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of CWM in Northern coniferous forests suggested that it may play a small role in nutrient cycling in those forests (Laiho and Prescott 2004). A review of scientific data suggests that nutrient capital can be protected when both sensitive sites (including low-nutrient) and clearcutting with whole-tree removal are avoided (see also Hacker 2005). However, there is no scientific consensus on this point because of the range of treatments and experimental sites (Grigal 2000). A study of an aspen/mixed-hardwood forest showed that even with a clear-cut system, calcium (Ca) stocks would be replenished in 54 years (Boyle et al. 1973). Minnesota’s biomass guidelines present data that showed soil nutrient capital to be replenished in less than 50 years even under a whole-tree harvesting scenario (Grigal 2004, MFRC 2007). Whole-tree clearcutting and whole-tree thinning (Nord-Larsen 2002) did not greatly reduce amounts of soil carbon or nitrogen (N) in some studies (Hendrickson 1988, Huntington and Ryan 1990, Olsson et al. 1996, Johnson and Todd 1998). Lack of significant reduction in carbon and N may be due to soil mixing by harvesting equipment (Huntington and Ryan 1990). However, intensive cutting, such as clear-cutting with whole-tree removal, can result in significant nutrient losses (Hendrickson 1988, Federer et al. 1989, Hornbeck et al. 1990, Martin et al. 2000, Watmough and Dillon 2003)—in one case, an initial 13% loss of Ca site capital (Tritton et al. 1987). Overall, the impact of biomass harvesting on soil nutrients is site dependent. Low-nutrient sites are much more likely to be damaged by intensive biomass removal than sites with greater nutrient capital or more rapid nutrient inputs, which is one reason scientific studies on the nutrient effects of whole-tree harvesting may yield different results. Low-impact logging techniques that reduce soil disturbance can help protect nutrient capital (Hallett and Hornbeck 2000). Harvesting during the winter after leaf fall can reduce nutrient loss from 10 to 20% (Boyle et al. 1973, Hallett and Hornbeck 2000). Alternatively, if logging occurs during spring or summer, leaving tree tops on site would aid in nutrient conservation. Nordic countries have demonstrated that leaving cut trees on the ground in the harvest area until their needles have dropped (one growing season) can also reduce nutrient loss (Nord-Larsen 2002, Richardson et al. 2002). Implications for Massachusetts Policies: The scientific literature makes clear that DWM plays a critical role in ensuring continued soil health and productivity. Modeling indicates that biomass harvests have the potential to reduce soil nutrient capital and cause long-term productivity declines (Janowiak 2010) at some sites; but other studies identify cases where soil nutrient capital is replaced in reasonable time periods even under whole-tree harvesting scenarios. A recent report, Silvicultural and Ecological Considerations of Forest Biomass Harvesting In Massachusetts, suggested that with partial removals (i.e., a combination of crown thinning and low thinning that removes all small trees for biomass and generates from 9 to 25 dry t/ac or 20 to 56 Mg/ha) stocks of Ca, the nutrient of greatest concern, could be replenished in 71 years (Kelty et al. 2008). The Massachusetts study was based on previous research with similar results from Connecticut (Tritton et al. 1987, Horn- beck et al. 1990). During the Forest Guild’s working group discussions of soil productivity, the Kelty study was investigated thoroughly as it raised serious questions of long-term sustainability. As general cautionary context for soil productivity, it should be noted that leaching, particularly of Ca due to acidic precipitation, can reduce the nutrients available to forests even without harvests (Pierce et al. 1993). In the case of Ca and the Connecticut research there are important questions as to whether the input rates from natural weathering were accurate. Other researchers believe the weathering rates are much higher and the Ca-phosphorus mineral apatite may provide more sustainable supplies of Ca to forests growing in young soils formed in granitoid parent materials (Yanai et al. 2005). For example, a recent study using long-term data from Hubbard Brook Ecosystem Study indicated that “the whole-tree harvest had little effect on the total pool of exchangeable calcium” after 15 years (Campbell et al. 2007). Consequently, the analysis provided in the Kelty study does not provide sufficient scientific justification to generalize about Ca depletion. The bottom line is that even while some available studies suggest that soil capital should be protected by avoiding sensitive sites and prohibiting clearcutting with whole-tree removals, there is no scientific basis for concluding that avoiding clearcutting or whole-tree harvesting are necessary at all sites to maintain produc- tivity. Sensitive soil types should be determined and appropriate guidelines applied. We recommend a conservative approach that includes the retention of some DWM in all harvests. The Forest Guild Biomass Retention and Harvesting Guidelines deal directly with these issues and are summarized in this report. 4.2.2.4 QuantitiesofDeadWood Site productivity and the rate of decomposition help determine the amount of dead wood in a given stand (Campbell and Laroque 2007, Brin et al. 2008). As mentioned above, DWM decomposi- tion varies greatly but generally occurs over 25–85 years in the U.S. (Harmon et al. 1986, Ganjegunte et al. 2004, Campbell and Laroque 2007). All mortality agents including wind, ice, fire, drought, disease, insects, competition, and senescence create dead wood (Jia-bing et al. 2005). These mortality agents often act synergistically. A review of 21 reports of quantitative measures of DWM in Eastern forest types shows great variability across forest types and stand-development stages (Roskoski 1980, Gore and Patterson 1986, Mattson et al. 1987, McCarthy and Bailey 1994, Duvall and Grigal 1999, Idol et al. 2001, Currie and Nadelhoffer 2002). The reports ranged from 3 to 61 t/ac (7 to 137 Mg/ha) with a median of 11 t/ac (24 Mg/ha) and a mean of 15 t/ac (33 Mg/ha). Measurements of old forests (>80 years old), had a median of 11 t/ac (24 Mg/ha) and a mean of 13 t/ac (29 Mg/ha) in DWM. BIOMASS SUSTAINABILITY AND CARBON POLICY STUDY MANOMET CENTER FOR CONSERVATION SCIENCES 65 NATURAL CAPITAL INITIATIVEPDF Image | NATURAL CAPITAL INITIATIVE AT MANOMET
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