any significant improvement in soil properties in 2010. The study results suggest that early and discontinuous fertilization and absorbent practices may be sufficiently effective in forestation aimed at combating desertification in arid lands where continuous maintenance cannot be expected.

Species-specific Growth Responses of Betula costata, Fraxinus rhynchophylla, and Quercus variabilis Seedlings to Open-field Artificial Warming

Evaluation of tree responses to temperature elevation is critical for a development of forest management techniques coping with climate change. We conducted a study on the growth responses of Betula costata, Fraxinus rhynchophylla, and Quercus variabilis seedlings to open-field artificial warming. Artificial warming set-up using infra-red heater was built in 2012 and the temperature in warmed plots was regulated to be consistently 3 o C higher than that of control plots. The seeds of three species were sown, and the responses of growth, biomass allocation, and net photosynthetic rate of newly-germinated seedlings on the open-field artificial warming were determined. As a result, the growth responses of the seedlings differed with the species. B. costata showed decreases in the height to diameter ratio (H/D ratio), biomass, root weight to shoot weight ratio, and net photosynthetic rate. However, root collar diameter (RCD), height, biomass, and net photosynthetic rate of Q. variabilis were increased, while the response of F. rhynchophylla was rather obscure. There was no significant difference between warmed and control plots in seedling growth for 3 species in July, whereas, RCD, height, and H/D ratio of Q. variabilis were increased and H/D ratio of B. costata was decreased in November under warming. Species-specific growth responses to warming were similar to the speciesspecific responses of net photosynthetic rate and biomass allocation; therefore, net photosynthetic rate and biomass allocation might attribute to growth responses to warming. Besides, a relatively obvious response in autumn compared to summer might be affected by the phenological change following artificial warming. Species-specific responses of three deciduous species to warming in this study could be applied to the development of adaptive forest management policies to climate change. Key wordss: Artificial warming, Biomass partitioning, Elevated temperature, Korean birch, Oriental oak