derness, Montana (Cole 1983), and the Boundary. Waters Canoe Area Wilderness, Minnesota (Marion and Merriam 1985a), were applied in three areas in.
Recreation Impacts in Some Riparian Forests of the Eastern United States DAVID N. COLE* USDA Forest Service P.O. Box 8089 Missouta, Montana 59807, USA JEFFREY L. MARION Star Route 38 National Park Service Milford, Pennsylvania, USA
ABSTRACT / Ecological impacts on camp and picnic sites were examined in three National Park Service units along the Delaware and New rivers, in the eastern United States. All sites experienced pronounced impact to trees, groundcover vegetation, and soils. The nature and magnitude of impacts
Recent studies have documented the impacts of recreational use in areas with management objectives that stress preservation of natural communities and processes (see Cole 1987 for a review). Many of these studies have focused on the effects of camping in places not accessible by car, often in designated wilderness and portions of the national park system. Generally, such studies have found that considerable impact occurs rapidly and with only light use, while recovery will only occur after lengthy periods without any use. This suggests that the most effective management strategy for places that consistently receive at least moderate amounts of use is to confine camping to a small number of frequently used sites that are located in places that can support such use indefinitely. These conclusions have been drawn from work conducted almost exclusively in the vast wilderness and parklands of the western United States (see, for example, Cole and Fichtler 1983, Cole 1986, Stohlgren and Parsons 1986)and the Boundary Waters Canoe Area in northern Minnesota (Merriam and others 1973, Marion and Merriam 1985a). Such areas are generally characterized by harsh growing conditions that include aridity, short growing seasons, and infertile soils. In Great Smoky Mountains National Park, where growing conditions are more favorable, a KEY WORDS: Riparian forests; Campsites; Ecelogical impacts; Wild and scenic rivers; Recreationmanagement
*Author to whom communicationsshouldbe addressed. EnvironmentalManagementVol. 12, No. 1, pp. 99-107
in these riparian forests were quite similar to those reported in wilderness areas in the mountainous western states and northern Minnesota, despite more favorable growing conditions. The relationship between amount of use and amount of impact and the importance of differences in type of use and environment were also roughly comparable. High-use sites were more heavily impacted than low-use sites, but differences were small when compared with differences in amount of use. The areal extent of impact was the major difference between sites in different environments and sites used by different clienteles. This suggests that the effectiveness of basic strategies for managing impact should not differ greatly between regions. Here, as elsewhere, actions taken to control the areal extent of impact appear to be particularly important.
survey of campsites found, in contrast to these other studies, that amount of visitation is the primary factor influencing campsite damage and deterioration (Bratton and others 1978). This suggests that other management strategies, such as the policy of spreading use out on a large number of sites, as is done in Shenandoah National Park, may be effective in some eastern areas. The question we raise, then, is whether or not the conclusions drawn from western wilderness and park areas and northern Minnesota also apply in eastern areas, where growing conditions are more favorable. To evaluate this question, the same research techniques used to monitor impacts in the Eagle Cap Wilderness, Oregon (Cole 1982), the Bob Marshall Wilderness, Montana (Cole 1983), and the Boundary Waters Canoe Area Wilderness, Minnesota (Marion and Merriam 1985a), were applied in three areas in the East. Three areas along rivers managed by the National Park Service--the Upper Delaware Scenic and Recreational River, Delaware Water Gap National Recreation Area, and New River Gorge N a t i o n a l River--were selected. On recreation sites in these areas (campsites in Upper Delaware and Delaware Water Gap and both picnic sites and campsites in New River), growing conditions are quite favorable; moisture is seldom limiting; growing seasons are long; and frequent flooding maintains a high level of soil fertility. This article describes impacts on recreation sites accessed primarily by boat in these three Park Service 9 1988 Spdnger-VedagNew York Inc.
100
D.N. Cole and J. L. Marion
areas. Differences in amount of impact related to amount and type o f use are evaluated, as are differences related to environment. These impacts and relationships are compared with those reported from similar studies in areas with harsher growing conditions. Implications of these results for prescribing differing management strategies are discussed.
Study Areas and Methods The Study Areas T h e Upper Delaware Scenic and Recreational River includes 73 miles (117 kin) of fiver along the New York and Pennsylvania border. T h e river valley is rural, with paved roads and a railroad track paralleling much o f the river's length. T h e r e were approximately 163,000 recreational visits in 1986. Most use is day use in canoes, but about 35% of visitors camp overnight, either in outfitter campgrounds or on private lands at undeveloped user-selected sites. T h e Delaware Water Gap National Recreation Area includes 35 miles (56 kin) of the Delaware River, immediately southeast and downstream from the Upper Delaware, along the New Jersey and Pennsylvania border. T h e river valley is rural, with paved roads occasionally visible from the river. T h e r e were approximately 2,247,000 recreational visits in 1986. As at the U p p e r Delaware most use is day use in canoes, although about 35% of the floaters camp overnight in designated primitive sites (limited to one night per
site). T h e New River Gorge National River includes 50 miles (80 km) o f river in southeastern West Virginia. T h e river valley is rural in some areas and undeveloped in others. This segment has some of the finest whitewater rafting in the East, as well as intermediate and advanced canoeing. T h e r e were approximately 394,000 recreational visits in 1986. Most use on the river is day use in commercially guided rafts. About 10% o f river users camp along the fiver, either in outfitter campgrounds or on private lands at undeveloped user-selected sites.
Field and Laboratory Techniques Each sample site consisted of both a recreation site and an undisturbed control site in the vicinity. An arbitrarily located center point was established on e a c h recreation site. T h e distances from this point to the first significant amount of vegetation and to the edge o f the obviously disturbed site boundary were measured in 16 directions. This defined the central devegetated area and the larger disturbed area. Within
the disturbed area, all tree reproduction (< 140 cm tall, but at least one-half yr old) was counted, by species. All trees larger than this were counted, by species and damage level: none (no human-caused tree damage); slight (nails, nail holes, small branches cut off or broken, small superficial trunk scars); moderate (large branches cut off or broken, trunk scars and mutilations that may be numerous but do not total more than 1 ft 2 [0.09 m 2] in area); and severe (trunk scars that total more than 1 ft ~ or complete girdling of the tree). Stumps were also counted. Within the disturbed area, 15-20 quadrats, 1-m2, were located along four transects, originating at the center point and oriented perpendicular to each other. Within each quadrat the percentage of cover of understory vegetation, exposed mineral soil, exposed rock, and tree trunks and roots was estimated, as was the cover of organic litter, whether under vegetation or not, and the cover o f each vascular plant species, and of mosses and lichens, each as a group. Cover estimates were in 10% coverage classes between 10% and 100% and to the closest percent if under 10%. Within each quadrat the thickness of the surface organic horizons was also measured. Where the only organic matter consisted of this year's leaf fall, due to removal of litter by annual floods, this variable was considered missing. Two penetration resistance readings were also taken, with a pocket soil penetrometer, in each quadrat. On each site, eight soil samples were collected with a T u b e Density Soil Sampler (Model CN-1025 with 7.6 cm diameter, 7.6 cm high tubes). Four were located in the highly impacted central part of the site; four others were taken in peripheral parts of the site. Samples were placed in sealed plastic bags, for later calculation of moisture content and stone-free bulk density. Control sites were circular with a total area of 30 m ~. T h e cover o f understory vegetation, exposed mineral soil, exposed rock, tree trunks and roots, litter (whether under vegetation or not), each vascular plant species, and mosses and lichens was estimated for the entire control. T r e e reproduction was counted in a 50-m 2 circle. Twenty regularly distributed measurements of surface organic horizon thickness, where more than one year's accumulation existed, as well as 20 penetration resistance readings, were taken. Finally, four soil samples were collected to determine moisture content and bulk density.
Data Analysis T h e amount o f change that has occurred on recreation sites is inferred by comparing these sitesIand as-
Recreation Impacts in Some Riparian Forests
sociated controls. Two different estimates were used. Absolute difference is the difference between recreation site and control. This was the preferred measure of change where conditions on different control sites were not highly variable. Where conditions on control sites were variable, relative difference--absolute difference as a percentage of control m e a s u r e s - - w a s used. Beyond the calculation of simple descriptive statistics, such as means, medians, and ranges, two synthetic indexes were calculated and tree reproduction was expressed on a density basis. One index was for tree damage (Marion and Merriam 1985a) and was calculated as follows: I n d e x = ((number of trees in "no damage" category) + (2 x number of trees in slight damage category) + (3 x number of trees in moderate category) + (4 x number of trees in severe category)) / total number of trees excluding stumps T h e second index was for the difference in the g r o u n d c o v e r species composition of recreation sites and controls (Cole 1978). It was calculated as follows: Floristic Dissimilarity = 0.5 ~ [Pl - P2[ where Pl = the mean relative cover of a given species on the recreation site and p~ = the relative cover of the same species on the control T w o different analyses were used to determine the statistical significance of results. T h e first analysis involved testing whether conditions on the recreation site were different from those on the control. Most parameters did not meet the assumptions required to use parametric tests. Consequently, medians are reported as m e a s u r e s o f central tendency. T h e Wilcoxon matched-pairs, signed-ranks test was used to test the null hypothesis that recreation sites were identical to controls, except where data were normally distributed; in these cases, a paired t-test was used. T h e second set of tests evaluated whether differences in amount of use, type of use, or environment were related to amount of impact. T o test the null hypotheses that these differences had no effect on amount o f impact Mann-Whitney tests were used, except in the few cases where data were normally distributed. In those cases, t-tests were used. In all tests, a significance level o f 0.05 was used.
Results Amount of Impact Impacts were pronounced in all three o f these Park
1 01
units (Figure 1). T h e only parameters for which differences between recreation sites and controls were not statistically significant were percentage of rock cover and soil moisture levels. T h e size o f the disturbed area varied greatly between sites and park units (Table 1). T h e largest sites were those at New River, with a median and maxi m u m size of 286 m 2 and 791 m s, respectively. Sites were typically smallest, at U p p e r Delaware, with a median of 177 m s and one site only 45 m s in area. T h e size of the devegetated area also tended to be largest at New River (median of 118 m s) and smallest at U p p e r Delaware (median of 87 mS), although the site with the largest devegetated area (696 m s) was at Delaware Water Gap. Shoreline disturbance was greatest at sites in New River (median of 20 m), as was the quantity of litter--nearly a full 33-gallon garbage bag on the typical site. Improperly disposed h u m a n waste was most evident on sites at U p p e r Delaware. One reason for higher levels of cleanliness at Delaware Water Gap sites is weekly cleanup by rangers and the presence of trash barrels and toilets at several of the more popular camping areas. Amount of tree damage was greatest at Upper Delaware; both the number (median of 12 trees) and percent (100%) of damaged trees was greatest there. Damage to standing trees was least pronounced on sites at New River, where the median tree damage index was only 1.9, compared with 2.2 at Delaware Water Gap and 2.8 at Upper Delaware; however, New River sites had the most felled trees. Perhaps, at New River, trees are felled once they are damaged. I f so, trees are felled by users; park rangers have not been felling trees. More than 90% o f tree reproduction has been eliminated on sites at New River and Delaware Water Gap, but close to 50% survives on U p p e r Delaware sites. Sites at U p p e r Delaware h a d also lost less vegetation cover than sites at the other park units. Median cover loss was only 76% on U p p e r Delaware sites, compared to 89% and 94% on Delaware Water Gap and New River sites, respectively. Compositional changes were also less pronounced on U p p e r Delaware sites. Floristic dissimilarity values were 80% on both New River and Delaware Water Gap sites, but only 64% on U p p e r Delaware sites. In all three units, many sites lack a permanent organic horizon because loose organic matter is removed by frequent flooding. Consequenfly, when trampling eliminates vegetation cover, mineral soil is exposed over most of the site. Although soil exposure was negligible on control sites, the median soil exposure was about 75% on New River and Delaware Water Gap sites and 50% on U p p e r Delaware sites. On those sites
102
D.N. Cole and J. L. Marion
Figure 1. A designated campsite at Delaware Water Gap, exhibiting pronounced loss of vegetation cover and exposure of mineral soil. Not included in our survey, this site has only been opened to use for several months. with organic horizons, about 0.5 cm remains on sites in all three areas, although the amount lost varies from a median o f I. 1 cm at Delaware Water Gap to only 0.3 at Upper Delaware. Thin organic horizons are often associated with pronounced compaction of the mineral soil, because organic m a t t e r cushions the soil f r o m trampling stresses (Marion and Merriam 1985b). Both penetration resistance and bulk density were greatest o n Delaware Water Gap sites; the increase in penetration resistance was also greatest on Delaware Water Gap sites (2.5 kg/cm2), but the increase in bulk density was greatest on U p p e r Delaware sites (0.23 g/cm3). Amount of Use T o evaluate the extent to which differences in amount o f use influence amount of impact, 11 highuse campsites at Delaware Water Gap were compared with 11 low-use campsites. Site-specific data on use levels were lacking, as they have been in virtually all studies of individual long-established wilderness campsites. Use estimates by experienced river rangerg and 9 limited use data from registration boxes (from several sites close to those included in this study) suggest that the high-use sites selected are used approximately 4 0 - 7 0 nights/year; these were the most frequently used sites on the river. Use estimates for low-use sites are 3 - I 0 nights/year. Sites were placed in use categories on the basis o f their location and estimated use, not on the basis o f apparent amount o f impact. With the exception of amount of litter and loss of organic horizons, all types of impact w e r e more pronounced on the high-use sites (Table 2). For most of
these parameters, this higher level of impact was consistent enough to be statistically significant, despite the small sample size. However, levels of impact were quite high even on the low-use sites. Differences in the areas of disturbance and devegetation were particularly pronounced. T h e median high-use site is three times the size of the median lowuse site; the median devegetated area is four times larger on high-use sites than on low-use sites. Shoreline disturbance, which is absent on most low-use sites, is typically about 10 m on high-use sites. T h e amount of trash left on sites is similarwprobably reflecting the regular ranger cleanup of sites, but human waste is more evident around high-use sites. T r e e damage is also more pronounced on the highuse sites. This is expressed most succinctly in the tree damage index, which was 2.8 on high-use sites and 2.1 on low-use sites. On most high-use sites, all of the trees have experienced at least slight damage. Typically, high-use sites had 11 damaged trees, compared to 3 on low-use sites. Felled trees were also more common on high-use sites, although the difference was not statistically significant. Typically, 26% o f the trees on high-use sites had been felled, while only 8% of the trees on low-use sites had been felled. Groundcover differences are also dramatic. Median values for high-use sites are 5% vegetation cover, 74% mineral soil exposure, and 24% litter cover; on lowuse sites median values are 16% for vegetation, 44% for mineral soil, and 64% for litter. Typically, high-use sites lost 89% o f their vegetation, significantly m o r e than the median 68% lost on low-use sites. Change in species composition is nearly complete (median flo-
103
Recreation Impacts in Some Riparian Forests
Table 1. Amount of impact on recreation sites at New River Gorge, Delaware Water Gap, and Upper Delaware River.
Table 2. Differences between 11 high- and 11 low-use campsites at Delaware Water Gap National Recreation Area. Amount of use
Park Service unit
Impact parameter
New River N = 16
Delaware Water Gap N = 29
Upper Delaware N = 10
Disturbed area (m2) Devegetated area (m2) Shoreline disturbance (m) Litter (number of trash bags) Human waste (number of sites) Damaged trees (number/site) Damaged trees (%) Felled trees (%) Tree damage index Floristic dissimilarity (%) Seedlings (stems/ha) Relative difference (%) Vegetation cover (%) Relative difference (%) Soil exposure (%) Absolute difference (%) Organic litter cover (%)" Relative difference (%) Organic thickness (cm)" Absolute difference (cm) Penetration resistance (kg/cm ~) Absolute difference (kg/cm ~) Bulk density (g/cms) Absolute difference (g/cm 3) Volumetric moisture (g/cm s) Absolute difference (g/cm s)
286 I 18 20 0.8 1.0 8 73 35 1.9 80 106 - 92 5 - 94 77 70 53 - 44 0.4 -0.9 2.3 1.8 1.24 0.18 19 4
184 90 7 0.1 0.5 9 81 18 2.2 80 314 - 95 6 - 89 73 71 47 - 39 0.4 - 1.1 2.9 2.5 1.26 0.16 18 0
177 87 I0 0.4 1.5 12 100 I1 2.8 64 936 - 54 23 - 76 48 48 40 - 58 0.5 -0.3 2.1 1.9 I. 15 I).23 23 2
aValues for those sites with an organic horizon (1 at New River. I3 at Delaware Water Gap, 5 at Upper Delaware River).
ristic dissimilarity of 90%) on high-use sites; on lowuse sites median floristic dissimilarity is only 50%. Exposure of mineral soil is also considerably more pronounced on high-use sites--74% on high-use sites compared to 44% on low-use sites. Some of the soil impacts are more pronounced on high-use sites, while others are not. Although soil exposure is more pronounced on high-use sites, loss of organic horizon cover and depth is not consistently greater. T h e small sample size and the confounding effect o f frequent flooding may contribute to this surprising result. Elsewhere, disturbance of organic horizons has been much more severe on high-use sites (Cole and Fichtler 1983, Marion and Merriam 1985a). T h e median increase in penetration resistance is about 50% higher on high-use sites--2.9 kg/cm 2 compared to 1.9 kg/cm 2, a statistically significant difference. T h e median increase in bulk density is also about 50% higher on high-use sites--0.23 g/cm 3 compared to 0.16 g/cm 3, but this difference is not statistically significant. In sum, high-use sites are substantially more severely impacted than low-use sites. They are larger, have experienced more tree damage, loss of tree re-
Impact parameter Disturbed area (ms) Devegetated area (ms) Shoreline disturbance (m) Litter (number of trash bags) Human waste (number of sites) Damaged trees (number/site) Damaged trees (%) Felled trees (%) Tree damage index Floristic dissimilarity (%) Seedlings--relative difference (%) Vegetation cover--relative difference (%) Organic litter cover~--relative difference (%) Soil exposure--absolute difference (%) Organic horizon thicknessa absolute difference (cm) Penetration resistance--absolute difference (kg/cm2) Bulk density--absolute difference (g/cm3)
High
Low
90 288 165 43 0 10 0.1 0.1 0 1 11 3 71 100 8 26 2.1 2.8 90 55 -76 -96
pb .004* .006 .002 .405 .045 .030 .026 .129 .003* .030 .065
- 89
-68
.050
- 39
-33
.228
74
44
.125"
-0.5
- 1.1
.365
2.9
1.9
0.23
0.16 .106"
.004*
*Values are for those with an organic horizon (5 high- and 3 low-use sites). bSignificance was tested with Mann-Whitney tests or, for those denoted by an asterisk, with t-tests, p > 0.05 is not significant.
production and groundcover alteration, and their soils are m o r e compacted. While the high-use sites are clearly more highly impacted, the low-use sites have also been dramatically altered by recreational use. Conditions on low-use sites are more similar to those on high-use sites than to conditions on control sites, despite the fact that high-use sites are used many times more often than low-use sites.
Environmental Differences Certain tree species, groundcover vegetation, and soil types are more susceptible to being damaged than others. Because all campsites are located close to rivers, under closed tree canopies, environmental variability is relatively limited. O n e major difference at Delaware Water Gap was that certain sites located close to the river are flooded on an annual basis; other sites are located on higher benches that are rarely, if ever, flooded. This difference has a pronounced influence on composition of the overstory and groundcover, soil organic matter, and characteristics~ of the mineral soil. T o evaluate whether or not this differ-
104
D.N. Cole and J. L. Marion
ence influences amount of impact, we compared nine lowland and nine upland sites. Lowland sites were located less than 5 m above and 25 m from the level of the river in summer; upland sites were located more than 5 m above and 17 m from the river; all were high-use sites. T h e only substantial difference between upland and lowland sites is the greater size o f upland sites. T h e disturbed area of the median lowland site (172 m 2) is less than the area of the smallest upland site; the median disturbed area for upland sites is 409 m 2. T h e median devegetated area is also much higher on upland sites (308 m 2) than lowland sites (90 m2); however, upland sites do not always have more devegetated area and, consequently, upland and lowland sites are not significantly different. T h e large size Of upland sites results from the abundance o f flat terrain, without thick, tall vegetation, underneath a dense tree canopy. These characteristics prov!de little resistance to campsite expansion, in contrast to the more uneven topography and dense tangle of vegetation commonly found on lowland sites. T h e r e is no clear distinction between locations in the prevalence of tree damage. Upland sites have more damaged t r e e s m a median of 24 trees, as opposed to 10 damaged trees on lowland sites; however, they also have more undamaged trees. None of the differences in tree reproduction, groundcover conditions, or soil conditions are statistically significant. Essentially all tree reproduction and vegetation is lost on both lowland and upland sites. This lack of any sizeable differences, other than in area disturbed, is surprising, given the pronounced differences in vegetation, organic matter cover, and cycling and natural disturbance regime of these two locations.
Differences in Type of Use At New River we were able to compare site impacts caused primarily by two very different types of u s e - local fishermen and commercially outfitted rafting parties. T h e fishing sites were among the most popular on the river, but they are generally less heavily used than the outfitter sites. Thus, in this comparison, a m o u n t o f use and type of use (large outfitted raft parties o n day trips vs smaller parties o f locals, often staying overnight) both influence results. Moreover, some locals use outfitter sites and some outfitters use fishing sites; it is the predominant use that differs. Environmental conditions were roughly comparable. Areal measures of disturbance are much more pronounced on the commercial outfitter sites (Table 3). Outfitter sites are typically 50% larger than fishing sites, and the largest site, at 791 m 2, was the largest on any o f the three river segments. T h e devegetated area
Table 3. Differences between 8 sites .used primarily by local fishermen and 8 sites used by commercial rafters at New River Gorge National River. Type of use Impact parameter Disturbed area (m2) Devegetated area (m~) Shoreline disturbance (m) Litter (number of trash bags) Human waste (number of sites) Damaged trees (number/site) Damaged trees (%) Felled trees (%) Tree damage index Floristic dissimilarity (%) Seedlings - - relative difference (%) Vegetation cover--relative difference (%) Soil exposure--absolute difference (%) Penetration resistance-absolute difference (kg/cm2) Bulk density--absolute difference (g/cm3)
Fisherman Outfitter
p~
236 47 9 1.3
354 208 26 0.3
.028* .012 .016 .027
0.5 7.5 I00 33 2.0 76
1.5 7.5 64 45 1.8 86
.407 .874 .094 .908 .120* .529
- 93
- 91
.848
-83
-97
.013
64
78
.526*
1.6
2.2
.195"
0.19
0.17
.280*
*Significancewas tested with Mann-Whitney tests or, for those denoted by an asterisk, with t-tests,p > 0.05 is not significant. of the outfitter sites (median of 208 m 2) was typically more than four times that on fishing sites (47 mU). T h e shoreline distance disturbed by use was also typically about three times greater on outfitter sites. This is not surprising since the average size of outfitted parties is over 30, while the size o f fishing parties is typically fewer than 5. T r a s h - - o n e o f the most visually obtrusive impacts on recreation sites--was much less abundant on the outfitter sites. Compared to a median of 1.3 trash bags on fishing sites, the median on outfitter sites was only 0.3 bags. Clearly, the outfitters are effective in discouraging littering and/or picking up their trash. Although the median number of improperly disposed human waste sites was higher on outfitter sites, the maximum was higher on fishing sites, and differences between the two were not statistically significant. None o f the differences in amount o f tree damage were statistically significant. T h e tendency for sites at New River to have little damage to standing trees but a large proportion o f felled trees transcends differences between local fishermen and commercial outfitters. Similarly, over 90% of seedlings have been eliminated on most sites, regardless o f whether they are used by fishermen or commercial outfitters, and most of the groundcover impacts do not differ significantly be-
Recreation Impacts in Some Riparian Forests
tween these two types of sites. T h e major exception is vegetation loss, which is substantially more pronounced on outfitter sites (median 97% loss) than on fishing sites (83% loss). More mineral soil is also exposed on outfitter sites, although this difference is not statistically significant. Finally, there were no pronounced or significant differences in amount of impact to soils between the two classes of sites. In sum, the commercial outfitter sites have experienced more profound recreational impacts than the fishing sites. T h e fishing sites have more trash, but the outfitter sites have more of the types of impact that are unusually pronounced on New River sites; in particular, they are very large and almost entirely devegetared.
Discussion and Conclusions Comparisons with Other Areas Many of these results can be readily compared with those obtained in studies of campsites in the Eagle Cap (Cole 1982), Bob Marshall (Cole 1983), and Boundary Waters Canoe Area Wildernesses (Marion and Merriam 1985a), because similar methods were used. Some results can be compared with those from a study o f campsites at Grand Canyon National Park (Cole 1986), but methods sometimes differed. Use levels differed between these areas, however. We estimate that median use levels on the sites examined were highest on New River sites, followed by those at Grand Canyon, Boundary Waters, Delaware Water Gap, Eagle Cap, Upper Delaware, and Bob Marshall. As will become clear during the following discussion, these differences in amount of use do little to explain differences in amount of impact. T h e median size of disturbance on sites in the three eastern areas is similar to that in the Eagle Cap (193 m 2) and Boundary Waters Canoe Area Wildernesses (220 m2), but much smaller than in the Bob Marshall Wilderness (405 m~), where use of packstock greatly increases the disturbed area. T h e devegetated area, however, is often larger than in the Eagle Cap (87 m 2) and is much larger than in the Bob Marshall (14 m 2) and the Grand Canyon (32 m~). The single most unique characteristic of sites in all three of these Park units was the dramatic increase in mineral soil exposure. Increases o f about 70% on New River and Delaware Water Gap sites and 48% on Upper Delaware sites can be compared with increases of 7% on Bob Marshall sites, 10% on Boundary Waters sites, and 25% on Eagle Cap sites. This unusually high level o f impact results from severe loss o f a relatively fragile vegetation cover and the removal of Organic horizons by flooding. Despite this high level of soil exposure,
105
the magnitude o f impacts to the mineral soil is comparable to what has been found elsewhere. Several other types of impact were less pronounced on sites in some o f these units than has been reported elsewhere. Damage to standing trees was unusually low on New River sites. For example, the median tree damage index at New River (1.9) is much lower than that on even low-use Boundary Waters sites (2.6), despite the fact that sites are close to three times as large and have lost about twice the vegetation cover. T h e median number of damaged trees on New River sites (9 trees) is also less than the medians of 12 and 63 trees on Eagle Cap and Bob Marshall sites. T r e e felling is particularly pronounced on New River sites, however. Sites at Delaware Water Gap also have" relatively low levels o f tree damage, but those at the Upper Delaware have levels as high as in other areas. This low incidence of tree damage, particularly at New River, may result from the frequent felling of damaged trees, but it might also reflect a difference in the behavior of users. We noticed, while working, that there was much less random hacking of trees and carving of initials than in western areas or the Boundary Waters. Perhaps such a behavioral norm could be transferred to these other areas. Compared with a loss of only 54% of tree reproduction on sites at Upper Delaware, sites elsewhere have typically lost more than 90%. T h e lesser extent of damage to tree reproduction at Upper Delaware may reflect low-use levels on these sites, where all camping is trespass use. Our perception was that these sites were recovering somewhat from heavier use in the past. Impacts on these riparian forest sites in the eastern United States, then, are quite similar to those found on campsites in wilderness areas in the mountainous western states a n d northern Minnesota. T h e r e is nothing about impact levels to suggest that these sites are less fragile than sites in harsher environments. In fact, groundcover disturbance--loss o f Vegetation and exposure of mineral soil--has been unusually severe, especially on New River sites. T h e nature of the general relationship between amount of impact and amount of use can also be compared with that found in the Eagle Cap and Boundary Waters studies. In each study, high-use sites received close to an order of magnitude more use than low-use sites and category definitions were roughly comparable. T h e statistical significance of resul~s varied between areas, probably primarily because the sample size was smaller at Delaware Water Gap than in the Boundary Waters study and larger than in the Eagle Cap study; however, the magnitude o f differences between high- and low-use sites were generally compa-
106
D.N. Cole and J. L. Marion
rable. For example, in each place high-use sites were three or four times the size of low-use sites, and vegetation loss is about 20% greater on high-use sites. T h e most divergent response was the lack of a more severe reduction in organic horizons on high-use sites at the Delaware Water Gap. This response was probably complicated by the irregular distribution of organic horizons and the effects of removal by floods. T h e importance of the environmental differences on Delaware Water Gap sites and of differences in type o f use on New River sites cannot be readily compared with other places. T h e importance of environmental differences is clearly determined by both the magnitude o f these differences and whether or not sizeable environmental differences result in sizeable differences in fragility; two very different, envir0iiments may be comparable in terms of fragility. Nevertheless, the major difference between various environments at both the Delaware Water Gap and the Grand Canyon and between sites used b~/different types o f user at both New River and the Bob Marshall was in the areal extent o f disturbance and devegetation. Both at Delaware Water G a p and Grand Canyon, the roughness of terrain varied between locations. Roughness, by determining the ease of site expansion, is clearly an important environmental d e t e r m i n a n t of a m o u n t of impact. T h e larger area of impact on sites used by outfitted parties probably results from large party sizes and the tendency for unaffiliated subgroups, within a large outfitted party, to spread out more than smaller groups of friends and family. It made little difference whether outfitted parties traveled in rafts, as at New River, or on horseback, as in the Bob Marshall. Conclusions These results lead us to conclude that there is nothing about the nature and magnitude of recreation site impacts in these riparian forests that suggests they would profit f r o m unique management strategies. Despite much more favorable growing conditions and more fertile soils than sites in most wilderness areas of the western United States and northern Minnesota, similar management practices are called for. Confining recreational use to a small number of sites is the optimal strategy for minimizing impact wherever use exceeds negligible levels. This strategy has already been offidally adopted at Delaware Water Gap, where camping is only allowed on designated sites. Most use at New River also occurs on a small number of sites because each commercial outfitter tends to use the same picnic site every day. Management actions to limit the size of individual
sites are also of critical importance. Campsites tend to become very large where use levels are high, where groups are outfitted, and where the environment presents little resistance to expansion. Again, this situation is similar to what has been found elsewhere. Although we have little data at the present time, the characteristic of these campsites that is different is their ability to recover from impact. Favorable growing condidons and fertile soils are reflected more in high resilience than in high resistance. We observed several sites at Delaware Water Gap that had been heavily impacted less than 10 years ago but cannot be identified today because they are covered with dense vegetation. Along the New River, mining towns abandoned less than a half-century ago are no longer evident to the casual observer. Studies o f closed campsites in western wilderness areas, in contrast, have found minimal recovery over 3 - 5 year periods (Cole and Ranz 1983, Stohtgren and Parsons 1986). In a separate long-term study at Delaware Water Gap, we are documenting these more rapid recovery rates on campsites we have closed and on sites that have received carefully controlled levels of trampling. We are also documenting rates of deterioration on newly opened campsites (Figure 1) and in controlled trampling experiments. Results, after one year, indicate considerable recovery; however, deterioration still occurs much more rapidly than recovery, Unfortunately, the ability to recover rapidly following disturbance is of little relevance to management of established sites that receive more than very low levels o f use. T h e principal implication of rapid recovery rates is that if unacceptable impacts do occur or if impacts occur in undesired places, these problems can be corrected relatively rapidly. Management does not have to be as conservative as in places where recovers/ requires decades or centuries. Still, given the fragility of these sites there is little opportunity to pursue management strategies such as dispersing use among a number of sites or practicing "rest-rotation" of campsites, except where use levels are much lower than they are in these park units. T h e absence of more reliable use data for individual recreation sites did not allow us to precisely identify use thresholds below which impacts are substantially reduced. We hope to identify these thresholds in our studies o f newly opened campsites and our controlled trampling experiments. Comparisons o f these thresholds with those identified in other areas will further improve understanding o f site-specific differences in the nature and magnitude o f recreational impacts and the management implications of these differences.
Recreation Impacts in Some Riparian Forests
Acknowledgments Financial support for this study was provided by the U S D I National Park Service, Mid-Atlantic Regional Office and was facilitated by a cooperative a g r e e m e n t with the U S D A Forest Service, N o r t h Central Forest E x p e r i m e n t Station. We appreciate the dedicated assistance o f Sharon T i m k o in the field, lab, and office and the logistical support o f Park Service staffs.
Literature Cited Bratton, S. P., M. G. Hickler, and J. H. Graves. 1978. Visitor impact on backcountry campsites in the Great Smoky Mountains. EnvironmentalManagement 2:431-442. Cole, D.N. 1978. Estimating the susceptibility of wildland vegetation to trailside alteration. Journal of Applied Ecology 15:281-286. Cole, D.N. 1982. Wilderness campsite impacts: effect of amount of use. USDA Forest Service Research Paper INT-284, Ogden, Utah, 34 pp. Cole, D. NI 1983. Campsite conditions in the Bob Marshall Wilderness, Montana. USDA Forest Service Research Paper INT-312, Ogden, Utah, 18 pp. Cole, D.N. 1986. Recreational impacts on backcountry campsites in Grand Canyon National Park, Arizona, USA. Environmental Management 10:651-659.
107
Cole, D.N. 1987. Research on soil and vegetation in wilderness: a state-of-knowledge review. Pages 135-177 in R. C. Lucas (comp.), Proceedings, national wilderness research conference: perspectives, state of knowledge, and future directions. USDA Forest Service General Technical Report INT-220, Intermountain Research Station, Ogden, UT. Cole, D.N., and R. K. Fichtler. 1983. Campsite impact on three western wilderness areas. Environmental Management 7:275-288. Cole, D. N., and B. Ranz. 1983. Temporary campsite closures in the Selway-Bitterroot Wilderness. Journal of Forestry 81:729-732. Marion, J. L., and L.C. Merriam. 1985a. Recreational impacts on well-established campsites in the Boundary Waters Canoe Area Wilderness. University of Minnesota Agricultural Experiment Station Bulletin AD-SB-2502, St. Paul, Minnesota, 16 pp. Marion,J. L., and L. C. Merriam. 1985b. Predictability of recreational impact on soil. Soil ScienceSocietyof AmericaJournal 49:751-753. Merriam, L.C., Jr., C.K. Smith, D.E. Miller, and others. 1973. Newly developed campsites in the Boundary Waters Canoe Area: a study of 5 years' use. University of Minnesota Agricultural Experiment Station Bulletin 511, St. Paul, Minnesota, 27 pp. Stohlgren, T.J., and D.J. Parsons. 1986. Vegetation and soil recovery in wilderness campsites closed to visitor use. Environmental Management 10:375- 380.
