Neil W. Foster

Simulations of pre- and post-harvest soil temperature, soil moisture, and snowpack for jack pine: comparison with field observations.

Quantifying temporal changes in soil temperature and moisture conditions is an important part of characterizing pre- and post-disturbance conditions that influence the health, productivity, and sustainability of forest ecosystems. In this paper, we present an experimental case study that was used to evaluate the ability of the forest hydrology model ForHyM2 to simulate field-observed changes in root-zone soil moisture and temperature, as well as snowpack depth, throughfall volume and forest floor percolate volume, for a jack pine (Pinus banksiana Lamb.) site in northeastern Ontario. The experiment refers to two post-harvest treatment factors, each involving two treatments: (a) blading (removing) or non-blading the forest floor and part of the mineral topsoil, (b) herbiciding or non-herbiciding. It was found that harvesting increased the average daily soil temperature by 4‐68C on all treatment plots during summer (5 cm soil depth). Blading increased the soil temperature further by 1‐28C. Herbiciding did not have significant effects on soil temperature. Eliminating competing forest vegetation significantly increased soil moisture level on the non-bladed treatment plots. The model simulations were based on daily precipitation (snow and rain), air temperature, and a few site descriptors such as longitude and latitude, soil depth, soil texture, and leaf area index. The resulting simulations compared well (graphically) with the pre- and post-harvest field observations regarding soil moisture, soil temperature, and snowpack water equivalents. Good graphical agreements suggest that the approach taken with this case study can be applied to the evaluation of soil moisture and temperature conditions to a variety of pre- and post-disturbance forest conditions. The results from the study would be useful for addressing below ground processes such as root growth, soil respiration, rate of organic matter decomposition, rate of soil weathering, nutrient cycling, etc., all of which strongly influence site productivity. # 2000 Elsevier Science B.V. All rights reserved.

A forest nutrient cycling and biomass model (ForNBM) based on year-round, monthly weather conditions, part I: assumption, structure and processing

A forest nutrient cycling and biomass growth model was developed to simulate nutrient cycling and NPP based on site and monthly mean weather conditions. A modular design was used to partition northern forest ecosystems into separate modules that address the following ecological variables: (1) hydrologic processes and temperatures to estimate moisture, percolation and temperature in forest floor, soil and subsoil; (2) soil acidity to estimate the H-ion balance in the soil, in the context of atmospheric deposition, nutrient uptake, weathering, and soil-ion retention; (3) cycling of N, S, Ca, Mg, and K to estimate nutrient uptake, mineralization, nitrification, immobilization, mineral soil weathering, nutrient exchange between soil exchange sites and solution, and nutrient leaching associated with atmospheric deposition; and (4) biomass to estimate NPP and its allocation to foliage, wood, and root, as well as litterfall and decomposition. After the model calibration, verification and validation, the model can be applied (1) to predict the rate of sustainable nutrient harvesting based on nutrient geochemical balance; (2) to determine limiting nutrients for forest growth; (3) to evaluate the effects of atmospheric acidic deposition on soil chemistry and growth; and (4) to evaluate the effects of forest harvesting on environmental issues, such as stream water quality.

Fifteen-year Change in Forest Floor Organic and Element Content and Cycling at the Turkey Lakes Watershed

To assess the long-term effects of atmospheric deposition on forest floor chemical composition, we took quantitative samplings of L-(Oi), F-(Oe), and H-(Oa) layers at an old-growth sugar maple–yellow birch stand on a till soil at the Turkey Lakes Watershed near Lake Superior, Ontario, Canada, in 1981 and 1996. We then assessed these samples for contents of organic matter (OM), total N, K, Ca, Mg, S, and Na, and exchangeable NH4+, NO3−, K+, Ca2+, Mg2+, SO42−, and Na+. Over the 15-year period, total OM and element contents remained unchanged, with the exception of N, which increased significantly from 61.3 kmol/ha in 1981 to 78.4 kmol/ha in 1996. On an area basis, there were significant increases in exchangeable Ca2+ (from 3.8 to 4.6 kmol/ha) and Na+ (from 0.05 to 0.08 kmol/ha) and decreases in exchangeable NH4+-N (from 1.41 to 0.95 kmol/ha) and SO42−-S (from 1.29 to 0.96 kmol/ha). There were no significant differences in average annual litterfall OM, N, Ca, Mg, S or Na inputs between 1980 and 1985 and between 1992 and 1997. Average annual wet-only SO42−-S deposition during 1981–86 was 0.30; during 1992–97, it was 0.21 kmol/ha. Annual wet-only NO3−-N averaged 0.33 kmol/ha during 1981–86 and was similar during 1992–97. Throughfall was less rich in SO42− and Ca2+, Mg2+, and Na+ during 1992–97 than earlier. Throughfall NH4+ and NO3− fluxes were unchanged. Efflux of cations from the forest floor reflected reduced throughput of SO42−. Overall, the results suggest that in spite of atmospheric inputs, active biological processes—including litter input, fine-root turnover, and tree uptake—serve to impart stability to the mineral composition of mature sugar maple forest floor.

A Forest Nutrient Cycling and Biomass Model (ForNBM) based on year-round, monthly weather conditions: Part II: Calibration, verification, and application

Abstract The ForNBM was applied to the Nashwaak Experimental Watershed Project in central New Brunswick, Canada. The data represented a mixed hardwood site and included information about nutrient leaching, foliage and wood biomass, leaf fall, and ancillary information required for model initialization. Ancillary information included forest cover type, stand density, forest floor depth, soil rooting depth, soil texture, soil substrate type, initial amounts of biomass and N, S, Ca, Mg, and K content in foliage, wood, and roots, and mineral soil nutrient contents in soil solution, on ion-exchange sites, and in the soil. The authors were able to calibrate the model with existing data. The model simulated observed monthly leaching reasonably well. The r2-values of model simulations compared with field observations of monthly leaching of NO3−_N, NH4+_N, Ca, Mg, and K were 0.78, 0.7, 0.78, 0.84, and 0.75, respectively. Modeled multi-year cumulative leaching of NO3−_N, NH4+_N, Ca, Mg, and K compared with actual values gave r2-values close to one for all cases considered. The results also showed that soil nutrient leaching had increased approximately five-fold for NO3−_N, 80% for NH4+_N, 71% for K, 20% for Ca, and 14% for Mg during the 3 years following a stem-only harvest operation applied watershed-wide. However, the model simulation showed that increased nutrient leaching during the 11 years following the stem-only harvest was small compared with the amounts removed in the biomass during the harvest. Increased nutrient leaching following harvesting did not appear to impact site productivity over the long term.

Evaluating Critical Soil Acidification Loads and Exceedances for a Deciduous Forest at the Turkey Lakes Watershed

Critical soil acidification loads (CL) and related exceedances, base cation leaching, N leaching, and forest biomass growth were evaluated for a well-studied deciduous forest site within the Turkey Lake Watershed (TLW). The assessment was done by way of steady-state mass balance considerations of primary inputs for N, Ca, Mg, and K. Critical soil acidification rates were found to be high at TLW. These rates amounted to about 900 or 1400 eq/(ha yr) depending on the forest harvesting regime (selective harvest or maintainence of old-growth condition, respectively). The TLW soil substrate (till derived from basaltic bedrock) appeared to weather well, thereby buffering against natural and anthropogenic soil acidification. As a consequence, soil acidification exceedances were estimated to be relatively low for both the selective harvest and old-growth scenarios. In comparing overall S and N input/output data (atmospheric deposition data vs soil leaching losses), we found that the TLW site was essentially near or at S and N saturation. We also found that atmospheric deposition and soil leaching rates have been declining since about 1980. The figures for CL and exceedance varied to some extent depending on the quality of input data and related uncertainties. Estimated exceedances were increased when dry- as well as wet-deposition rates were considered. They varied depending on the yearly sulfate/nitrate/base-cation mix, and the definition of “acceptable acid leaching.” In addition, they were dependent on whether the forest was considered old growth or not.