Forest ecosystems field studies

The second level of interaction, the intermediate-dose level, can result in measurable effects on forest ecosystems. These effects consist of a reduction in forest growth, change in forest species, and susceptibility to forest pests. Both laboratory investigations and field studies show SO2 to be an inhibitor of forest growth. When various saplings have been exposed to SO2 in the laboratory, they show reduction in growth compared with unexposed... 

These gases deposit rapidly due to their reactivity with surfaces, and exhibit elevated dry deposition velocities rapid dry deposition has been confirmed in recent field studies in forests and the Arctic (Lindberg and Stratton 1998 Lindberg et al. 2002). At concentrations typical of raral or remote ecosystems, the dry deposition of RGHg and Hg(0) are far greater than PHg, although this species may be of importance under dry conditions near sources (Pirrone et al. 2000). 

Denitrification, a dissimilatory pathway of nitrate reduction (see Section 3.3 also) into nitrogen oxides, N2O, and dinitrogen, N2, is performed by a wide variety of microorganisms in the forest ecosystems. Measurable rates of N20 production have been observed in many forest soils. The values from 2.1 to 4.0 kg/ha/yr are typical for forest soils in various places of Boreal and Sub-Boreal Forest ecosystems. All in situ studies (field monitoring) of denitrification in forest soils have shown large spatial and temporal variability in response to varying soils characteristics such as acidity, temperature, moisture, oxygen, ambient nitrate and available carbon. 

Field Studies. We have attempted to compare the relative availability of actinides to small mammals living in contaminated environments near ORNL. Shrews, rats and mice have been collected from a 30 year old contaminated floodplain forest ecosystem ( ). Cotton rats (Sigmodon hispidus) have been collected from the banks of a former liquid radioactive waste pond which contains Pu, Am and Cu in sediments and shoreline vegetation. Analyses were performed by isotope dilution mass spectrometry (U, Th and Pu) or by alpha spectrometry (Pu, Am and Cm). 

Meentemyer (1995) asked the question Is the chmate of decay processes measured at weather stations The microclimate at the scale of an individual leaf may be nearly fully decoupled from what a nearby weather station measures. For field studies following decomposition processes at short time intervals, this decoupling may have important consequences. However, for smdies comparing annual mass losses across large geographic regions, the average climate at the weather station will probably suffice. Additionally, as Lavelle et al. (1993) noted, climate is not an equally important constraint across all ecosystems. Whitford (1989) hypothesized that abiotic controls on decomposer food webs are least important in moist, closed-canopy forests and most important in hot deserts. 

Cleveland, C.C., Townsend, A.R. and Schmidt, S.K. (2002) Phosphorus limitation of microbial processes in moist tropical forests evidence from short-term laboratory incubations and field studies. Ecosystems 5, 680-691. 

Frescholtz 2002). Although ongoing and new planned field and laboratory studies are designed to further test this hypothesis, we feel that it is warranted at this time to develop a pilot-scale network of aimual ecosystem fluxes of THg in TF and LF as indicators of total atmospheric deposition. These fluxes can then be compared with measured wet plus modeled diy deposition based on both inferential and regional-scale models to develop independent estimates of total atmospheric deposition for forested catchments. We also believe that this approach could eventually be applied to a national network, such as the MDN. Although this method is best aimed at forested sites, ongoing research will address methods appropriate for other ecosystems. 

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