Forest floor

When a forest system is subjected to acid deposition, the foliar canopy can initially provide some neutralizing capacity. If the quantity of acid components is too high, this limited neutralizing capacity is overcome. As the acid components reach the forest floor, the soil composition determines their impact. The soil composition may have sufficient buffering capacity to neutralize the acid components. However, alteration of soil pH can result in mobilization or leaching of important minerals in the soil. In some instances, trace metals such as Ca or Mg may be removed from the soil, altering the A1 tolerance for trees. 

Agee, J.K. Prescribed fire effects on physical and hydrologfc properties of mixed conifer forest floor and soil Report 143 Univ. of CA, Water Resources Center Davis, CA, 1973. 

As inputs of THg appear to be strongly retained in the forest floor, we reconunend a forest floor survey be conducted in areas that are receiving elevated Hg deposition and where it is expected that deposition will change markedly. In this site, permanent sampling sites would be established. We envision that forest floor samples would be resurveyed at appropriate time intervals (e.g., 10 years). A forest floor survey would help clarify current patterns of total Hg deposition and potentially quantify the response of forests to decreases in Hg emissions and deposition. 

Andresen AM, Johnson AH, Siccama TG. 1980. Levels of lead, copper and zinc in the forest floor in the northeastern U.S. J Environ Qual 9 293-296. 

Friedland AJ, Craig BW, Miller EK, Herrick GT, Siccama TG, Johnson AH. 1992. Decreasing lead levels in the forest floor of the northeastern USA. Ambio 21 400 03. 

Unlike records of stable isotope variations, records of ring width variations depend on many factors besides temperature alone, for example also on amount of rainfall and for example on amount of volcanic dust fall-out, forest fire, animal use of the forest floor, and it is impossible to deduce periodicities from them [63]. 

The regulation of biogeochemical cycles by microbial populations is of most direct importance in the cycling of N, S, P, and C. Most of the ecosystem pool of these elements resides as organic forms in forest floor and mineral soil compartments. These organic complexes are subjected to microbial transformations, which regulate nitrate, sulfate and phosphate ions dynamics and availability. In turn, this influences indirectly... 

Similarly to N, most S pools are found in organic form in forest floor and soil humus. However, unlike nitrogen, there are important abiotic processes, especially sulfate sorption processes, which play a critical role in regulating sulfate dynamics in forest ecosystems. An example of this type of exposure pathway was shown in the Habbard Brook whole-tree harvesting experiment, where the decrease in sulfate output from the watershed was attributed to sulfate adsorption, which was enhanced by soil acidification from nitrification (see above). 

The input of airborne lead to the Forest ecosystems has been studied at the Hubbard Brook Experimental Forest in New Hampshire. The small catchment approach has been used to study the lead biogeochemical cycle since 1963 (Likens et al., 1977 Driscoll et al., 1994). By monitoring precipitation inputs and stream output from small watersheds that are essentially free of deep seepage, it is possible to constmct accurate lead mass balance. The detailed study of soil and soil solution chemistry and forest floor and vegetation dynamics supplemented the deposition monitoring. 

The atmospheric deposition of lead was 190 g/ha/yr and this value was connected with declining of leaded petrol use in USA from 1975. The mineral soil and forest floor were the major pools of Pb in the ecosystem. Mineral soil pools (<2 mm size fraction) are generally the largest element pools for the HBEF, however this includes relatively unreactive soil minerals. Deposition and accumulation of Pb in the forest floor have been the focus of a number of investigations. It has been shown that at... 

Figure 25. Temporal pattern of the concentration of Pb in the bio geochemical reference watershed at the Hubbard Brook Experimental Forest, NH, USA (a) bulk precipitation (b) the forest floor (c) stream water (after Driscoll etal., 1994).

HBEF, much of the lead entering the ecosystem from the atmosphere appears to be retained in the forest floor. Concentrations and fluxes of lead in bulk deposition are much greater than in Oa horizon leachate. Solution concentrations and fluxes of Pb decrease through the soil profile and losses in stream water are low. There was a strong correlation between concentrations of Pb and dissolved organic carbon (DOC) in soil solution and stream water at Hubbard Brook Driscoll et al., 1994, 1998). 

Using our definition for alkalinity or ANC whereby any decrease (increase) in concentrations of base cations (e.g., K+, Ca2+, Fe2+, etc.) or any increase (decrease) in concentrations of "acid anions" (e.g., NO3, HPO2, SOf, etc.) is accompanied by a decrease (increase) in alkalinity. Thus, as illustrated in Fig. 5.17 net synthesis of terrestrial biomass (e.g., on the forest and forest floor, where more cations than anions are taken up by the plants (trees), is accompanied by a release of H+ to the environment. 

These sites attract enough flies that beetles are assured of a satisfying meal. But what if the sites themselves are in short supply Dung and carrion are in strong demand among local consumers and do not long persist on the forest floor. When they are absent, the beetles must look elsewhere for food. Showing considerable... 

The decomposition of tree leaves is not entirely confined to the litter layer on the forest floor. Leaves and needles are invaded by bacteria and fungi even as they grow these microorganisms may be either pathogens or saprophytes. ... 

In California, spotteds prey mainly on the dusky-footed wood rat. California s managed woodlands [industrial forests] have sunlight on the forest floor, because foresters space and trim trees to maximize yield. The warm climate further encourages plant growth. The result is forests with lots of wood rats.4... 

---