Recreational mountain biking: A case study of sustainable trail development at Boggs Demonstration State Forest, Cobb, California.

by Lauren N. Claussen

A CAPSTONE PAPER

submitted to

Oregon State University

in partial fulfillment of the requirements for the degree of

Master of Natural Resources

Presented March 23, 2021

1 ACKNOWLEDGEMENTS

First and foremost, a sincere thank you to my graduate advisor, Dr. Michael Harte, for mentoring me through the MNR program, providing guidance and constructive comments as I developed my project, and for your encouraging feedback and wisdom over the past few years.

It has been a pleasure to work with my committee members, and I am so grateful for the time and knowledge they have shared with me through this process. Dr. Ashley D’Antonio, thank you for opening my eyes to the field of recreation ecology and providing your expertise on my mapping and analysis questions, and Lynette de Silva who provided assistance with feedback and final edits on my project.

I could not have done this without support from my family, who have always been my biggest cheerleaders. Thank you to my husband, Nicholas, who first introduced me to the sport of mountain biking, and always encourages me to find comfort and growth in the uncomfortable

– whether on a trail or in life. Your assistance in data collection at Boggs was invaluable, and there’s nobody I’d rather do field work in the freezing rain with!

All the professors and faculty I have learned from and interacted with during my time at

Oregon State have helped further my research, writing, and analysis skills, and I am so grateful for this opportunity and experience.

2 Table of Contents

I. Introduction…………………………………………………………….……………5

1. Types of mountain biking……………………………………….…………..6

2. User motivations and preferences…………………………..…….…………8

3. Conflict ………………………………………………………….…………..9

II. Recreation ecology……………………………………………………….…………10

1. Outdoor Recreation Impacts…………………………………….……..……12

III. Mountain Bike: Ecology…………………………………………………….……....15

1. Soils impacts……………………………………………………….………..16

2. Vegetation, wildlife, and water impacts…………………………….………18

3. Formal vs. informal trails………………………………………….………..19

4. Future research……………………………………………………….……..20

IV. Mountain Bike: Trail Management…………………………………………………21

1. Trail design……………………………………………………………….…22

2. Social sustainability…………………………………………………………25

V. GIS and Recreation Management…………………………..……………………….26

VI. Boggs Mountain Demonstration State Forest………………………………….……30

1. Site information………………………………………………………….….30

2. 2015 Valley Fire and Restoration……………………………………….…..34

VII. Methods……………………………………………………………………………..36

VIII. Results……………………………………………………………………………...39

IX. Discussion and Management Implications………………………………..………..44

X. References………………………………………………………………………….49

Table of Figures

Figure 1: Sustainability parameters for mountain bike trails……………………………….23

3 Figure 2: Trail slope alignment……………………………………………………………..24

Figure 3: BMDSF Trail Overview………………………………………………………….39

Figure 4: Trail sustainability inventory……………………………………………………..40

Figure 5: ANOVA statistical analysis………………………………………………………41

Figure 6: Paired t-test analysis……………………………………………………………...41

Figure 7: GIS trail slope analysis…………………………………………………………...43

Table of Maps

Map 1: BMDSF overview map……………………………………………….…………….31

Map 2: Trail system slope map……………………………………………………………..42

Map 3: Trail suitability analysis…………………………………………………………….44

Table of Photos

Photo 1: Berm mountain bike feature………………………………………..……………..45

Photo 2: View of site on Mac’s trail……………………………………………….……….45

Photo 3: Rock armoring on Jethro’s trail…………………………….………………..……47

Photo 4: Rock armoring on Jethro’s trail………………………….………..……………....47

Abstract

This study identifies contemporary research in the field of recreation ecology focusing on ecological impacts of mountain biking and establishing best management practices for sustainable trail development and management.

A site analysis at Boggs Mountain Demonstration State Forest (BMDSF) takes existing knowledge and research on sustainable trail development and applies those lessons through geographic information systems (GIS) analysis and on-site trail observations. This research is timely as trails are being planned and re-built after a catastrophic fire in 2015. GIS analysis can help identify limitations of the site and guide management recommendations.

4 I. Introduction

Recreational mountain biking began in the mid-twentieth century and its popularity has increased exponentially over the past decades. The origins of the sport are believed to come from

Marin, California in the 1970’s, where innovators used and adapted bike frames to ride off-trail on what became known as “clunkers” (Buenstorf, 2003). Early mountain bike development was distinguished by the situation where the producers were also the consumers; they often modified or developed their own bicycles without sophisticated equipment to race and ride downhill and off-trail (Buenstorf, 2003).

When the Specialized brand developed the first off-the-rack mountain bike in 1981, the modern mountain bike industry was born, and by 1999 mountain bikes accounted for 50% of retail bicycle sales in the United States. Mountain biking has remained one of the fastest growing recreation activities in the world for the past 20 years (Hill et al., 2017). By 2003, there were an estimated 10 million mountain bike users in the US, and currently the International Mountain

Biking Association (IMBA) has membership in 17 countries, with the sport becoming increasingly popular in Australia, Germany, the United Kingdom, and Switzerland (Hardiman &

Burgin, 2014). In 2019, an estimated 48.9 million (16.1% of the population) people rode bicycles recreationally in the United States, with 8.6 million riding mountain bikes on unpaved trails

(Outdoor Foundation, 2020).

Users of recreational mountain bikes are primarily found in affluent countries where users enjoy leisure time and are motivated to exercise as a means to maintain or improve their health (Hardiman & Burgin, 2014). The sport has historically been dominated by young males, comprising 86% of riders in the United States, 97% in the United Kingdom, and 85% in

Australia (Hardiman & Burgin, 2014). In recent surveys, the ratio of men to women participating

5 in recreational cycling is estimated 2:1, indicating an increase in female participation and fueling economic growth and development in the bicycle industry (Outdoor Foundation 2020). In the

United States, a majority of users are between 35-55 years of age, with most mountain bikers in their 30s (Hill & Gomez, 2020).

1a. Types of mountain biking

There are multiple sub-disciplines of mountain biking that attract a variety of users. This includes riding styles of cross country, endurance, all-mountain, free riding, downhill, and dirt jumping. Each of these disciplines utilize different terrain, obstacles and environments, and attract different athletes with varying cultural attitudes (Hagen & Boyes, 2016). A range of bikes are used depending on the style of riding. These include full-suspension for downhill or all- mountain, hardtail, or even no suspension for endurance or gravel riding.

While some cross-over may occur between disciplines depending on the style of bike and terrain, a majority of users pursue cross-country riding, which includes uphill and downhill segments, and usually occurs on multi-use trails or trails originally developed for a different activity such as hiking or equestrian use (Quinn & Chernoff, 2010). An analysis of rider styles shows that cross country riding has a low risk of impact on formed surfaces, likely due to slower speeds and less desire for technical difficulty than other styles of riding (Newsome & Davies,

2009). More technical trails and intense riding is known as “trail” or “all-mountain” riding.

Much of the published literature on ecological impacts of mountain biking are referring to cross- country or all-mountain styles, as these are the most common types of recreational riding.

Free ride, downhill, and dirt jumping attract users looking for speed, adrenaline, and technical trail features like logs, jumps, berms, and steep slopes. These styles of riding have a

6 high impact potential if trails are not sustainably planned and designed, as impacts are likely to be greater if a person is riding faster, less controlled, and on steeper slopes.

Downhill mountain biking takes place on steep, uneven terrain and has obstacles like jumps, drops, or rocks for a rider to navigate. Analyzing the links between rider affects, or biological sensation, in the body, and elements of mountain bike trails suggest that experienced riders have little interest in smooth tracks, seeking instead mud ridges, steep shoots, jumps, drops, and speed (Hagen & Boyes 2016). Hazardous and more exposed trails require more concentration, which increases the quality of the experience a rider has on these trails. These users tend to be younger and identify risk and thrill as motivating factors for biking (Roberts et al., 2019).

Over the past decade, technological advances have led to the creation of “pedal-assist” electric mountain bikes (eMTB), where the user still pedals the bike but with the electric capabilities they can attain up to 20 miles/hour increase in speed (Hall et al., 2019). Pedal-assist allows for a larger segment of the population to experience the health benefits of mountain biking; a study done with experienced mountain bikers illustrated the eMTB users experienced an average heart rate that was 94% of riding a traditional mountain bike, while their perceived exertion was low (Hall et al., 2019). The implications of this suggest an opportunity for both experienced cyclists as well as more sedentary citizens to engage in physical activity. This has the potential to increase diversity and attract new users to the sport, as evidenced by the eight- fold increase in eMTB sales from 2014 to 2019 (Schlemmer et al., 2019).

1b. User motivations & preferences

7 Only a few studies are specifically dedicated to user preferences, however there is an increasing focus on specific demographics, behavior, and perceptions. The traditional perspective of mountain bikers was as thrill-seeking adrenaline junkies; however most users are inspired by self-improvement, a desire for positive emotion, and outdoor experiences (Roberts et al. 2018). In multiple surveys, mountain bike users reported their primary motivations being exercise (74%), enjoying nature and the outdoors (44%), and adventure and challenge (45%)

(Pickering & Rossi 2016). Recent studies have found positive correlations between mountain biking and mental health, particularly among women who reported significant improvements in mood, reduction in stress, and increased self-esteem (Roberts et al. 2018, Hill & Gomez 2020).

These surveys suggest mountain biking as an accessible avenue for people to experience both physical and mental health benefits.

Preferences for mountain biking terrain and conditions is subjective and has a strong correlation with a person’s skill and riding style. Discussions of site preferences with riders determined that key features of steep slopes, sharp turns, and water accessibility increased the value of those trails (Goeft & Adler, 2001). Novice riders often prefer smooth, open trails with few or no obstacles, while advanced and expert riders seek rough terrain and technical challenges

(Symmonds & Hammit, 2000, Taylor & Sand, 2021). Trail attributes like presence of singletrack, amount of vertical climbing, and length are important for all users although they vary depending on skill and experience (Koemle & Morawetz, 2016). Trail conditions can also influence mountain biker experiences, with most riders having a neutral or positive reaction to erosion factors like roots, rocks, and gullies added to a trail, but a negative reaction to mud

(Symmonds & Hammit, 2000).

8 1c. Conflict

Mountain bike users can share trails with other recreational users (Goeft & Adler, 2001).

However, perceived and real conflicts exist between mountain bikers and other user groups, with early management concerns revolving around safety, technological advances, and illegal trail access and use (Chavez et al., 1993).

Recreational conflict is defined as disruption in a user’s goals due to interference from another user. It can be experienced as interpersonal or social value conflict. Interpersonal conflict reflects direct or indirect conflict between users, while social value conflict results from different value orientations, such as anthropogenic versus eco-centric (Pickering & Rossi, 2016).

Pickering and Rossi (2016) studied the perceptions of mountain bike users in peri-urban areas, or regions adjacent to urban areas, and found strongly positive associations with mountain biking

(44%), hiking (14%), and running (8%). However, this research primarily surveyed educated, male users (83%), and only gauged the values, perceptions, and attitudes of mountain bike users but not how other users perceive mountain bikers, suggesting that there could be potential conflicts not analyzed by the authors. Increasing the diversity and activities of people surveyed can help better understand interactions between users.

There is potential to resolve conflicts by including multiple stakeholders in protected area management and focusing on their interactions and desired outcomes. In some instances, understanding the causes of conflicts can attain outcomes that benefit multiple parties, like legalizing bike trails on private land to reduce negative impacts to the environment, allow access for users, and allow forest owners to profit off use (Wilkes-Alleman et al., 2019). In many cases, biking can be assimilated into multi-use systems while reducing conflict if managers design

9 activity-specific trails while improving communication, outreach, and education of all trail users

(Neumann & Mason, 2019).

II. Recreation Ecology

Recreation activities in natural or protected areas will lead to some degradation of the environment, and disturbances create either short-term or permanent changes. These impacts can lead to undesirable visitor-related biophysical change to a site or region (Marion et al. 2016).

Ecological disturbance occurs when a physical force or process (whether abiotic or biotic) causes a disruption in an ecological system relative to a specified state (Quinn & Chernoff 2010). An important component of disturbances is understanding that whether the change is positive, negative, or neutral is a determination based on societal values.

While the study of recreation impacts on the environment has roots in the early twentieth century, the field of recreation ecology emerged in the 1960s and 1970s with over 1000 peer- reviewed studies published over the past several decades (Monz et al., 2013). Recreation ecology studies ecological changes associated with visitor activities with the intent of limiting or mitigating the severity of impacts to levels that aren’t significant to the ecology or management of a site, and do not reduce functionality or aesthetics (Marion et al., 2016). Some level of impact is inevitable when humans utilize a landscape, and land managers are responsible for making conscious decisions about what levels of impact are tolerable and implementing strategies to keep impacts to acceptable levels (Cole, 2004). Using an interdisciplinary approach, recreation ecologists often take into account not only the ecological factors present at a site but also sociological and cultural dynamics to understand how and why recreation causes disturbances (Monz et al., 2013).

10 Recreation experiences can vary widely depending on the visitor capacity of a site, which is defined as the maximum amount and type of use that can occur while achieving desired management outcomes (IVUMC, 2019). Recreational visitor capacity encompasses physical, social, ecological, and facility capabilities and influences user preferences and experiences

(Symmonds & Hammit, 2000). Similarly, the significance of recreation activities on an environment is a function not only of the amount of use, but of their relative impact, extent, duration, and intensity (Cole, 2019).

An important theory emerging from the field of recreation ecology is the curvilinear use- impact relationship, a framework that was derived from observations of vegetative cover loss and has guided recreation management decisions over several decades (Monz et al., 2013). This theory is based on the idea that in previously undisturbed areas, the greatest impact occurs early even with little use, and when subsequent use levels are high, they confer relatively little impact.

Early impacts can include building trails, when soil movement and compaction occurs, or trampling of vegetation that immediately impacts the ecology of the site by exposing soil or removing habitat, changing nutrient cycling and food sources for flora and fauna (Martin et al.,

2018). However, this framework may not address the use-impact relationship for ecological responses in particular habitats, and additional theories can explain how visitor recreation use affects these areas (Monz et al., 2013).

In highly resistant environments, degradation of substrates like hardened surfaces or rock has little correlation with increased use. Alternately, a “sigmoidal response” is observed in areas that have dispersed or low levels of use, because it takes a significant amount of use for effects to occur. Effects can also be linear in soils that are soft and deep, such as loam-sand substrates,

11 where increasing use is correlated with increasing effects over time, whether erosion, rutting, or widening.

Common ecological regions (CER) are an ecological framework used for classifying regions by environmental or social aspects and have been proposed as a way to standardize and guide recreation research (White et al., 2006). CER was developed to guide cooperative efforts, particularly between researchers and the BLM USFS, NPS, FWS, and is available as a GIS layer for use in mapping analysis. In Arizona and New Mexico, CER significantly impacted trail width and maximum trail incision, with these impacts much higher in mountainous areas than other regions (White et al., 2006).

2.1 Outdoor Recreation Impacts

Recreation ecology research initially focused on soil and vegetation impacts, and in recent years more studies have analyzed water and wildlife impacts (Marion et al., 2016). Topics of interest include soil loss and compaction, reduction of organic litter, changes in soil moisture, loss of ground cover vegetation and native plants, changes to vegetation composition, and introduced weeds and pathogens (Marion et al., 2016, Pickering et al., 2010). Researchers have increasingly conducted activity-specific studies to better understand the impacts of hiking, camping, skiing, horseback riding, biking, and off-highway vehicles on natural areas. Recreation impacts include biophysical characteristics like disruption in abiotic and biotic processes, and changes in human activity (White et al., 2006). The scale and intensity of impacts depend on the trail type and can vary greatly depending on the intensity of use as well as biophysical site conditions.

12 Trail research tends to be concentrated in biodiversity hotspots like temperate woodlands and Mediterranean climes, primarily in the USA and Australia. Geographical biases lead to limited research and data regarding desert, wetland, tropical, and subtropical regions (Ballantyne

& Pickering, 2015). Much gray literature exists for different regions in the form of protected area management plans and reports. As a whole, recreation ecology has historically focused on single issues at small scales, as a result more attention is needed at the landscape level over long time periods.

Research is experimental or observational, with observational studies comparing impacts on existing trails while experimental studies compare effects on undisturbed vegetation or soils, and are typically conducted over small spatial and temporal scales (Evju et al., 2021). A common theme of observational studies is assessing the design elements of initial trail construction such as trail grade, drainage, or topographic alignment, and their corresponding erosive effects on the surrounding area (Eagleston & Marion. 2020).

One of the most studied ecological impacts of recreation use is soil loss. Researchers work to understand soil movement through a landscape, whether erosion, compaction, or incision, a function of both erosion and compaction. Globally, soil erosion rates for trails are highly variable, extensive, and unsustainable, with losses ranging from 6.1 Mg/ha/yr to 2090

Mg/ha/yr (Salesa & Cerda, 2020). Multiple factors contribute to trail soil erosion, including topography, proximity to water resources, type and age of surrounding vegetation, geology and whether the soil texture is fine or coarse, and heterogeneous or homogenous (Olive & Marion,

2009).

Varying methods are used to quantify soil erosion, from terrestrial laser scanning, GIS analysis using light detection and ranging (LiDAR) data, and comparisons of aerial

13 orthophotomaps. Remote sensing methods can incorporate models to predict soil loss, recording changes over time, and pinpointing problem areas in a trail system for land managers. These methods can be integrated with field research to build an understanding of large areas or trail systems (Eagleston & Marion, 2020). In the field, researchers commonly use the cross-sectional area (CSA) method to estimate the volume of soil lost, but other methods include measuring tree root exposure compared to soil surface or maximum incision from the trail surface (Salesa &

Cerda, 2020).

A large body of recreation research focuses on hiking. In the United States, a hiking resistance index has been created for 28 types of vegetation, documenting the number of passes it takes to reduce vegetation by 50%. While variations can exist between location and growth form, subtropical vegetation is usually the most resistant to recreation, while grasslands and forest understories are the least resistant (Pickering et al., 2010).

Equestrian use has similar ecological impacts as hiking, including soil compaction and erosion, reduction of litter and groundcover, erosion, and trail widening. The weight of horses puts up to ten times more pressure per point than a person hiking, which can lead to more severe effects on soil degradation through compaction and erosion and reduction of plants by grazing

(Pickering et al., 2010). Waste can be a major contributing factor of ecological impacts with equestrian use, as the feces and urine excreted contains high levels of Nitrogen, Phosphorous and heavy metals which create nutrient hotspots along trails or runoff that degrades water quality in nearby waterways.

Current gaps in trail-related research include informal trails, comparing trail types, temporal scale impacts, and impacts on threatened species (Ballantyne & Pickering, 2015).

While trails cover a relatively small area compared to other land uses, recreation ecologists work

14 to better understand the impacts of soil erosion, water and sediment movement in recreation areas to illustrate the ecosystem impacts of recreation (Salesa & Cerda, 2020). Comparative studies with logging, agricultural, or post-fire impacts can illustrate the degree to which recreation impacts compare to other intensive land use activities (Salesa & Cerda, 2020).

Recreation trail management recommendations include avoiding building straight up- and-down slopes, preferring steady ascents and descents that run along contour, avoiding highly sensitive ecosystems, and minimizing cumulative spatial impacts and fragmentation by limiting the number of trails (Ballantyne & Pickering, 2015). To limit soil erosion, damage prevention is often more advantageous than mitigation, and land managers often evaluate the areas of greatest risk in a trail system and target those for monitoring and management (Salesa & Cerda, 2020).

Other management strategies to limit soil erosion include minimizing water runoff, and keeping trail grades under 10% or 10-15% for short sections with water diversions built in. Physical barriers can discourage creation of informal trails, and signage can help alert users to sensitive areas or act as ecological education opportunities (Salesa & Cerda, 2020).

III. Mountain Biking Research:

Mountain biking has fewer studies dedicated to ecological impacts compared to hiking, and most focus on soil erosion, soil compaction, vegetation or other conditions that degrade trails. Mountain biking shares similarities with other trail-based recreation, specifically that soil type, terrain, relief, and amount of moisture has the greatest influence on mountain biking soil impacts (Quinn & Chernoff, 2010). Impacts are similar to hiking when measuring indicators like width, incision, and cross-sectional area of a trail (White et al., 2006). When hiking and biking are of similar intensity, the short-term soil and vegetative impacts are similar, with immediate

15 impacts of both activities but rapid recovery within a year of the activities stopping (Thurston &

Reader, 2001). Many impacts result from poor trail design or from trails being used for a different activity than originally intended (Davies & Newsome 2009). Planning, maintenance, and designating trails to specific activities can reduce negative impacts of mountain biking

(Marion & Wimpey, 2007).

3.1. Soil Impacts

Historically, there was a perception that mountain biking contributes disproportionately to soil degradation compared to other recreation activities (Quinn & Chernoff, 2010). However, multiple studies have found mountain biking to have no statistical difference from hiking on soil loss from recreational trails (Olive & Marion, 2009). Most studies focus on soil erosion or compaction, and conditions that degrade trails like trail widening and incision. Multiple studies suggest that site, situation, and landscape characteristics of a trail have more potential to affect soils than the activities itself (Quinn & Chernoff, 2010; Meadema et al., 2020). Biophysical attributes that contribute to trail soil erosion include the geology, topography, vegetation characteristics of the site, and use related impacts, whether user behaviors or intensity of use

(Olive & Marion, 2009; Stavi & Yizhaq, 2020). Specifically, homogenous soil textures, particularly super fine or coarse soils can increase erosive effects, as well as steep slopes at high elevations, or areas close to rivers or streams. Trail substrates matter immensely in trail sustainability, as sandy soil drains better than clay due to its’ coarse nature but moves more easily, making it prone to erosion & impacts from wheels (Marion & Wimpey, 2017).

The two primary determiners of soil degradation potential are trail steepness and orientation to terrain fall lines (Quinn & Chernoff, 2010; Marion & Wimpey, 2017, Evju et al.,

16 2021). Mountain bikes traveling uphill have increased friction and pressure exerted on the ground by the rear wheel, resulting in shear forces that can kick up rocks, displace soil, and cause rutting on trails (Stavi & Yizhaq, 2020). Electric mountain bikes can disproportionately impact the soil on uphill trails because of their increased speed and weight compared to conventional mountain bikes. Multiple studies have correlated increasing grade with soil loss, particularly for slopes greater than 10%; at these grades water moves with greater velocity and erosivity, combined with increased likelihood of slippage or gouging by feet, wheels, or hooves (Martin et al., 2018). In the southwest of the United States, mountain biking trails with slopes over 12% are associated with increased potential erosion and degradation (White et al., 2006). As slope increased up to a maximum of 38%, maximum trail incision also increased, but increasing slope had no significant effect on width. While trail grades do have complex interactions with variables like soil texture and drainage, some research suggests that trail slope alignment (TSA) is a more important indicator of soil loss (Olive & Marion, 2009).

Trail slope alignment can play an important role in soil loss in mountainous or steeper terrain but has a lesser impact in flatter areas. Fall line trails, which are characterized as up-and- down slope, are aligned congruent to the landform slope in the direction followed by water drainage. These trails are susceptible to degradation because initial traffic can compact or displace soil which then allows water to incise down a given trail, compounding over time to create gullies and rilling (Marion & Wimpey, 2017). Contour aligned trails, or “side hill” trails, help slow water movement, particularly if the trail is outsloped.

Soil moisture can be beneficial because it increases cohesion between soil particles, however too much moisture in certain soil types can increase compaction, channeling, or soil movement by wheels (Pickering et al., 2010). When wet, the friction between soil particles

17 decreases, so soil is more easily moved, which is why precipitation events make trails more susceptible to compaction and rutting (Stavi & Yizhaq, 2020). In Norway and New Hampshire, greater impacts from mountain biking and hiking were observed based on soil moisture compared to effects from soil substrate, slope, or trail slope alignment (Evju et al., 2021,

Eagleston & Marion, 2020). In steep coastal mountain ranges as well as inland high-elevation trails, soil moisture was the most important predictor of trail width increase, also creating rutting and footprint incisions after rain events.

3.2. Vegetation, wildlife, water impacts

Vegetation impacts follow a curvilinear use-impact relationship, where vegetation can be altered or eliminated after even a few passes (Quinn & Chernoff, 2010). Age and type of vegetation can influence its’ resilience and likelihood of long-term ecological change or erosion

(Olive & Marion, 2009). These impacts are typical in multiple recreation activities, and often occur during initial trail building efforts. Differences in vegetation are highly dependent on climate, plant physiology, and other landscape factors (White et al., 2006).

Differences in vegetation are highly dependent on climate, plant physiology, and other landscape factors (White et al., 2006, Havlick et al., 2016). At low levels of use (25 passes), mountain and cyclo-cross bikes have been found to have a significant impact on vegetation compared to hikers, but at higher levels of use (400 passes), all activities have similar impacts

(Martin et al., 2018). It is presumed that the continuous track created by bicycles contributes to this obvious initial impact, and at the study site vegetation was able to recover within a season on hiking and downhill bike tracks. However, uphill biking has been correlated with more

18 significant decreases in vegetation and long-term degradation, with shearing forces by the bike tires likely damaging roots and preventing plant recovery (Havlick et al., 2016).

Recreation can affect wildlife by disturbing them or invoking a stress response, altering habitats (as through fragmentation), and through collision or mortality. With stress or disturbance, animals can become startled by human activity and flee in response, alter their behavior, or attack because they feel threatened. Ungulates are recorded to have decreased daytime activity in the presence of mountain bikers, and give trails a wide, 40-meter berth in impacted areas (Scholten et al., 2018). Even in peri-urban areas where animals were regularly exposed and adapted to human activity, coyotes and rabbits avoided trails when they were re- opened to mountain bikers and hikers after a period of closure (Larson et al., 2020). In British

Columbia, Canada, several recreation types had impacts on different animal species, but mountain biking specifically negatively affected moose and bear presence (Naidoo & Burton,

2020). These displacements can be short term or permanent, and animal responses vary widely between species, individuals, and even activity type (Quinn & Chernoff, 2010, Larson et al.,

2020). These findings have implications for management of sensitive species, as seasonal or periodic trail closures could help migrating or breeding animals. Future studies can help identify animal behavior and their responses to human disturbances.

Little research discusses impacts of mountain biking on water resources. Most impacts are indirect and would likely result from soil loss and movement into bodies of water or degradation of stream crossings (Pickering et al., 2010). GIS analyses focusing on trail corridors and their associated watersheds could help guide future research of trail impacts on water sources

(Eagleston & Marion, 2020).

19 3.3. Formal versus Informal Trails

Informal trails (also known as “social” or “illegal” trails) often result from user desires to increase connectivity or create additional features within a trail system without waiting for formal approval (Havlick et al., 2016). These trails can be particularly problematic in regions with sensitive habitats which don’t recover well from disturbance. In some places, informal trail creation occurs in conjunction with unauthorized building of technical features like jumps, mounds, or ditches which can lead to increased environmental degradation, management challenges, and safety issues (Pickering et al., 2010b).

Informal trails have been found to have more soil loss due to people cutting down steeper slopes rather than following formal trails which run along hillsides, and can result in more fragmentation and overall forest loss than formal trails (Ballantyne & Pickering, 2015).

However, there was not a statistically significant difference between these trail types when a combined 116-acres were lost between formal and informal trails over a 2,000-acre region in eastern Australia, because formal trails exhibited more habitat degradation and fewer mature trees than informal trails which caused more fragmentation.

In prairie habitats that are generally resilient to impacts, informal trail creation by mountain bikes can have noticeable effects on vegetation after relatively few passes (Havlick et al., 2016). If vegetative cover fails to recover the following season, there is an increased likelihood of further impacts and establishment of new, unauthorized trails.

3.4 Future Research

The full impact of mountain biking on the ecological processes of a site are site-specific and depend on the style and intensity of use. Some current research aims to incorporate “normal”

20 riding conditions into observational and experimental studies, but further data on realistic riding styles and conditions is needed (Evju et al., 2021; Martin et al., 2018). Future research can identify which behaviors lead to ecological degradation, including but not limited to; skidding, turns, high speeds, or braking. If some styles of riding increase the likelihood of ecological impacts, they may need modified locations at parks and wouldn’t be appropriate for all areas or highly sensitive habitats. Additional opportunities for future research include interdisciplinary studies of environmental and social effects of mountain biking, seasonal differences, or more studies in diverse habitats, outside of mountainous and high relief terrain.

IV. Mountain Biking Management:

Most ecological impacts to a site appear during trail development and initial use. It’s during the planning and building stage that land managers are able to design for the long-term sustainability of a trail network. Mountain biking management issues include resource degradation, conflict, crowding and safety (IMBA/BLM, 2017). However, with appropriate site planning and management, many of the ecological impacts of erosion, compaction, or vegetation damage can be reduced (Goeft & Adler, 2001).

An important component of managing mountain biking is designing trails for the appropriate use, as some designs can cater to all users while others are use-specific. By understanding user needs and maximizing an affinity for the environment, trail builders can safely and subtly guide riders in a way that enhances user experiences in a sustainable way

(Taylor & Sand, 2021). Utilizing this approach can simultaneously aim to reduce ecological impacts and user conflicts. Creating one-way trails can aid in erosion reduction, as mountain

21 bikes can cause more erosion on climbs compared to hikers who cause more erosion on downhills (Koemle & Morawetz, 2016).

Trail surveys aid managers in assessing formal and informal trails, whether by performing a trail attribute survey, trail condition assessment, prescriptive management assessment, or use components from all these surveys to fit the needs at their given location

(Marion et al., 2012). Using global positioning systems (GPS) units to map trail system characteristics, a trail attribute survey allows for creation of GIS trail layers for mapping, planning, analytics and decision making. Trail condition assessments document existing trail resource conditions, logging data on the type, severity, and location of trail impacts to help direct trail maintenance. Prescriptive management assessments evaluate and document maintenance needs, sustainability attributes, use-type capabilities, and options for relocation if needed.

Sustainability analyses and models are being developed to collect and analyze data on trail grade, trail slope alignment, and tread substrates (Tomczyk & Ewertowski, 2013). Several studies have included LiDAR data to assess trail grade or sustainability based on landform grade and topography (Marion et al., 2012).

4.1. Trail Design

For the sustainability of mountain bike trails, trail design is perhaps the most important factor to assess. A well-designed trail will create rhythm and flow, present psychological challenges and the reward of optimal experiences to users while also understanding the management implications of trail builds (Taylor & Sand, 2021). The user desire for “flow” correlates with its’ positive impacts on management by reducing a need for sharp turns and abrupt braking. Trail builders should fit the landscape, enhance natural features like rocks or

22 slopes, while also understanding how the trail impacts natural processes like erosion (Taylor &

Sand, 2021). By identifying the influence of factors that impact soil and vegetation loss, land managers can work to maintain visitor use while minimizing negative ecological impacts

(Marion & Wimpey,

2017). Trail grade and slope alignment, trail drainage, and trail substrates are the primary drivers of trail design that dictate the long-term sustainability of a recreation trail Figure 1. Overview of indicators of sustainable trail development. (Foti et al., 2006; Marion (Figure 1). To limit & Wimpey, 2017; Salesa & Cerda, 2020; Taylor & Sand, 2020; Stavi & Yizhaq, 2020). soil erosion, damage prevention is often more advantageous than mitigation, so land managers can evaluate the areas of greatest risk in a trail system and target those for monitoring and management (Salesa & Cerda, 2020).

Trail grade impacts long-term sustainability of trails, as multiple studies have found correlations between increasing grade and soil loss. This is particularly apparent at grades higher than 10% because of the greater erosivity of running water, combined with increased slipping or gouging from wheels, feet, or hooves (Marion & Wimpey, 2017). IMBA advocates for the “half rule”, dictating that the trail grade should not exceed half the grade of the hill. Using this rule, if the slope of a hill is 16%, the trail grade along that contour would not exceed 8%; however each trail location has a maximum sustainable trail grade, usually depending on soil type. Except in

23 rare cases, such as areas of exposed rock, trail grade should not exceed 15%, and in erosion prone soils, the maximum grade might be close to 5% (IMBA, 2017). Many trail maintenance books and management plans recommend trail grade maximums, however these are often generalizations and future peer-reviewed research can help establish specific thresholds of trail grade for different substrates and climates.

Trail slope alignment has been identified as a primary indicator of trail sustainability (Eagleston &

Marion, 2020; Meadema et al. 2020). The most sustainable trails are side hill between 46 and 90 degrees off the fall line, with 68 to 90 degrees as the lowest risk of erosion. Trails between 0 and 45 degrees off the fall line are the least sustainable, with the highest likelihood of degradation between 0 to 22 degrees (Figure 2; Marion Figure 2. Trail slope alignment diagram (Marion & Wimpey, 2017). & Wimpey, 2017).

A primary goal in sustainable trail development is to minimize the concentration of surface water runoff on a trail by diverting it quickly. Drainage can be controlled on side hills by shaping the tread through an outslope, inslope, or crowning to shunt water off to each side of the trail (Marion & Wimpey, 2017). Common recommendations are two to three percent outslope for hiking or five percent outslope for biking to ensure sheet flow across the trail and down a hillside in a non-erosive manner (Stavi & Yizhaq, 2020). Traditionally, angled drainage ditches, including drainage dips, water bars, or rubber water bars, were dug to shunt water off trails.

However, a contemporary best management practice is to build grade reversals into a trail as it travels across a contour (Marion & Wimpey, 2017). Grade reversals create mini “watersheds”

24 along the trail so drainage in one section will not affect other areas. When trail grade temporarily reverses, all water is forced off the trail making maintenance needs nearly nonexistent. Depending on soil type and rainfall, these are recommended every 6 to 15 meters

(IMBA, 2007). For this reason, grade reversals are usually the most effective and sustainable permanent feature to be built in new trail construction. (IMBA, 2017).

To minimize soil displacement from users, particularly in high traffic areas or locations with loose soil, managers or builders can create insloped turns, consistent flow, or armoring.

Insloped turns, also known as berms, may require more frequent maintenance than other trail features but can reduce skidding, lateral soil displacement, or trail widening at grade reversal points (Stavi & Yizhaq, 2020). By designing trails for consistent flow, builders aim to avoid abrupt transitions and minimize soil displacement while controlling speed and momentum through trail elements that are exciting for trail users (Taylor & Sand, 2021). Tread hardening can aid managers in dealing with wet areas or moderate user-caused erosion using wood, rock, or other armoring materials that prevent compaction and reduce shearing forces (Stavi & Yizhaq,

2020). These features are particularly sustainable if materials are found and utilized on site.

4.2 Social Sustainability and Trail Management

The popularity and rapid growth of mountain biking outpaced research and efforts to understand impacts on the environment. This led to a backlash against the sport by land managers. They perceived a negative environmental impact by the sport and mountain biking was banned in many areas, despite a lack of research in this field to verify or repute their opinions (White et al., 2006). To develop and maintain sustainable mountain biking trails, these

25 recreation areas must meet user needs while also addressing social impacts and mitigating conflict between different user groups (IMBA, 2017).

More interaction with mountain bikers can help managers develop trails in a way that leads to less likelihood of trail damage, as well as mitigating potential conflicts with other user groups (Neumann & Mason, 2019; Taylor & Sand, 2021). Innovation in approaches to stakeholder interactions and governance approaches to forest management involve technical advances, organizing groups of mountain bikers and involving public actors like land managers

(Wilkes-Alleman et al., 2019). This approach focuses on understanding the causes of conflict between different user groups and encouraging stakeholders to work toward mitigating conflicts while working toward a desired outcome for multiple user groups. In managing forests and lands with public access and recreation, bike associations that self-organize and develop a “critical mass” of action are more likely to lead and initiate trail development innovations (Wilkes-

Alleman et al., 2019). Trail systems can be designed to reduce conflict, particularly if advocacy groups and managers aim to provide diverse trail opportunities for all users, spread out trails based on difficulty, or create preferred use and single-use trails (IMBA, 2017).

Practical solutions to user conflict can include passive education in the form of trail signage, including right-of-way, marking use-specific trails, or passing etiquette (IMBA, 2017;

Neumann & Mason, 2019). This approach can help reach larger groups of people with diverse recreation interests and standardize user expectations in protected spaces.

V. GIS Analysis and Recreation Management:

GIS is a spatial data management and analysis tool used across to make decisions in the public and private sector. The use of GIS has become ubiquitous in natural resource

26 management as a method to map, inventory, manage and predict ecological impacts and changes over time. GIS allows for remote analysis of a site, temporal or spatial comparisons, can be particularly valuable after natural disasters or other changes in land composition, and is used in forestry, agriculture, and water resource management (Kumar et al., 2015).

Through creation of maps and models in GIS, researchers combine information about topography, soil properties, vegetation, and other factors to assess overall environmental sensitivity to recreational trails (Tomczyk, 2011). This allows for the study of spatial diversification and assessment of which factors are the most important for environmental sensitivity in particular areas. Surveys utilizing GPS technology to map trail system characteristics allow for the creation of GIS trail layers for mapping, planning, analytics, and decision-making (Marion et al., 2012). In particular, sustainability analyses can be developed using LiDAR data to collect and analyze data on trail grade, trail alignment angle to prevailing landform grade, and tread substrate. LiDAR data is a remote sensing technology used to create high resolution digital elevation models (DEM) that can be analyzed in conjunction with GIS environmental data like soil type, geology, land use, or land cover to create or enhance prediction models (Eagleston & Marion, 2020).

Researchers can achieve different goals using GIS models, and any of these methods can aid in decision making with regards to planning or management of a site or region. One option for analysis is to create a multi-criteria evaluation (MCE) model that is used to combine attribute layers and weight them by relative importance (Carver et al., 2012). Using this approach, each response is viewed as a weight, and subsequent buffers created in a GIS map show planning zones that highlight different areas of management.

27 Common variables used to model erosion on trails include slope, curvature, topographic roughness, and wetness. In GIS analysis, researchers have used LiDAR data from the United

States Geological Survey (USGS) to create a bare-earth DEM, and then derived trail slope alignment and trail grade in ArcMap (Eagleston & Marion, 2020). Other geomorphic variables processed in ArcMap included slope, aspect curvature, flow accumulation, topographic wetness index, topographic roughness, and watershed length. This was done at three spatial scales; at the transect location, the trail corridor watershed, and the upslope landform watershed. This multi- spatial scale had not been previously studied, likely because the increased access to LiDAR technology only now allows for the study of multiple trail corridor and upslope watershed variables (Eagleston & Marion, 2020).

These models determined that precipitation was the single most important variable in predicting trail erosion, followed by the transect landform slope, trail corridor grade, and finally trail corridor slope ratio. Slope has different effects on soil loss at different spatial scales, but was a significant factor at each scale. This has implications for trail management, to understand where water is entering the trail and that small-scale or micro-watersheds should be considered when planning trail design (Eagleston & Marion, 2020).

A study analyzing slope as a critical factor affecting travel rates while hiking or running on a trail used an algorithm inspired by the LandTrendr temporal segmentation process

(Campbell et al., 2019). Researchers placed points at 2-meter intervals and extracted LiDAR derived terrain elevation at each point, then labeled the first and last points along a trail as inflection points, creating trail segments by connecting these points. Trail segment slope was calculated as the arctangent of each trail segment’s elevation grail divided by horizontal segment

28 distance. Slope distance, which is a more realistic measure of true distance, was calculated at the horizontal distance of each segment divided by the cosine of the slope (Campbell et al., 2019).

Public participation GIS (PPGIS) is an avenue to gather georeferenced information from non-experts (i.e. the public) for use in spatial analysis (Buendia et al., 2019). Data can be gathered using simple methods like handwritten symbols on a map, or people can utilize GPS software and tracking apps on a phone or other device to record their recreation activity, count plants or animals, and record user experiences. Similar to PPGIS, volunteered geographic information (VGI) utilizes user generated content and is more focused on the data itself rather than utilizing a participatory process (Verplanke et al., 2016). Both PPGIS and VGI have the ability to provide quality spatial information more quickly and at a lower cost than traditional research methods (Campelo & Mendes, 2016; Verplanke et al., 2016). However, these types of heterogenous data can make it difficult to validate accuracy and quality of data due to the lack of control over the sample with regards to phone, tracking quality, or even personal motivations

(Korpilo et al., 2012).

In protected areas that are used for recreational activities, volunteered spatial data can be applied to understand intensity and frequency of use, gather attitudes of users toward protected areas, evaluate trade-offs between conservation and land use, and look at conflicts or user behavior (Buendia et al., 2019). With the ability to rapidly collect and analyze volunteered geographic data, adaptive management and decision making can occur in real time (Korpilo et al., 2017). Using PPGIS data and GIS kernel density estimation tools, hotspots of heavy off-trail use were identified in an urban forest, and at this site it was discovered that mountain bikers have a very structured movement pattern and are 45% more likely to go off trail than runners (Korpilo et al., 2017).

29 Multiple webshare services allow users to track their recreation activities and upload them for others to view, using the concept of VGI. Wikiloc and GPSies (now AllTrails) are two popular webshare applications and had comparable results when used for research on user conflict between runners and mountain bikers (Campelo & Mendes, 2016). Using webshare data to download tracks as GPX files and converting them to shape files, researchers can overlay tracks along popular recreation routes of a forest park and study spatial overlap to predict areas of potential conflict between runners and mountain bikers (Santos et al., 2016).

Potential benefits of PPGIS and VGI in public planning include its’ use as a tool in consensus-based decision making, as well as a way to improve management decisions in real- time. GPS data can be collected to track and assess the location and characteristics of technical features, and their conditions (Zeidler et al., 2019). Monitoring features through GPS can be useful during seasonal changes like rain or extreme dryness, and to track erosion, trail widening, or vegetation disruption. This type of data collection and analysis can aid land managers in addressing both ecological and social concerns on public and protected lands and allow for establishing site-specific protocols for working in sensitive habitats, impacts of high visitor populations, and countless other scenarios.

VI. Boggs Mountain Demonstration State Forest (BMDSF)

6.1. Location and site features

Boggs Mountain Demonstration State Forest (BMDSF) is a 3,498-acre forest located in

Cobb, California, an hour and a half north of San Francisco in Lake County. Historically, this region was inhabited by the Lake Miwok and Wappo tribes (Smith & Broderson, 1989). In

1880, Henry C. Boggs purchased this property, and through a series of sales it was purchased

30 and clear-cut in 1948 by Setzer Forest Products. Following this, the site was purchased by the

State of California to create a demonstration forest and study the recovery following clear-

cutting (CalFire, 2008). No logging occurred between 1950 and 1966, and through 1976, the

remaining old growth forests were harvested in inaccessible areas, totaling 31 million board feet.

Map 1. Overview map of BMDSF showing the existing trial system and fire roads.

The site is currently managed by the California Department of Forestry and Fire Protection

(CalFire), and the 2008 BMDSF Management Plan emphasizes forest research and

demonstrations while also encouraging recreation, maintaining wildlife habitat, and protecting

water resources.

The Mediterranean climate at BMDSF results in long, dry summers and rainy winters,

ranging from 20 to 130 inches of rain per year (average 65 inches). The forest lies within four

31 separate watersheds; Big Canyon Creek, Upper Kelsey Creek, Anderson Creek and Hoodoo

Creek. These are all designated as “Evolutionary Significant Units” for Chinook and Coho salmon, as well as steelhead trout, but downstream barriers prevent fish passage to this region

(CalFire, 2008). Within BMDSF also lies the headwaters to Kelsey Creek and Putah Creek drainages, which are part of the Clearlake and Lake Berryessa watersheds. Natural water resources on the mountain include three springs, and perennial streams Houghton, Malo and

Spikenard Creeks.

Boggs Mountain lies in the northern reaches of the Mayacamas Mountains, part of the northern Coast Range in California. This area was formed from volcanic activity in the late

Pliocene to Holocene periods that created a lava field of ash and a cap of andesite, basalt, and dacite igneous rock that sits above Mesozoic marine rocks (Burns et al., 1993). The resulting soils range from moderately deep to very deep, well-drained gravelly loam. These igneous rock Map 1. Boggs Trail System overview with roads and site boundary. soils, Collayomi, Aiken, and Whispering complexes are the most productive and foster the majority of conifers on the mountain.

The USGS indicates the primary soil series found at Boggs is the Collayomi-Aiken-

Whispering complex (5-30% slopes, and 30-50% slopes), followed by the Collayomi-

Whispering complex (30-50% slopes) (Smith & Broderson, 1989). These complexes are approximately 35% Collayomi very gravelly loam, 35% Aiken loam, and 15% Whispering loam.

The Collayomi soils often have a small percentage of the surface showing rocks and boulders, and are very deep, well drained, with moderate permeability and rapid runoff, resulting in moderate susceptibility to erosion. Aiken soils are very deep, well drained, and the surface is often covered in a layer of duff. Aiken soil has moderately slow permeability, with rapid surface runoff and moderate erosion hazard. Whispering soil is also well drained and moderately deep,

32 with about 5% coverage of rocks on the surface and the remainder a mat of decomposing pine needles and twigs. Whispering soils have moderate permeability and rapid surface runoff, resulting in a sever erosion hazard. As these soils are productive for conifers and therefore valuable timber land, it is important to note that disturbance of the duff layer can result in slippage and erosive potential in the rainy season. In particular, Aiken soils can be slippery when wet and caution should be exercised when using wheeled or tracked equipment. Revegetating can be difficult on Collayomi and Whispering soils because they have such a high rock content, so establishing seedlings is a concern in timber production and reforestation (Smith &

Broderson, 1989). Most of the non-timber soil comes from Great Valley formation sandstone, made with shale parent materials.

Three primary forest types are Ponderosa pine (Pinus ponderosa), Douglas fir

(Pseudotsuga menziesii), and Ponderosa Pine/Douglas fir. Ponderosa pines have historically dominated the landscape, particularly the west slopes and mountain tops, while Douglas fir populates the lower slopes of the northeast side of the mountain. Hardwood species comprise

15% of the forest, mostly lower elevations and particularly the northeast boundary of the forest

(Baad, 1993). Species composition includes black oak (Quercus kelloggii), white oak (Quercus garryana), canyon live oak (Quercus chysolepsis), bay laurel (Californica laurel), Pacific dogwood (Cornus nuttallii) & madrone (Arbutus menziesii).

The forest understory consists of small shrubs typically found in inland region of

Northern California. This can include common forest understory plants squawcarpet, coffeeberry, poison oak, brackenfern, manzanita, and perennial grasses (Smith & Broderson,

1989). A plant survey based on a search of likely habitats indicates no sensitive species at Boggs

Mountain (Baad, 1992). Permanent springs throughout the forest host the largest number of

33 native species, while the most non-native plant species are found near parking areas and entrances.

In 1992, a resources inventory studied vertebrate animal populations during two separate time periods in the winter and spring. Birds were sampled by sight and sound, small vertebrates were trapped with Sherman live traps in summer 1991 and 1992, and mammals were surveyed with a multitude of methods, including pit traps, Sherman live raps, and smoked tracking plates for carnivores (Baad, 1993).

Pit traps for reptiles and amphibians had limited success, with snakes and amphibians absent in the surveying data. The most common reptiles trapped were the western fence lizard, sagebrush lizard, western skink, southern alligator lizard, and western rattlesnake (Baad, 1993).

Of bird species present, 59 breeding bird species were detected in the springtime, while

48 species were counted in the winter months. Models predict 89 possible species with the appropriate habitat, but the history of clear-cut logging and intensive management could be a primary reason for the low species diversity of vertebrates found at Boggs. Areas recovering from logging had much higher species density than logged areas, and the most species diversity occurred in open, mid-successional areas, suggesting that forest management strategies like selective logging could improve the number and variety of species. Additionally, more than four decades of hunting squirrels and deer likely impacted the populations of those species while also reducing the availability of food for predators (Baad, 1993).

6.1. BMDSF Fire History and Recovery

On September 12, 2015, the Valley Fire ignited on a windy afternoon, and subsequently burned 76,067 acres of dry tinder and mountainous topography over 33 days (CalFire N.D.). In

34 BMDSF, 98% of the forest was burned, with 48% of this area burned at high severity, 34% moderate severity, and 15% low severity in the valleys (Cole et al., 2020). Post-fire ecological threats include increased surface runoff, erosion, and water quality degradation.

Land management activities after fires are often focused on emergency stabilization, rehabilitation, and restoration – all of which have a variety of benefits and tradeoffs (Cole et al.,

2020). While future research will help managers better understand the effects of post-fire management on runoff and erosion, some of the current measures commonly taken to mitigate soil movement and loss include salvage logging, replanting and subsoiling. Salvage logging can reduce the likelihood of pests, reduce the likelihood of future fire severity, and provide economic incentives. Replanting helps re-establish vegetation, particularly in conifer forests where burned trees are less likely to recover than oak woodlands. Subsoiling creates farrows along hillside contours to break up soil and encourage vegetative growth while slowing water movement down a hillside (Cole et al., 2020).

At BMDSF, sediment yields were lower from salvage-logged hillsides than burned-only hillsides for the first 3 years following the Valley Fire, but by year four and five there was no significant difference between these management activities (Cole et al., 2020). Additionally, researchers found evidence suggesting a correlation between vegetation recovery at a rate of 2.4 times faster in burned-only versus salvaged-logged areas in 2017. These findings suggest that road and trail rebuilding is unlikely to experience high rates of sediment movement throughout the burned and logged forest areas, and that vegetative recovery will continue over several years.

Following the fire, foresters flagged trees for retention, however the majority of the forest was salvage-logged, totaling 50 million board feet of timber harvested from June to September

2016. Remaining charred vegetation and logging slash were burned over two winters, in 2016

35 and 2017. In spring of 2017, a mix of Ponderosa pine, Sugar pine, and Douglas fir were planted, totaling 300,000 seedlings over approximately 1,200 acres of the forest (Friends of Boggs

Mountain, 2017). In subsequent years approximately 400,000 seedlings, including Giant sequoia and incense cedar were planted over 1,900 acres bringing the total restoration effort to 702,345 trees planted (CalFire N.D.).

When the Valley Fire and subsequent salvage logging all but destroyed the original roads and recreation trails at Boggs, an opportunity for redevelopment of the trail network was created, fostering a working relationship between advocacy groups and state government agencies. By

2018, 21 miles of forest roads were repaired by CalFire, and rebuilding of recreation trails began in 2019 (Friends of Boggs Mountain, 2017). The non-profit organization Friends of Boggs

Mountain (FOBM) and CalFire are collaborating to establish multi-use trails that can be accessed by hikers, mountain bikers, and equestrian users. This working relationship is focused on bringing in individuals from different disciplines to create trails appropriate for all user groups.

The trails that have been rebuilt as of 2020 have bike-friendly features aimed at reducing erosion and trail damage, while enhancing the user experience. More trail building is planned through

2022.

VII. Methods

Through field data collection and spatial analysis at BMDSF using ArcGIS, existing trail features were inventoried, and potential management challenges identified as this site continues to recover from the 2015 Valley Fire. The intent of this research was to aid sustainable management of multi-use trails and mountain bike features at this site and guide future management activities by CalFire and FOBM.

36 For use in the field, trail surveys were built with the Environmental Systems Research

Institute’s (Esri) smartphone applications Collector and QuickCapture, with the goal of inventorying trail features and sustainability attributes on the existing multi-use trails. Trail features were recorded as GPS points collected with Esri QuickCapture and had a 3-meter accuracy when recorded by an iPhone integrated with a BadElf GPS receiver. Trail features noted in the inventory included drainage features such as rolling dips, grade reversals, and water bars, signage and intersections, and mountain-bike specific features of rock gardens, jumps, and berms. No other descriptive data was collected in the trail feature survey.

Trail sustainability attributes included trail width, trail grade, trail slope alignment, outslope, trail substrate, and feature type. All points were inventoried using Esri Collector on an iPhone integrated with a BadElf GPS receiver with 3-meter accuracy. The trail sustainability attributes were collected at locations where signs of erosion were observed or degradation risk was inferred due to steep slopes, natural drainages, or mountain bike features. Trail grade, landform grade, and trail outslope was measured in percentages using a clinometer. A compass was used to measure trail slope alignment, calculated in the field by taking the difference of the degree measurement of the slope alignment and the trail alignment. Trail width was measured in centimeters with a meter stick laid across the trail, and maximum incision was recorded in centimeters perpendicular to the meter stick at the most recessed location of the trail.

GIS data analysis was performed in ArcGIS Pro, which synced to ArcGIS Online to upload Esri Collector and QuickCapture survey data as vector layers containing points for viewing and analysis. Trail and fire road data were gathered as .GPX and .KML files through

TrailForks.com, an open-source webshare service relying on VGI user data. These files were converted to raster shapefiles and vector polylines in ArcGIS Pro for visualization and analysis,

37 following a strategy used by Santos et al. (2016). Cartographic layers were accessed through the

ArcGIS Living Atlas, which allows a user to import datasets into ArcGIS Pro for visualization and analysis. The elevation raster dataset used in this study was the “Terrain” digital elevation model (DEM) created by ESRI and derived from the USGS 3D elevation program (3DEP) at a one-meter resolution. Geoprocessing tools allowed for creation of slope and aspect layers originating from this DEM. The soil data layer was produced by the USGS National Resource

Conservation Service (NRCS) Soil Survey and include soil erodibility factors to determine erosion risk for this site.

Analysis in ArcGIS Pro focused on determining the variance of trail grades throughout the trail system at BMDSF, with the goal of identifying areas of high erosion risk. Trail vector polylines were segmented at 20-meter increments, and those segments were then interpolated using spatial analyst geoprocessing tools, incorporating DEM data from the terrain layer, and finally, calculating the percent slope of each segment. This process was repeated for each trail segment to allow for analysis between each trail. Counts of trail slopes were extracted from attribute tables and analyzed to understand spatial differences.

Finally, multi-criteria suitability model was created, incorporating landform slope data (in degrees) as well as soil erodibility factors to predict areas of BMDSF with the highest suitability for trails. The landform slope raster layer was reclassified by grouping slope ranges based on soil erosion “average susceptibility” as laid out in Tomczyk’s (2011) GIS modeling, and ranking these classifications from one to five. Landform slopes below 6 degrees (10%) received the highest classification values (4 or 5), slopes from 6 to 15 degrees (10%-30%) were classified as moderately suitable (3), and slopes above 15 degrees (30%) received the lowest suitability scores

(1 or 2). There was a lesser range of values for soil erodibility factors at Boggs, with K-factors

38 below 0.3 (least erosion potential) with the highest suitability classifications, moderate suitability for K factors between 0.3-.4, and K factors above 0.4 with the lowest suitability classifications.

These layers were equally weighted and combined to create a suitability map with values ranging from one to ten. A model was run to designate an area based on the highest average values of surrounding cells, resulting in a one value for suitable locations and a zero value for unsuitable locations.

VIII. Results

Eight distinct trails comprise the current BMDSF trail system, covering 11.7 kilometers and ranging from 911 meters to

1068 meters above sea level (Figure 3). Six of the trails were fully rebuilt following the fire, while parts of Hardtail and Gail’s trail remained intact and other sections were rebuilt, with fewer visual logging scars and Figure 3. BMDSF descriptive trail summary. established trees and vegetation still present.

This trail system was designed to be suitable for multi-use, however the Scout, Jethro’s, and

Mac’s trail are built with mountain bike specific features and constitute 38% of the entire trail system. On the steep, northeast aspect slopes of Crew and Berry trail, visual observations of the conifer saplings planted in 2017 indicate rapid growth with some nearing two meters in height.

On the Mac, Karen, and Scout trails, replanted conifer seedlings appeared to measure closer to one meter in height, possibly due to the more exposed ridgetop location of those slopes.

39 Figure 4. Trail sustainability attributes, measured in the field and recorded using Esri Collector application. Throughout the trail system, particularly the Mac and Karen trails, many drainage features appear to have been built within the footprint of logging skid tracks. It is unknown whether this has any implications for long-term drainage or erosive effects on the landform slope or trails.

The trail sustainability inventory attributes were measured at trail locations where significant features were observed, such as rock gardens, berms, ephemeral drainage ditches, or noted erosion. There were 27 instances of sustainability attributes documented throughout the trail system (Figure 4). This included 10 large berms, 3 rock gardens, 5 instances of steep slopes

(>15%), 3 ephemeral drainage crossings, 1 drop, and 5 instances of inslope or trail incision. The average trail slope for these attributes was 11%, with average maximum incision of 10.7 centimeters.

40

ANOVA statistical analysis of the combined influence of trail grade, landform grade, and soil loss measured by maximum incision indicated significance between these variables (F = 22.95, p < 1.5 e^-8, df =

3.11) (Figure 5). Subsequent T-tests showed a significant relationship between the observed landform slope and maximum incision, while the difference Figure 6. T-tests showing significant between trail slope and maximum incision (cm) was not relationship between land form slope and maximum trail incision. significant (Figure 6). Trail width was not included in statistical analysis because the berm trail features are built differently than other trail features, so are naturally Figure 5. ANOVA statistical analyses of the combined influence of trail grade, land form grade, and maximum incision. wider, making this measurement not appropriate for analysis.

The trail features inventory was collected using the Esri QuickCapture phone application and was used to document presence of specific features that could prevent or indicate erosion and are mountain bike specific. In total, there were 208 observed instances of drainage features

(rolling dips, armored creek/drainage crossing or water bars), 49 instances of mountain bike- specific features (rock gardens, jumps, drops, tabletops, or berms), 22 trail intersections, and 20 signs. This equates to a drainage feature spaced at an average of every 55 meters throughout the trail system, and a mountain bike related feature every 238 meters in the trail system.

41 Map 2. Map of trail grades throughout Boggs, with steepest sections indicated by dark orange color, and flatter sections symbolized by light orange. Trail grade analysis in ArcGIS Pro helps identify trail segments with the steepest slopes

(Map 2; Figure 7). In total, 78% of the entire trail system has between a 1.5% and 10% slope, an indicator of sustainable trail construction. Nearly 15% of the trail system is almost flat, between

0-1.5% slope. Flat slopes can lead to trail widening or muddiness, particularly if they are fall aligned. Only 7% of the trail system (40 segments) measures over 10% slope, with only nine additional segments above 15% slope.

The Crew trail, Jethro 1, and Jethro 2 are the only trails with segments identified as over

15% grade, or very high erosion risk. On the Jethro trail options, although approximately 30% of both these trails were identified as very high risk, data collected in trail sustainability attribute survey indicated presence of rock substrates in these areas, which can armor trail tread and

42 reduce the likelihood of erosion. The Crew trail had both rock and soil substrates present near the steepest slope sections, and those were located in areas with ephemeral drainage.

Multiple trails had segments with slopes Figure 7. Results from trail segment slope analysis in ArcGIS Pro. between 10% and 15%, indicating a high risk of erosion, with the most segments present on

Jethro’s trail. The only trails with all segments under 10% slope are Karen, Gail’s Alternate, and

Berry trail. These trails had few or no trail sustainability attributes recorded, indicating low risk for soil erosion.

The suitability model yielded a map of suitable trail locations based on soil erosive factors and landform slope (Map 3). This model predicts the most suitable location at Boggs for trail development to be the southwest corner of the forest. This encompasses portions of the

Hardtail, Crew, Berry, Gail, and Scout trails, as well as several fire roads. Visual observation of this map indicates the steepest trail segments at Boggs are in areas designated “not suitable”, likely influenced by the surrounding landform slopes and some areas of more erosive soils. The suitability map that the model is based on showed the least suitable areas, or areas with lowest combined values of soil erosion risk and slope, all concentrated on the eastern half of BMDSF.

43 Map 3. Map of trail suitability model results, with shaded area indicating positive suitability based on landform slope and soil erosion factor.

IX. Discussion and management implications

This trail system currently appears to be in excellent condition overall, with minimal instances of erosion or trail degradation as indicated by the sustainability attribute survey. Each trail has slightly different topographical and geologic characteristics, suggesting a need for dynamic management based on landform slope, trail features, trail slope, and maximum incision.

Most of trails follow the side-hill of the landform and are gently sloping along the contour. Jethro and its’ alternate routes have the steepest trail slopes and least-sustainable trail slope alignment (under 45 degrees) but they boast mountain bike features built into the landscape

44 that utilize rocks as natural tread-

armoring, and alternate trail routes guide

non-experienced users around the features

at highest risk for erosion.

The Scout trail has relatively few

steep slopes, but wide berms with incision

could pose erosion risks, particularly with

equestrian users who are likely to

exacerbate the existing inslope incisions Photo 1. Scout trail: Berm bike feature to encourage “flow” and reduce braking on steeper trail sections. (Photo 1). The inslope incision of the

berms on both Jethro’s and Scout trail could be armored with rocks found on-site to reduce the

likelihood of erosion. This can help slow water flow along the inside drainage and limit the

likelihood of slipping or compaction by non-bike users.

The Berry, Crew, Hardtail, Karen, Mac, and Gail trails have sustainable trail slope

alignments (average 60 degrees) and low average trail slopes (average 9%) (Photo 2). However,

the steep landform slope on the Berry

and Crew trails, and multiple trail

segments above 10% grade on Crew

trail, could result in further inslope

incisions or erosion of the six recorded

sustainability attributes on those trails.

The trail locations inslope drainage

Photo 2. View of Mac trail toward the north.

45 currently have visible erosion, which could be mitigated by armoring with rocks to decrease the need for future management.

The Karen, Hardtail, and Mac trails had minimal features analyzed in the sustainability attributes, although they did have numerous drainage features of rolling dips and water bars spaced along the gently sloping trails to help shunt water downhill.

In future years with high-precipitation events, these features may be a source of erosion and trail degradation. It is valuable to track any changes to the drainage and bike-specific features on site, a task that could be done by volunteers or trail users. Due to the fairly remote location of this site, the land managers could utilize a PPGIS approach for monitoring trail status and targeting any future areas for trail repairs and management. As a trail advocacy non-profit,

Friends of Boggs Mountain has a membership list and currently hosts yearly trail events in collaboration with other Northern California mountain bike groups. By doing outreach and education about trail management, they could compile a team of volunteers who periodically inventory and assess the trail system utilizing GPS smartphone applications similar to Esri’s

Collector or QuickCapture.

If user conflicts occur as the site continues to recover and attract new visitors, the addition of right-of-way signage in key intersections throughout the system could help mitigate negative interactions. Although the trails are clearly marked at each intersection, only 2 small signs were observed near the parking area to educate and remind users of trail etiquette. As this site has historically allowed campers, hunters, equestrian users, hikers, and mountain bikers, increased signage and outreach will be imperative to allow all future users enjoy a high quality and safe outdoor experience.

46 Although this study was successful at establishing a baseline of information related to trail attributes and performing preliminary spatial analysis, it was limited in scope and therefore less exhaustive than many peer-reviewed studies referenced in this project. More systematic monitoring could result in an inventory of trail sustainability attributes at a set interval, allowing for more analysis of overall trail features rather than only focusing on locations with apparent erosion or high-risk features. This would result in more meaningful statistical analysis on which to base management decisions.

The suitability model and subsequent map validates many of the observations collected in sustainability surveys and slopes calculated in ArcGIS. The suitability model showed that much of the eastern portion of BMDSF is characterized by highly erosive soils and very steep slopes, making it unlikely to be developed in the future. However, the southwestern portion, already accessible by fire road, is the most suitable for trail building, and cost-distance GIS analysis could be used to propose new trails in this area based on a more extensive inventory of site

Photo 4. Utilizing natural rock armoring of a slope >15% Photo 3. Jethro’s trail: rock armoring >15% slope. on Jethro’s option 1. 47 features. Future GIS analysis to estimate trail sustainability could utilize terrain or LiDAR data at a finer scale (<0.5-meter) and utilize other spatial models, like regression tree analysis as proposed by Tomczyk and Ewertowski (2013), for a better predictive model that incorporates several variables.

The current status of the trail system as sustainable implies that future trail building should continue to follow a similar strategy by building gently sloping side-hill trails, incorporating drainage features along hillsides, and reinforcing trail substrates or steep slopes with bountiful rocks available throughout the site (Photo 3, 4). While some activities could improve long-term management of this trail system, is clear through the development of the landscape to date that the managers of Boggs Mountain Demonstration State Forest are working to build trails and rehabilitate the forest in a way that will allow users to utilize it for many years.

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