M
Mike Vandeman
Guest
The Impacts of Mountain Biking on Wildlife and People --
A Review of the Literature
Michael J. Vandeman, Ph.D.
July 3, 2004
"Every recreationist -- whether hiker, biker, horsepacker, or posey sniffer --
should not begin by asking, 'What's best for ME?' but rather 'What's best for
the bears?'" Tom Butler
"Will we keep some parts of the American landscape natural and wild and free --
or must every acre be easily accessible to people and their toys? … Mountain
bikes' impacts on the land are large and getting worse. … The aggressive push of
mountain bike organizations to build ever-growing webs of trails poses serious
problems of habitat fragmentation, increased erosion, and wildlife conflicts.
As interest in extreme riding continues to grow, as trail networks
burgeon, and as new technology makes it possible for ever-more mountain
bicyclists to participate, even the most remote wild landscapes may become
trammeled -- and trampled -- by knobby tires. … The destruction of wilderness
and the fragmentation of habitats and ecosystems is death by a thousand cuts.
Will introduction of mountain bikes -- and their penetration farther into
wilderness -- promote additional fragmentation and human conflicts with the
natural world? Yes." Brian O'Donnell and Michael Carroll
"Some things are obvious: mountain bikes do more damage to the land than hikers.
To think otherwise ignores the story told by the ground. Although I have never
ridden a mountain bike, I am very familiar with their impacts. For the last
seven years I have regularly run three to six miles several times a week on a
network of trails in the Sandia Mountain foothills two blocks from my home. …
These trails receive use from walkers, runners, and mountain bikers; they are
closed to motorized vehicles.
Because I'm clumsy, I keep my eyes on the trail in front of me. I run or
walk in all seasons, in all kinds of weather. I have watched the growing erosion
on these trails from mountain bike use. The basic difference between feet and
tires is that tire tracks are continuous and foot tracks are discontinuous.
Water finds that narrow, continuous tire tracks are a rill in which to flow.
Also, because many mountain bikers are after thrills and speed, their tires cut
into the ground. Slamming on the brakes after zooming downhill, sliding around
sharp corners, and digging in to go uphill: I see the results of this behavior
weekly. …
I regularly see mountain bikers cutting off cross-country, even on steep
slopes, for more of a challenge. They seem blind and deaf to the damage they
cause. Admittedly, backpackers and horsepackers can cause damage to wilderness
trails. But this is a poor argument to suggest that we add another source of
damage to those trails." Dave Foreman
"Studies show that bike impacts are similar to those of other non-motorized
trail users." Jim Hasenauer (professor of rhetoric and member of the board of
directors of the International Mountain Bicyclists Association)
Introduction:
I first became interested in the problem of mountain biking in 1994. I
had been studying the impacts of the presence of humans on wildlife, and had
come to the conclusion that there needs to be habitat that is entirely
off-limits to humans, in order that wildlife that is sensitive to the presence
of humans can survive (see Vandeman, 2000). But what is the best way to minimize
the presence of people? Restricting human access is repugnant, and difficult and
expensive to accomplish. It occurred to me that the best way to reduce the
presence and impacts of humans is to restrict the technologies that they are
allowed to utilize in nature: e.g. prohibit bicycles and other vehicles (and
perhaps even domesticated animals, when used as vehicles).
Having been a transportation activist for eight years (working on
stopping highway construction), and having a favorable view of my fellow
bicyclists as environmentalists, I turned to them to help me campaign to keep
bicycles out of natural areas. Was I ever surprised! I discovered that many
bicyclists (e.g. many mountain bikers) aren't environmentalists at all, but are
simply people who like to bicycle -- in the case of mountain bikers, many of
them just use nature, as a kind of playground or outdoor gymnasium! (Of course,
there are also hikers, equestrians, and other recreationists who fall into this
category.) To my suggestion to keep bikes off of trails in order to protect
wildlife, they reacted with hostility! (There is a degree of balkanization among
activists, where some transportation activists ignore the needs of wildlife, and
some wildlife activists eschew bikes and public transit.)
In 1994 I attended a public hearing held by the East Bay Municipal
Utility (water) District to decide whether to allow bikes on their watershed
lands. Mountain bikers were there asking for bike access, and the Sierra Club
was there to retain the right to hike, while keeping out the bicycles. I said
that I had no interest in using the watershed, but that I wanted to ensure that
the wildlife are protected -- hence, I asked that bikes not be allowed.
Afterward, the EBMUD Board of Directors took a field trip to Marin County, the
birthplace of mountain biking, to see the effects of mountain biking there.
While they were hiking along a narrow trail, a mountain biker came racing by,
swearing at them for not getting out of his way fast enough. That helped them
decide to ban bikes. Today bikes are still restricted to paved roads, and EBMUD
is still one of the public agencies most protective of wildlife.
It is obvious that mountain biking is harmful to some wildlife and
people. No one, even mountain bikers, tries to deny that. Bikes create V-shaped
ruts in trails, throw dirt to the outside on turns, crush small plants and
animals on and under the trail, facilitate increased levels of human access into
wildlife habitat, and drive other trail users (many of whom are seeking the
tranquility and primitiveness of natural surroundings) out of the parks. Because
land managers were starting to ban bikes from trails, the mountain bikers
decided to try to shift the battlefield to science, and try to convince people
that mountain biking is no more harmful than hiking. But there are two problems
with this approach: (1) it's not true, and (2) it's irrelevant.
I will examine (1) in a moment. But first, let's look at relevance:
whether or not hiking (or All Terrain Vehicles or urban sprawl or anything else)
is harmful really has no bearing on whether mountain biking is harmful: they are
independent questions. Such a comparison would only be relevant if one were
committed to allowing only one activity or the other, and wanted to know which
is more harmful. In reality, hiking is always allowed, and the question is
whether to add mountain biking as a permitted activity. In that case, the only
relevant question is: Is mountain biking harmful? Of course, it is. However,
since many people seem interested in the outcome of the comparison, I will
examine the research and try to answer it.
The mountain bikers' other line of research aims to prove that mountain
bikers are just like hikers, implying that they should have the same privileges
as hikers. (Of course, they already have the same privileges! The exact same
rules apply to both groups: both are allowed to hike everywhere, and neither is
allowed to bring a bike where they aren't allowed.) Using surveys, they have
tried to show that mountain bikers are really environmentalists, lovers of
nature, and deep ecologists. Of course, surveys are notoriously unreliable:
statements of belief don't easily translate into behavior. I'm going to ignore
this research, since I am (and the wildlife are) more interested in actual
impacts, not intentions.
The International Mountain Biking Association (IMBA) has done me the
favor of collecting all the research they could find that seemed favorable to
mountain biking. Gary Sprung (2004) summarized it in his carefully worded essay,
"Natural Resource Impacts of Mountain Biking". Gary says "the empirical studies
thus far do not support the notion that bikes cause more natural resource
impact". I will show that this is not true; in fact, those studies, if their
data are interpreted properly, show the exact opposite: that mountain biking has
much greater impact than hiking! Gary says that we should make "make rational,
non-arbitrary, less political decisions regarding which groups are allowed on
particular routes". This is disingenuous. Mountain bikers (but not bikes) are
already allowed on every trail.
Impacts on Soil (Erosion):
Gary says "No scientific studies show that mountain bikers cause more
wear to trails than other users". He cites Wilson and Seney (1994) and claims
that "hooves and feet erode more than wheels. … Wilson and Seney found no
statistically significant difference between measured bicycling and hiking
effects". He quotes the study: "Horses and hikers (hooves and feet) made more
sediment available than wheels (motorcycles and off-road bicycles) on prewetted
trails" (p.74).
This study is frequently cited by mountain bikers as proof that mountain
biking doesn't cause more impact than hiking. But it has a number of defects
that call its conclusions into question. The authors used a "rainfall simulator"
to measure "sediment made available" by the various treatments. They
"[collected] surface runoff and sediment yield produced by the simulated
rainstorms at the downslope end of each plot", which they claim "correlates with
erosion" (they don't say what the correlation coefficient is). This doesn't seem
like a good measure of erosion. For example, if a large rock were dislodged, the
very weak "simulated rainfall" wouldn't be capable of transporting it into the
collecting tray; only very fine particles would be collected. In fact, they
admit that the simulator's "small size … meant that the kinetic energy of the
simulated rainfall events was roughly one-third that of natural rainstorms".
Another reason to suspect that the measurements aren't valid is that "none of
the relationships between water runoff and soil texture, slope, antecedent soil
moisture, trail roughness, and soil resistance was statistically significant".
The authors also ignored the relative distances that various trail users
typically travel (for example, bikers generally travel several times as far as
hikers, multiplying their impacts accordingly) and the additional impacts due to
the mountain bike bringing new people to the trails that otherwise would not
have been there (the same omission is true of all other studies, except Wisdom
et al (2004)). They do say "Trail use in the last ten years has seen a dramatic
increase in off-road bicycles" (p.86), but they don't incorporate this fact into
their comparison. In addition, there is no recognition of different styles of
riding and their effect on erosion. We don't know if the mountain bikers rode in
representative fashion, or, more likely, rode more gently, with less skidding,
acceleration, braking, and turning. There was also no recognition that soil
displaced sideways (rather than downhill) also constitutes erosion damage. It
seems likely that they underestimated the true impacts of mountain biking. I
don't think that these results are reliable. (Note that the study was partially
funded by IMBA.)
Gary next cited Chiu ([email protected]) and Kriwoken
([email protected]), claiming that there was "no significant difference
between hiking and biking trail wear". I wasn't able to acquire this study, but
it is apparent from Gary's description of it that he (and perhaps the authors)
misstated the conclusions. If we assume, as they claim, that bikers and hikers
have the same impact per mile (which is what they measured), then it follows
that mountain bikers have several times the impact of hikers, since they
generally travel several times as far. (I haven't found any published
statistics, but I have informally collected 72 mountain bikers' ride
announcements, which advertise rides of a minimum of 8 miles, an average of 27
miles, and a maximum of 112 miles.)
Impacts on Plants:
Gary says "No scientific studies indicate that bicycling causes more
degradation of plants than hiking. Trails are places primarily devoid of
vegetation, so for trail use in the center of existing paths, impacts to
vegetation are not a concern." However this is a concern for plants that try to
establish themselves in the trail, and for roots that cross the trail and end up
being killed or damaged.
He cites Thurston and Reader (2001), claiming that "hiking and bicycling
trample vegetation at equal rates … the impacts of biking and hiking measured
here were not significantly different". Actually, that is not true. Although
overall impacts weren't significantly different, "soil exposure [was] greater on
biking 500 pass lanes than hiking 500 pass lanes" (p.404). In other words, after
500 passes, mountain biking began to show significantly greater impacts. Thus
their conclusion, "the impacts of biking and hiking measured here were not
significantly different" (p.405) is unwarranted.
The authors said "Bikers traveled at a moderate speed, usually allowing
bicycles to roll down lanes without pedaling where the slope would allow." Thus
it would appear that the mountain biking that they measured is not
representative: it was unusually slow and didn't include much opportunity for
braking, accelerating, or turning, where greater impacts would be expected to
occur.
The authors also said "Some hikers feel that bikers should be excluded
from existing trails" (p.397). Of course, this is not true. Hikers are only
asking that bikes be excluded, not bikers. On page 407 they admit the
"possibility … that mountain bikers simply contribute further to the overuse of
trails". In other words, allowing bikes on trails allows trail use to increase
over what it would be if bikes weren't allowed. This is probably true, and
deserves to be recognized and researched.
They found that "One year following treatments, neither vegetation loss
nor species loss was significantly greater on treated lanes than on control
lanes" (p.406). They conclude that the recreation impacts are "short-term", and
experience "rapid recovery". This is unjustified. Killing plants and destroying
seeds modifies the gene pool, and introduces human-caused loss of genetic
diversity, and evolution. Dead plants and lost genetic diversity do not
"recover" (see Vandeman, 2001).
However, the greatest defect of the study and its interpretation is that
is that it doesn't consider the distance that bikers travel. Even if we accepted
their conclusions that impacts per mile are the same, it would follow that
mountain bikers have several times the impact of hikers, since they are easily
able to, and do, travel several times as far as hikers. Try walking 25 or 50 or
100 miles in a day!
Impacts on Animals:
Gary cites Taylor and Knight (1993), claiming that "hiking and biking
cause [the] same impact to large mammals on Utah island". First, as noted by
Wisdom et al (2004), this study lacked a control group, and hence can't infer
causation. Second, the authors made the same mistake that all other researchers
made: they ignored the different distances that hikers and bikers travel. I also
wonder how realistic it was to have all recreationists continue past the animals
without stopping to look at them. (All of those researchers also failed to
implement blind measurement and analysis: the researchers were aware, as they
were measuring, which treatment they were testing. Only Wisdom et al were able
to carry out their measurements (electronically) without any people even being
present.)
This is a very informative paper. The authors "examined the responses of
bison …, mule deer …, and pronghorn antelope … to hikers and mountain bikers …
by comparing alert distance, flight distance, and distance moved" (p.951). They
noted, significantly, that "Outdoor recreation has the potential to disturb
wildlife, resulting in energetic costs, impacts to animals' behavior and
fitness, and avoidance of otherwise suitable habitat. … outdoor recreation is
the second leading cause for the decline of federally threatened and endangered
species on public lands" (p.951). They also noted that "Mountain biking in
particular is one of the fastest-growing outdoor activities, with 43.3 million
persons participating at least once in 2000" (p.952). However, they didn't draw
on this fact when they concluded "We found no biological justification for
managing mountain biking any differently than hiking" (p.961).
The authors also surveyed the recreationists, and found that they
"failed to perceive that they were having as great an effect on wildlife as our
biological data indicated. Most recreationists felt that it was acceptable to
approach wildlife at a much closer distance (mean acceptable distance to
approach = 59.0 m) than wildlife in our experimental trials would typically
allow a human to approach (mean flight distance of all species = 150.6 m). … Of
all visitors surveyed, 46%, 53%, and 54%, respectively, felt that bison, deer,
and pronghorn were being negatively affected by recreation on Antelope Island. …
Visitors expressed little support for allowing only one type of recreational use
on island trails, having fewer trails on the island, for requiring visitors to
watch an educational video about the effects of recreation on wildlife, and for
allowing recreation only on the north (developed) end of the island" (p.957).
(Gary Sprung omitted this information from his summary.)
They noted that the wildlife might habituate to the presence of humans,
but that exactly the opposite happened with the pronghorn: they "in fact used
areas that were significantly farther from trails than they had prior to the
start of recreational use on the island" (p.961). They also noted: "Because
flushing from recreational activity may come at the cost of energy needed for
normal survival, growth, and reproduction …, and because it may cause animals to
A Review of the Literature
Michael J. Vandeman, Ph.D.
July 3, 2004
"Every recreationist -- whether hiker, biker, horsepacker, or posey sniffer --
should not begin by asking, 'What's best for ME?' but rather 'What's best for
the bears?'" Tom Butler
"Will we keep some parts of the American landscape natural and wild and free --
or must every acre be easily accessible to people and their toys? … Mountain
bikes' impacts on the land are large and getting worse. … The aggressive push of
mountain bike organizations to build ever-growing webs of trails poses serious
problems of habitat fragmentation, increased erosion, and wildlife conflicts.
As interest in extreme riding continues to grow, as trail networks
burgeon, and as new technology makes it possible for ever-more mountain
bicyclists to participate, even the most remote wild landscapes may become
trammeled -- and trampled -- by knobby tires. … The destruction of wilderness
and the fragmentation of habitats and ecosystems is death by a thousand cuts.
Will introduction of mountain bikes -- and their penetration farther into
wilderness -- promote additional fragmentation and human conflicts with the
natural world? Yes." Brian O'Donnell and Michael Carroll
"Some things are obvious: mountain bikes do more damage to the land than hikers.
To think otherwise ignores the story told by the ground. Although I have never
ridden a mountain bike, I am very familiar with their impacts. For the last
seven years I have regularly run three to six miles several times a week on a
network of trails in the Sandia Mountain foothills two blocks from my home. …
These trails receive use from walkers, runners, and mountain bikers; they are
closed to motorized vehicles.
Because I'm clumsy, I keep my eyes on the trail in front of me. I run or
walk in all seasons, in all kinds of weather. I have watched the growing erosion
on these trails from mountain bike use. The basic difference between feet and
tires is that tire tracks are continuous and foot tracks are discontinuous.
Water finds that narrow, continuous tire tracks are a rill in which to flow.
Also, because many mountain bikers are after thrills and speed, their tires cut
into the ground. Slamming on the brakes after zooming downhill, sliding around
sharp corners, and digging in to go uphill: I see the results of this behavior
weekly. …
I regularly see mountain bikers cutting off cross-country, even on steep
slopes, for more of a challenge. They seem blind and deaf to the damage they
cause. Admittedly, backpackers and horsepackers can cause damage to wilderness
trails. But this is a poor argument to suggest that we add another source of
damage to those trails." Dave Foreman
"Studies show that bike impacts are similar to those of other non-motorized
trail users." Jim Hasenauer (professor of rhetoric and member of the board of
directors of the International Mountain Bicyclists Association)
Introduction:
I first became interested in the problem of mountain biking in 1994. I
had been studying the impacts of the presence of humans on wildlife, and had
come to the conclusion that there needs to be habitat that is entirely
off-limits to humans, in order that wildlife that is sensitive to the presence
of humans can survive (see Vandeman, 2000). But what is the best way to minimize
the presence of people? Restricting human access is repugnant, and difficult and
expensive to accomplish. It occurred to me that the best way to reduce the
presence and impacts of humans is to restrict the technologies that they are
allowed to utilize in nature: e.g. prohibit bicycles and other vehicles (and
perhaps even domesticated animals, when used as vehicles).
Having been a transportation activist for eight years (working on
stopping highway construction), and having a favorable view of my fellow
bicyclists as environmentalists, I turned to them to help me campaign to keep
bicycles out of natural areas. Was I ever surprised! I discovered that many
bicyclists (e.g. many mountain bikers) aren't environmentalists at all, but are
simply people who like to bicycle -- in the case of mountain bikers, many of
them just use nature, as a kind of playground or outdoor gymnasium! (Of course,
there are also hikers, equestrians, and other recreationists who fall into this
category.) To my suggestion to keep bikes off of trails in order to protect
wildlife, they reacted with hostility! (There is a degree of balkanization among
activists, where some transportation activists ignore the needs of wildlife, and
some wildlife activists eschew bikes and public transit.)
In 1994 I attended a public hearing held by the East Bay Municipal
Utility (water) District to decide whether to allow bikes on their watershed
lands. Mountain bikers were there asking for bike access, and the Sierra Club
was there to retain the right to hike, while keeping out the bicycles. I said
that I had no interest in using the watershed, but that I wanted to ensure that
the wildlife are protected -- hence, I asked that bikes not be allowed.
Afterward, the EBMUD Board of Directors took a field trip to Marin County, the
birthplace of mountain biking, to see the effects of mountain biking there.
While they were hiking along a narrow trail, a mountain biker came racing by,
swearing at them for not getting out of his way fast enough. That helped them
decide to ban bikes. Today bikes are still restricted to paved roads, and EBMUD
is still one of the public agencies most protective of wildlife.
It is obvious that mountain biking is harmful to some wildlife and
people. No one, even mountain bikers, tries to deny that. Bikes create V-shaped
ruts in trails, throw dirt to the outside on turns, crush small plants and
animals on and under the trail, facilitate increased levels of human access into
wildlife habitat, and drive other trail users (many of whom are seeking the
tranquility and primitiveness of natural surroundings) out of the parks. Because
land managers were starting to ban bikes from trails, the mountain bikers
decided to try to shift the battlefield to science, and try to convince people
that mountain biking is no more harmful than hiking. But there are two problems
with this approach: (1) it's not true, and (2) it's irrelevant.
I will examine (1) in a moment. But first, let's look at relevance:
whether or not hiking (or All Terrain Vehicles or urban sprawl or anything else)
is harmful really has no bearing on whether mountain biking is harmful: they are
independent questions. Such a comparison would only be relevant if one were
committed to allowing only one activity or the other, and wanted to know which
is more harmful. In reality, hiking is always allowed, and the question is
whether to add mountain biking as a permitted activity. In that case, the only
relevant question is: Is mountain biking harmful? Of course, it is. However,
since many people seem interested in the outcome of the comparison, I will
examine the research and try to answer it.
The mountain bikers' other line of research aims to prove that mountain
bikers are just like hikers, implying that they should have the same privileges
as hikers. (Of course, they already have the same privileges! The exact same
rules apply to both groups: both are allowed to hike everywhere, and neither is
allowed to bring a bike where they aren't allowed.) Using surveys, they have
tried to show that mountain bikers are really environmentalists, lovers of
nature, and deep ecologists. Of course, surveys are notoriously unreliable:
statements of belief don't easily translate into behavior. I'm going to ignore
this research, since I am (and the wildlife are) more interested in actual
impacts, not intentions.
The International Mountain Biking Association (IMBA) has done me the
favor of collecting all the research they could find that seemed favorable to
mountain biking. Gary Sprung (2004) summarized it in his carefully worded essay,
"Natural Resource Impacts of Mountain Biking". Gary says "the empirical studies
thus far do not support the notion that bikes cause more natural resource
impact". I will show that this is not true; in fact, those studies, if their
data are interpreted properly, show the exact opposite: that mountain biking has
much greater impact than hiking! Gary says that we should make "make rational,
non-arbitrary, less political decisions regarding which groups are allowed on
particular routes". This is disingenuous. Mountain bikers (but not bikes) are
already allowed on every trail.
Impacts on Soil (Erosion):
Gary says "No scientific studies show that mountain bikers cause more
wear to trails than other users". He cites Wilson and Seney (1994) and claims
that "hooves and feet erode more than wheels. … Wilson and Seney found no
statistically significant difference between measured bicycling and hiking
effects". He quotes the study: "Horses and hikers (hooves and feet) made more
sediment available than wheels (motorcycles and off-road bicycles) on prewetted
trails" (p.74).
This study is frequently cited by mountain bikers as proof that mountain
biking doesn't cause more impact than hiking. But it has a number of defects
that call its conclusions into question. The authors used a "rainfall simulator"
to measure "sediment made available" by the various treatments. They
"[collected] surface runoff and sediment yield produced by the simulated
rainstorms at the downslope end of each plot", which they claim "correlates with
erosion" (they don't say what the correlation coefficient is). This doesn't seem
like a good measure of erosion. For example, if a large rock were dislodged, the
very weak "simulated rainfall" wouldn't be capable of transporting it into the
collecting tray; only very fine particles would be collected. In fact, they
admit that the simulator's "small size … meant that the kinetic energy of the
simulated rainfall events was roughly one-third that of natural rainstorms".
Another reason to suspect that the measurements aren't valid is that "none of
the relationships between water runoff and soil texture, slope, antecedent soil
moisture, trail roughness, and soil resistance was statistically significant".
The authors also ignored the relative distances that various trail users
typically travel (for example, bikers generally travel several times as far as
hikers, multiplying their impacts accordingly) and the additional impacts due to
the mountain bike bringing new people to the trails that otherwise would not
have been there (the same omission is true of all other studies, except Wisdom
et al (2004)). They do say "Trail use in the last ten years has seen a dramatic
increase in off-road bicycles" (p.86), but they don't incorporate this fact into
their comparison. In addition, there is no recognition of different styles of
riding and their effect on erosion. We don't know if the mountain bikers rode in
representative fashion, or, more likely, rode more gently, with less skidding,
acceleration, braking, and turning. There was also no recognition that soil
displaced sideways (rather than downhill) also constitutes erosion damage. It
seems likely that they underestimated the true impacts of mountain biking. I
don't think that these results are reliable. (Note that the study was partially
funded by IMBA.)
Gary next cited Chiu ([email protected]) and Kriwoken
([email protected]), claiming that there was "no significant difference
between hiking and biking trail wear". I wasn't able to acquire this study, but
it is apparent from Gary's description of it that he (and perhaps the authors)
misstated the conclusions. If we assume, as they claim, that bikers and hikers
have the same impact per mile (which is what they measured), then it follows
that mountain bikers have several times the impact of hikers, since they
generally travel several times as far. (I haven't found any published
statistics, but I have informally collected 72 mountain bikers' ride
announcements, which advertise rides of a minimum of 8 miles, an average of 27
miles, and a maximum of 112 miles.)
Impacts on Plants:
Gary says "No scientific studies indicate that bicycling causes more
degradation of plants than hiking. Trails are places primarily devoid of
vegetation, so for trail use in the center of existing paths, impacts to
vegetation are not a concern." However this is a concern for plants that try to
establish themselves in the trail, and for roots that cross the trail and end up
being killed or damaged.
He cites Thurston and Reader (2001), claiming that "hiking and bicycling
trample vegetation at equal rates … the impacts of biking and hiking measured
here were not significantly different". Actually, that is not true. Although
overall impacts weren't significantly different, "soil exposure [was] greater on
biking 500 pass lanes than hiking 500 pass lanes" (p.404). In other words, after
500 passes, mountain biking began to show significantly greater impacts. Thus
their conclusion, "the impacts of biking and hiking measured here were not
significantly different" (p.405) is unwarranted.
The authors said "Bikers traveled at a moderate speed, usually allowing
bicycles to roll down lanes without pedaling where the slope would allow." Thus
it would appear that the mountain biking that they measured is not
representative: it was unusually slow and didn't include much opportunity for
braking, accelerating, or turning, where greater impacts would be expected to
occur.
The authors also said "Some hikers feel that bikers should be excluded
from existing trails" (p.397). Of course, this is not true. Hikers are only
asking that bikes be excluded, not bikers. On page 407 they admit the
"possibility … that mountain bikers simply contribute further to the overuse of
trails". In other words, allowing bikes on trails allows trail use to increase
over what it would be if bikes weren't allowed. This is probably true, and
deserves to be recognized and researched.
They found that "One year following treatments, neither vegetation loss
nor species loss was significantly greater on treated lanes than on control
lanes" (p.406). They conclude that the recreation impacts are "short-term", and
experience "rapid recovery". This is unjustified. Killing plants and destroying
seeds modifies the gene pool, and introduces human-caused loss of genetic
diversity, and evolution. Dead plants and lost genetic diversity do not
"recover" (see Vandeman, 2001).
However, the greatest defect of the study and its interpretation is that
is that it doesn't consider the distance that bikers travel. Even if we accepted
their conclusions that impacts per mile are the same, it would follow that
mountain bikers have several times the impact of hikers, since they are easily
able to, and do, travel several times as far as hikers. Try walking 25 or 50 or
100 miles in a day!
Impacts on Animals:
Gary cites Taylor and Knight (1993), claiming that "hiking and biking
cause [the] same impact to large mammals on Utah island". First, as noted by
Wisdom et al (2004), this study lacked a control group, and hence can't infer
causation. Second, the authors made the same mistake that all other researchers
made: they ignored the different distances that hikers and bikers travel. I also
wonder how realistic it was to have all recreationists continue past the animals
without stopping to look at them. (All of those researchers also failed to
implement blind measurement and analysis: the researchers were aware, as they
were measuring, which treatment they were testing. Only Wisdom et al were able
to carry out their measurements (electronically) without any people even being
present.)
This is a very informative paper. The authors "examined the responses of
bison …, mule deer …, and pronghorn antelope … to hikers and mountain bikers …
by comparing alert distance, flight distance, and distance moved" (p.951). They
noted, significantly, that "Outdoor recreation has the potential to disturb
wildlife, resulting in energetic costs, impacts to animals' behavior and
fitness, and avoidance of otherwise suitable habitat. … outdoor recreation is
the second leading cause for the decline of federally threatened and endangered
species on public lands" (p.951). They also noted that "Mountain biking in
particular is one of the fastest-growing outdoor activities, with 43.3 million
persons participating at least once in 2000" (p.952). However, they didn't draw
on this fact when they concluded "We found no biological justification for
managing mountain biking any differently than hiking" (p.961).
The authors also surveyed the recreationists, and found that they
"failed to perceive that they were having as great an effect on wildlife as our
biological data indicated. Most recreationists felt that it was acceptable to
approach wildlife at a much closer distance (mean acceptable distance to
approach = 59.0 m) than wildlife in our experimental trials would typically
allow a human to approach (mean flight distance of all species = 150.6 m). … Of
all visitors surveyed, 46%, 53%, and 54%, respectively, felt that bison, deer,
and pronghorn were being negatively affected by recreation on Antelope Island. …
Visitors expressed little support for allowing only one type of recreational use
on island trails, having fewer trails on the island, for requiring visitors to
watch an educational video about the effects of recreation on wildlife, and for
allowing recreation only on the north (developed) end of the island" (p.957).
(Gary Sprung omitted this information from his summary.)
They noted that the wildlife might habituate to the presence of humans,
but that exactly the opposite happened with the pronghorn: they "in fact used
areas that were significantly farther from trails than they had prior to the
start of recreational use on the island" (p.961). They also noted: "Because
flushing from recreational activity may come at the cost of energy needed for
normal survival, growth, and reproduction …, and because it may cause animals to