ABSTRACT. outdoor recreation. Contemporary carrying capacity frameworks rely on formulation of

Transcription

1 ABSTRACT Day Use Social Carrying Capacity Estimating Day Use Social Carrying Capacity in Yosemite National Park Carrying capacity has been a long standing issue in management of parks and outdoor recreation. Contemporary carrying capacity frameworks rely on formulation of indicators and standards of quality of the recreation experience to define and manage carrying capacity. This paper describes a program of research to support application of carrying capacity to Yosemite Valley, the scenic heart of Yosemite National Park, USA. Research included 1) a series of visitor surveys at selected sites within Yosemite Valley to identify indicators and standards of quality, 2) development of computer simulation models of visitor use at study sites to estimate maximum daily use levels without violating standards of quality, and 3) a park exit survey to determine the percentage of day users at study sites. Study findings are used to estimate a range of day use carrying capacities at study sites and for Yosemite Valley as a whole. Keywords: Carrying capacity; indicators and standards of quality; Yosemite National Park Estimating Day Use Social Carrying Capacity in Yosemite National Park 1

2 Carrying Capacity The question of how much public use can be accommodated in a national park or related area is often framed in terms of carrying capacity. Indeed, much has been written, in both the scientific literature and popular press, about the carrying capacity of national parks (Stankey and Manning 1986; Mitchell 1994; Wilkinson 1995; Manning 2001). The underlying concept of carrying capacity has a rich history in the natural resource professions. In particular, it has been applied in wildlife and range management where it refers to the number of animals that can be maintained in a given habitat (Dasmann, 1964). Carrying capacity has obvious parallels and intuitive appeal in the field of park management. In fact, it was first suggested in the mid-1930s as a park management concept in the context of national parks (Sumner, 1936). However, the first rigorous applications of carrying capacity to management of parks and outdoor recreation did not occur until the 1960s. These initial scientific applications suggested that the concept was more complex in this new management context. At first, as might be expected, the focus was placed on the relationship between visitor use and environmental conditions. The working hypothesis was that increasing numbers of visitors cause greater environmental impact as measured by soil compaction, destruction of vegetation, and related variables. It soon became apparent, however, that there was another critical dimension of carrying capacity dealing with social aspects of the visitor experience. Wagar (1964), for example, in his early and important monograph on the application of carrying capacity to outdoor recreation, reported that his study was initiated with the view that carrying capacity of recreation lands could be determined primarily in terms of ecology and the deterioration of areas. However, 2

3 it soon became obvious that the resource-oriented point of view must be augmented by consideration of human values. Wagar s point was that as more people visit a park, not only can the environmental resources of the area be affected, but the quality of the visitor experience as well. Again, the working hypothesis was that increasing numbers of visitors cause greater social impacts as measured by crowding and related variables. Thus, as applied to national parks, carrying capacity has two components: environmental and social. The early work on carrying capacity has since blossomed into an extended literature on the impacts of outdoor recreation and their application to carrying capacity (e.g., Lime and Stankey, 1971; Stankey and Lime, 1973; Graefe et al., 1984; Manning, 1985; Shelby and Heberlein, 1986; Kuss et al., 1990; Hammitt and Cole 1998; Manning, 1999). But despite this growing scientific literature, efforts to determine and apply carrying capacity to areas such as national parks have sometimes failed. The principle difficulty lies in determining how much impact, such as crowding, is too much. Theoretical development, backed up by empirical research, generally confirms that increasing use levels and encounters among visitors leads to increased environmental and social impacts. But how much impact should be allowed in a national park? This basic question is often referred to as the limits of acceptable change (Lime, 1970; Frissell and Stankey, 1972). Given substantial demand for public use of a national park, some decline or change in the quality of park resources and the visitor experience appears inevitable. But how much decline or change is acceptable or appropriate before management intervention is needed? This issue is illustrated graphically in Figure 1. This figure addresses the social impact of crowding. In this figure, a hypothetical relationship (line A) between visitor use and crowding is shown. It is clear from this figure that visitor use and crowding are 3

4 related: increasing numbers of visits cause visitors to feel increasingly crowded. However, it is not clear at what point carrying capacity has been reached. The hypothetical relationship in Figure 1 suggests that some crowding is inevitable, given even relatively low levels of visitor use. Thus, some level of crowding must be tolerated if national parks are to remain open for public use. For the relationship defined by line A, X 1 and X 2 represent levels of visitor use that result in differing levels of crowding as defined by points Y 1 and Y 2, respectively. But which of these points Y 1 or Y 2, or some other point along this axis represents the maximum amount of crowding that is acceptable? Ultimately, this is a value judgment. Again, the principal difficulty in carrying capacity determination lies in deciding how much crowding (or of some other impact) is acceptable. Empirical relationships such as that in Figure 1 can be helpful in making informed decisions about carrying capacity, but they must be supplemented with other information and, ultimately, management judgments. To emphasize and further clarify this issue, some writers have suggested distinguishing between descriptive and evaluative (or prescriptive) components of carrying capacity (Shelby and Heberlein, 1984; Shelby and Heberlein, 1986). The descriptive component of carrying capacity focuses on factual, objective data such as the types of relationships in Figure 1. For example, what is the relationship between the number of visitors entering a park and the number of encounters that occur among groups of visitors? Or what is the relationship between the level of visitor use and visitor perceptions of crowding? The evaluative or prescriptive component of carrying capacity determination concerns the seemingly more subjective issue of how much impact or change in resource conditions and the quality of the visitor experience is acceptable. For example, how many contacts between visitor groups are appropriate? What level of perceived crowding should be allowed before management intervention is needed? 4

5 Recent experience with carrying capacity suggests that answers to the above questions can be found through formulation of management objectives and development of associated indicators and standards of quality (Stankey et al., 1985; Graefe et al., 1990; Manning, 1997; National Park Service 1997; Manning, 1998; Manning et al., 1998). This approach to carrying capacity focuses principal emphasis on defining the degree of resource protection and the type of visitor experience to be provided and maintained, monitoring conditions over time, and adopting management practices to ensure that acceptable conditions have been maintained. Management objectives are broad, narrative statements that define the degree of resource protection and the type of visitor experience to be provided. They are based largely on review of the purpose and significance of the area under consideration. Formulation of management objectives may involve review of legal, policy and planning documents; consideration by an interdisciplinary planning and management team; historic precedent; local, regional, national or international context of the park; and public involvement. Indicators of quality are measurable, manageable variables that reflect the essence or meaning of management objects; they are quantifiable proxies or measures of management objectives. Indicators of quality may include elements of both the biophysical and social environments. Standards of quality define the minimum acceptable condition of indicator variables. An example of management objectives, indicators and standards may be helpful. Review of the U.S. Wilderness Act of 1964 suggests that areas of the national park system contained in the National Wilderness Preservation System are to be managed to provide opportunities for visitor solitude. Thus, providing opportunities for solitude is an appropriate management objective for most wilderness areas. Moreover, research on 5

6 wilderness use suggests that the number of visitors encountered along trails and at campsites is important to wilderness visitors in defining solitude. Thus, trail and camp encounters may be good indicators of quality and help to make the general management objective of solitude more operational. Further research suggests that wilderness visitors may have normative standards about how many trail and camp encounters are acceptable before the quality of the visitor experience declines to an unacceptable degree (Heberlein et al., 1986; Vaske et al., 1986; Whittaker and Shelby, 1988; Roggenbuck et al., 1991; Shelby and Vaske, 1991; Lewis et al., 1996; Manning et al., 1996a; Manning et al., 1996b; Manning et al., 1999). Such data may help to define standards of quality. By defining indicators and standards of quality, carrying capacity can be determined and managed through an associated program of monitoring and management. Indicators of quality can be monitored and management actions taken to ensure that standards of quality are maintained. If monitoring suggests that standards of quality have been violated, then carrying capacity has been exceeded and management action is required. This basic approach to carrying capacity is central to contemporary park and outdoor recreation management frameworks, including Limits of Acceptable Change (LAC) (Stankey et al., 1985), Visitor Impact Management (VIM) (Graefe et al., 1990), and Visitor Experience and Resource Protection (VERP) (National Park Service 1997). When feasible, the above approach to carrying capacity might be supplemented by computer simulation modeling. Computer simulation models of park use have been developed to estimate the relationship between park use levels and selected indicators of quality, such as the number of encounters among hiking groups (Smith and Krutilla, 1976; Schechter and Lucas, 1978; Manning and Potter, 1984; Potter and Manning, 1984; Wang and Manning, 1999). Such models could be used to estimate the maximum use 6

7 level that could be accommodated in a park (or sites within a park) without violating specified standards of quality. In this way, carrying capacity could be estimated. Study Objectives The purpose of this study was to gather information to support application of the concept of carrying capacity to Yosemite National Park. The study was focused on social carrying capacity of Yosemite Valley for day use. The study had three specific objectives: 1. Formulate indicators and standards of the quality of the visitor experience at selected sites within Yosemite Valley. 2. Develop a series of computer simulation models to estimate the maximum daily visitor use levels of each study site without violating crowding-related standards of quality. 3. Estimate maximum daily visitor day use levels of Yosemite Valley based on the percentage of day users who visit each of the study sites. Study Methods Setting Yosemite Valley in the scenic heart of Yosemite National Park, arguably the first national park in the United States, and certainly one of America s best known and most popular national parks (Runte, 1987; Runte, 1990). Yosemite Valley is a glacially carved area of approximately seven square miles and features sheer granite walls of up to five thousand feet and several of the world s highest waterfalls. Yosemite National Park draws over four million visits annually, and carrying capacity has been a longstanding and controversial issue. Day use carrying capacity is of special concern because overnight accommodations in Yosemite Valley are fixed at current levels by park policy. 7

8 Indicators and Standards of Quality Three elements of research were conducted. The first focused on gathering data that would help formulate indicators and standards of quality for the visitor experience at strategic locations in and around Yosemite Valley. Seven sites were studied, including the base of Yosemite Falls, the trail to the base of Yosemite Falls, the base of Bridalveil Fall, the trail to the base of Bridalveil Fall, the trail to Vernal Fall, the trail to Mirror Lake, and Glacier Point. These sites were chosen in conjunction with park staff and represent a diversity of places that are important to visitors and to the park. At each of these locations a survey of a representative sample of visitors was conducted. Respondents were selected and contacted by a trained surveyor, and questionnaires were self-administered. On each sampling day, the surveyor approached the first visitor who completed his or her visit, briefly described the study, and asked the visitor if he or she would be willing to participate in the study. Nearly all visitors agreed to participate. After the initial respondent completed the questionnaire, the next visitor to complete his or her visit was selected for participation, and this process continued for the duration of the sampling day. Sampling dates and sample sizes are shown in Table 1. Questionnaires administered at these sites addressed both indicators and standards of quality. Indicators of quality were addressed through a series of open- and closeended questions. Open-ended questions probed respondents for what added to or detracted from the quality of their visit to Yosemite Valley. Questions included the following: We would like to know what added to or detracted from the quality of your visit to Yosemite Valley. 8

9 a. What have you enjoyed most about your visit to Yosemite Valley today? b.what have you enjoyed least about your visit to Yosemite Valley today? c. If you could ask the National Park Service to improve some things about the way visitors experience Yosemite Valley, what would you ask managers to do? Close-ended questions asked respondents to rate the seriousness of several potential problem issues. Using a response scale that ranged from 1( Not a problem ) to 3 ( Big problem ), respondents were asked to rate the seriousness of the following potential problems: traffic congestion on roads, difficulty finding a parking place, inconsiderate drivers, too many tour buses, too many people on trails, too many people at places like the base of Yosemite Falls, too much noise, too many rules and regulations. Standards of quality focused on crowding-related issues, including the number of people on trails and at attraction sites. A series of questions measured visitor crowding norms. Since use levels are relatively high in Yosemite Valley, a visual approach was used to measure crowding norms (Manning et al. 1996). A series of computer-edited photographs was prepared for each study site showing a range of visitor use levels. Study photographs are shown in Figure 2. Respondents were asked to rate the acceptability of each photograph on a scale that ranged from +4 ( very acceptable ) to -4 ( very unacceptable ) and included a neutral point of 0 (only the anchor points of this numerical 9

10 scale were labeled narratively). In addition, respondents were asked to judge the photographs using several other dimensions of evaluation to gain additional insights into how respondents judge alternative use levels (Manning et al. 1999). These included preference ( Which photograph shows the level of use that you would prefer to see? ), tolerance ( Which photograph shows the level of use that would be so unacceptable that you would no longer visit [this site]?), and management action (Which photograph shows the highest level of use that the National Park Service should allow? In other words, at what point should people be restricted from visiting [this site]? ). Computer Simulation Model The second element of research focused on developing a series of computer-based simulation models of visitor use at all study sites. The models were built using the commercial simulation package, Extend by Imagine that, Inc. Extend is an objectoriented, discrete-event dynamic simulation package that has been used extensively in business, manufacturing, and electronics applications to improve quality and efficiency. The object orientation makes code writing unnecessary, and the programming algorithm can easily be expressed by the graphic display of objects and connections. For example, Figure 3 shows the top layer of the simulation model developed for Glacier Point. The model was built with a series of blocks to represent components of this study site. The block labeled Hiker Generator in the top left section of the model is where simulated visitors are generated. Connected to it are groups of blocks that provide data concerning empirical visitor arrival rates and group sizes. (These data are derived from field observation.) The block Total Use allows the researcher to specify the daily total visit use level to be simulated. The simulated visitors then spend a randomly assigned length of time (based on field observations) at the Viewing Area block which represents the 10

11 Glacier Point visitor attraction. The associated blocks (those underneath the Viewing Area block) measure the number of people-at-one-time (PAOT) at the Glacier Point viewing area. A more detailed description of this computer simulation modeling approach can be found in Wang and Manning (1999). Model input was based on detailed counts and observations of visitor use at each study site during the summers of 1998 and Variables included length of trails, length of typical trail viewscapes (how far along the trail a hiker can typically see), number of visitors arriving per hour, visitor group size, length of time visitors stop at attractions, and the speed at which visitors hike trails. Model output was the number of people-at-one-time (PAOT) at attraction sites and the number of people-per-viewscape (PPV) along trails, and these model outputs corresponded to the crowding-related normative standards measured using the study photographs described above. Resulting simulation models were designed to estimate PAOT and PPV for alternative total daily use levels. In this way, maximum total daily use levels could be estimated for each study site without violating alternative standards of quality. In effect, these maximum total daily use levels are estimates of social carrying capacity for each study site. Percentage of Day Users The final element of research focused on applying carrying capacity estimates specifically to day users. As noted earlier, overnight visitor capacity of Yosemite Valley is fixed at current levels by park policy. Application of carrying capacity estimates to day users required two types of information. First, the percentage of day users at each study site was determined by a short series of questions in the visitor questionnaires described above. Respondents were simply asked if they had spent last night or were planning to spend tonight in Yosemite Valley. Second, the percentage of day visitors to Yosemite Valley who visit each of the study sites was determined through a park exit 11

12 survey. Visitors exiting the park were randomly selected and administered a short questionnaire that asked if they were day visitors to the park and, if so, had they visited each of the study sites. Exit surveys were conducted by personal interview with visitors during August, Study Findings: Estimates of Day Use Carrying Capacity Indicators and Standards of Quality The first element of research yielded information on potential indicators and standards of quality for the visitor experience in Yosemite Valley. Crowding-related issues, particularly the number of visitors on trails and at attraction sites, emerged as potentially important indicators of quality. In the open-ended questions, crowding was reported by respondents as the least enjoyable aspect of their visit to all study sites. Moreover, in the close-ended questions, between 45.8 and 68.1 percent of respondents across the five study sites judged too many people on the trails to be a small or big problem, and between 49.4 and 59.2 percent of respondents judged too many people at places like the base of Yosemite Falls to be a small or big problem. Data on crowding-related standards of quality are shown in Table 2. Acceptability -based standards of quality were derived by plotting average acceptability ratings for each of the visitor use levels shown in the six photographs for each study site. PAOT and PVV standards of quality shown in the table are points at which average acceptability ratings cross the 0 or neutral point on the acceptability scale (i.e., fall out of acceptable range and into the unacceptable range). Preference, management action, and tolerance -based standards of quality were derived by calculating the average number of people in the photographs selected by visitors in response to the questions described earlier. 12

13 These data suggest a potential range of standards of quality for each study site. None of the points within these ranges for each study site is more valid than any other. Each point has potential strengths and weaknesses. For example, standards of quality based on preference-related norms may result in very high quality recreation experiences but would restrict access to a relatively low number of visitors. In contrast, standards of quality based on acceptability, management action, or tolerance allow access to greater numbers of visitors but may result in recreation experiences of lesser quality. Findings that offer insights into multiple evaluative dimensions provide a rich base of information and may lead to formulation of the most thoughtful and informed standards of quality. Such data allow more explicit understanding of the potential trade-offs between use level and quality of the recreation experience. Computer Simulation Model The second element of research developed a computer-based simulation model of visitor use at each study site. These models were used to estimate the maximum total daily use levels (i.e., daily carrying capacities) that could be accommodated at each study site without violating the normative crowding standards shown in Table 2. Model output could be generated in several graphic and numerical forms. For example, Figure 4 traces minute-by-minute PPV levels along the trail to Bridalveil Fall over the duration of a day. This particular model run was generated using an average summer day total use level of 1,415 visitors (derived from the counts of visitor use taken to help construct the model). All models were run multiple times (to average out the randomness associated with each individual model run) to estimate the maximum total daily use level that could be accommodated at each study site without violating each of the crowding norms shown in Table 2 more than 10 percent of the time. (This 10 percent allowance is discussed later in this paper.) The range of daily carrying capacities for each study site is shown in Table 13

14 3. It is clear from the table that daily carrying capacities vary substantially across the range of normative standards and across study sites. Percentage of Day Users The third element of research determined the percentage of visitors at each study site who where day users, and the percentage of Yosemite Valley day users who visited each study site. The former was obtained from the survey of visitors at each study site, and the latter was obtained from the park exit survey. Findings are shown in Table 4. It is clear these figures vary substantially from site to site. Estimates of Day Use Carrying Capacity Based on findings from the three elements of this program of research, a range of daily day use carrying capacities can be estimated for Yosemite Valley as shown in Table 5. These estimates are the maximum daily number of day use visitors that can be accommodated in Yosemite Valley without violating PPV or PAOT standards of quality at each study site. The estimates are based on findings from the three elements of research described above, and are applied in three steps or mathematical calculations. First (step 1), the number of overnight visitors in Yosemite Valley at all study sites was estimated using findings from the visitor surveys and the counts of visitor use. Second (step 2), the number of overnight visitors to each study site was then subtracted from the maximum total daily use levels that can be accommodated at each study site. This leaves the maximum number of day visitors that can be accommodated at each study site. Third (step 3), this number was then expanded to account for the fact the park exit survey found that only certain percentages of all day visitors to Yosemite Valley visit each of the study sites. An example will help illustrate how these estimates were calculated. Table 2 indicates that the preference-based standard of quality along the trail to Bridalveil Fall 14

15 is 7 PPV. This number was derived from the survey of visitors to this site and respondents assessment of the photographs showing a range of visitor use levels. Table 3 indicates that a maximum of 1,200 visitors could use this trail per day without violating this preference-based standard of quality. This number was derived from the computerbased simulation model of this site. The three steps or mathematical calculations described above are then applied to derive the estimate of the daily day use carrying capacity of Yosemite Valley based on the findings for the trail to Bridalveil Fall. The number of overnight visitors at Bridalveil Fall was estimated (step 1). This was done by multiplying the percentage of day users at this site ( 77 %) (taken from the first row of Table 4) by the average daily number of all visitors to this site (3,501) (taken from the counts used to develop the computer simulation model of visitor use). From this operation, it is estimated that an average of 805 visitors to the trail to Bridalveil Fall are overnight visitors to Yosemite Valley on an average summer day. This leaves a capacity of 395 day visitors at this site (1,200 minus 805)(step 2). Finally, the number of day users that can be accommodated on the trail to Bridalveil Fall needs to be expanded to estimate the number of day users that can be accommodated in Yosemite Valley (step 3). Since only 43.4 percent of all day users who visit Yosemite Valley visit the trail to Bridalveil Fall, (taken from the second row of Table 4), this means that 910 day users can be accommodated in Yosemite Valley (395 divided by.434) without violating the preference-based standard of quality for the trail to Bridalveil Fall. Discussion The program of research described in this paper raises a number of issues regarding estimation and management of carrying capacity of parks and related areas. As noted at the beginning of this paper, an emerging principle is that carrying capacity decision-making must be guided by management objectives and associated indicators and 15

16 standards of quality. A corollary of this principle is that there is no one, inherent carrying capacity of a park or recreation area. Rather, each park (or even site within a park) has a range of capacities depending upon the degree of resource protection and type of recreation experience to be provided. Data developed in this study illustrate this point. The number of people encountered at all study sites is important to most visitors, therefore measures of PPV and PAOT are good indicators of quality. However, standards of quality for this indicator vary substantially depending upon the evaluative dimension used in the study (i.e., the type of recreation experience). Crowding norms ranged consistently (with one small exception) from a low associated with preference (a high quality experience) to a high associated with tolerance (a lower quality experience) for all study sites. The carrying capacities of these sites, and ultimately Yosemite Valley, vary accordingly. A related principle of carrying capacity is that some element of management judgment must be exercised. Again, the data developed in this study illustrate this principle. What point (or points) along the range of standards of quality and associated carrying capacities should be selected for management purposes? This is ultimately a judgment that should consider a variety of other factors inherent in carrying capacity, including the purpose and significance of the area (as may be defined in law or policy), the fragility of natural and/or cultural resources, financial and/or personnel resources available for management, historic precedent, and interest group politics. Management judgments about standards of quality and associated carrying capacities are not necessarily either/or decisions. In fact, it may be highly desirable to provide a spectrum of recreation opportunities among parks within a region. These considerations may suggest valid reasons to formulate certain standards of quality that in turn define carrying capacities. For example, there may be valid reasons 16

17 for the trail to Mirror Lake to be managed for a PPV standard of quality that is close to the preference end of the range of crowding norms identified in this study. This trail is less accessible than the other trails included in this study, has relatively low historic use levels, and traverses areas containing fragile cultural resources. The trail to the base of Yosemite Falls, however, is easily accessible, highly used, does not contain especially sensitive natural or cultural resources, and leads to an icon feature of the park that most visitors want to experience. Thus, it may be reasonable to manage this trail for a PPV standard of quality that is more toward the management action or even tolerance end of the range of standards, and therefore, for a relatively high carrying capacity. In this way, management judgments can lead to a spectrum of recreation opportunities that serve a diversity of public desires and appropriately balance competing carrying capacity considerations. However, such management judgments should be as informed as possible, based on data such as those developed in this study, and fashioned deliberately within the structured, rational context of a framework such as LAC or VERP. This approach to carrying capacity is most likely to lead to thoughtful park and outdoor recreation management that serves the needs of society and can withstand the inevitable test of public scrutiny. The carrying capacity-related data gathered in this study has potentially important implications to other components of park and outdoor recreation management. For example, Yosemite National Park is one of many national parks being considered for new or expanded public transit systems. Data on social carrying capacity of alternative sites within Yosemite Valley are instrumental in designing a transit system that will deliver the right number of visitors to the right locations at the right times. The program of research described in this paper relies on several distinctive methodological approaches. First, visitor surveys provide the empirical foundation for 17

18 the indicators and standards of quality developed, and the carrying capacities ultimately derived. This is important as it involves those who are most directly interested in the park and who have much to gain or lose as a result of park managing decisions. It may be wise, when and where feasible, to expand this research to other interest groups as well, including residents of local communities and even the general population (Manning et al. 1999). Second, a visual approach is used to measure crowding norms. A visual approach may be more realistic and valid than conventional narrative and numeric approaches (i.e., asking respondents to evaluate encountering selected numbers of other people), especially in relatively high use contexts (Manning et al. 1999). Research suggests that visitors may process some encounters with other people at a subconscious level, especially when such people are perceived to be like the respondent in terms of recreation activity, behavior, or other appearance. A visual approach to measuring crowding norms allows for such subconscious processing, while narrative/numerical approaches call explicit attention to all persons encountered. When and where feasible, visual approaches might be extended to normative evaluation of other recreation-related impacts such as resource damage to trails and campsites (Manning et al., 1996). Third, multiple evaluative dimensions (preference, acceptability, management action, and tolerance) were employed in asking respondents to evaluate alternative use densities. Resulting data are complex, but provide empirical, detailed insights into how visitors feel about alternative use levels, including how use levels affect the quality of the visitor experience, and tradeoffs visitors might make between solitude and maintaining reasonable public access to park attractions (Manning et al., 1999; Lawson and Manning, 2001). 18

19 Fourth, respondents to the surveys conducted at each study site were asked to assess the questionnaire items designed to measure crowding norms (Manning et al., In Press). Most respondents agreed that they 1) understood the questions that were asked, 2) thought the photographs realistically represented different numbers of people at study sites, 3) had confidence in their responses, and 4) agreed that the National Park Service should use data from studies like this in deciding how to manage the park. These findings support the validity of study data and suggest public support for carrying capacity decisions based on study findings. Fifth, computer simulation modeling was used to estimate carrying capacities at each study site. Contemporary carrying capacity frameworks such as LAC and VERP suggest that carrying capacity is determined through monitoring of indicators of quality. When monitoring suggests that standards of quality have been violated, carrying capacity has been reached. However, computer simulation modeling allows estimation of visitor use levels (i.e., carrying capacities) that will violate selected standards of quality. This facilitates a more proactive approach to defining and managing carrying capacity. Sixth, the study focused primarily on carrying capacity for day use. Many park and related areas have established carrying capacities for overnight visitors, and these are managed through mandatory permit systems. However, day use is often the dominant and fastest growing component of park visitation, may be responsible for substantial resource and social impact and warrants added management attention (Roggenbuck et al. 1994). Clearly, the program of research described in this paper has important limitations. First, it addresses social carrying capacity only. The resource component of carrying capacity noted at the beginning of this paper also needs research and management attention. However, the methodological approaches outlined in this paper may have 19

20 some application to the resource component of carrying capacity, or at least the interaction between these components. For example, recreation impacts to soil and vegetation at campsites have a potentially important aesthetic component, and the visual approach to measuring normative standards for such impacts may be useful in formulating standards of quality for these resource-related indicators of quality. Second, even within the social component of carrying capacity, this study addresses only crowding-related indicators and standards of quality. The visitor surveys conducted at each study site suggest the importance of crowding-related indicators, but also suggest other potential indicators of quality such as automobile traffic congestion, noise, and lack of information. Expanded treatment of other potential indicator variables and associated standards is warranted. Third, data reported in Table 2 suggest that some of the standards of quality derived in the study may be underestimated. Questions addressing the management action and tolerance dimensions of standards of quality allowed respondents to report that visitor use should not be limited at study sites or that none of the photographs used in the study were so unacceptable that respondents would no longer visit study sites. These responses could not be included in the calculation of standards of quality. The percentage of respondents selecting these response options varied from 9 to 38 percent depending upon the question and the study site. Fourth, estimation of carrying capacities from the computer simulation models allowed for standards of quality to be violated 10 percent of the time. This allowance was factored into modeling because it may not be reasonable to prescribe that standards of quality will never be violated. Park and outdoor recreation use has an inherent random element that tends to result in occasional peaks or spikes of activity or encounters. The graph in Figure 4 tracing minute-by-minute use and PPV levels for the trail to Bridalveil 20

21 Fall is representative. Occasionally, by happenstance, several visitor groups may arrive at the trailhead simultaneously, and this may result in isolated spikes in encounter levels. Total use levels would have to be kept very low to ensure that these spikes never (or rarely) occurred, and this may not serve public interests for reasonable access to parks. A 10 percent allowance was adopted in this study, but this figure was arbitrarily chosen. Additional research is warranted to derive a more empirically sound basis for specifying this allowance. Conclusions The program of research described in this paper was designed to support application of the concept of carrying capacity to day use of Yosemite Valley. In particular, it was designed to help provide an empirical foundation for application of a contemporary carrying capacity framework such as LAC and VERP. Study findings suggest crowding-related indicators of quality, a range of standards of quality for these indicator variables, and associated estimates of carrying capacity for each study site and for Yosemite Valley as a whole. Management judgments must still be rendered in choosing among alternative standards and carrying capacities, or perhaps more appropriately, in choosing a suite of standards of quality and associated carrying capacities that facilitate a spectrum of recreation opportunities in Yosemite Valley. However, study data help provide an informed basis for such management judgments. This paper also outlines principles and frameworks that underlie the theoretical foundation of carrying capacity, and describes and applies several research methods and issues that can be used to help define and manage carrying capacity. This discussion, and its application to Yosemite Valley may provide guidance for future applications of carrying capacity and a program of research that is needed to support this work. 21

22 Literature Cited Day Use Social Carrying Capacity Dasmann, R. (1964). Wildlife Biology. New York: John Wiley and Sons. Frissell, S., and Stankey, G. (1972). Wilderness environmental quality: Search for social and ecological harmony. Proceedings of the Society of American Foresters Annual Conference, Hot Springs, AR: Society of American Foresters, Graefe, A., Vaske, j., and Kuss, F. (1984). Social carrying capacity: An integration and synthesis of twenty years of research. Leisure Sciences, 6, Graefe, A., Kuss, F., and Vaske, J. (1990). Visitor Impact Management: The Planning Framework. Washington, D.C.: National Parks and Conservation Association. Hammitt, W., and Cole, D. (1998). Wildland Recreation: Ecology and Management. New York: John Wiley. Heberlein, T., Alfano, G., and Ervin, L. (1986). Using a social carrying capacity model to estimate the effects of marina development at the Apostle Islands National Lakeshore. Leisure Sciences, 8, Kuss, F., Graefe, A., and Vaske, J. (1990). Visitor Impact Management: A Review of Research. Washington, D.C.: National parks and Conservation Association. Lawson, S., and Manning, R. (2001). Solitude Versus Access: A Study of Tradeoffs in Outdoor Recreation Using Indifference Curve Analysis. Leisure Sciences 23: Lewis, M., Lime, D., and Anderson, P. (1996). Paddle canoeists encounter norms in Minnesota s Boundary Waters Canoe Area wilderness. Leisure Sciences, 18, Lime, D. (1970). Research for Determining Use Capacities of the Boundary Waters Canal Area. Naturalist 21(4): Lime, D., and Stankey, G. (1977). Carrying capacity: Maintaining outdoor recreation quality. Recreation Symposium Proceedings. USDA Forest Service, Manning, R., and Potter, F. (1984). Computer simulation as a tool in teaching park and wilderness management. Journal of Environmental Education. 15, 3-9. Manning, R. (1985). Crowding norms in backcountry settings: A review and synthesis. Journal of Leisure Research, 17, Manning, R., Lime,D., and Hof, M. (1996b). Social carrying capacity of natural areas: theory and application in the U.S. National Parks. Natural Areas Journal, 16,

23 Manning, R., Lime, D., Freimund, W., and Pitt, D. (1996a). Crowding norms at frontcountry sites: A visual approach to setting standards of quality. Leisure Sciences, 18, Manning, R. (1997). Social carrying capacity of parks and outdoor recreation areas. Parks and Recreation, 32, Manning, R. (1998). To provide for the enjoyment : Recreation management in the National Parks. The George Wright Forum, 15, Manning, R., Jacobi, C., Valliere, W., and Wang, B. (1998). Standards of quality in parks and recreation. Parks and Recreation, 33, Manning, R. (1999). Studies in Outdoor Recreation. Corvallis: Oregon State University Press. Manning, R., Valliere, W., Wang, B., and Jacobi, C. (1999). Crowding norms: Alternative measurement approaches. Leisure Sciences, 21, Manning, R. (2001). Visitor Experience and Resource Protection: A Framework for Managing the Carrying Capacity of National Parks. Journal of Park and Recreation Administration 19(1): Manning, R., Newman, P., Valliere, W., Wang, B., and Lawson, S. (In Press). Respondent Self-Assessment of Research on Crowding Norms in Outdoor Recreation. Journal of Leisure Research. Mitchell, J. (1995). Our National Parks. National Geographic 186(4): National Park Service. (1997). VERP: The Visitor Experience and Resource Protection (VERP) Framework A Handbook for Planners and Managers. Denver, CO: Denver Service Center. Potter, F., and Manning, R. (1984). Application of the wilderness travel simulation model to the Appalachian Trail in Vermont. Environmental Management, 8, Roggenbuck, J., Williams, D., Bange, S., and Dean, D. (1991). River float trip encounter norms: Questioning the use of the social norms concept. Journal of Leisure Research, 23, Roggenbuck, J., Marion, J., and Manning, R. (1994). Day users of the backcountry: The neglected national park visitor. Trends, 31, Runte, A. (1987). National Parks: The American Experience. Lincoln: University of Nebraska Press. 23

24 Runte, A. (1990). Yosemite: The Embattled Wilderness. Lincoln: University of Nebraska Press. Schechter, M., and Lucas, R. (1978). Simulation of Recreational Use for Park and Wilderness Management. Baltimore: John Hopkins University Press. Shelby, B., and Heberlein, T. (1984). A conceptual framework for carrying capacity determination. Leisure Sciences, 6, Shelby, B., and Heberlein, T. (1986). Carrying Capacity in Recreation Settings. Corvallis, OR: Oregon State University Press. Shelby, B., and Vaske, J. (1991). Using normative data to develop evaluative standards for resource management: A comment on three recent papers. Journal of Leisure Research, 23, Smith, V., and Krutilla, J. (1976). Structure and Properties of a Wilderness Travel Simulator. Baltimore, MD: Johns Hopkins University Press for Resources for the Future, Inc. Stankey, G., and Lime, D. (1973). Recreational Carrying Capacity: An Annototed Bibliography. USDA Forest Service General Technical Report INT-3. Stankey, G., Cole, D., Lucas, R., Peterson, M., Frissell, S., and Washburne, R. (1985). The Limits of Acceptable Change (LAC) System for Wilderness Planning. USDA Forest Service General Technical Report INT-176. Stankey, G., and Manning, R. (1989). Carrying capacity of recreation settings. A Literature Review: The President s Commission on Americans Outdoors. Washington, D.C.: U.S. Government Printing Office, M-47-M-57. Sumner, E. (1936). Special Report on a Wildlife Study in the High Sierra in Sequoia and Yosemite National Parks and Adjacent Territory. Washington, D.C: U.S. National Park Service Records, National Archives. Vaske, J., Graefe, A., Shelby, B., and Heberlein, T. (1986). Backcountry encounter norms: Theory, method, and empirical evidence. Journal of Leisure Research, 18, Wagar, J.A. (1964). The carrying capacity of wild lands for recreation. Forest Science Monograph 7, Washington, D.C: Society of American Foresters. Wang, B., and Manning, R. (1999). Computer simulation modeling for recreation management: A study on carriage road use in Acadia National Park, Maine, USA. Environmental Management, 23, Whittaker, D., and Shelby, B. (1988). Types of norms for recreation impact: Extending the social norms concept. Journal of Leisure Research, 20,

25 Wilkinson, T. (1995). Crowd Control. National Parks 69(7-8):

26 Table 1. Sample Sizes and Sampling Dates for Visitor Surveys Day Use Social Carrying Capacity Study Site Number of Completed Questionnaires Dates Questionnaires Administered Trail to Vernal Fall 407 August, 1998 Yosemite Falls (included both 390 August and September, 1998 trail to Falls and base of Falls) Bridelveil Fall (including both 295 August, 1999 trail to Fall and base of Fall) Glacier Point 322 August, 1999 Trail to Mirror Lake 317 August and September,

27 Table 2. Alternative Crowding-Related Standards for All Study Sites Day Use Social Carrying Capacity Normative Standard of Quality Trail to Vernal Fall (PPV) Trail to Yosemite Falls (PPV) Base of Yosemite Falls (PAOT) Trail to Bridalveil Fall (PPV) Base of Bridalveil Fall (PAOT) Glacier Point (PAOT) Trail to Mirror Lake (PPV) Preference Acceptability Management Action 1 Tolerance Number of respondents who reported that the NPS should not limit use: Trail to Vernal Fall = 66 Tail to base of Yosemite Falls = 59 Base of Yosemite Falls = 57 Trail to Bridalveil Fall = 73 Base of Bridalveil Fall = 88 Glacier Point = 97 Trail to Mirror Lake = 74 2 Number of respondents who reported that none of the photographs were so unacceptable that they would no longer visit this site: Trail to Vernal Fall = 37 Tail to base of Yosemite Falls = 40 Base of Yosemite Falls = 46 Trail to Bridalveil Fall = 95 Base of Bridalveil Fall = 113 Glacier Point = 99 Trail to Mirror Lake = 65 27

28 Table 3. Range of Daily Carrying Capacities At All Study Sites 1. Day Use Social Carrying Capacity Normative Standard Trail to Vernal Fall Trail to Yosemite Falls Base of Yosemite Falls Trail to Bridalveil Fall Base of Bridalveil Fall Glacier Point Trail to Mirror Lake Preference 2,100 4,500 3,000 1, ,500 1,800 Acceptability 6,000 9,500 5,500 3,200 1,700 4,000 5,000 Management 7,000 11,000 5,900 3,500 1,700 4,800 5,500 Action Tolerance 9,300 13,000 7,300 4,800 2,300 6,300 7,700 1 Daily carrying capacities were calculated to allow normative standards of quality to be exceeded a maximum of 10 percent of the time. 28

29 Table 4. Percentage of Day Users at All Study Sites. Day Use Social Carrying Capacity Trail to Vernal Fall Trail to Yosemite Falls Base of Yosemite Falls Trail to Bridalveil Fall Base of Bridalveil Fall Glacier Point Trail to Mirror Lake Percentage of visitors at each study site who were day users Percentage of Yosemite Valley day users who visited each study site

30 Table 5. Estimated Daily Day Use Carrying Capacities of Yosemite Valley Based on All Study Sites. Day Use Social Carrying Capacity Normative Standard of Crowding Trail to Vernal Fall Trail to Yosemite Falls Base of Yosemite Falls Trail to Bridalveil Fall Base of Bridalveil Fall Glacier Point Trail to Mirror Lake Preference 6,274 3, ,774 Acceptability 44,510 17,228 5,929 5,518 2,062 14,807 48,869 Management Action 54,314 21,465 7,059 6,210 2,062 19,227 54,821 Tolerance 76,863 27,116 11,015 9,205 3,445 27,514 81,012 30

31 Perceived Crowding Day Use Social Carrying Capacity Figure 1. Hypothetical Relationship Between Visitor Use and Perceived Crowding A Y2 Y1 X1 X2 Visitor Use 31

32 Figure 2. Study Photographs for All Study Sites. Day Use Social Carrying Capacity 32

33 Figure 2A. Trail to Vernal Fall Day Use Social Carrying Capacity 33

34 Figure 2B. Trail to Yosemite Falls Day Use Social Carrying Capacity 34

35 Figure 2C. Base of Yosemite Falls Day Use Social Carrying Capacity 35

36 Figure 2D. Trail to Bridalveil Fall Day Use Social Carrying Capacity 36

37 Figure 2E. Base of Bridalveil Fall Day Use Social Carrying Capacity 37

38 Figure 2F. Glacier Point Day Use Social Carrying Capacity 38

39 Figure 2G. Trail to Mirror Lake Day Use Social Carrying Capacity 39

40 Figure 3. Schematic Diagram of Computer Simulation Model of Glacier Point. 40