ABSTRACT
While the biophysics of anemophilous pollen dispersal is understood in principle, empirical studies for testing such principles are rare, particularly in native ecosystems. This paper describes mechanisms underlying the dispersal of Artemisia pollen in a Wyoming sagebrush steppe. The relationships between meteorological variables and pollen flux were defined during the 1999 Artemisia flowering season, and detailed processes at the individual plant level were experimentally tested in the field in 2000. Results indicated that Artemisia pollen presentation is continuous but with early morning maxima. Atmospheric pollen concentrations and potential dispersal rates are controlled at diurnal time scales by individual flower development together with characteristic changes in temperature/humidity and wind speeds, at multi-day scales by frontal weather patterns, and at week-long scales by flowering phenology.
Subject(s)
Artemisia/physiology , Pollen/physiology , Atmosphere , Biological Evolution , Biophysical Phenomena , Biophysics , Circadian Rhythm , Ecosystem , Meteorological Concepts , Models, Biological , WyomingABSTRACT
There 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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
