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This research investigates ways of measuring impacts of visitors on formal and informal (user-created) trails as well as resource impacts.

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Formal and Informal Trail Monitoring Protocols and Baseline Conditions

By Jeremy Wimpey and Jeffrey L. Marion


The presence of large numbers of hikers is a major challenge in managing popular parks and trails. Too many visitors may cause unacceptable impacts to fragile natural and cultural resources, and may also cause crowding and other social impacts which can also degrade the quality of visitor experiences. How many visitors can ultimately be accommodated in a park or related area? How much resource and social impact should be allowed?

Photo of man measuring trail width

Trail assessment and paperless data recording using a GPS unit at a transect
established on a sample point located by pushing a measuring wheel

Park managers operate under legislative mandates to provide appropriate recreational opportunities while protecting and preserving park resources and natural processes. While a variety of recreational uses, including trail-related activities, are clearly appropriate, park managers must also ensure that they avoid significant impairment of natural and cultural resources.

Responding to these concerns, managers at C&O Canal National Historical Park (CHOH) in Maryland and George Washington Memorial Parkway (GWMP) in Virginia supported this research investigating visitation-related impacts to formal and informal (visitor-created) trails in Great Falls Park, Virginia, and adjacent sections of CHOH. To better understand the extent and severity of these resource impacts and identify effective management techniques, this research develops monitoring protocols, collects baseline data, and identifies suggestions for management strategies. The study area, extending approximately five miles along the Potomac River from Great Falls to the downstream end of Carderock, is one of the most biologically significant natural areas in the eastern United States, supporting more than 400 occurrences of 200 rare species and communities. Located in a densely populated urban landscape, the Potomac Gorge is also recognized for its exceptional recreational and scenic features. More than four million people live within the Washington metro region and the Potomac Gorge is a noted tourist attraction in the area.

The potential environmental impacts from recreational activities includes the trampling and loss of vegetation, including rare plants and plant communities, alteration in vegetation composition, possible introduction and spread of non-native plants, compaction and loss of soil, and disturbance or displacement of wildlife.

Resource impacts on informal trails can be severe, partially because of the absence of professional design, construction, and maintenance practices (Wimpey & Marion 2010). While some degree of visitor impact is unavoidable, excessive trampling impacts can threaten natural resource conditions and processes, visitor safety, and the quality of recreational experiences (Leung et al. 2002).

This program of research has the following specific objectives:

1) developing and refining assessment protocols for monitoring conditions along the park’s formal and informal trail systems,

2) applying the protocols to collect and summarize baseline data on formal and informal trail resource conditions and impacts, and

3) providing suggestions on appropriate and effective trail and visitor management practices to avoid or reduce trail-related resource impacts.

photo of trail with roots and rocks

A graphic demonstration of soil loss caused by water
running down This fall-line trail alignment

This research developed and applied state-of-the-art trail condition assessment and monitoring procedures and applied them to the park’s formal and informal (visitor-created) trails. A variety of trail condition indicators were identified in consultation with park staff for potential use in future park management or VERP carrying capacity planning and decision-making. Protocols were developed, field-tested and applied with results fully summarized to provide baseline data to inform managers regarding the current condition of their formal trails, guide potential selection of indicators and standards, and allow comparison to future condition assessments to evaluate trends over time.

Management Suggestions: Formal Trails

Trail widening appears to be the most common problem affecting formal trails within Potomac Gorge. Wimpey and Marion (2010) identify six general behaviors that contribute to trail widening:

1) passing other trail users,

2) side-by-side travel,

3) avoidance of tread problems (e.g., muddiness, erosion, roughness),

4) inability to remain on the intended tread due to poorly marked trails or ambiguous tread borders,

5) roaming associated with picking the easiest route when traversing steep grades, and

6) attraction and avoidance behaviors (e.g., gaining a view or staying away from a drop-off).

Trail widening behaviors can be substantially modified by a number of environmental and managerial factors. Trails in flatter terrain are particularly prone to widening, unless prevented by dense woody vegetation. Relocation to side-hill alignments is the most effective permanent solution but is often impractical, so establishing trail borders with rocks, logs, or fencing can be considered when this form of impact becomes excessive.

photo of trail with smooth surface

A sidehill trail alignment sheds water rather than
concentrating it and is less prone to erosion


Managers can also contain the lateral spread of traffic along trails by adequately addressing tread problems, such as muddiness, erosion, and excessive rockiness, which visitors will seek to circumvent. Managers can provide physically challenging trails, but keeping visitors on them requires design and maintenance practices that ensure the provision of a tread that is more inviting to traffic than the adjacent trailside terrain. A tread that always appears to the trail user as the most direct or easiest route will likely be used consistently with minimal lateral dispersal of traffic.

To address tread widening in problem areas trail maintainers can strategically place large rocks or cut ends of fallen trees placed perpendicular to the tread to force visitors to the center of widened treads. Low impact education encouraging visitors to walk single file and stay to the center of the trail can also assist.

Excessive soil loss is also generally best addressed through sidehill trail relocations that avoid steep fall line alignments. Trail grades of less than 10-12% and alignments greater than 22 degrees from the fall line are best. Alternate actions include hardening treads through the application of gravel or rockwork, or installing wooden or rock steps when grades are steep. Effective trail maintenance solutions include the incorporation of periodic grade reversals (rolling grade dips) within steeper treads that are carrying water. A combination of water bars and outsloped treads are additional alternatives which reduce soil loss from trails. Properly designed grade reversals require no subsequent maintenance but water bars and outsloped treads need to be maintained once or twice each year or they will fail and allow water to run down treads with increasing erosive force.


Management Suggestions: Informal Trails

The creation and proliferation of informal trails has been a substantial, and common long-term management problem at both parks. Informal trails may be considered appropriate under some circumstances to provide visitor access to various park locations not accessed by formal trails. Indeed, many informal trails appear to have been created because the formal trail networks do not provide access to attraction features of interest to visitors. Unfortunately, visitors often create unsustainable trails that are highly duplicative, creating impacts that could be avoided by improved trail design and management. Informal trails that pass through areas with rare or sensitive flora or fauna, or sensitive cultural or archaeological resources, are inappropriate and unacceptable. Informal trails that directly ascend steep slopes and/or will easily erode are less acceptable than trails with a side-hill design. Informal trails prone to muddiness and widening are also less acceptable, as are trails that may contribute eroded soils to water resources. These and other factors must be evaluated by park managers before selecting and applying corrective actions.

Readers are referred to results from a companion study at CHOH’s Bear Island that sought to reduce off-trail hiking rates (Hockett et al. 2010: Deterring off-trail hiking in protected natural areas). This study experimentally applied combinations of site management and educational practices and reduced self-reported off-trail hiking from 70% of surveyed visitors to 43% along the 1.7 mile Billy Goat Trail. Observations at two specific formal trail locations reported a reduction in off-trail hiking from 30% to 0%. Study treatments were applied in an additive fashion, and included educational signs placed at formal trailheads, educational messages delivered through personal contact at trailheads, symbolic prompter signs placed at all formal/informal trail intersections, log barriers and symbolic fencing, light brushing to hide informal trails, and restoration work and signing. Visitor surveys also documented off-trail hiking motivations and preferences for alternative management actions. The most common motivations for hiking off-trail were to get to a scenic vista or take a photo (50.7%), to avoid or pass others (45.4%), or because of poor or challenging trail conditions (43.0%). Hikers with a greater knowledge of off-trail hiking impacts were less likely to hike off- trail than those who had less knowledge.

The Bear Island study includes some key management suggestions here to highlight effective practices for decreasing off-trail travel:

Improve Communication with Visitors: Many visitors do not know about the special and rare plant and animal communities that live within the Potomac Gorge. Trail stewards are more effective in communicating educational messages than the trailhead signs, in part because they are able to contact a greater percentage of visitors. Most visitors simply do not read signs.

Improve Maintenance and Trail Markings: Some hikers hike off-trail accidentally because formal trails may be poorly marked or indistinguishable from informal trails. Managers must ensure that formal trails are maintained to be a better and preferred route than alternate trail-side terrain or informal trails. During wet periods managers should identify muddy sections and apply corrective actions so that visitors can remain on them.

Consider Formalizing Some Informal Trails: Some informal trails were created as by-passes around difficult or crowded trail sections. Others were created to access scenic vistas or favorite places. Managers should consider if those trails are acceptable. If they are, they should be formalized, or closed and replaced by formal trails designed by a trail professional with more sustainable alignments.

Close and Restore Unacceptable Trails: The closure and recovery of all remaining informal trails will be a formidable management challenge. Trampling impacts and trail creation occur with limited or low levels of traffic, while unassisted natural recovery requires little to no use over years for vegetation to return. We suggest use of both informative trailhead signs and symbolic prompter signs at formal/informal trail intersections.

An array of educational and site management actions is necessary to reach visitors who are hiking off-trail for different reasons. Trail stewards and educational signs can convey information about off-trail hiking impacts to reduce the number of visitors who hike off-trail because they do not know it is harmful. Small symbolic prompter signs can more clearly communicate where not to hike and provide reminders of appropriate behavior at decision points. These reminders at the decision points have been shown to be more effective at reducing off-trail hiking than trailhead signs alone. Brushing the beginning of an informal trail removes the evidence that many others have taken that path. Fencing and restoration signs provide additional cues that the park is really concerned about an area and have been shown to be very effective in this and other studies in keeping visitors from using informal trails. However, there is a risk that if a fence is applied to a very popular place, where there is a strong motivation for leaving the trail, visitors might create additional trails to access the area so such an occurrence must be carefully monitored.


Trail Monitoring Manual

The study also includes procedures for conducting assessments of resource conditions on both formal (designated) and informal (user-created). The principal objective of these procedures is to document and monitor changes in trail conditions trails.

These protocols are designed to document the number, lineal extent, spatial distribution, area of trampling disturbance, and resource condition of all informal trails within a specified study area. Assessment procedures are efficiently applied through walking surveys that employ sub-meter accuracy Global Positioning System (GPS) units providing field staff a paperless method for collecting trail inventory and resource condition data. When periodically collected over time, these data assist with the monitoring of onsite resource conditions and provide long-term documentation of the existence, location, and condition of informal trails. The data also provide supporting information for management decisions, such as to evaluate which informal trails should be closed or left open, and later to evaluate the success of management efforts to close selected trails, prevent the creation of new trails, or prevent further deterioration of existing trails.

Informal trail management requires an ongoing adaptive management program, where actions are implemented, evaluated periodically, and findings used to support the selection of additional actions as needed to achieve management objectives. A long-term monitoring program could prove valuable to document and evaluate progress. Finally, we suggest that a workshop with NPS and various representatives of the public be convened to discuss these or other general strategies and actions in a collaborative process. Regardless of what actions are adopted, we suggest that an adaptive management decision-making process be implemented to evaluate management success and alter actions over time as needed to best accomplish management objectives.


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