Into the Wild: Vegetation, Alien Plants,
and Familiar Fire at the Exurban Frontier
Abstract The spatial expansion of human populations threatens or alters ecosys-
tems on much of the country’s privately owned exurban land. These impacts affect
the many ways that plants, animals, and environments interact and inﬂuence one
another. This chapter considers exurban impacts to plant habitat, plant species, plant
community structure, ecological processes, and social conditions within, nearby,
and at a distance from development. The properties of major vegetation eco-regions
in the United States are described and how and why exurban development alters eco-
logical processes over varying spatial and temporal scales is explained. Issues such
as ﬁre suppression, land fragmentation, and the introduction of nonnative vegetation
are discussed as artifacts of exurban land development. The chapter also draws on
the research literature to discuss why speciﬁc development densities and conﬁgura-
tions are best suited for particular vegetation regimes and points to the mitigation
techniques that have proven most successful.
As primary producers of ecosystems, plants capture solar energy that sustains life,
while also serving as the foundation of ecosystem biodiversity. Vegetation provides
habitat and food for wildlife, protects and feeds the soil, and stores and cycles water
and other nutrients. Exurban development changes vegetation within and adjoining
it, but also can change conditions far from the development site. Direct displacement
and alteration of vegetation and indirect effects on ecological processes and species
composition are characteristic impacts. Long-term effects may be cumulative and
affect entire landscapes and distant areas. Fire and introduced species associated
with exurban development are extraordinarily costly and far-reaching. This chapter
L. Huntsinger (B)
Department of Environmental Science, Policy, and Management, University of California,
Berkeley, Berkeley, CA 94720, USA
A.X. Esparza, G. McPherson (eds.), The Planner’s Guide to Natural Resource
!Springer Science+Business Media, LLC 2009
134 L. Huntsinger
explores what is known about the effects of exurban development on vegetation.
The speciﬁc impacts of exurban development vary with the ecosystem and the char-
acteristics of the development, so while this chapter presents general concepts, it
cannot capture every situation. Instead the focus is on concepts of broad applicabil-
ity to generic forest, rangeland, and desert ecosystems. These concepts have much
in common with development impacts on wildlife but, unlike animals, plants cannot
move from one spot to another except through reproduction and growth.
Before discussing the inﬂuence of exurban change, it is important to consider
what kinds of land uses might precede exurban development. Presumably exur-
ban expansion occurs on privately owned land that is rural in character (Fig. 8.1).
While some of this land may truly be “vacant,” it is more likely used by the
owner for farming, grazing, forestry, hunting, and/or recreation. Vegetation often
has already been exposed to management for various goods and services and has
changed and adjusted as a result. For example, plant communities may have devel-
oped based on irrigation ponds and canals, and a spectrum of exotic species may
have been introduced intentionally or inadvertently. Trees and shrubs may have
been cleared for grazing, forests thinned or genetically improved for timber pro-
duction, game brought in for hunting, and ﬁelds created and plowed for farming.
Exurban development ends these uses and introduces new factors that shape plant
Fig. 8.1 The term “ranch”
takes on new meaning in an
Photograph by Lynn
For decades, maintaining biological diversity through protection of particular
species and habitats has been a primary focus of conservation. Ecologists now real-
ize the need to maintain the integrity of an ecosystem, rather than only elements of it.
“Ecological integrity” means that ecosystems are self-sustaining over long periods
of time. Thus, conserving the ecological integrity of an ecosystem means maintain-
ing not only biodiversity but also the processes that create structural and biological
diversity and enable the persistence of plant communities. These processes include
the many ways plants, animals, and environments interact and inﬂuence one another.
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 135
This chapter considers exurban impacts to plant habitat, plant species, plant com-
munity structure, ecological processes, and social conditions within, nearby, and at
Plant habitats are places where populations of plants normally are found. Habitats
are determined by the soils, climate, water dynamics, and topography of an area,
contemporary as well as historical inﬂuences, and the interactions among species at
statured plants that need abundant sunlight. Creation of a pond or watercourse
creates habitat for plants that need consistent access to water, often referred to as
riparian vegetation (see Chapter 10 for a discussion of riparian habitats). A history
of plowing for crop production changes the kinds of seeds and soils found on a site
and may inﬂuence vegetation long into the future, creating habitat for plants that
grow well in previously plowed areas. The suburban landowner, by regularly mow-
ing the lawn and adding fertilizer, hopes to create habitat for lawn grasses—though
the wily dandelion has found a way to occupy the same habitat.
Plant communities are groups of plants that share a habitat. The concept of com-
munity can be applied across a wide range of scales, from the plant community
along the shores of a small pond to the Amazon rain forest. The species in a plant
community interact with each other and with the environment and exist in recog-
nizable forms that develop repeatedly over space and time, such as oak woodlands,
pine forests, desert grassland, or sagebrush grassland. Plant communities are named
for the characteristic plant species within them or for characteristic environmental
The location of exurban development often is correlated with high levels of biodi-
versity because both are inﬂuenced by biophysical factors, particularly the presence
of water. Unusual rock outcrops or landscapes with abundant visual complexity,
which attract development, often harbor unusual habitats (Fig. 8.2). The ecological
importance of a habitat can be much greater than is suggested by its size (Naiman
and Décamps 1997). Consequently, the effects on biodiversity may be dispropor-
tionately large relative to the size of the exurban development (Hansen et al. 2005).
Rare habitats include those on unusual or endemic soils, where only long-adapted
natives can grow. The few small wetlands in a desert area, or the meadows in an
otherwise heavily forested landscape, are relatively rare habitats that also are desir-
able places for humans to live.
that are genetically different from those growing elsewhere. These habitats may
contribute signiﬁcantly to the compositional and structural complexity of a region
(Dale et al. 2005). An example of a relatively rare habitat is the vernal-pool habitat
that develops temporarily in spring on soils with a hardpan that slows or prevents
water drainage. The unique chemistry of the water, the harsh and variable growing
136 L. Huntsinger
Fig. 8.2 Although this
vacant ranch is now within
a preserve, the setting
illustrates the convergence
of attractive scenery and
riparian vegetation that leads
to high interest in exurban
development but also
relatively high levels
of biodiversity. Photograph
by Lynn Huntsinger
conditions, and the geographic isolation of individual pools lead to the development
of unique, very localized, species (Solomeshch, Barbour and Holland 2007). Exur-
ban development changes plant habitats profoundly (Table 8.1). Rural land uses
such as forestry or livestock grazing are heavily constrained by the environmental
conditions native to a site. Exurban development can bring far more resources to
bear on changing habitat, using intensive fertilization, pest and weed control, water
application, seeding, planting, and manipulation of existing plants. Because of this
manipulation, and the displacement of habitat by paving, construction, and associ-
ated disturbance, habitats often are completely eliminated and replaced with others
within a development. Nearby habitats are inﬂuenced directly by road construction,
changes in management, and the introduction of new species that are able to natu-
ralize and spread into the undeveloped land (Table 8.1). Further, additions of water
and nutrients may exceed levels that can be used by plants in the local climate, and
the excess may create polluted runoff that affects other habitats. Additions of water
and fertilizer typically alter and often reduce biodiversity (Dale et al. 2005).
Species and networks of interacting species have broad, ecosystem-level impacts
(Dale et al. 2005). One species may play a more obviously crucial role in an ecosys-
tem than others, as when it occupies a large area, or provides habitat for pollinators,
or is a crucial link in a complex food web (Dale et al. 2005). One species may mod-
ify habitat so that another can use it, by building soil or ﬁxing nitrogen. Endemic
or rare species are restricted to very small areas, yet they provide functions that are
critical to other species. The ultimate impacts of species change to biodiversity are
difﬁcult to predict and may have unexpected results because of the complexity of
plant interactions with each other and with the environment (Power et al. 1996).
Sometimes the processes associated with a single species can turn out to be critical
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 137
Tabl e 8.1 Impacts of exurban development on vegetation
With in the development Sur rounding area Dis tant but li nked areas
Structure Vegetation structure altered
directly by pruning, removal,
additions, clearing of defensible
space, construction, and paving
Fragmentation of previously continuous habitat
into spatially separated and smaller patches.
Additional edge and more patchy environment,
loss or creation of corridors for species
migration, less core habitat. Pollination may be
inﬂuenced by changes in patchiness or
connectivity and introduction of new species.
Roads and trails become vectors for the spread
of invasive plants, plant pests, and diseases
Reservoirs to hold water, levees and
channelization, and draining of
wetlands may all be caused by the
need to supply water to exurban
developments and to protect them
from ﬂooding. Road, pipelines and
power lines fragment habitat
Suppression of most ecological
processes, including disturbance
regimes, nutrient cycling,
Ecosystem processes, feedbacks between
environment and plants, interactions between
plants, nutrient cycling, disturbance regimes
may be changed or suppressed by management
or the introduction of new species
Vegetation adapted to water-based
disturbance regimes or access to wet
soils and riparian areas will be
altered. Air quality change may
affect plant communities
Massive displacement of wild with
domesticated plants, new species
are introduced, and others are
controlled or reduced. Plant
pests and diseases, and
herbivores, may be introduced or
Spread of invasive species, plant pests and
diseases, and new herbivores. Plants that can
live under natural conditions may naturalize in
the surrounding areas, changing the character
of plant communities and altering ecological
processes. New diseases and herbivores, or
herbivore predators, may also affect the
surrounding vegetation. These changes are
continuous and do not have a foreseeable end
The spread of invasive species, plant
pests and diseases, and new
herbivores may extend over huge
138 L. Huntsinger
Table 8.1 (continued)
With in the development Sur rounding area Dis tant but li nked areas
Signiﬁcantly altered because of
large inputs of chemicals, water,
and materials. Changes in water
availability, soils, wind and
thermal patterns, erosion, ﬁre,
ﬂooding, localized pollution. May
lose small habitats entirely, new
ones created. May extend and
increase supply of green growth
or biomass through year
Risks to nearby homes makes prescribed burning,
use of herbicides, tree thinning, more costly
and sometimes impossible. Changes in water
use and availability as streams are allocated,
diverted, or controlled. Tree thinning, fuel
breaks, vegetation manipulation may extend to
nearby areas and inﬂuence habitats.
Suppression of disturbance regimes changes
Roadside habitats created, riparian
Landowner goals for residential
living are dominant and may
require complete change in
vegetation; management for
defensible space; pets. New
residents may not recognize or
comply with social norms of
behavior. Absentee ownerships
may make community
management strategies less
New constituencies favoring one type or another
of management and protection for surrounding
lands. Loss of community, infrastructure,
political voice, and conﬂicts with new residents
makes forestry, ranching, farming, and hunting
more difﬁcult and more regulated. This leads to
habitat and vegetation change. New groups
seek to inﬂuence traditional uses and
management of public and private lands. Local
economy may come to depend on commuter
and/or retiree economy. Loss of infrastructure
and community may accelerate conversion to
Change in the relative inﬂuence of
different groups on local and
eventually more distant planning and
political processes. Need for services
may extend impacts
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 139
to ecosystem functions (Dale et al. 2005). Exurban development creates widespread
change by introducing new species or changing habitat, adding barriers to move-
ment or dispersal, introducing new herbivores, and changing competitive dynamics
among species (Table 8.1).
Ecosystems vary in the number and density of plants and plant species they con-
tain. The absolute number of species or density of plants is not necessarily an indica-
tor of the status of an ecosystem or plant community. Redwood forests in California,
for example, have comparatively few species, despite being a relatively intact native
plant community. The density of plants may be very low in desert areas, reﬂecting
limited soil and water resources. However, one general statement is that the native
species present on a site have adapted to the site and to each other over evolutionary
time, creating a persistent plant community. In turn, the wildlife species, soil condi-
tions, water, nutrient cycling, and other ecological processes linked to this particu-
lar complex of plants will change if the plant community changes. For this reason,
the proportion of native species on a site is sometimes considered an indicator of
Exurban developments favor species that are adapted to human-altered environ-
ments. Nonnative and weedy species generally increase (Hansen et al. 2005). New
residents bring in exotic species for landscaping or gardening and control native
species that are not desirable to the owner. Humans act as unwitting vectors for inva-
sive plants whose seeds are carried on clothing or pet fur. Introduction of nonnative
species can have profound affects on plant communities, because the relationships
among plants and environment that has evolved over time can be severely altered, in
turn changing species composition and ultimately, wildlife habitats and site charac-
teristics. For example, a new species that uses water more rapidly than native desert
species can prevent natives from obtaining the water they need. Highly aggressive
plants out-compete the natives, shading them or excluding them from their habitat.
Nonnative plants may assume a focal role in an ecosystem and change community
composition and ecosystem processes in their roles as competitors or vectors for
pathogens and disease and through effects on water balance, soils, productivity, and
habitat structure (Drake et al. 1989).
In some areas, rural land uses have already changed plant communities signif-
icantly. Yet these communities may have achieved relative stability over time by
adjusting to or persisting despite rural land uses over the last 200 or so years. Exur-
ban development will inevitably introduce new species into these and other nearby
plant communities, causing new kinds of change. The extent and impact of this
change is unknown. Increased ﬁre frequency and air pollution during the last sev-
eral decades in southern California facilitated the widespread conversion of coastal
sage shrubland to exotic grassland systems (Talluto and Suding 2008). Effects on
biodiversity are cumulative and often nonlinear and continue to emerge for decades
after development occurs (Maestas, Knight and Gilgert 2003; Hansen et al. 2005).
In addition to introduction of new species, exurban development fosters vegeta-
tion change by altering water availability. The new and/or better-watered plants have
characteristics that attract some wildlife species and increase their numbers. Plants
may remain green when native species are dry during the summer or in drought,
140 L. Huntsinger
or produce fruits and leaves that are particularly tasty and nutritious. One com-
mon animal that can prosper from exurban practices is the deer. In much of the
United States, local deer species adapt well to exurban food sources and battles
ensue as landowners struggle to protect their landscaping from the rapacious her-
bivores. Pocket gophers enjoy the softer, irrigated soils of irrigated landscaping.
Each plant species responds differently to changes in habitat, and regardless of the
type of change, some species will beneﬁt and others will decline. Three levels of
development in coastal California did not alter overall numbers and diversity of
woodland birds, but the species present did change (Merenlender, Heise and Brooks
1998). Speciﬁcally, more nonnative species were associated with the more inten-
sively developed areas. A survey of rangelands conducted in Colorado found that
private ranchlands had plant communities with higher native species richness and
lower nonnative species richness and cover than did exurban areas or protected areas
(Maestas, Knight and Gilgert 2003).
Plant communities have structure that creates habitat and affects species composi-
tion. Vertical layers of vegetation, canopy, shrub, and herb layers – comprise vertical
structure. Across a landscape – varying proportions of rock outcrops, shrubs, trees,
grasses, and watercourses create a horizontal landscape mosaic of habitat patches of
varying sizes, termed horizontal structure (Giusti, McCreary and Standiford 2005).
In grasslands, vegetation is short and ﬂexible. Shrubs introduce a woody component,
adding height and complexity. Trees add further height, large trunks, and extensive
canopies. Each increase in vertical complexity adds additional habitats for plants as
well as wildlife in the landscape. Trees and shrubs provide shady habitats for plants,
for example, or arboreal habitat for mosses and lichens.
Horizontally, a continuous forest provides one kind of vegetation structure with
relatively few low-growing species and extensive, contiguous canopy. A patchy for-
est provides a mix of treed and open areas where grasses and shrubs can grow. The
roads, clearings, houses, and pipelines associated with exurban development inter-
rupt horizontal structure and create new habitats, fragmenting contiguous areas into
smaller patches (Table 8.1). This results in greater amounts of “edge” habitat and
smaller amounts of “core” or interior habitat, beneﬁting edge species while reducing
core plant and animal species. The edges and cores of plant communities can have
quite different conditions and habitats, and the abundance of edge and interior habi-
tat varies with patch size. Fragmentation of plant communities may enhance suscep-
tibility to a variety of disturbances, including windthrow, pest epidemics, invasion
by nonnative species (Franklin and Forman 1987), and increased grazing pressure
from native or nonnative herbivores.
Housing and pavement obviously eliminate vegetation structure, and plantings
create new structure. A road creates patches where sunlight can reach plants, but
reduces the connectedness and extent of contiguous canopy in a forest, thereby
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 141
fragmenting the habitat. Roads fragment deserts and rangelands and act as vectors
for nonnative species (Gelbard and Belnap 2003). Corridors, or linkages among
plant communities that are often recommended for wildlife, also provide opportu-
nities for the spread of invasive plant species (see Chapter 5 for a discussion of
fragmentation, corridors, patches, and edges). Fuel breaks constructed to protect
developments facilitate the spread of nonnative species. A statewide study in Cali-
fornia found that nonnative plant abundance was over 200% higher on fuel breaks
than in adjacent wildland areas. There was a signiﬁcant decline in relative non-
native cover with increasing distance from the fuel break (Merriam, Keeley and
Exurban development can have other direct impacts on vegetation structure. In
addition to the complete replacement of native communities with residential land-
scaping, remnant native vegetation may be thinned, cleared, or pruned, sometimes
for ﬁre prevention. Particular plants may be encouraged to grow with watering or
protection from herbivores and ﬁre. Indirectly, impacts to surrounding vegetation
structure can be strong. For example, the need to suppress wildﬁres near develop-
ments may change vegetation with the inﬁlling of trees and shrubs into more open
woodlands or grasslands. Unfortunately, together with the increased likelihood of
ﬁre with increased human activity, over time this will in turn increase ﬁre hazard to
Ecosystem processes are critical to the persistence of plant communities and are
affected directly and indirectly by exurban development (Table 8.1). Ecosystems
are shaped by processes such as herbivory, competition, interrelationships of plants
and environment, pollination, and nutrient cycling. Exurban development alters bio-
geochemical cycles that can change the pace or direction of ecosystem change for
decades or centuries (Dale et al. 2005) (Table 8.1). For example, deposition of nitro-
gen from auto exhaust favors nonnative grasses in northern California, eliminat-
ing the habitat of the rare, endemic Bay checkerspot butterﬂy (Euphydryas editha
ent cycling (Vitousek 1986; Lyons and Schwartz 2001). An overall loss of nitro-
gen in an ecosystem resulting from the takeover of a sagebrush site by nonnative
cheatgrass (Bromus tectorum)hasbeendocumented(Evansetal.2001).Clearingof
vegetation releases carbon and nitrogen, and changes soil moisture regimes.
Species interactions can change or stabilize plant communities. For example, in
some environments competition between plants leads to the development of plant
communities dominated by the tallest species or suite of species capable of occupy-
ing a particular habitat. These communities, sometimes termed “climax communi-
ties,” can be quite stable in the absence of disturbance. On the other hand, in arid
environments a lack of soil nutrients or water overwhelms the effects of compe-
tition among plants, and the community that develops is determined more by the
142 L. Huntsinger
ability of a particular species or a suite of species to use the available habitats.
Internal regulating forces and relationships, such as competition and nutrient avail-
ability and cycling, maintain a plant community within certain bounds (Perry, Oren
and Hart 2008). To cross those bounds and become a different plant community is
often represented as crossing a threshold of some sort, where return to the origi-
nal plant community is unlikely to happen without external intervention. The plant
community settles into a conﬁguration within a new set of boundaries, sometimes
represented as similar to the way a ball rests in a cup.
Vario u s d i s t u r b a n c e s c a n d i s r u p t t h e e c o s y s t e m ’s internal regulating processes,
including competition and nutrient cycling (Dale et al. 2005). Disturbance is often
it. Fire is perhaps the most classic example, but ﬂooding, severe drought, wind-
storms, plowing, clearing, and even cessation of herbivory are disturbances. Some
plant communities depend on native disturbance regimes—particular patterns and
frequencies of disturbance––to maintain stability. For example, in some shrub com-
munities, there are many ecological processes and adaptations that enable swift
recovery from a common disturbance such as wildﬁre. After the ﬁre a suite of spe-
cially adapted ﬁre-following species occupies the site, some of which require ﬁre to
germinate or to create suitable habitat. Shrubs are quickly able to reseed or resprout
and reoccupy the site within a few years. The shrub plant community is resilient to
ﬁre, in that wildﬁre does not move it beyond the bounds that deﬁne it. The plant
community may look different after burning and take a while to recover its former
appearance, but it does not change to a different plant community for any signiﬁcant
length of time.
Ecological feedback processes create resilience and persistence despite distur-
bance. Resilience is the capacity of an ecosystem or plant community to recover
structure and function after disturbance (Walker and Fortmann 2003). In a forest
community that experiences frequent ﬁre, the understory has little to burn, limiting
the possibility of ﬁre getting into the canopy layer and killing the trees. The forest is
quite resistant to ﬁre, or resilient, because of this feedback cycle, where ﬁre begets
less severe ﬁre. On the other hand, changes in the frequency and type of ﬁres or other
disturbances can destabilize plant communities (Keeley, Lubin and Fotheringham
2003), because the ecological processes that enable persistence may only function
within the native ﬁre regime. For example, a forest may recover very quickly from
ﬁre frequency, trees become more tightly packed and smaller trees carry the next
ﬁre into the canopy, resulting in high tree mortality. Exurban development generally
entails ﬁre suppression, disrupting ﬁre feedback processes and leading to a loss of
resilience to ﬁre.
Land-use changes that alter natural disturbance regimes or initiate new distur-
bances are likely to cause changes in species abundance and distribution, species
composition, and ecosystem function (Yarie et al. 1998). Flood control or water
appropriation for exurban development may disrupt ecological processes in plant
communities that are adapted to frequent ﬂooding or particular patterns of water
availability, changing habitat characteristics, species composition, nutrient cycling
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 143
and habitat characteristics, among other things. Fires that are too frequent may pre-
vent the woody component of a shrub-dominated community from coming back,
and create habitat for invasive species.
The introduction of a new species can affect resilience by derailing native
response processes. Even if a disturbance regime is not changed, the presence of
invasive plant is able to take over the site after a ﬁre, the native species that would
otherwise come in may be unable to establish. This can cause permanent change
to the plant community. In Sierran forests, Keeley (2006) found that because of the
presence of new species, wildﬁre, and even prescribed low intensity ﬁre to which
Sierra forests once would have been quite resilient, now serves to spread invasive
species and further change ecosystems. A critical problem for ecologists today is
that ecosystems have changed, and the processes that maintained stability in the
past may not work in present and future conditions.
As opposed to feedbacks that maintain stability within bounds, cycles may be
initiated that, if not dampened or mitigated, can lead to costly and self-perpetuating
changes in vegetation at the landscape scale. A relentless positive feedback can
lead to great change, as with the introduction of cheatgrass (Bromus tectorum)to
intermountain sagebrush rangelands (Menakis, Osborne and Miller 2003). Cheat-
grass successfully makes use of available habitat opened up by land clearing, over-
grazing, wildﬁre, and other disturbances to the existing vegetation, maintaining site
occupancy by quickly using up available water resources early in the spring. The
annual growth habit of the species results in an abundant dry biomass over the sum-
mer that leads to frequent ﬁre, much more frequent than is believed to occur under
natural ﬁre regimes, thereby reducing the native shrubby component and opening
up more areas to cheatgrass, which in turn leads to more ﬁre. Ultimately, the vege-
tation changes to a cheatgrass-dominated grassland. This grassland may continue to
expand into other plant communities by fostering ﬁres that open up more habitats
for cheatgrass, affecting the distribution and character of plant communities at the
Changes in ecological processes may be slow to reveal themselves. The effects
of increased ﬁre hazard resulting from the introduction of new species, or inﬁlling
of native species due to ﬁre suppression, or the cessation of forestry and agricul-
ture in areas surrounding development may not manifest for decades. The impacts
of new pests on desert species, or a lack of reproduction in slow growing and slow
changing desert environments, may take a long time to detect. Yet these changes
can have far-reaching and persistent effects. The loss of pollinators due to decline in
habitats that support the reproduction of native bees and wasps may not ever be rec-
ognized. Instead, the disappearances of the plants that depend on them are attributed
to something else. Impacts may also take a long time to develop. The cumulative
effects of development may lead to gradual change, as when increased nitrogen
from automobile exhaust alters the composition of plant communities over time.
Exurban development can be seen as a form of disturbance, but it is not a
form to which existing plant communities are adapted. Millennia of exposure to
certain kinds of disturbance, including drought, ﬂooding, and ﬁre, has resulted in
144 L. Huntsinger
some western plant communities being quite resilient to certain frequencies and
types of each, with feedback processes that maintain stability. There has been no
such opportunity for the evolution of stability-maintaining feedbacks with exurban
development, including the introduction of new species and changes in site char-
acteristics that accompany it. The impacts take us into uncharted territory, and our
ability to anticipate long-term outcomes is limited.
Social and Economic Impacts
Private rural lands are an important buffer between public lands and urban devel-
opment, but exurban development on the edges of public lands disrupts that buffer
(Talbert, Knight and Mitchell 2007). Exurban development affects many social and
economic conditions, which in turn alter vegetation (Table 8.1). Public lands add
value to development, but this means that for the foreseeable future the new devel-
opment will inﬂuence, and be inﬂuenced by, the management of public lands. Once
houses are introduced into the mix, vegetation management priorities and options
are changed, essentially forever. Ecological processes such as ﬁre can no longer
be allowed to occur, and invasive plants, pets, human ﬁre starts, and other exur-
ban impacts will more directly affect nearby public lands. Prescribed burning and
grazing are often lost as management options (Fried and Huntsinger 1998).
impacts on plants, but the loss of farm, ranch, and forestry enterprises can also
establish a feedback cycle that can lead to even greater loss of rural land and fos-
ter more exurban development. Exurban expansion into farms, forest, or rangeland
fragments rural lands and results in development surrounded by privately owned
production land. Suburban neighbors may object to timber harvest, animal manage-
ment, and crop management practices, and conﬂicts and vandalism increase costs
to rural enterprises. Exurban residents may be unaware of or unwilling to follow
the social norms of behavior and interaction that have been a part of rural commu-
nities for decades (Ellickson 1991; Yung and Belsky 2007). Producers draw on a
community of other producers for support, shared labor, and information. As rural
enterprises disappear, this community grows smaller and farmers, ranchers, and for-
est owners become more isolated.
Further, ranches and farms require access to infrastructure, including veteri-
narians, packing houses, processing facilities, and agricultural advisory services
(Huntsinger and Hopkinson 1996). Forestry enterprises require equipment and
mills, as well as skilled labor. As lands are developed, there are fewer rural enter-
prises to support this infrastructure. With each forest, farm, or ranch that ceases to
exist, the remaining enterprises become more vulnerable to conversion (Liffmann,
Huntsinger and Forero 2000) (Fig. 8.3). This feedback cycle can eventually lead to
the loss of rural enterprises over a wide area. In one study of exurbanizing commu-
nities, ranchers had seen an average of 10 neighboring ranches sold for development
and stated that this was an important reason they might sell their ranch (Sulak and
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 145
Fig. 8.3 Development
feedback loop. As rural
enterprises are converted
to exurban development,
pressure to sell on the
increases. Source: Lynn
For historical reasons, privately owned rural lands generally have more water and
better soils than publically owned land. In addition, private rural lands offer habitats
unavailable on public or urban lands. For example, privately owned wetlands pro-
vide migratory waterfowl in conjunction with rice production in the central valley
of California. In the Sierra Nevada, where public and private lands are interwoven,
public forests have been profoundly changed by ﬁre suppression, while ranchers his-
torically have maintained relatively ﬁre-resilient open woodlands through grazing,
brush control, prescribed burning, and tree thinning (Sulak and Huntsinger 2002).
Another form of “exurban expansion” is the purchase of production-oriented
properties for urban refugees who then manage the properties for amenity values:
ership emphasis leads to a shift in ecosystems. In southwestern Montana, Gosnell,
Haggerty and Byorth (2007) found that new owners managed water differently than
long-time owners, inﬂuencing the region’s ﬁsheries in positive and negative ways.
In the Rocky Mountain region, Gosnell and Travis (2005) found that about half of
the ranches sold were going to amenity buyers, who often had quite different views
about land and vegetation use and management than the rural populace. In some
high-amenity developments, properties are often vacation or second homes. Absen-
tee owners are less likely to take part in the community and in collaborative efforts
at vegetation management and ﬁre-hazard reduction and may be difﬁcult to contact.
Amenity buyers add a new political dimension to local communities and a different
set of goals for land management.
Exurban residents may quickly outnumber rural residents and change the eco-
nomics and politics of a region (Gosnell and Travis 2005; Sheridan 2007). While
the rural community may value its historical connection with and shaping of the
landscape, new residents may be attracted to exurban development because of a
perceived lack of people and human impacts in an area. Exurban and rural resi-
dents may have very different expectations of the “country life” and how vegetation
should be managed (Masuda and Garvin 2008). In-migrants may bring with them
particular “aesthetic” or “consumption” views of a landscape that long-time res-
idents view as political threats. In one example these tensions ignited a political
ﬁrestorm over a proposal by the environmentalist-dominated county government
to incorporate landscape-scale aesthetic and environmental principles into county
planning (Walker and Fortmann 2003) (see Chapter 13 for further discussion of
rural attitudes toward land use and regulation).
146 L. Huntsinger
An increased population can also mean an increased positive presence on the
land. Local conservation areas will have a larger body of volunteers for restoration
work. Fire agencies will have more eyes on the land to watch for smoke. Lake
Taho e, in N eva da an d C ali for n ia, h a s ex p eri ence d a tre m end ous bu ild -up o f f uel s
in its forests. However, large ﬁres are rare in part because the large number of peo-
ple in the area report ﬁres quickly. One California rancher reported that in an area
where residents appreciated grazing for reduction of ﬁre hazard, exurban residents
would notify him when a calf was in trouble or a fence was breached (Fried and
Verti c a l s t r u c t u r e a n d s p e c i e s c o m p o s i t i o n a r e k e y e l e m e n t s o f e c o l o g i c a l i n t e g r i t y
in native forests (Yongblood, Max and Coe 2004) and, although readily measured
and managed, they can be difﬁcult to retain in urban settings (Sanders 1984). For
example, a 48-year study of changes in forest canopy in a 16 ha remnant forest
patch in the New York Botanical Garden showed that overstory canopy composi-
tion had been signiﬁcantly altered by changes in disturbance regime (Rudnicky and
McDonnell 1989). In addition, activities by local residents can contribute to the loss
of standing and down woody material (Matlack 1993), as well as changes in vegeta-
tion. Snags are commonly removed in areas with high recreation use or near houses
and roads because of concerns that they may fall. Logs and snags are often gath-
ered as ﬁrewood as well. Remnant native vegetation is sometimes manicured to be
more pleasing to the eye or easier for people to navigate by reducing the density
of the overstory and removing dead woody material (Tyrväinen, Silvennoinen and
Kolehmainen 2003). In forested areas, edges caused by development and roads tend
to be sunnier, warmer, drier, and more favorable to invasive nonnative species at the
expense of many native species.
In some exurban environments, efforts are made to save individual trees within
the development. Such trees are cut off from the network of ecological processes
that sustain them. Soil changes due to watering or soil compaction may eventu-
ally kill the trees. In addition, the trees are cut off from nutrient-cycling processes
that formerly took place underneath and around them. Pollinators, native to the for-
mer herbaceous vegetation, may not be able to locate scattered trees surrounded
by development. Without nearby habitats suitable for the growth of new trees, the
preserved trees will eventually simply die off.
On the other hand, remnant native forests can contribute signiﬁcantly to main-
taining native species in an urbanizing landscape, especially if there is some
degree of connectivity to larger areas of forest and regulations restricting site alter-
ation (Heckmann, Manley and Schlesinger 2008). Despite an increase in non-
native species, remnant forests equal to or greater than 0.1 ha in size in the
Lake Tahoe basin retained much of their compositional and structural character
along a development gradient, including large tree density, total canopy cover, and
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 147
plant species richness (Heckmann, Manley and Schlesinger 2008). One substan-
tive difference was the removal of downed woody material by local residents in
remnant forests. Remnant forests with high ground cover by native plants, high
canopy closure, and low ground disturbance may be less susceptible to inva-
sion by nonnative plants (Mandryk and Wein 2006; Merriam, Keeley and Beyers
Higher levels of human activity bring a variety of risks to the forest. In California,
patterns of sudden oak death seem to be related to the prevalence of human
recreation (Cushman and Meentemeyer 2008). Human activities such as construc-
tion, trenching, paving, sewage efﬂuent disposal, insecticidal spraying of trees for
mosquito control, and road de-icing can promote disease by injuring trees (Ferrell
1996). Soil compaction from various human activities, including keeping horses and
other animals, can also degrade tree health by reducing leaf growth and changing
root morphology (Lambers, Chapin and Pons 1998).
The greatest challenge for exurban development in western forests is coping
with ﬁre hazard. Many exurban developments are adjacent to public lands, where
forest management is seemingly always controversial and is not under the con-
trol of the community affected by it. Western forests generally have been sub-
jected to ﬁre suppression for more than a century, resulting in ecological and
human safety problems, such as altered forest structure, increased tree density,
increased accumulation of dead wood, increased insect outbreaks, lowered biodi-
versity, and vulnerability to catastrophic ﬁres (McKelvey and Johnson 1992; Ferrell
1996; McKelvey et al. 1996; Keeley, Lubin and Fotheringham 2003; Jensen and
Within developed areas, landowners may choose quite different levels and types
of management for ﬁre-hazard reduction and may or may not collaborate and plan
together to reduce the possibility of a conﬂagration. There is a typical pattern of
attitudes toward trees held by exurban residents: when they ﬁrst move into the forest
they want to protect every tree. After living in an area for a while they begin to
see the danger of too many trees more clearly. The management of the Lake Tahoe
Basin is a case in point: management for ﬁre-hazard reduction has been and remains
highly controversial, with some residents wanting fewer trees, some wanting more,
and much disagreement on the types of fuels reduction that are appropriate. The
scientiﬁc debate is also vociferous, with some arguing that fuel-reduction programs
increase invasion by nonnative plants and destroy wildlife habitat and others arguing
that there is no alternative, as ﬁres are inevitable and the kinds that happen after
decades of ﬁre suppression are far more damaging to air quality, wildlife habitat,
and plant communities than fuel treatments such as thinning, prescribed burning,
and brush crushing.
Unfortunately, forest fuel-reduction programs have the potential to enhance for-
est vulnerability to alien invasions. In part this is due to the focus on reestablishing
native ﬁre regimes in a landscape that differs from pre-Euro-American landscapes in
the abundance of aggressive nonnative species (Keeley 2006). The common intro-
duction of nonnative plants may disrupt the ability of the forest to recover after a
ﬁre, harvest, or thinning treatment.
148 L. Huntsinger
The author deﬁnes rangelands as woodlands, shrublands, and grasslands. Distur-
bance and fragmentation in shrublands at the edges of exurban or urban development
lead eventually to the complete replacement of the native vegetation and most of the
fauna by exotic plants and a combination of generalist native and exotic animals.
The ﬁrst fragmentation event is often road construction, with associated housing
developments. Fuel breaks may be established and pose a special invasive plant risk
because they promote alien invasion along corridors into wildland areas (Keeley
2006). Later, habitat remnants may be subdivided by additional development. But
these isolated events are just the beginning. As described by Soulé, Alberts, and
Bolger (1992), trails soon appear, and vagrants and neighborhood children remove
the plant cover for camping sites and “forts.” The edges of the remnant are nibbled
by expanding gardens and back yards. These incursions are essentially irreversible
in scrub and chaparral-type associations because the vegetation is slow to reestablish
following removal. The proportion of core habitat in a fragment decreases over time,
and before long no point in the remnant is more than a meter or two from some kind
of artiﬁcial opening. These internal disturbances represent secondary fragmentation
that occurs within the larger scale fragmentation of the area.
In a study of the effects of fragmentation in a shrub habitat in California, effects
on plants and wildlife were found to go hand in hand. Extinctions after fragmenta-
tion occur quickly, with the least common species disappearing ﬁrst. The size of the
remnant was the major predictor of extinction, with larger reserves generally supe-
rior for conserving species. In chaparral habitats in southern California, it was found
that in habitat remnants in the 10–100 ha range, only the most abundant chaparral-
dependent animal species survive for long, and most of these are doomed within
lative habitat disturbance and perhaps also because of changes in the frequency of
ﬁre. In conclusion, Soulé, Alberts and Bolger (1992) argue that much more needs to
be learned about managing habitat remnants.
Exurban residents may plant species capable of naturalizing and moving out into
wildlands. The shrubs French broom (Genista monspessulana)andScotchbroom
showy yellow ﬂowers. They have now spread throughout the west coast and cre-
ated new plant communities, thus changing the appearance of landscapes, shading
out native species, and altering soil characteristics to favor weedy, invasive species
(Vitousek et al. 1997).
Many shrubland ecosystems, such as intermountain west sagebrush steppe and
California chaparral, have natural, high-intensity crown ﬁre regimes that do not mix
well with exurban development (Keeley 2006). A major contributor to increased
ﬁre-suppression costs and increased loss of property and lives is the continued
urban sprawl into wildlands naturally subjected to high-intensity crown ﬁres. Dif-
ferent shrublands have different kinds of ﬁre regimes, however, requiring differ-
ent ﬁre-management tactics, yet in most cases, our knowledge is far from adequate
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 149
Shrub invasion can occur in western ecosystems as a result of ﬁre suppression,
ultimately increasing ﬁre risk. In the San Francisco Bay area, ﬁre suppression and
reduced grazing have resulted in plant community change in the open spaces sur-
rounding the urbanized areas of the San Francisco Bay. There has been signiﬁ-
cant conversion of grassland to shrubland dominated by coyote brush (Baccharis
pilularis). A signiﬁcant increase in biomass resulting from the change from grass-
dominated to shrub-dominated communities was evident. Using ﬁre modeling to
examine the effects of shrub increases on ﬁre hazard showed that the replacement
of grass-dominated areas with shrub-dominated landscapes has increased the prob-
ability of high-intensity ﬁres (Russell and McBride 2003).
On the other hand, frequent ﬁres can obliterate the woody component of some
shrublands. For example, if ﬁre occurs too often in sagebrush steppe, sagebrush
is unable to recover. Invasion by cheatgrass, as discussed previously, facilitates this
conversion. In chaparral, ﬁres create opportunities for invasion of nonnative species.
There is considerable argument about the appropriate ﬁre regimes in the various
shrubby regions of the west, but it is clear that ﬁre regimes vary among ecosystems
(Jensen and McPherson 2008). In addition, the increasing presence of nonnative
species complicates predictions of ﬁre outcomes.
In desert ecosystems, water is the key to life. Natural and artiﬁcial ponds and water-
ways may be focal habitat for plant communities that depend on consistent access to
water. Areas with water are rare and should be focal points for conservation. These
areas contain key habitats, have a high diversity of species in need of conserva-
tion, and are highly attractive to people for recreation and residence. Ranches and
farms typically center on water, and these areas are highly attractive for exurban
As development occurs in desert areas, land is re-contoured, vegetation is planted
or removed, road networks are built, and buildings are erected. New landscapes and
plant communities attractive to residents are created. In arid and semiarid ecosys-
tems, these designed, engineered ecosystems are often characterized by plantings
with high water demand, so water must be brought in from elsewhere. Assessing the
impacts of development on a wash in central Arizona, Roach et al. (2008) found that
the construction of canals created new ﬂowpaths that cut across historic stream chan-
nels, and the creation of artiﬁcial lakes produced changed nutrient cycling. Further
hydrologic manipulations, such as groundwater pumping, linked surface ﬂows to
the aquifer and replaced ephemeral washes with perennial waters. These alterations
of hydrologic structure are typical by-products of urban growth in semiarid regions.
Wash es ar e u sua lly di stu r bed o r tran sfo r med i nto dr ain a ge st r uct ure s , cha n gin g ﬂood
disturbance regimes characteristic of these waterways and eliminating habitat for
desert vegetation (Stiles and Scheiner 2008).
Desert plant communities are slow to recover from the impacts of volunteer
roads, campsites, and plant removal, all of which can be associated with exurban
150 L. Huntsinger
development. Slow-growing desert plants such as ironwood (Olneya tesota), cre-
osote bush (Larrea tridentate), and saguaro cactus (Cereus giganteus)maybe
harmed directly by construction and roads. Plant theft and vandalism also increase
with an increased human presence and more roads. Erosion from roads and soil com-
paction increases, as planned roads are augmented by volunteer roads and off-road
vehicle tracks. These can serve as vectors for nonnative species introduction. Non-
native species that produce biomass and can support ﬁres are especially dangerous
to desert ecosystems.
Species within deserts can respond to fragmentation in varied and potentially
contradictory ways. For example, contrary to expectations, low-density exurban
development beneﬁts some species by providing water, forage, and shade; these
beneﬁts disappear as housing density increases (Bock, Jones and Bock 2008).
One of the most important conclusions to be drawn from this review is that plan-
ning should consider ways to reduce the introduction and spread of nonnative plant
species. Nonnative plant species change the outlook for neighboring vegetation in
unpredictable ways. The changes wrought by the introduction of nonnatives can
be widespread, altering habitats, structure, species composition, and ecological pro-
cesses. The patterns of vegetation response and stability of the past become less use-
ful in predicting the outcomes of development. Retaining as much of the native ﬂora
and ground cover as possible can help reduce the spread of nonnatives. Research
in forests, rangelands, and deserts supports the notion that invasive plants invade
more quickly when gaps in tree or plant cover are created, especially when this
exposes open ground. Encouraging or requiring use of native species for landscap-
ing within developments would be ideal, but seems unlikely to be implemented or
enterprises such as agriculture, grazing, or forestry lands is a good idea (Fig. 8.4).
These working landscapes ideally act as a buffer, providing a barrier to new nonna-
tive species and limiting the direct impacts of the activities of exurban residents. In
addition, such lands can help prevent the spread of wildﬁre to residences, because
crop, livestock, and forestry enterprises manipulate vegetation in ways that, if prop-
erly managed, can reduce ﬁre hazard. In addition, prescribed burning and grazing
are still available as vegetation management tools on many of these lands.
waterways and wetlands. This reduces the possibility of ﬂooding and also pro-
tects habitats that are often peak areas for wildlife activities, and important small-
scale plant habitats. In arid lands, water is of particular importance, and the associ-
ated habitats are relatively rare. Waterways, whenever possible, should be buffered
from the direct impacts of development and if possible, native ﬂood disturbance
regimes should be allowed to continue. Vegetated riparian buffers contribute terres-
trial biomass to the aquatic food chain, regulate water temperature, control ﬂoods,
8 Into the Wild: Vegetation, Alien Plants, and Familiar Fire 151
Fig. 8.4 Rural working
landscapes can buffer
wildland and urban
by Lynn Huntsinger
provide wildlife habitat, and reduce erosion, sedimentation, and pollution (Perlman
and Milder 2005).
Fourth, for western ecosystems, planners should make the assumption that wild-
land ﬁre is likely to occur. The costs of ﬁre ﬁghting and suppression should be taken
into account when determining where exurban development should take place. It is
unlikely that “natural” ﬁre regimes will ever be restored in areas near or intermixed
with development because of the risks to residents and property, air quality concerns,
and the changes in the vegetation that have occurred because of ﬁre suppression. If
employed, prescribed burning should be strategically designed to insure the most
efﬁcient ﬁre-hazard reduction and to minimize the amount of landscape exposed to
unnaturally high ﬁre frequency (Keeley 2006). Leaving some overstory canopy and
minimizing exposure of bare ground may be less likely to promote nonnative plants
(Merriam, Keeley and Beyers 2006).
Fifth, development should strive to protect as much core habitat as possi-
ble. Various development strategies are proposed to minimize fragmentation and
edge effects. The ability of conservation development to protect biodiversity and
152 L. Huntsinger
ecosystem services depends on the size of remnant undeveloped areas, the amount
of change to natural disturbance regimes and ecological processes, and the relation-
ship of the exurban development to the rest of the landscape—whether remnants are
connected with larger wildlands, or whether the development abuts public lands, and
so forth. Ultimately, undeveloped fragment size affects the total number of individ-
uals present in a continuous patch of vegetation. Larger patches have more individ-
uals, which allows for larger populations and a lower extinction rate for the remnant
vegetation. Smaller patches have larger edges and lack buffer zones, so that their
limited expanse is exposed to repeated impacts from people (Stiles and Scheiner
Although it has been suggested that developments can be designed to reduce
impacts, for example by clustering dwellings, Lenth, Knight and Gilgert (2006)
found no evidence that cluster development had any impact on the proportion of
nonnative species found in remnant areas compared to more typical dispersed devel-
opment. Although the proportion of land area in clustered developments further
than 200 m from development was nearly twice that of dispersed housing devel-
opments, nonnative vegetation dominated both clustered and dispersed develop-
ments (Fig. 8.5). The habitat patches left undeveloped by clusters were signiﬁcantly
smaller than those of undeveloped areas, and patches were often not connected. Sub-
urban edge effects may extend up to 200 m into grasslands and shrublands (Bock,
Bock and Bennett 1999; Odell and Knight 2001). Most of the open area in a typical
clustered development is within this zone, and as a result, edge species dominate.
Finally, the open spaces of clustered developments may not be managed in ways
that promote conservation values.
Fig. 8.5 This cluster
development retains patches
of open lands. Photograph by
Lynn Hunts inger
The value of clustered housing developments can be enhanced by planning
that connects clusters with each other or with other wildlands (Lenth, Knight and
Gilgert 2006). When possible, the location and conﬁguration of open areas should
be planned on a regional scale, aggregating open-space areas and minimizing the
construction of roads and power lines. It is also possible that clustering homes may
8 Into the Wild: Vegetation, Alien Plants,and Familiar Fire 153
foster stronger community relationships, enabling collaborative community efforts
in the long run. Providing places where people will naturally meet each other helps
to develop a sense of community. Developed areas have an important role in the
maintenance of native ecosystems and the ability to maintain ecological integrity
will depend as much on the activities, practices, and politics of the local population
as on management conducted by land management agencies (Heckmann, Manley
and Schlesinger 2008).
An assessment of conservation-oriented limited development projects in the east-
ern United States found that they were protecting threatened conservation resources,
including rare biodiversity and ecosystem functions. They also resulted in signiﬁ-
cantly more conservation beneﬁts than other types of conservation developments,
including typical cluster developments (Milder 2007). On average more than 85% of
each site was protected as interior habitat, and project design and management gen-
erally addressed the conservation, restoration, and stewardship needs of site-speciﬁc
conservation targets (Milder, Lassoie and Bedford 2008). Despite containing rela-
tively little development, most are ﬁnancially self-sustaining and many realize a
proﬁt. The sale of a relatively small amount of subdivided land ready for con-
struction can ﬁnance the protection of a much larger amount of undivided land.
In addition, many of these developments beneﬁt from federal, state, and/or local
tax incentives for land conservation (Milder 2007; Wright and Anella 2007). More
study of these kinds of options is needed.
Finally, it is important to remember that ongoing changes in plants, vegetation
structure, and climate make the exurban environment a true frontier, in the sense that
our ability to look beyond the boundaries of the present and anticipate the future is
limited. Turning back to the past for answers about how plant communities will
respond to future impacts is of limited use. To cope with this changing and new
world will require tough decisions, with special attention to decision-making pro-
cesses and to who is included in them. Planning should seek to maintain options for
vegetation management in order to be able to cope with the unanticipated changes
of the future.
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