Residual Timber Values within Piedmont Streamside Management Zones of Different Widths and Harvest Levels

Forested streamside management zones (SMZs) provide numerous societal benefits including protection of water quality and enhancement of in-stream and riparian habitats. However, values of residual timber in SMZs are often ignored, yet maintenance of unnecessarily wide SMZs can potentially reduce merchantable timber. Therefore, forestland owners, managers, and logging contractors are interested in determining minimum SMZ widths and stocking levels that can effectively maintain water quality while minimizing residual SMZ stand values. A larger SMZ efficacy study evaluated the efficacy of 7.6-m SMZs with no thinning, 15.2-m SMZs with no thinning, 15.2-m SMZs with thinning, and 30.2-m SMZs without thinning within 16 operational clearcuts. All SMZs widths provided effective sediment control (Lakel et al. 2010). The substudy presented here evaluated residual values in the SMZs of the larger study. Analyses examined immediate values associated with foregoing removal of SMZ timber and provide insight into future SMZ management issues. Across 16 harvested tracts, SMZs accounted for approximately 12% of the total harvest area with an average SMZ residual timber value of $1,064.78/ha. This study supports the financial benefits of partial harvests within the SMZs that remove higher value trees as typically recommended or permitted by best management practice guidelines. However, partial harvests may promote less valuable shade-tolerant species. Results also indicated that almost one-half of the SMZs had notable wind and/or ice damage within 2 years of installation. Financial analysis including opportunities for a tax credit indicate that longer term management of SMZs may be financially feasible if valuable products continue to be thinned from these stands along with rotational harvesting of the adjacent upland stands. Overall, results indicate that society and landowner short-term goals for typical southern Piedmont sites can generally be achieved by leaving 15.2-m SMZs and thinning the stands where practical. best management practices, riparian forests, streamside management zone costs Forested streamside management zones (SMZs) are riparian areas within managed forests that are often maintained primarily for the protection of water quality and secondarily for wildlife benefits (Broadmeadow and Nisbet 2004, Lee et al. 2004). Water quality benefits associated with SMZs include sediment retention (Lowrance et al. 1986, White et al. 2007), nutrient retention and cycling (Daniels and Gilliam 1996, Secoges et al. 2013), reduction of thermal pollution (Beschta 1997), and increased stream channel stability (Fraser et al. 2012). Riparian zones may benefit wildlife by maintaining older habitats, forested corridors (Wigley and Roberts 1994), inputs of coarse and particulate woody debris to streams (De Steven and Lowrance 2011), and diversity of habitats within stream channels (Castelle et al. 1994, Blinn and Kilgore 2001). It is widely accepted that SMZs positively affect water quality in and around headwater streams where forestland management activities often occur (Aust and Blinn 2004, Ice 2004, Anderson and Lockaby 2011a); however, relatively few studies have examined the efficacy and efficiency of various SMZ widths (Richardson et al. 2012) or considered the financial implications of SMZ maintenance for forest landowners (Cubbage 2004, Hickey and Doran 2004). Recent reviews of research for forestry best management practices (BMPs) across the southeastern United States generally conclude that SMZs are the single most effective BMP for protection of water quality (Aust and Blinn 2004, Ice 2004, Anderson and Lockaby 2011b). Studies have also indicated that practices such as roads, skid trails, and firelines, which compromise the integrity of the SMZ, can lead to decreased water quality (Keim and Schoenholtz 1999, Aust et al. 2011, Secoges et al. 2013, Wear et al. 2013). Keim and Schoenholtz (1999) evaluated different harvest disturbance levels within SMZs and found elevated levels of total suspended sediment in streams having SMZs with unrestricted traffic in the SMZ. Conversely, Aust et al. (2012) found that harvesting within riparian areas increased herbaceous vegetation and enhanced sediment trapping. Lakel et al. (2010) evaluated the effects of four different widths of SMZs ranging from 7.6 to 30.4 m and included an evaluation of thinning for the recommended SMZ width of 15.2 m. This study concluded that all SMZ widths provided effective sediment control (86–97% efficiencies). Subsequently, Secoges et al. (2013) conducted a follow-up study on the same SMZs to evaluate nitrogen retention by SMZs when adjacent plantations were fertilized. This study concluded that the 15.2-m SMZ without thinning and the 30.4-m SMZ without thinning were the more effective SMZs. Vaidya et al. (2008) evaluated the water quality effects of SMZs of 20 m, 20 m with select cut, and 30 m with select cut. Their analyses indicated that the 30-m select cut SMZ was most effective for protection of water quality and that partial harvests decreased water quality for SMZs of 20 m width. Clinton (2011) evaluated total suspended solids on harvest sites having no SMZs, 10-m SMZs, and 30-m SMZs and found that 10-m-wide SMZs adequately protected streams from total suspended sediment, stream nutrients, and temperature. Sanders and McBroom (2013) compared the effects of partial harvests in a 15-m-wide SMZ versus no SMZ and found that the SMZ with partial harvest provided a 10 times improvement in water quality. Rivenbark and Jackson (2004) examined the causes of SMZ failures where surface water flow with suspended sediments penetrated the SMZ and entered the stream channel on 30 SMZs below harvested and site prepared sites. The majority of SMZ failures and increased sediment loads in streams were caused by existing gullies and swales or inadequate water control on roads and skid trails. This research identified one SMZ failure for approximately every 20 harvested acres. The authors suggested that SMZ widths of 30.2 m could be overwhelmed by these circumstances. Ward and Jackson (2004) examined the sediment trapping within swales leading to SMZs and concluded that the SMZs trapped 71–99% of the sediment and that SMZs were a critical BMP for protection of water quality. Fraser et al. (2012) compared the sediment trapping of 6-m-wide SMZs versus 12- to 21-m-wide SMZs on the same watersheds over a 34-year period. Although the original 6-m SMZs were found to be insufficient, the 12- to 21-m SMZs provided adequate water quality protection. The researchers also pointed out the importance of better water control on roads and improved stream crossings compared with the original 6-m SMZs. The research indicates that some levels of disturbances within SMZs are acceptable and also indicates that disturbances can cause problems when the activities concentrate water movement to the streams or compromise the integrity of the (...truncated)