William A. Reiners

Nitrate Losses from Disturbed Ecosystems

A systematic examination of nitrogen cycling in disturbed forest ecosystems demonstrates that eight processes, operating at three stages in the nitrogen cycle, could delay or prevent solution losses of nitrate from disturbed forests. An experimental and comparative study of nitrate losses from trenched plots in 19 forest sites throughout the United States suggests that four of these processes (nitrogen uptake by regrowing vegetation, nitrogen immobilization, lags in nitrification, and a lack of water for nitrate transport) are the most important in practice. The net effect of all of these processes except uptake by regrowing vegetation is insufficient to prevent or delay losses from relatively fertile sites, and hence such sites have the potential for very high nitrate losses following disturbance.

Cloud droplet deposition in subalpine balsam fir forests : hydrological and chemical inputs

Subalpine forests of the northern Appalachians are subject to significant deposition of water and chemicals via cloud droplet impaction. This deposition has been estimated by a method linking micrometeorological measures of turbulent transfer, a detailed representation of canopy structure, and experimentally derived capture efficiencies. Water inputs from clouds are about 46 percent, and chemical inputs range from 150 to 430 percent of the bulk precipitation.

Loss of mass and chemical change in decaying boles of a subalpine balsam fir forest

Decay of balsam fir (Abies balsamea) boles was examined in an upper subalpine forest of the White Mountains, New Hampshire, USA. Fifty percent of the initial mass was lost in 23 yr; 90% was lost in 77 yr. High decay rates were attributed to the small diameters of the boles, ample moisture, and a nitrogen-rich environment. Average dead wood mass in this forest was 4.9 kg/M2, representing 25% of the sum of dead wood, live plant biomass, and forest floor organic matter. Changes in density and moisture and in the concentrations and content of various chemical com- ponents of the boles were traced over the decay sequence. Changes in the content of cellulose, lignin, carbon and sodium followed loss of mass during decay. Contents of calcium, magnesium, potassium and phosphorus decreased faster than loss of mass in the early stages of decay. Much of this initial loss was acribed to sloughing of nutrient-rich bark which in these small boles comprised 13% of dry mass. Later in decay, the loss rates of calcium, magnesium and potassium were about the same or slightly less than the loss rate of mass. After a steep initial drop, phosphorus content of the boles remained approximately constant between years 12 and 33. Thereafter the loss rate paralleled loss of mass. Nitrogen content was approximately constant in the first 33 yr after which it declined in parallel with loss of mass.

Vegetational Patterns and Processes in the Balsam Fir Zone, White Mountains New Hampshire

Vegetation structure and dynamics of the upper subalpine or fir zone were studied in the White Mountains of New Hampshire. The fir zone extends from 1220 m, the approximate upper limit of Picea rubens occurrence, to treeline (°1450 m) where it is usually represented by a low krummholz. Live tree density in the part of the zone in which trees are >2 m tall averages 5000 stems/ha. Eighty—four percent of these are Abies balsamea, and most of the rest are Betula papyrifera var. cordifolia. Basal area averages 30 m2/ha; canopy height averages 6.8 m. Stands tend to be dominated by discrete age classes. Tree ages range up to 111 yr (average 55 yr). Fir zone vegetation is subject to a number of processes that lead to a hierarchical set of overlapping patterns. Elevation and wind exposure produce general, or first—order, patterns over the landscape, e.g., canopy height decreases with elevation and exposure. Overlying this general pattern are a series of second—order patterns. Two acute disturbance factors–hurricanes and avalanches–have stamped discrete impressions over the general pattern. Other, more endogenously generated patterns, marks the landscape with more subtle textures. These patterns include fir waves, broken gaps, strips, and glades. A conceptualization of vegetation as a hierarchical series of overlapping patterns is an extension of Watts view of vegetation dynamics and bears important ecological implications.

Protein-binding phenolics and the inhibition of nitrification in subalpine balsam fir soils

Abstract Nitrification in a highly active Al horizon of a balsam fir forest floor soil can be greatly inhibited by an aqueous methanol extract of the forest floor. This extract was fractionated in an attempt to identify the compounds responsible for the inhibition. Condensed tannins, smaller molecular weight phenolics, and their distribution on particulate matter in the extract were the most important inhibiting components of the extract. When all phenolic material was removed from the extract, the remaining solution stimulated nitrification.

Canopy processing of acidic precipitation by coniferous and hardwood forests in New England

SummaryThere are several important factors that may influence how forest canopies interact with acidic deposition, including forest community species composition, phenological status, and differences in atmospheric loading of strong acids. Results from comparative throughfall chemistry studies in New Hampshire, where precipitation pH is 4.1, indicate that northern hardwood canopies produce a throughfall solution chemistry that is less acid and higher in basic cations than either direct precipitation or throughfall solutions derived from nearby subalpine balsam fir forests. Neutralization of acid precipitation in the hardwood canopy appears to occur through two major processes: ion exchange removal of free H+ by the foliage, and Brønsted base leaching from the plant canopy. Data obtained during the period of senescence preceding leaf-drop suggest a strong link between alkalinity release and potassium leaching in the hardwood canopy. Compared with the hardwood canopy, the coniferous forest canopy exhibits several distinct quantitative differences in canopy processing.

Forest Floor Leaching: Contributions from Mineral, Organic, and Carbonic Acids in New Hampshire Subalpine Forests

Analyses of soil water and groundwater samples from a high-elevation coniferous ecosystem in New England indicate that sulfate anions supply 76 percent of the electrical charge balance in the leaching solution. This result implies that atmospheric inputs of sulfuric acid provide the dominant source of both H+ for cation replacement and mobile anions for cation transport in subalpine soils of the northeastern region affected by acid precipitation. In soils of relatively unpolluted regions, carbonic and organic acids dominate the leaching processes.

Plant Diversity in a Chronosequence at Glacier Bay, Alaska

Eight sites of known age were sampled in Glacier Bay National Monument, Alaska, to examine the changes in plant diversity during primary succession in that region. Four strata–trees, tall shrubs, low shrubs—herbs, and bryoid—thalloids–were sampled independently. Data suggested a sequence of wave—like invasions on sites by strata, largely in order of increasing size. Bryoid—thalloids were exceptional in demonstrating a late peak in cover values. In general, diversity of a particular stratum declined during the period in which the stratum dominated the community in terms of foliar cover. Richness (species number) of communities increased rapidly in the first 100 years, then more gradually to reach a maximum in the muskeg steady state. Equitability (evenness of distribution of foliar cover among species) was erratic, but tended to increase with age. After initial rises, three diversity indices showed nearly flat curves with two exceptions: marked decreases in the 30— to 50—year period; and a rise to maximum levels in the final steady state. Total information per unit area calculated from diversity and foliar cover increased in a sigmoid manner with peak information in the final muskeg stage.

Size distribution and expansion of canopy gaps in a northern Appalachian spruce-fir forest

Canopy gap area/age distributions and growth mechanisms were examined in a virgin subalpine forest in the White Mountains, New Hampshire, USA. The gap area distribution was negative exponential in form. Whithin gap tree ages varied widely in response to stepwise gap expansion caused by windthrow of peripheral trees or death of standing mature Picea rubens at gap edges. As a consequence, the density of small gaps may have been underestimated and the density of large gaps overestimated. The estimates of canopy turnover time, 303 yr, and of patch birth rate on an area basis, 3.3×10-3 ha new patches/ha land area/yr, were not affected by the gap expansion phenomenon. However, any estimate of patch birth rate as numbers of new patches formed per year would have been too low. Because of increasingly widespread Picea death, the patch area/age distribution of this forest may not currently be in steady-state.

Potential alteration of precipitation chemistry by epiphytic lichens

SummaryEpiphytic lichen growth is abundant on the boles and branches of balsam fir trees at high elevations in New Hampshire. These lichens absorb elements needed for growth from solutions flowing over their surfaces and from direct impaction of water droplets. This study describes how epiphytic lichens and fir needles altered the chemistry of simulated rain water solutions under laboratory conditions. Experiments showed: 1) lichens absorbed ammonium and nitrate from solution; the rate of uptake increased with increasing temperature of the solution, 2) lichens lost calcium, magnesium, and hydrogen to the solution, 3) lichen thalli also initially lost potassium, but in time, net movement was reversed back into the thallus, 4) cation movement increased with increasing temperature, and 5) fir needles responded in a manner similar to that of the lichens, but the amount of change was much less. From these results it seems that epiphytic lichens have potential ecological importance in altering the chemistry of throughfall and stemflow.