Effects of Clearcutting on Nongame Small Mammals
     1.  Clearcutting
     2.  Age of Stands
     3.  Associated Treatments
          a.  Site Preparation
          b.  Thinning
          c.  Fuelwood Harvesting
          d.  Stream Management Zones
 

The numerous species of small mammals have many needs and frequent many habitats, such as open terrain (e.g., lawns, fields), below ground, the forest floor, old logs, woodpecker holes, abandoned bird nests, houses, tidal marshes, brushy woodlots, and coniferous woods (Roth et al. 1978). Most published studies describe community responses and include a mixture of species.

1. Clearcutting

Not all species react in the same way to clearcutting; some increase and some decline in abundance at each stage of succession. Those found to increase in abundance soon after clearcutting were the white-footed mouse (Dykema 1990, Ambrose 1975, Root et al. 1990), the meadow jumping mouse and the woodland jumping mouse (Dykema 1990), the eastern chipmunk (Dykema 1990, Ambrose 1975), the masked shrew, the cloudland deer mouse, and the yellow-nosed vole (Kirkland 1974), the red-backed vole (Yahner 1988), and the short﷓tailed shrew (Ambrose 1975). Kirkland (1977) also found small mammal increases in clearcuts in a northern Appalachian hardwood forest.

In contrast, several species were reduced by clearcutting, including the red-backed vole and Peromyscus (Probst and Rakstadt 1987), the cotton mouse (Wolfe and Lohoefener 1987), and the white-footed mouse (Yahner 1986, 1988). Note that these last two papers from Pennsylvania report results that are the opposite to the findings of Ambrose (1975) in Tennessee, Dykema (1990) in Massachusetts, and Root et al. (1990) in Missouri, suggesting that there are regional differences in the reaction of certain species to clearcuts.

Small mammals also may respond differently to different forms of clearcutting. A comparison of the effect of whole-tree clearcut versus conventional harvesting of aspen on small mammal populations was made by Eaton (1986) in north-central Michigan. One-half of the rodent species preferred conventional sites while the other half preferred whole-tree harvested sites.

Bat activity (primarily little brown bats) was compared among 4 age classes of northern hardwood and spruce/fir forest stands in New Hampshire and Maine (Krusic et al. 1996). Bat activity was highest in overmature hardwood stands and in regenerating stands (0-9 yr) of both forest types. The data indicated that a mixture of forest types and age classes, including areas of regeneration (clearcuts and group cuts) and overmature hardwoods, help fulfill the summer habitat requirements of bats.

2. Age of Stands

Most studies have found that certain species characteristically are associated with one or more stand age class. Even﷓aged management appears to be favorable to the majority of small mammals by providing them with a variety of stand age classes. Often, stand structure is more important to small mammals than stand age per se. However, structural characteristics often vary with stand age. For example, newly regenerated stands usually have open canopies and abundant herbaceous vegetation while older stands are most likely to have snags and down wood.

In the Upper Piedmont of South Carolina, Mengak et al. (1989) compared small mammal populations in 10 loblolly pine stands (regenerated naturally), which ranged in age from 3 to 22 years. They also compared small mammal numbers in 15 stands of planted loblolly pines ranging in age from 2 to 18. Capture rates did not differ between natural stands and plantations. In the young natural stands, herbivores (cotton rats and field mice) initially dominated and then declined until they had virtually disappeared at the older age classes. Insectivores (shrews) also were not common at the older ages, while gramnivores generally were most abundant.

Due to the high reproductive rates of most small mammals, changes in populations come quickly. Trousdell (1954) found that before and immediately after cutting in a loblolly pine forest, density of the small mammal population was low. However, by the time the second crop of grass and forb seed was on the ground, the small mammal population had peaked. It declined slowly through the remainder of the regeneration period.

Young forest age classes can support relatively abundant small mammal communities which closely resemble those in unmanaged forests. Mitchell et al. (1995) found that young, open-canopy loblolly pine plantations and natural pocosin stands in North Carolina supported highly diverse and relatively dense small mammal communities. Small mammal communities in managed pocosins (pine plantations) closely resembled those found in unmanaged pocosins, possibly because pocosin-like habitat persisted in the plantations. In loblolly﷓shortleaf pine stands (seedling, sapling, pole, and sawtimber) in east Texas, the highest numbers of species and individuals of small mammals were found in young seedling stands (Whiting and Fleet 1987).

For some small mammals in some locations, stand age does not appear to be an important consideration. The abundance of small mammals was studied in 12 even-aged northern hardwood stands ranging in age from 8 to 205 years in northeast West Virginia (Healy and Brooks 1988). Capture rates of the southern red-backed vole, deer mouse, northern short-tailed shrew, woodland jumping mouse, eastern chipmunk, southern flying squirrel, and rock vole were not correlated with stand age or overstory structure. Species composition of the catch was similar in all stands. These 7 mammals seemed compatible with even-age silviculture.

3. Associated Treatments

a. Site Preparation
Factors such as intensity of the site preparation method, edaphic considerations, and prevailing climate greatly influence the effects of site preparation on soil characteristics, vegetation, and vertebrate communities. Most studies suggest that the effects of site preparation are temporary and, although the abundance of small mammals can be greatly changed, few species are totally eliminated from a site.

The effects of 4 site preparation treatments (hexazinone, imazapyr, picloram + triciopyr, and mechanical) on small mammal communities at 1 and 2 years post-treatment were studied in the upper Coastal Plain of South Carolina by Sparling and Miller (1995). Total capture rates during year 1 did not differ among treatments. However, in year 2, captures were lower on the mechanically-prepared sites than on chemically-treated areas. For both years, capture rates for old-field mice and least shrews were highest in the hexazinone-treated areas and lowest in the mechanically-prepared sites. Fewer small mammals were captured on glyphosate-treated clearcuts than untreated clearcuts in north-central Maine (Santillo et al. 1989). Small mammals became less abundant but retained moderate diversity and species richness.

In the upper Piedmont of Georgia and South Carolina, Evans (1990) studied the effects on small mammals of the fell-and-burn site preparation technique, following clearcutting, to control low-quality hardwoods. Because of the high-intensity of the fires in the Georgia Piedmont, the unburned sites supported more productive plant communities and more species of small mammals than burned sites. However, in South Carolina low-intensity burning produced the richest plant communities and highest numbers of individual small mammals. Mengak et al. (1989) found, in the same region, that when site preparation consisted of chop and burn, this practice produced similar small mammal populations to areas not treated. In Kemper County, Mississippi, Perkins et al. (1989) found that prepared sites supported 50 to 100 times more small mammals than mature pine-hardwood forests.

b. Thinning
When the canopy of an even-aged pine stand closes, small mammal populations become less dense (Langley and Shure 1980). Canopy closure occurs in natural stands as well; and in both instances thinning mitigates its undesirable consequences. For example, three levels of improvement-cut thinning were applied to a natural stand of pole-sized coastal hardwoods in Louisiana (Gardiner 1988). One year after thinning, biomass production increased from 44.9 lbs/ac to 138.0 lbs/ac, and cotton mice increased in abundance.

c. Fuelwood Harvesting
Dickson and Michael (1986) evaluated the response of small mammals to various methods of fuelwood harvesting in intermediate stands of Appalachian hardwoods in West Virginia 2 years after clearcutting. Small mammal abundance and diversity increased during the early successional stages.

d. Streamside Management Zones (SMZs)
Inclusion of SMZs in pine plantation management can enhance habitat diversity. Populations of small mammals were sampled in 6 SMZs of 3 widths: narrow (50 ft), medium (100 ft), and wide (164 ft), which extended through a 3-year-old pine plantation in the Upper Coastal Plain of Georgia (Thurmond and Miller 1994). A mature pine plantation and a nearby mature riparian forest also were sampled. SMZs supported populations of rice rats, golden deermouse, and eastern wood rat, 3 species not found in pine plantations.

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