Topographic and climatic controls on soil environments and net primary production in a rugged temperate hardwood forest in Korea

Assessing Forest Ecosystems across the Vertical Edge of the Mid-Latitude Ecotone Using the BioGeoChemistry Management Model (BGC-MAN)

The mid-latitude ecotone (MLE)—a transition zone between boreal and temperate forests, which includes the regions of Northeast Asia around 30°–60° N latitudes—delivers different ecosystem functions depending on different management activities. In this study, we assessed forest volume and net primary productivity changes in the MLE of Northeast Asia under different ecological characteristics, as well as various current management activities, using the BioGeoChemistry Management Model (BGC-MAN). We selected five pilot sites for pine (Scots pine and Korean red pine; Pinus sylvestris and P. densiflora), oak (Quercus spp.), and larch forests (Dahurian larch and Siberian larch; Larix gmelinii and L. sibirica), respectively, which covered the transition zone across the MLE from Lake Baikal, Russia to Kyushu, Japan, including Mongolia, Northeast China, and the Korean Peninsula. With site-specific information, soil characteristics, and management descriptions by forest species, we established their management characteristics as natural preserved forests, degraded forests, sandy and cold forest stands, and forests exposed to fires. We simulated forest volume (m3) and net primary productivity (Mg C ha−1) during 1960–2005 and compared the results with published literature. They were in the range of those specified in previous studies, with some site-levels under or over estimation, but unbiased estimates in their mean values for pine, oak, and larch forests. Annual rates of change in volume and net primary productivity differed by latitude, site conditions, and climatic characteristics. For larch forests, we identified a high mountain ecotype which warrants a separate model parameterization. We detected changes in forest ecosystems, explaining ecological transition in the Northeast Asian MLE. Under the transition, we need to resolve expected problems through appropriate forest management and social efforts.

The Influence of Slope Positions on the Recovery Response of Compacted Soil Properties and Enzyme Activity in an Oriental Beech Stand in the Hyrcanian Forests, Iran

Several studies emphasize the effects of slope position on divergences of soil properties in forest ecosystems, but limited data is available on the impact of slope position on recovery levels of soil, which were exposed to compaction due to machine traffic. This study examined the effects of slope position (i.e., S; summit, BS; backslope, and TS; toeslope) on recovery rate of soil properties and enzyme activity four years after ground-based harvesting operations were performed on machine operating trails, compared to the undisturbed areas (UND) in the Hyrcanian forests (north of Iran). Soil properties and enzyme activity of compacted soil in machine operating trails showed significant trend differences among the slope positions. A significantly lower soil bulk density, penetration resistance, soil moisture, aggregate stability, pH, sand, and C/N ratio were found in TS compared to the values recorded in the BS and S treatments. Conversely, total porosity, macroporosity, silt, clay, organic C, total N, available nutrients (i.e., P, K+, Ca2+, and Mg2+), fulvic and humic acid, earthworm density and dry mass as well as fine root biomass were higher in TS than in the BS and S treatments. Soil microbial respiration, MBC, NH4+, NO3−, N mineralization, and MBN were significantly higher in the UND areas followed by TS > BS > S treatment. The highest activity levels of enzymes (i.e., urease, acid phosphatase, arylsulfatase, invertase, and ß-N-acetylglucosaminidase) were detected in the UND areas, followed by TS > BS > S treatment. The highest recovery levels of all soil properties and enzyme activity were found in TS, followed by BS > S treatment. However, the full recovery of soil properties did not occur even after a 4-year period, compared to the UND areas. Our study results highlight the significance of the slope position in augmenting divergence in soil properties and enzyme activity after ground-based machine traffic.

Interactive effects of hydrological conditions on soil respiration in China's Horqin sandy land: An example of dune-meadow cascade ecosystem

Soil moisture (M_s) strongly influences dynamic changes in soil respiration (R_s) and is thus an important factor when predicting soil carbon emissions. However, the various sources of M_s (rainfall, groundwater, and condensation) exert complicated and uncertain effects on R_s. This study examined the growth seasonal variation (from April to October) of R_s and the diurnal variation in a cascade ecosystem consisting of sandy bare ground, a transitional artificial Populus forest, and a meadow Phragmites communis community in China's Horqin sandy land. Simultaneous measurements of the 0-10 cm depth soil temperature (T_s) and M_s, rainfall, the surface air relative humidity and the groundwater depth were collected. The results revealed that in sandy bare ground with M_s below field capacity, M_s had a greater impact on R_s than T_s, and rainfall could increase R_s. The effect of condensation on R_s during periods of continuous drought could not be ignored. In the meadowlands with M_s above field capacity, the groundwater affected R_s indirectly by regulating M_s and the relationship with T_s, and rainfall had an adverse effect on R_s. The effects of rainfall, M_s and T_s on R_s were minimum as M_s approached the saturation water content. In the transitional forest, M_s and T_s were the main factors controlling R_s. The most favorable M_s for R_s was close to the field capacity. The results emphasize that field capacity and saturation water content are the demarcation points of a soil carbon emissions prediction model, and the effect of different hydrological conditions and T_s on R_s at each segment are reconsidered accordingly. Ultimately, the carbon emission patterns of the cascade ecosystems in arid and semi-arid areas are extremely complicated and have to be considered specially for estimating terrestrial carbon emissions.

Gravel bars are sites of increased CO2 outgassing in stream corridors

Streams are significant sources of CO₂ to the atmosphere. Estimates of CO₂ evasion fluxes (f _CO2) from streams typically relate to the free flowing water but exclude geomorphological structures within the stream corridor. We found that gravel bars (GBs) are important sources of CO₂ to the atmosphere, with on average more than twice as high f _CO2 as those from the streamwater, affecting f _CO2 at the level of entire headwater networks. Vertical temperature gradients resulting from the interplay between advective heat transfer and mixing with groundwater within GBs explained the observed variation in f _CO2 from the GBs reasonably well. We propose that increased temperatures and their gradients within GBs exposed to solar radiation stimulate heterotrophic metabolism therein and facilitate the venting of CO₂ from external sources (e.g. downwelling streamwater, groundwater) within GBs. Our study shows that GB f _CO2 increased f _CO2 from stream corridors by [median, (95% confidence interval)] 16.69%, (15.85-18.49%); 30.44%, (30.40-34.68%) and 2.92%, (2.90-3.0%), for 3^rd, 4^th and 5^th order streams, respectively. These findings shed new light on regional estimates of f _CO2 from streams, and are relevant given that streamwater thermal regimes change owing to global warming and human alteration of stream corridors.

Forest soil CO2 efflux models improved by incorporating topographic controls on carbon content and sorption capacity of soils

Improved models are needed to predict the fate of carbon in forest soils under changing environmental conditions. Within a temperate sugar maple forest, soil CO₂ efflux averaged 3.58 µmol m^-2 s^-1 but ranged from 0.02 to 25.35 µmol m^-2 s^-1. Soil CO₂ efflux models based on temperature and moisture explained approximately the same amount of variance on gentle and steep hillslopes (r² = 0.506, p < 0.05 and r² = 0.470, p < 0.05 respectively). When soil carbon content and sorption capacity were added to the models, the amount of explanation increased slightly on a gentle hillslope (r² = 0.567, p < 0.05) and substantially on a steep hillslope (r² = 0.803, p < 0.05). Within the organic-rich surface of the mineral soil, carbon content was positively related and sorption capacity was negatively related to soil CO₂ efflux rates. There were general patterns of smaller carbon pools and lower sorption capacity in the upland positions than in the lowland and wetland positions, likely a result of hydrological transport of particulate and dissolved substances downslope, leading to higher soil CO₂ efflux in the upland positions. However, the magnitude of the soil CO₂ efflux was mitigated by the higher sorption capacity of the organic-rich surface layer of the mineral soils, which was negatively correlated to soil CO₂ efflux. More accurate estimates of forest soil CO₂ efflux must take into account topographic influences on the carbon pool, the environmental factors that affect rates of carbon transformation, as well as the physicochemical factors that determine the fraction of the carbon pool that can be transformed.

Adding ecosystem function to agent-based land use models

The objective of this paper is to examine issues in the inclusion of simulations of ecosystem functions in agent-based models of land use decision-making. The reasons for incorporating these simulations include local interests in land fertility and global interests in carbon sequestration. Biogeochemical models are needed in order to calculate such fluxes. The Century model is described with particular attention to the land use choices that it can encompass. When Century is applied to a land use problem the combinatorial choices lead to a potentially unmanageable number of simulation runs. Century is also parameter-intensive. Three ways of including Century output in agent-based models, ranging from separately calculated look-up tables to agents running Century within the simulation, are presented. The latter may be most efficient, but it moves the computing costs to where they are most problematic. Concern for computing costs should not be a roadblock.