Effects of forest management on biogeochemical functions in southern forested wetlands

Abstract

Southern forested wetlands perform two important biogeochemical functions on the landscape: 1) nutrient (N and P) removal from incident surface, subsurface, and ground waters, and 2) export of organic carbon and associated nutrients to aquatic ecosystems downstream, tn addition to P sediment deposition. which can range from 1.6 to 36.0 kg ha -t yr -a P, denitrification of NO3-N (0.5 to 350 kg ha i yr ') and P adsorption (130 to 199 kg ha k yr ') can be important mechanisms associated with N and P removal, respectively'. Biological processes, uptake by plants (15.0 to 51.8 kg ha-' yr-' for N; 0.2 to 3.8 kg ha -t yr-' for P) and microorganism absorption (16.2 to 87.0 kg ha-' yr -~ for N; 6.6 to 40.0 kg ha -~ yr -t for P) are also important and are intimately associated with organic matter export. Clearcut harvests (ground-based or aerial), followed by natural regeneration, are the most common silvicultural techniques used in forested floodplains in the South. Ground-based methods have been shown to increase soil bulk density and decrease hydraulic conductivity and redox potential in wetter soils. In addition to the increases in soil temperature and soil wetness that frequently occur following forest harvesting, these added effects may be responsible for the reduced productivity and altered species composition observed following ground-based vs. aerial harvests. Changes in denitrificalion will be a function of the degree to which harvesting affects soil redox potential, substrate (C) availability, and nitrate production. In theory, denitrification rates should increase following harvesting, but low nitrate availability in acid soils may limit this effect. The effects of harvesting on P adsorption processes in forested wetland soils have not been studied. Reductions in plant uptake and litterfall and changes in species composition following harvesting could alter both nutrient retention/transformation and organic C export functions. On wetter sites, canopy removal may stimulate algal populations, providing a short-term mechanism for conserving geochemical exports. Clearcut harvest systems that minimize alterations in soil hydrology and promote rapid vegetation regrowth should have the least effect on biogeochemical functions in southern forested wetlands.

Phosphorus release from forest harvesting on an upland blanket peat catchment

“…The increase in WEP in the soil not covered by the windrow/brash material after harvesting could be due to the decay of the surface organic layer, dead fine roots and lack of plant uptake. After clearfelling, a rise in soil temperature due to increased light penetration to the forest floor can increase decomposition rates (Messina et al, 1997;Perison et al, 1997), which increases the labile P sources (Walbridge and Lockaby, 1994).…”

“…Forest operations such as drainage, fertilisation, harvesting and reforestation result in increased P release (Lebo and Herrmann, 1994;Ensign and Mallin, 2001;Cummins and Farrell, 2003), and may increase the P concentration of receiving water bodies (Paavilainen and Päivänen, 1995;Ahtiainen and Huttunen, 1999;Nisbet, 2001;Cummins and Farrell, 2003). Clearfelling disrupts P cycling and significantly reduces the uptake of P by plants, resulting in an increased labile P pool in the harvested area (Walbridge and Lockaby, 1994;Herz, 1996). The decomposition of logging residues (i.e.…”

Soil N cycling in harvested and pristine Boreal forests and peatlands

“…Peatland nitrogen dynamics are driven by their hydrological condition and thus tend to exhibit high spatial variation in N cycling processes (Devito and Dillon, 1993;Hill and Devito, 1997). Higher soil moisture and degree of soil anoxia has been shown to increase soil N availability post-harvest in a peatland (Walbridge and Lockaby, 1994). Additionally, altered soil microclimate and peat disturbance (rutting and compaction) may lead to higher N cycling rates in peatlands following harvest (Grigal and Brooks, 1997;Groot, 1987).…”

Ecological functions and human values in wetlands: A framework for assessing forestry impacts

“…In another study, Craft et al (1988) reported that macroorganic matter and soil nutrient reservoirs were smaller in transplanted (1 to 15 years old) marshes than in comparable natural marshes. This type of research must be completed in forested systems so that specific quantitative standards for the relationships between function and values can be assessed, as well as for harvesting effects and BMPs (see Walbridge and Lockaby 1994). The relationship between wetlands and adjacent lands, as they are affected by timber harvesting in either area, is also critical and leads to principle three.…”