Potential Contributions from Harvesting

In addition to pollution-associated depletion, tree harvests have the potential to exacerbate cation depletion within forests if they contribute to net cations losses that exceed long-term inputs (Adams 1999, Federer and others 1989, , Huntington 2000, Mann and others 1988, Nykvist 2000). Sequestration in above-ground woody biomass is an important cation sink within forest systems (Federer and others 1989, Mann and others 1988), and this is particularly true for Ca, which is highly concentrated in woody cell walls (Marschner 2002). Because of this, tree harvests can lead to the disproportionate removals of Ca relative to other cations (e.g., Adams 1999, Federer and others 1989). Harvests can also affect nutrient cycling through increased site acidification and leaching (Federer and others 1989), and reduced stocking following harvest may diminish stand-level transpiration and associated Ca uptake, further promoting Ca loss via leaching (Hornbeck and others 1993). In addition, varying methods of harvest can differentially alter Ca loss. For example, in one study, whole-tree (stems and branches) harvests removed up to 530 kg/ha, whereas sawtimber sales (bole wood only) removed about 442 kg/ha (Mann and others 1988). The frequency of tree harvest may also influence overall cation removal. Calculations from one study estimated a 15 percent loss of Ca due to leaching even with no harvest, a 28 percent loss of Ca with one harvest (at 80 years), and a 41 percent Ca loss for an equal intensity harvest performed in two stages: once at 40 years and once at 80 years (Adams 1999).