Charles C. Grier

Production, Turnover, and Nutrient Dynamics of Above- and Belowground Detritus of World Forests

Publisher Summary Evergreen forests accumulate higher forest floor masses than deciduous in similar climatic zones. In needle-leaved forests, none of the climatic factors or latitude explains the variation in amount of aboveground litterfall mass or litterfall nitrogen (N) input. This is in contrast to the broad-leaved forests in which half of the variation in aboveground litterfall mass or litterfall N input is explained by latitude, mean annual temperature, minimum monthly mean temperature, or logarithmic transformations of precipitation. Lower total root masses were measured in cold temperate needle-leaved deciduous, Mediterranean needle-leaved evergreen, and tropical broad-leaved semi-deciduous forests while higher total mean root masses occurred in tropical broad-leaved evergreen forests. In the warm temperate zones, evergreen forests had similar mean total root masses whether broad-leaved or needle-leaved. However, deciduous forests averaged 5000 kg ha -1 less total root mass than evergreen forests. In cold temperate forests, the proportion of total detrital input to forest floor occurring as aboveground litterfall varied from 23 to 80%. Inclusion of root turnover as part of total litter input changed the calculated mean residence time of organic matter in the forest floor from 7.8 to 6.3 years in a red pine plantation and 68.6 to 15.7 years in a Pacific silver fir stand.

A Comparative Analysis of Potential Nitrification and Nitrate Mobility in Forest Ecosystems

The controls of potential nitrogen mineralization, nitrate production, and nitrate mo- bilization in a wide range of forest ecosystems were investigated through a combination of field and laboratory experiments. Trenched plot experiments were performed in 17 forests, and laboratory incubation studies of potential ammonium and nitrate production were made on soils from 14 of these sites. The site with the greatest potential for nitrate production in the laboratory was a New Hampshire northern hardwoods forest. Several other sites, including New Hampshire balsam fir, Indiana maple- beech, New Mexico aspen, and Oregon western hemlock forests, also had high potential nitrate production. All of these sites also had rapid nitrate movement to below the rooting zone following trenching in the field. Of nine processes which could be important in preventing or delaying solution losses of nitrate from disturbed forests, two appeared most important among the forests we examined. Low net nitrogen mineralization (caused by either nitrogen immobilization or low gross nitrogen mineralization) and lags in nitrification (probably caused by either low initial populations of nitrifying bacteria or the allelochemic inhibition of nitrification) were identified as important in several sites and in different regions. A direct relationship between the amount of nitrogen in annual litterfall and the proportion of forest floor nitrogen mineralized in laboratory incubations was observed, suggesting that refractory organic nitrogen compounds are produced in nitrogen-poor sites. An inverse relationship was found between the amount of nitrogen in litterfall in these and other sites and the carbon:nitrogen ratio of that litterfall, suggesting that the immobilization capacity of litter is increased in nitrogen-poor sites. The presence and length of lags in nitrification were inversely correlated with the mean concentration of mineral nitrogen in mineral soil. These patterns suggest that nitrogen retention within disturbed forest ecosystems can be caused by low nitrogen availability prior to disturbance.

CARBON DYNAMICS OF ROCKY MOUNTAIN DOUGLAS-FIR: INFLUENCE OF WATER AND NUTRIENT AVAILABILITY'

Changes in biomass distribution, canopy dynamics, and above- and be- lowground net primary production were examined in a Rocky Mountain Douglas-fir (Pseu- dotsuga menziesii var. glauca forest in New Mexico. Nutrient and water availability were experimentally altered by: fertilization (F), irrigation (I), carbon in the form of wood chips (WC), carbon + irrigation (WC/I), and control (C). Prior to treatment, aboveground tree biomass ranged from 238 to 369 000 kg/ha, projected leaf area index (LAI) ranged from 5.4 to 8.7 m2/m2 and aboveground net primary production (ANPP) ranged from 9200 to 11 900 kg* ha-I yr-i. Aboveground NPP was correlated positively (R2 = 0.85) with LAI before the treatments. Canopy dynamics were strongly influenced by water and nutrient availability. For trees of similar diameter, irrigated and fertilized trees supported a signif- icantly greater biomass of new twig and new foliage than control trees. During the 2-yr study leaf area index (LAI) increased by 5, 12, 18, and 24% in the C, I, WC/I, and F plots, respectively, and decreased by 3% in the WC plots. Stand level biomass distribution and production patterns were also affected by the availability of nutrients and water. Two years after the treatments were initiated, new foliage masses were 2400 (F), 2300 (WC/I), 2000 (I), 1900 (C), and 1800 (WC) kg/ha. In 1986, aboveground NPP was 33% greater in the F than WC treatment. Irrigation also increased ANPP. Fine root net primary production ranged from 1540 to 4200 kg ha-i yr-i and was significantly greater (P < .1) in the control than in the four treatments. BNPP comprised 46 (C), 32 (WC), 31 (I), 23 (WC/I), and 23 (F) % of total NPP. Total NPP was correlated positively with LAI (R2 = 0.66) and ranged from 15 360 kg ha- Iyr-I in the WC treatment to 21 140 kg ha-l yr-I in the F treatment. Many of the physiological relations between water or nutrient availability and production and carbon allocation reported in this study are consistent with results from studies on lowland Douglas-fir and other conifer forests in the Pacific Northwest. Collectively, these studies provide a mechanistic understanding of how water and nutrient availability govern production and carbon allocation of conifer forests in the western United States.

Old‐Growth Pseudotsuga menziesii Communities of a Western Oregon Watershed: Biomass Distribution and Production Budgets

Living biomass, organic matter distribution, and organic matter production budgets were determined for plant communities of a small watershed dominated by 450—yr—old Pseudotsuga menziesii (Mirb.) Franco forests. Dominant trees in the communities were large, up to 175 cm diam and 80 m tall. Aboveground tree biomass of the various communities ranged from 491.8—975.8 tonnes/hectare, total aboveground living biomass ranged from 500.4—982.5 t/ha, total leaf biomass ranged from 10.4—16.3 t/ha and total organic matter accumulations ranged from 1,008.3—1,513.7 t/ha. Total tree biomass in the various communities was more related to past mortality than habitat differences. Biomass of standing dead trees and fallen logs was generally inversely related to aboveground tree biomass. Amounts of woody detritus were large, ranging from 59.0—650.6 t/ha or 4.3%—43.0% of total community organic accumulation. Aboveground tree biomass increment was negative in all communities, ranging from —2.9 to —6.2 t/ha. Positive increment...

Long‐Term Trends in Forest Net Primary Productivity: Cascade Mountains, Washington

Estimates of annual net primary productivity since 1880 for four high—elevation forest stands in western Washington indicated that productivity has increased 60% during the 20th century. Because these stands were separated by up to 200 km and differed in species composition, elevation, and time since establishment, the observed trends in productivity imply a response to regionwide changes in environmental factors rather than to site—specific stand dynamics. Annual production is significantly correlated with long—term variation in summer temperature and short—term variation in annual precipitation since 1983, the beginning of continuous local meteorological records. Production is uncorrelated with atmospheric CO2 concentrations, suggesting that direct CO2 fertilization is currently unimportant in these forests. See full-text article at JSTOR

Soil nitrogen cycling and nitrous oxide flux in a Rocky Mountain Douglas-fir forest - Effects of fertilization, irrigation and carbon addition

Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average of 0.66 kg/ha of N2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen mineralization and nitrate production were estimated in soil and forest floor usingin situ incubations; fertilized soil mineralized 277 kg ha−1 y−1 in contrast to 18 kg ha−1 y−1 in control plots. Relative recovery of15NH4-N applied to soil in laboratory incubations was principally in the form of NO3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in the atmosphere.

Coniferous forests of the Pacific Northwest

The coniferous forests described in this chapter are primarily those of Oregon, Washington, southern British Columbia, western Montana, and Idaho. This forest region is sharply bounded on the west by the Pacific Ocean, on the east by the crest of the Rocky Mountains, and ranges from central coastal California and southern Oregon to the southeast Alaskan coast. Altogether the region includes several major forest zones, their distributions mainly reflecting differences in annual temperature and moisture balances.

Effects of aphid honeydew on soil nitrogen availability and net primary production in an Alnus rubra plantation in western Washington

The effect of honeydew from an aphid (Pterocallis alni DeGeer) infesting a red alder (Alnus rubra Bong.) plantation in western Washington, USA, was studied experimentally. The purpose of the study was to examine the hypothesis that melezitose, an aphid-synthesized sugar in honeydew, causes an increase in the available soil nitrogen which improves tree assimilation thus benefitting the aphids. Aphids were removed from one plot by periodic spraying with Malathion and were left undisturbed on a control plot. The hypothesis was not supported by this study. Honeydew reaching the soil caused a reduction in available soil nitrogen, nitrogen mineralization rates, aboveground net primary production and nitrogen uptake by trees.