Monitoring visitor activity and informal trail disturbance in Yosemite Valley meadows to assess changes in use and impacts over time

Sheri A. Shiflett^a, Jeffrey S. Jenkins^b*, Rachel F. Mattos^a, Kai Thiry^a, Peter C. Ibsen^c, Melissa Booher^a, Angela Tricomi^a, Nicole D. Athearn^a 

^aDivision of Resources Management and Science, Yosemite National Park

^bDepartment of Management of Complex Systems, School of Engineering, University of California, Merced

^cGeoscience and Environmental Change Science Center, United States Geological Survey, Denver, Colorado

Basecamp, Moab, UT – October 14th, 2024

Introduction

• 90-95% of 3.9 million (2023) annual visitors to the park spend their time primarily in the Yosemite Valley
• Meadows are vital for hydrology and offer essential feeding and breeding grounds for a considerable portion of fauna (NPS 2021)
• Meadows are particularly susceptible to human impacts (Pearce-Higgins and Yalden 1997, Eagen et al. 2004, Barros and Pickering 2015)
• Past research in Yosemite shows meadow vegetation was significantly affected by trail use (Foin et al. 1977, Sydoriak 1989, Leung et al. 2011a)
• The growth of “social trail” networks can:
• increase habitat fragmentation
• endanger delicate environments by altering water flow
• serve as entry points for invasive species
• all of which can limit the occupancy and movement of endemic species

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Yosemite Valley meadows

Informal trails

• The extent and condition of informal trails is indicative of the contiguity and ecological functioning of meadows (Holmquist 2004, NPS 2014a,b)
• Informal trails don’t follow a park’s formal system so aren’t planned, don’t receive maintenance, and are often located in poor terrain (Leung et al. 2011a)
• These factors substantially increase their potential to deteriorate meadows in comparison to formal trails
• A web of informal trails creates a visually scarred landscape and may lead to safety & liability concerns
• Social trails can impair not only biophysical resources but also scenic resources and experiences that underpin user satisfaction (Marion et al. 2006)

Study objectives

• Use: Leung et al. (2011) observed where visitors were located and what types of activities they engaged in
• One of our objectives is to compare change in visitor use patterns
• And to quantify visitors per hour, the nature of activities they engage in, and patterns of their movement
• Impacts: Staff from the Visitor Use and Impact Monitoring Program have monitored meadows since 2004
• Includes mapping and measurement of social trails and disturbed areas, classified by condition
• While these data are collected annually, they haven’t previously been analyzed across years to compare trends over time
• Monitoring both visitors and impacts at Yosemite Valley meadows enables pinpointing areas with high visitor frequency and identifying potential use zones and activities contributing to meadow impacts

Methods

• ArcGIS Field Maps to monitor visitor locations and activities
• Data were collected in summer 2023
• Two main time periods: 8 am – 11:59 am and 12:00 pm – 4:00 pm, with data collected in 30-minute time slots
• High priority: Cooks, El Capitan, Leidig, Sentinel, Slaughterhouse
• Low priority: Ahwahnee, Bridalveil, and Stoneman
• Meadow social trails and disturbed area impacts are monitored annually by NPS, typically Jun – Aug
• Social trails and disturbed areas are classified according to condition (e.g., stunted vegetation, some bare ground, or barren)
• Linear regression analysis to assess change over time in extent of informal trails and amount of disturbed area by meadow
• Analyze change from 2004 –2023
• + immediately before visitation exceeded 4,000,000 annual visitors in 2015 (2011 – 2023)
• + recent years pre/post-pandemic (2019 – 2023) to capture recent management actions in meadows and variable visitor use, including both non-reservation and reservation periods.

Total visitors observed and use by time of day

Meadow use by activity type

Active vs. Stationary Activities

Trail Conditions and Visitor Activities

*Low priority meadows

*High priority meadows

Impacts

Use

Impacts

Use

Ahwahnee

Bridalveil

Cooks

El Capitan

Trail Conditions and Visitor Activities

*High priority meadows

*Low priority meadows

Leidig

Sentinel

Slaughterhouse

Stoneman

Impacts

Use

Impacts

Use

Informal Trail Length

Informal trail length by cover type

Disturbed Area

Disturbed Area by cover type

Impacted Area

*Impacted area within each meadow as associated with either informal trails, which included a 5 m buffer, or disturbed area (unbuffered). Each respective impact type was divided by total meadow area to determine the impacted area.

Overall trends

• 2004-2023: there is a significant decrease in social trail length at El Capitan Meadow
• 2008 – 2023: there is a significant increase in disturbed area for Cooks A, Sentinel A, and Slaughterhouse B sub-meadows.
• 2011 – 2023: the proportion of those engaged in active versus stationary pursuits changed with less stationary activity and more active use in multiple meadows.
• Meadow locational context was linked to activity preference and types of impacts.

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Management Implications

• Prevalent trend of adherence to official trails, likely attributed to well-maintained and physically delineated paths, such as elevated wooden walkways or wooden fences
• Factors contributing to informal trails and impacts: cumulative seasonal or yearly impacts of long-standing social trails, adjacency to rivers, lack of barriers, lack of signage, or ambiguous distinctions between formal and informal trails
• Introduction of physical barriers might be an unavoidable necessity for certain areas and is more effective with signage that communicates access restrictions (Park et al. 2008)
• Barriers serve dual purposes: aiding the restoration of areas that have endured significant wear and ensuring that visitors remain on well-maintained paths, thereby limiting further impacts (Hockett et al. 2017)

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Questions?