ChapterPDF Available

CHAPTER 34: INVASIVE SPECIES AND ECOLOGICAL RESTORATION 1

Authors:
CHAPTER 34: INVASIVE SPECIES AND ECOLOGICAL RESTORATION
1
J. C. Dudney1,†, L. M. Hallett1, E. N. Spotswood1, and K. N. Suding2
2
1Department of Environmental Science Policy and Management, University of California at Berkeley,
3
Berkeley, CA 94720
4
2Department of Ecology and Evolutionary Biology and Institute of Arctic and Alpine Research,
5
University of Colorado, Boulder, CO 80309
6
†Corresponding author email: jdudney@berkeley.edu
7
8
INTRODUCTION
9
10
Exotic species invasions have dramatically increased over the past century (Pyšek and Richardson 2010),
11
and are considered one of the greatest threats to endangered and vulnerable species worldwide
12
(D’Antonio and Vitousek 1992). Some exotic species that become invasive in a new geographic range
13
severely disrupt reproductive mutualisms (Traveset and Richardson 2006), reduce ecosystem services
14
(Peltzer et al. 2010), and decrease biodiversity (Gaertner et al., 2009). Although conservationists and
15
restoration ecologists typically prioritize invasive species management, several issues preclude success. In
16
many settings, it is impractical if not impossible to restore systems to pre-disturbed states, especially with
17
increasing external forcings, such as climate change, development, and nitrogen eutrophication (Seastedt
18
et al. 2008). There is also growing evidence that exotic species can serve important functional roles within
19
ecosystems (Davis et al. 2011). Given these constraints, it is becoming increasingly difficult to develop
20
practical invasive species restoration goals.
21
A number of conceptual frameworks for invasive species control have been proposed, including
22
integrated pest management that emphasizes the use of multiple control methods (Flint 2012), adaptive
23
management for broader conservation planning, as well as approaches that focus on managing multiple
24
species and multiple landscapes simultaneously (Green et al. 2013). An increasingly common theme is to
25
integrate monetary value with other ecological and social information (Larson et al. 2011) by viewing
26
invasive species management within an ecosystem services or biodiversity offsetting context. In this
27
chapter, we focus specially on invasive species management within a restoration setting, highlighting
28
important factors to consider at the site level (Figure 1). Throughout the three main stages of management
29
assessment, prioritization, and control we review key factors and present case studies to illustrate
30
practical implementations of each stage. We conclude with a discussion of invasive species management
31
moving forward.
32
1.0 ASSESSMENT
33
The assessment stage is a helpful precursor of invasive species prioritization for restoration sites. Often
34
successful management outcomes are contingent on strategic goal setting, using detailed, site-specific
35
information about the social and ecological constraints on the system. For example, controlling invasive
36
species is very costly (Larson et al. 2011), and management plans benefit from comprehensive budgeting,
37
even when it changes project goals to incorporate follow-up species control and monitoring. In addition,
38
the public may respond negatively to removal efforts of exotic species, especially if they are culturally
39
valued (Shackelford et al. 2013). Expanding local partnerships and developing public outreach programs
40
are costly, but often important components of control efforts. Involving the public can also increase a
41
project’s sustainability, especially when ongoing management actions are limited financially. Finally,
42
recognizing ecological knowledge gaps at the site helps managers decide whether site-focused field
43
experiments or additional research are needed.
44
Taking a step back and considering the state of the restoration site first before examining the individual
45
invasive species can also improve long-term management strategies (Hobbs and Humphries 1995).
46
Gathering information about the current or historic cause of habitat degradation, the number and
47
distribution of invasive species at the site, and the interaction of the restoration site within the surrounding
48
landscapes can strengthen goal setting. As managers begin to compile this information, it may be possible
49
to place the site along a continuum from historical to altered (after Hobbs et al. 2009) (Figure 2).
50
Although often applied more broadly to restoration sites, we present one possible framework across this
51
continuum specifically focused on invasive species that could help simplify the often-daunting task of
52
invasive species prioritization (Figure 2).
53
1.1 Historical site. Historical sites are devoid of exotic or invasive species and the structure and function
54
of the ecosystem reflect prior conditions. For example, fire frequencies match historical records, trophic
55
levels are unaltered, and/or human impacts, such as road construction or nitrogen deposition, are
56
nonexistent or very limited. Keeping historical sites free of exotic species is the primary management goal
57
and conducting effective weed risk analysis and large-scale monitoring plans for early detection can be
58
effective management strategies. Few places, if any, on earth remain free of human influence, but those
59
that retain their historical heritage may persist with effective management. Such ecosystems are typically
60
remote and/or high in elevation. The Atacama Desert in Chile, for instance, is still considered relatively
61
undisturbed and exotic species free, though scientists predict that increased CO2 will change the abiotic
62
environment and encourage exotic plant invasions in deserts (Smith et al. 2000). Because invasive species
63
are spreading rapidly worldwide, emphasizing management of more pristine areas may be an important
64
goal for conservation and restoration in the future.
65
1.2 Intact site. Within an intact site, the vast majority of the biota is native and the structure and function
66
of the system remains unaltered. Natural disturbance regimes may have shifted, such as fire frequencies
67
and nitrogen deposition, but these anthropogenic changes have not severely disrupted the biota or
68
ecosystem processes. Traditional restoration goals of rehabilitating historic biodiversity can be feasible, as
69
the number of different invaders on the landscape is limited compared to more degraded sites. Redwood
70
forests in northern California are an example of intact ecosystems. Though fire regimes have been altered
71
and human traffic is on the rise, only a few exotic species threaten the landscape, such as New Zealand
72
mudsnails, Potamopyrgus antipodarum, and barred owls, Strix varia.
73
In an intact system, it may be realistic to curtail the spread of all invasive species to some degree. Alpine
74
zones, for example, are characterized by rapidly changing, steep environmental gradients. As a result,
75
they have dramatically reduced rates of species invasion compared to lower elevations (Baret et al. 2006).
76
However, propagule pressure from lower elevations, continued human disturbance, and climate change
77
will likely facilitate species invasions in the future (Pauchard and Alaback, 2004). Proactive management
78
to keep exotic species from spreading into higher elevations can be more cost-effective compared to post-
79
invasion control. Wilderness-wide management plans may still be impractical, however, and carefully
80
targeting areas where invasive species are likely to spread may be more feasible.
81
1.3 Modified site. A modified site is one that contains a mixture of invasive and native species, though
82
retains much of its original structure and function. These sites are typically influenced by human
83
disturbance, such as urbanization and globalization, and restoration is generally more costly or in some
84
cases impossible. For example, the Great Lakes of North America have been invaded by over 180 exotic
85
species within the last two centuries, some of which endanger underwater flora communities as well as
86
commercial fisheries (Vander Zanden and Olden 2008). Despite the strong presence of invasive species,
87
much of the ecosystem functioning in the Great Lakes region remains intact, suggesting that timely and
88
strategic management could increase native species composition.
89
A feasible management goal for a modified site may be to remove problematic organisms and accept the
90
existence of ubiquitous or naturalized species that improve the ecosystem or provide important services.
91
Problematic species include those that disrupt ecosystem functioning, cause further degradation, or alter
92
important characteristics, such as vegetation structure or aesthetic qualities. Species that facilitate invasion
93
of other exotics are also important management targets in modified systems. For example, nitrogen
94
enrichment following the invasion of nitrogen fixing plants has been well-documented (Scherer-Lorenzen
95
et al. 2008). In South Africa, the invasion of Acacia saligna led to a secondary increase in the exotic,
96
nitrophilous Ehrharta calycina. Understanding which species have higher impacts on ecosystem health
97
can be an important strategy to improve restoration outcomes in sites with abundant distributions and
98
numbers of invasive species.
99
1.4 Altered site. An altered site is one that is dominated by exotic and invasive species. The degree to
100
which ecosystem structure and function resembles historic conditions varies depending on the severity
101
and type of disturbance. Restoration is often very costly or infeasible and novel approaches for
102
management are advised (Hobbs and Humphries 1995). The goals of invasive species management within
103
an altered site should be highly strategic and pragmatic, focusing on species impacts and their interactions
104
with the broader landscape. Targeting problematic invasive species that reduce ecosystem functioning,
105
such as water retention or carbon cycling, may be a feasible goal even in highly disturbed sites. For
106
example, the giant reed, Arundo donax threatens riparian areas in California by increasing flammability in
107
historically fire retardant areas (Coffman et al. 2010). Reducing fire risk is important for the overall
108
functioning of the ecosystem, a goal that is less about origin and more about the species’ impacts. In
109
addition, monitoring for exotic species’ introductions in highly trafficked and disturbed sites could be an
110
important goal when considering the site’s effects on surrounding landscapes, as well as opportunities to
111
prevent further degradation.
112
1.5 Mosaic site. In many cases, the ecology of restoration sites is highly variable and the invasive species
113
distributions are fragmented across the landscape. Many restoration sites may contain habitats across
114
multiple states of degradation from historical to altered. In such cases, it may be useful to consider the
115
landscape as a mosaic of different states that each require goal-setting reflective of this variability.
116
Considering the altered ecosystem within a mosaic of urban and rural landscapes may also help managers
117
develop more effective management goals. For example, invasive fruit bearing species in Hawaii are often
118
spread by frugivorous birds (Simberloff and Holle 1999) and to protect surrounding islands from
119
invasion, it may still be more cost-effective in the long-term to control a highly altered site in order to
120
protect another less modified site.
121
PRIORITIZATION
122
Creating priority lists for invasive species is a useful management strategy, especially for modified,
123
altered, or mosaic sites where invasive species are often well established. Various classification trees have
124
been developed to assist managers and policy makers with species prioritization (Randall et al. 2008;
125
Skurka Darin et al. 2011). Lists are often created using multiple criteria, such as impact, potential for
126
spread, and feasibility of control. Although prioritization lists are useful for regional management
127
strategies, the high variability among restoration sites, as well as their corresponding social and ecological
128
constraints, often necessitates site-specific decision-making. In addition, numerous factors affect
129
management efficacy and it is often difficult to identify all the social and ecological constraints of a
130
system. For the scope of this chapter, we highlight three key factors that significantly affect management
131
outcomes and warrant careful consideration when developing species prioritization lists at a restoration
132
site.
133
2.1 Non-target ecosystem impacts. Management success is often contingent on understanding the
134
potential for non-target ecosystem impacts following invasive species removal (D’Antonio and Meyerson
135
2002). For example, has the invader been incorporated into trophic levels or do native species rely on the
136
exotic for habitat? The endangered California clapper rail is an archetype of non-target impacts, as its
137
population dramatically declined following removal of invasive Spartina in the San Francisco Bay Area.
138
When managers realized that the bird was using invasive Spartina as habitat, they responded by slowing
139
exotic removal until native habitat was restored (Buckley and Han 2014). The exotic legume, Ulex
140
europaeus, in New Zealand also played an important role in ecosystem function. While lowering native
141
biodiversity, it simultaneously provided essential microsites for native forest recovery following livestock
142
removal in pastureland (Norton 2009). The interactions between invasive species and the local ecology at
143
restoration sites can pose difficult choices for managers. Though easy solutions may be elusive, it is still
144
important to consider the negative and positive impacts of invasive species when developing prioritization
145
lists.
146
The act of invasive species control can also have non-target effects on native species diversity and
147
ecosystem function. For example, much of the Galapagos’ humid highlands have been invaded by the
148
exotic ground cover, Tradescantia flumiesis. When managers used chemical control to contain the
149
population, however, the compounds also reduced native species cover, thus providing a window of
150
opportunity for other invasive species to spread (Hallett et al. 2013). Disturbance due to mechanical
151
control can also facilitate invasion by other exotic species. Although topsoil removal has been touted as
152
an effective tool to reduce annual grass propagule pressure, as it can modify site hydrology (Holl et al.
153
2014), reduce the native seed bank, and alter the microbial community (Buisson et al. 2006). Thus,
154
assessing and weighing additional ecosystem effects of removal strategies is an important step when
155
deciding how to manage invasive species at a restoration site.
156
2.2 Recovery constraints. Invasive species may also alter ecosystem attributes and functions (e.g.,
157
geomorphology, hydrology, microbial communities, and disturbance regimes) that impede native species
158
recovery (Corbin and Antonio 2011). These changes may persist on the landscape following removal and
159
favor invasive over native species. For example, coastal dunes dominated by the invasive, Acacia
160
longifolia, have greater litter accumulation, available nitrogen and microbial biomass. These legacies
161
intensify with time following invasion (Marchante et al. 2008), creating a positive feedback that favors A.
162
longifolia over other native species. Invasive species establishment may also directly inhibit native
163
species. Garlic mustard, Alliaria petiolata, a widespread non-native species in North American forests,
164
produces a long-lasting compound that impedes symbiotic associations between mychorrizae and native
165
plants (Perry et al. 2005). In addition, invasive species can impede management goals for ecosystem
166
function and native species recovery, particularly when they alter disturbance regimes. Invasive annual
167
grasses in the Western United States, for instance, have increased fire frequency which threatens public
168
safety and prevents native species recovery (Brooks et al. 2004). Understanding the recovery constraints
169
affecting native species re-establishment following invasive species removal will likely improve decision-
170
making and help managers identify which species are more feasible to control.
171
2.3 Re-invasion risk. Invasive species removal efforts may be rendered ineffective if managers cannot
172
prevent subsequent re-invasion. Re-invasion is particularly likely if sites are located near a source
173
population, highlighting that knowledge of species distributions within the surrounding landscape is
174
integral for management success (Brudvig 2011). Depending on jurisdiction and cost, one option for sites
175
in invaded landscapes is to scale-up invasive control efforts (Holl et al. 2003). Alternatively, managers
176
may opt to prioritize removal in sites located far from source populations (Heller and Hobbs 2014). Life
177
history of the invasive species may also affect prioritization decisions. For example, re-invasion may be
178
unavoidable for sites located near populations of highly fecund (Larios, Aicher, and Suding 2013) or
179
widely dispersing invasive species (Osawa et al. 2013).
180
The risk of re-invasion may also be high for sites affected by land-use or global change that favors
181
invasive species over native species. Sites that experience ongoing local disturbance may be at particular
182
risk of re-invasion by invasive species with “weedy” traits (fast growing, high fecundity) (Larios year). In
183
addition, global change can alter interactions between native and exotic species (Dukes and Mooney
184
1998). Invasive species often benefit from increased resource availability (Dukes 2011), and consequently
185
may be more likely to re-invade areas affected by high nitrogen deposition or increased water availability
186
due to climate change. Similarly, environmental change can also reduce the efficacy of initial species
187
removal. Canadian thistle, Cirsium arvense, recovers from herbicide more quickly in areas with elevated
188
CO2, likely due to increased below-ground investment (Ziska et al. 2004). Distribution modeling can be
189
useful for predicting areas where invasive-native species interactions may change, and site-level
190
experimental tests can help managers predict re-invasion risk before implementing large-scale
191
restorations.
192
3.0 CONTROL
193
Invasive species management is typically not a linear process and each stage should inform the others,
194
enabling managers to adapt and adjust as new information and improved methods are developed. Here we
195
discuss important factors to consider when deciding which of the four strategies prevention, eradication,
196
containment, and observation - would be most effective for each target invasive species (Figure 3). The
197
literature describing these four strategies is extensive, and the definitions are highly variable and
198
overlapping (Pyšek and Richardson 2010). For the purpose of this chapter, we use control broadly to
199
encompass the ideas of prevention, eradication, containment, and observation, and in the sections below
200
parameterize these four terms with respect to restoration.
201
3.1 Prevention. Prevention is focused on precluding known or potentially new invasive species from
202
spreading into un-invaded habitats. Preventative strategies can be the most cost-effective, especially
203
considering the financial consequences of invasive species establishment (Pimentel et al. 2005). Because
204
it is difficult to predict invasiveness of exotic species, removing all arriving non-native species where
205
identified can help curtail the establishment of future invasions (i.e., guilty until proven otherwise). The
206
two common methods for detecting invasive species are surveys and remote sensing, though significant
207
limitations persist, such as small or cryptic offspring, dense vegetation structure, dormancy, herbivory and
208
observer error (Emry et al., 2011). To enhance the efficacy of early detection and mapping techniques,
209
rigorous, frequent surveys in conjunction with citizen science programs is recommended (Jordan et al.
210
2012).
211
A relatively new technique, pathway and vector management, can also greatly bolster prevention
212
strategies (Pyšek and Richardson 2010). By identifying the possible pathways (i.e., ports, roads, and
213
nurseries) and vectors (i.e., hikers, cattle, big machinery) leading to invasion, managers can improve
214
monitoring protocols in order to remove incipient invasions (Hulme 2009) or contain expanding
215
populations. Pathway and vector management strategies, as well other control efforts, are best
216
implemented with clear plans for monitoring, both to ascertain long-term success rates and to inform
217
future management practices (Blossey 1999).
218
3.2 Eradication. The goal of eradication is to eliminate all individuals and/or the seed bank of an invasive
219
species in a target area. Eradication decisions should be based on the invasive species’ population size and
220
distribution, and individuals that are farthest from population epicenters should be targeted first because
221
they are likely less established and more feasible to eradicate (Rejmánek and Pitcairn 2002). Typically,
222
successful eradications are associated with small, isolated populations less than one hectare in size.
223
Species that are highly visible with lower fecundity and dormancy rates are possible to eradicate. If one or
224
more of these criteria are not met, such species are better managed by a containment strategy (Ramsey et
225
al. 2009).
226
227
The literature is contradictory in its support of eradication efforts. In many cases, once a species is
228
established it is almost impossible to remove (Vander Zanden and Olden 2008). Certain situations,
229
however, may warrant eradication efforts. For instance, various island eradication efforts throughout the
230
world have succeeded. New Zealand land managers effectively restored native bird diversity to small
231
islands by removing all invasive predators (Veitch and Clout 2002). In addition, eradications of small
232
plant populations have also been successful, especially when detected early (Rejmánek and Pitcairn
233
2002). Eradication is often most efficacious when followed by prevention strategies, as pathways and
234
vectors may continue to facilitate species spread (Veitch and Clout 2002).
235
236
3.3 Containment. The goal of containment is to preclude or slow the spatial expansion of established
237
invasive species populations. Containment is useful for species that do not meet all criteria for eradication
238
(i.e., widespread distributions, prohibitively high removal costs, or populations not conducive for
239
monitoring surveys). Effective containment strategies ideally delineate the invasive species’ distribution
240
and important habitats threatened by the invasion. Thus managers can identify and remove smaller
241
satellite populations that are spreading into ecologically valuable areas. Because restorations are often
242
concentrated on degraded landscapes, containing problematic populations may be the most useful
243
strategy, as eradications are extremely costly and often ineffective when populations are well established.
244
Invasive grasses greatly reduce biodiversity in serpentine grasslands, and various containment strategies
245
are used to decrease invasive grass densities, such as gazing, fire, and mowing (Weiss 1999). Grass
246
eradications in these systems are probably impossible because removal techniques often miss small
247
populations, abutting landscapes continually provide propagules, and human influence, such as increased
248
nitrogen deposition, is difficult to control. Though containment strategies do not completely remove the
249
invasive species population, management can still effectively restore native biodiversity to degraded
250
landscapes when used strategically.
251
3.4 Observation. Observation strategies may mean that some of the site cannot be restored or that
252
restoration goals are adjusted to reflect the realities of control for a particular set of invasive species. For
253
example, it may be more cost-effective and pragmatic to watch that the invasive population does not
254
spread further and affect nearby areas. In highly disturbed sites dominated by exotic species, future
255
introductions are likely. These altered sites can provide a frontline of defense against new invasive species
256
or further spread. While removal may not be cost-effective or feasible, implementing “wait and watch”
257
monitoring programs can inform managers when to act. In some cases, it is better to focus on
258
reestablishing native species and increasing habitat resilience to further invasion than attempting to
259
control a ubiquitous invasive species. For example, managers can control certain invasive fish species by
260
restoring natural flow regimes below dams (Rahel and Olden 2008) or reduce numbers of shade-intolerant
261
invasive species in degraded riparian zones by planting native trees. Accepting the presence of an invasive
262
species and focusing on ecosystem health may be the best course of action in many highly altered sites.
263
4.0 FUTURE DIRECTIONS
264
Invasive species management can benefit from harnessing emerging technology to improve detection and
265
control techniques. Broader advances in technology are already being adapted, and this trend is likely to
266
continue into the future. For example, the internet will enable broad collaborations among diverse sets of
267
stakeholders, and big data analytics will drive analyses of larger genetic, remote sensing and citizen
268
science datasets. Social media and mobile apps will also allow more citizens to become involved in
269
invasive species detection and research. In addition, spatial data coupled with computing power will
270
enable spatially explicit simulations, allowing dynamic optimization of scarce dollars. In this section, we
271
highlight four areas where recent technological advancements have improved or will likely improve
272
invasive species management strategies.
273
4.1 Remote sensing. Remote sensing has emerged as a promising technology that can aid in mapping
274
infested areas and monitoring spread. Currently, remote sensing has been used to create distribution maps
275
to target the management of early invasion and model future invasion risk (Bradley 2014). The most
276
common approach is to utilize differences in spectral signatures (typically with hyperspectral data) to
277
differentiate invasive plants from surrounding vegetation. Textural (or object-based) and phenological
278
differences can also be effective (Bradley 2014). Obstacles to widespread implementation include
279
economic expense and poor resolution quality for small patch identification, especially if individuals are
280
small or early detection is the primary goal (Bradley 2014). The future is likely to see improvements in
281
satellite technology and reductions in the cost of aerial images, which could expand the utility and
282
efficacy of remote sensing.
283
4.2 Citizen science. Available technology has facilitated greater public participation in ecological
284
research (Newman 2012). By increasing the number of citizen science programs, managers engage larger
285
audiences that potentially improve early detection and control of invasive species (Dickinson et al. 2012).
286
Widespread adoption of mobile devices has increased the accuracy of species location information, and
287
mobile apps are currently experimenting with a broad range of methods to engage the public. Mobile apps
288
include platforms for learning about the natural world and can assist users with species identification. For
289
example, the app Leafsnap (http://www.leafsnap.com/) uses image recognition of leaf photos to help with
290
identification of trees in the eastern United States, while at the same time gathering occurrence and
291
location data for species of interest. Browser based visualization tools and social media can subsequently
292
facilitate the dissemination of such user data.
293
In some cases, citizen science projects are less expensive than traditional scientific research (Gardiner
294
2012), and even the more expensive and efficient programs have lower costs associated with data
295
collection and analysis (Goldstein 2014). While technology offers enormous promise for enabling citizen
296
science, constraints continue to arise. Perhaps the biggest challenge is ensuring data quality (Newman
297
2012). Volunteers, for example, can make more mistakes in identifying organisms than professionals,
298
which can lead to inflated species richness estimates (Gardiner 2012). Data quality can be addressed with
299
the addition of photograph specimens, but this necessitates expert validation and increases project costs
300
(Gardiner 2012, Newman 2012). Although future advances in technology are needed to increase accuracy
301
and decrease costs, the future will likely see more widely applicable and effective citizen science
302
programs.
303
4.3 Genetic tools. Contemporary genetic tools have been increasingly useful in invasive species research
304
and benefit from advancements in computational and statistical approaches. Understanding how historical
305
invasions progressed can improve predictive capacity for new invasions, as well as consequent impacts on
306
host communities. Environmental DNA using barcoding has been successfully applied to aquatic systems
307
(Dejean et al. 2012), where water samples can help detect incipient fish and amphibian invasions. In
308
terrestrial systems, genetic tools have quantified dispersal pathways (Medley et al. 2015) and identified
309
loci contributing to species adaptation during invasion (Vandepitte et al. 2014). In addition,
310
metagenomics approaches, including Roche/454 pyrosequencing, can create whole community interaction
311
networks much more easily (Pompanon et al. 2012). These networks (i.e., host-parasite, predator-prey,
312
and food webs) enable scientists to characterize and measure invasive species impacts at the community
313
level. Network patterns may also help uncover the conditions that helped communities resist invasion,
314
improving predictions of when and how invasions occur.
315
Advancements in computational power, as well as new statistical approaches for analyzing genetic data,
316
have paralleled the rapid development of genetic tools. Improvements relevant for invasion ecology
317
include approximate Bayesian computation, which allows invasion routes to be inferred from molecular
318
and historical data (Keller et al. 2012). Similarly, discriminant analysis of principal components is a
319
powerful approach to assign individuals to populations, broadening the application of population genetics
320
to better define invasion pathways. Coupling genetic and computational tools with GIS based landscape
321
analysis is also improving reconstruction of invasive species dispersal histories. The ability to evaluate
322
how landscape features and environmental parameters affect dispersal is key to predicting how invasive
323
species will spread in the future and provides important information for management strategies.
324
4.4 Collaborations. Invasive species management projects will likely increase collaborations across
325
agencies and international boundaries. Digital and online resources will also play a greater role in all
326
stages of weed management, from detection to strategic planning and control. A number of online
327
databases that aggregate information on the identity, impact, and location of invasive species already
328
exists. These databases function at the state, national and international levels, including the global
329
invasive species database (http://www.issg.org/database/welcome/), the National Invasive Species
330
Information Center in the United States (http://www.invasivespeciesinfo.gov/index.shtml), and the
331
Delivering Alien Invasive Species for Europe (DAISIE) database (http://www.europe-aliens.org/).
332
In addition, future collaborative efforts are likely to extend beyond databases and use online platforms to
333
integrate information from multiple stakeholders. The California Invasive Plant Council is attempting this
334
approach through an online tool, CalWeedMapper, which consolidates material from various stakeholders
335
about invasive species distributions, impacts, and management activities in California. The website
336
provides additional resources as well, such as upcoming conferences and training programs, policy
337
information, relevant scientific research, and priority areas for research and management. This integrative
338
approach recognizes that engagement with a broader community of partners is a necessary piece of
339
effective management.
340
5.0 CONCLUSION
341
Worldwide, it is hard to escape issues of invasive species when embarking on ecological restoration. In
342
this chapter, we described various strategies to address the challenges that arise with invasive species
343
management in restoration, highlighting three main stages assessment, prioritization, and control
344
(Figure 1). At each stage, we encourage the consideration of how climate and human modifications may
345
affect what restoration goals can be set and accomplished, including exotic species impacts on local
346
species interactions and ecosystem functioning. Future management efforts will likely see an emphasis on
347
more integrative conceptual frameworks and complex optimization tools to guide decision-making.
348
Increased globalization and climate change are expected to accelerate the rates of invasion, challenging
349
the ability of managers to keep pace with new invasions as they occur. Funding limitations will also likely
350
persist, as well as the high costs of invasive species control. Thus, a key to future management efficacy in
351
ecological restoration will be to build upon and document records of success in assessing, prioritizing, and
352
controlling invasive species.
353
354
FIGURES
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
Figure 1: Invasive species management framework for restoration sites. Defining the condition
of the restoration site during the assessment stage helps managers decide if they have to
prioritize invasive species or how to control species allotted for management. Though not
necessarily a linear process, by understanding the important factors that affect management
outcomes during the assessment, prioritization and control stages, more site-specific and
achievable goals may be developed.
372
373
374
375
376
377
378
Figure 2: Modified from Hobbs, Higgs and Harris, (2009). Placing sites into these four categories, historical, intact,
modified and altered, (or identifying a combination of these states at one site), helps managers prioritize invasive
species. For example, if the site is relatively intact and much of the historical biota are still present, then the managers
may decide that more traditional restoration goals of invasive species removal are feasible. However, if the site is
continuously disturbed and highly invaded, perhaps the only thing left to manage are incipient invasions and preventing
new exotic species from dispersing into less degraded areas.
379
380
381
382
383
WORKS CITED
384
385
1. Antonio, Carla D, and Laura A. Meyerson. 2002. Exotic Plant Species as Problems and
386
Solutions in Ecological Restoration: A Synthesis. Restoration Ecology 10 (4): 70313.
387
doi:10.1046/j.1526-100X.2002.01051.x.
388
options presented here are prevention, eradication, containment and observation. When to implement
these different strategies varies depending on the considerations listed at the far left of the figure.
Adapted from Shackelford et al (2014).
2. Antonio, Carla M. D, and Peter M. Vitousek. 1992. Biological Invasions by Exotic Grasses, the
389
Grass/Fire Cycle, and Global Change. Annual Review of Ecology and Systematics 23
390
(January): 6387.
391
3. Barbiero, Richard P., Mary Balcer, David C. Rockwell, and Marc L. Tuchman. 2009. Recent
392
Shifts in the Crustacean Zooplankton Community of Lake Huron. Canadian Journal of
393
Fisheries and Aquatic Sciences 66 (5): 81628. doi:10.1139/F09-036.
394
4. Baret, Stephane, Mathieu Rouget, David M. Richardson, Christophe Lavergne, Benis Egoh,
395
Joel Dupont, and Dominique Strasberg. 2006. Current Distribution and Potential Extent of
396
the Most Invasive Alien Plant Species on La Réunion (Indian Ocean, Mascarene Islands).
397
Austral Ecology 31 (6): 74758. doi:10.1111/j.1442-9993.2006.01636.x.
398
5. Becker, Thomas, Hansjörg Dietz, Regula Billeter, Holger Buschmann, and Peter J. Edwards.
399
2005. Altitudinal Distribution of Alien Plant Species in the Swiss Alps. Perspectives in Plant
400
Ecology, Evolution and Systematics 7 (3): 17383. doi:10.1016/j.ppees.2005.09.006.
401
6. Blossey, Bernd. 1999. Before, During and After: The Need for Long-Term Monitoring in
402
Invasive Plant Species Management. Biological Invasions 1 (2-3): 30111.
403
doi:10.1023/A:1010084724526.
404
7. Brooks, Matthew L., CARLA M. DANTONIO, David M. Richardson, James B. Grace, Jon E.
405
Keeley, JOSEPH M. DiTOMASO, Richard J. Hobbs, Mike Pellant, and David Pyke. 2004. Effects
406
of Invasive Alien Plants on Fire Regimes. BioScience 54 (7): 67788.
407
8. Brudvig, Lars A. 2011. The Restoration of Biodiversity: Where Has Research Been and
408
Where Does It Need to Go? American Journal of Botany 98 (3): 54958.
409
doi:10.3732/ajb.1000285.
410
9. Buckley, Yvonne M., and Yi Han. 2014. Managing the Side Effects of Invasion Control.
411
Science 344 (6187): 97576.
412
10. Coffman, Gretchen C., Richard F. Ambrose, and Philip W. Rundel. 2010. Wildfire Promotes
413
Dominance of Invasive Giant Reed (Arundo Donax) in Riparian Ecosystems. Biological
414
Invasions 12 (8): 272334. doi:10.1007/s10530-009-9677-z.
415
11. Corbin, Jeffrey D., and Carla M. DAntonio. 2011. Gone but Not Forgotten? Invasive Plants
416
Legacies on Community and Ecosystem Properties. Invasive Plant Science and Management
417
5 (1): 11724. doi:10.1614/IPSM-D-11-00005.1.
418
12. Davis, Mark A., Matthew K. Chew, Richard J. Hobbs, Ariel E. Lugo, John J. Ewel, Geerat J.
419
Vermeij, James H. Brown, et al. 2011. Dont Judge Species on Their Origins. Nature 474
420
(7350): 15354. doi:10.1038/474153a.
421
13. Emry, D. Jason, Helen M. Alexander, and Michael K. Tourtellot. 2011. Modelling the Local
422
Spread of Invasive Plants: Importance of Including Spatial Distribution and Detectability in
423
Management Plans. Journal of Applied Ecology 48 (6): 13911400.
424
14. Flint, Mary Louise. 2012. IPM in Practice: Principles and Methods of Integrated Pest
425
Management. UCANR Publications.
426
15. Gaertner, Mirijam, Alana Den Breeyen, Cang Hui, and David M. Richardson. 2009. Impacts of
427
Alien Plant Invasions on Species Richness in Mediterranean-Type Ecosystems: A Meta-
428
Analysis. Progress in Physical Geography 33 (3): 31938.
429
16. Green, Stephanie J., Nicholas K. Dulvy, Annabelle M. L. Brooks, John L. Akins, Andrew B.
430
Cooper, Skylar Miller, and Isabelle M. Côté. 2013. Linking Removal Targets to the Ecological
431
Effects of Invaders: A Predictive Model and Field Test. Ecological Applications 24 (6): 1311
432
22. doi:10.1890/13-0979.1.
433
17. Hallett, Lauren M., Sibyl Diver, Melissa V. Eitzel, Jessica J. Olson, Benjamin S. Ramage, Hillary
434
Sardinas, Zoe Statman-Weil, and Katharine N. Suding. 2013. Do We Practice What We
435
Preach? Goal Setting for Ecological Restoration. Restoration Ecology 21 (3): 31219.
436
doi:10.1111/rec.12007.
437
18. Heller, Nicole E., and Richard J. Hobbs. 2014. Development of a Natural Practice to Adapt
438
Conservation Goals to Global Change. Conservation Biology 28 (3): 696704.
439
doi:10.1111/cobi.12269.
440
19. Hobbs, Richard J., and Stella E. Humphries. 1995. An Integrated Approach to the Ecology
441
and Management of Plant Invasions. Conservation Biology 9 (4): 76170.
442
doi:10.1046/j.1523-1739.1995.09040761.x.
443
20. Holl, Karen D., Elizabeth E. Crone, and Cheryl B. Schultz. 2003. Landscape Restoration:
444
Moving from Generalities to Methodologies. BioScience 53 (5): 491502. doi:10.1641/0006-
445
3568(2003)053[0491:LRMFGT]2.0.CO;2.
446
21. Holl, Karen D., Elizabeth A. Howard, Timothy M. Brown, Robert G. Chan, Tara S. de Silva, E.
447
Tyler Mann, Jamie A. Russell, and William H. Spangler. 2014. Efficacy of Exotic Control
448
Strategies for Restoring Coastal Prairie Grasses. Invasive Plant Science and Management 7
449
(4): 59098. doi:10.1614/IPSM-D-14-00031.1.
450
22. Hulme, Philip E. 2009. Trade, Transport and Trouble: Managing Invasive Species Pathways
451
in an Era of Globalization. Journal of Applied Ecology 46 (1): 1018. doi:10.1111/j.1365-
452
2664.2008.01600.x.
453
23. Jordan, Rebecca C., Wesley R. Brooks, David V. Howe, and Joan G. Ehrenfeld. 2012.
454
Evaluating the Performance of Volunteers in Mapping Invasive Plants in Public
455
Conservation Lands. Environmental Management 49 (2): 42534. doi:10.1007/s00267-011-
456
9789-y.
457
24. Lampert, Adam, Alan Hastings, Edwin D. Grosholz, Sunny L. Jardine, and James N. Sanchirico.
458
2014. Optimal Approaches for Balancing Invasive Species Eradication and Endangered
459
Species Management. Science 344 (6187): 102831. doi:10.1126/science.1250763.
460
25. Larios, Loralee, Rebecca J. Aicher, and Katharine N. Suding. 2013. Effect of Propagule
461
Pressure on Recovery of a California Grassland after an Extreme Disturbance. Journal of
462
Vegetation Science 24 (6): 104352. doi:10.1111/jvs.12039.
463
26. Larson, Diane L., Laura Phillips-Mao, Gina Quiram, Leah Sharpe, Rebecca Stark, Shinya
464
Sugita, and Annie Weiler. 2011. A Framework for Sustainable Invasive Species
465
Management: Environmental, Social, and Economic Objectives. Journal of Environmental
466
Management 92 (1): 1422. doi:10.1016/j.jenvman.2010.08.025.
467
27. Levine, Jonathan M, Montserrat Vila, Carla M DAntonio, Jeffrey S Dukes, Karl Grigulis, and
468
Sandra Lavorel. 2003. Mechanisms Underlying the Impacts of Exotic Plant Invasions.
469
Proceedings of the Royal Society B: Biological Sciences 270 (1517): 77581.
470
doi:10.1098/rspb.2003.2327.
471
28. Marchante, Elizabete, Annelise Kjøller, Sten Struwe, and Helena Freitas. 2008. Short- and
472
Long-Term Impacts of Acacia Longifolia Invasion on the Belowground Processes of a
473
Mediterranean Coastal Dune Ecosystem. Applied Soil Ecology 40 (2): 21017.
474
doi:10.1016/j.apsoil.2008.04.004.
475
29. Norton, David A. 2009. Species Invasions and the Limits to Restoration: Learning from the
476
New Zealand Experience. Science 325 (5940): 56971. doi:10.1126/science.1172978.
477
30. Pauchard, Aníbal, and Paul B. Alaback. 2004. Influence of Elevation, Land Use, and
478
Landscape Context on Patterns of Alien Plant Invasions along Roadsides in Protected Areas
479
of South-Central Chile. Conservation Biology 18 (1): 23848. doi:10.1111/j.1523-
480
1739.2004.00300.x.
481
31. Peltzer, D. A., R. B. Allen, G. M. Lovett, D. Whitehead, and D. A. Wardle. 2010. Effects of
482
Biological Invasions on Forest Carbon Sequestration. Global Change Biology 16 (2): 73246.
483
32. Pimentel, David, Rodolfo Zuniga, and Doug Morrison. 2005. Update on the Environmental
484
and Economic Costs Associated with Alien-Invasive Species in the United States. Ecological
485
Economics, Integrating Ecology and Economics in Control Bioinvasions IEECB S.I., 52 (3):
486
27388. doi:10.1016/j.ecolecon.2004.10.002.
487
33. Pyšek, Petr, and David M. Richardson. 2010. Invasive Species, Environmental Change and
488
Management, and Health. Annual Review of Environment and Resources 35 (1): 2555.
489
doi:10.1146/annurev-environ-033009-095548.
490
34. Rahel, Frank J., and Julian D. Olden. 2008. Assessing the Effects of Climate Change on
491
Aquatic Invasive Species. Conservation Biology 22 (3): 52133. doi:10.1111/j.1523-
492
1739.2008.00950.x.
493
35. Ramsey, David S. L., John Parkes, and Scott A. Morrison. 2009. Quantifying Eradication
494
Success: The Removal of Feral Pigs from Santa Cruz Island, California. Conservation Biology
495
23 (2): 44959. doi:10.1111/j.1523-1739.2008.01119.x.
496
36. Randall, John M., Larry E. Morse, Nancy Benton, Ron Hiebert, Stephanie Lu, and Terri
497
Killeffer. 2008. The Invasive Species Assessment Protocol: A Tool for Creating Regional and
498
National Lists of Invasive Nonnative Plants That Negatively Impact Biodiversity. Invasive
499
Plant Science and Management 1 (1): 3649. doi:10.1614/IPSM-07-020.1.
500
37. Rejmánek, M., and M. J. Pitcairn. 2002. When Is Eradication of Exotic Pest Plants a Realistic
501
Goal. Turning the Tide: The Eradication of Invasive Species, 24953.
502
38. Scherer-Lorenzen, Michael, Harry Olde Venterink, and Holger Buschmann. 2008. Nitrogen
503
Enrichment and Plant Invasions: The Importance of Nitrogen-Fixing Plants and
504
Anthropogenic Eutrophication. In Biological Invasions, edited by Dr Wolfgang Nentwig,
505
16380. Ecological Studies 193. Springer Berlin Heidelberg.
506
http://link.springer.com/chapter/10.1007/978-3-540-36920-2_10.
507
39. Seastedt, Timothy R, Richard J Hobbs, and Katharine N Suding. 2008. Management of Novel
508
Ecosystems: Are Novel Approaches Required? Frontiers in Ecology and the Environment 6
509
(10): 54753. doi:10.1890/070046.
510
40. Shackelford, Nancy, Richard J. Hobbs, Nicole E. Heller, Lauren M. Hallett, and Timothy R.
511
Seastedt. 2013. Finding a Middle-Ground: The Native/non-Native Debate. Biological
512
Conservation 158 (February): 5562. doi:10.1016/j.biocon.2012.08.020.
513
41. Simberloff, Daniel, and Betsy Von Holle. 1999. Positive Interactions of Nonindigenous
514
Species: Invasional Meltdown? Biological Invasions 1 (1): 2132.
515
doi:10.1023/A:1010086329619.
516
42. Skurka Darin, Gina M., Steve Schoenig, Jacob N. Barney, F. Dane Panetta, and Joseph M.
517
DiTomaso. 2011. WHIPPET: A Novel Tool for Prioritizing Invasive Plant Populations for
518
Regional Eradication. Journal of Environmental Management 92 (1): 13139.
519
doi:10.1016/j.jenvman.2010.08.013.
520
43. Smith, Stanley D., Travis E. Huxman, Stephen F. Zitzer, Therese N. Charlet, David C. Housman,
521
James S. Coleman, Lynn K. Fenstermaker, Jeffrey R. Seemann, and Robert S. Nowak. 2000.
522
Elevated CO2 Increases Productivity and Invasive Species Success in an Arid Ecosystem.
523
Nature 408 (6808): 7982. doi:10.1038/35040544.
524
44. Traveset, Anna, and David M. Richardson. 2006. Biological Invasions as Disruptors of Plant
525
Reproductive Mutualisms. Trends in Ecology & Evolution 21 (4): 20816.
526
45. Vander Zanden, M. Jake, and Julian D. Olden. 2008. A Management Framework for
527
Preventing the Secondary Spread of Aquatic Invasive Species. Canadian Journal of Fisheries
528
and Aquatic Sciences 65 (7): 151222. doi:10.1139/F08-099.
529
46. Veitch, C. R., and Michael Norman Clout. 2002. Turning the Tide: The Eradication of Invasive
530
Species: Proceedings of the International Conference on Eradication of Island Invasives. IUCN.
531
47. Verbrugge, Laura NH, Gerard van der Velde, A. Jan Hendriks, Hugo Verreycken, and RSEW
532
Leuven. 2012. Risk Classifications of Aquatic Non-Native Species: Application of
533
Contemporary European Assessment Protocols in Different Biogeographical Settings.
534
Aquatic Invasions 7 (1): 4958.
535
48. Weiss, Stuart B. 1999. Cars, Cows, and Checkerspot Butterflies: Nitrogen Deposition and
536
Management of Nutrient-Poor Grasslands for a Threatened Species. Conservation Biology 13
537
(6): 147686.
538
539
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
The widespread recognition that nonnative plants can have significant biological and economic effects on the habitats they invade has led to a variety of strategies to remove them. Removal alone, however, is often not sufficient to allow the restoration of altered communities or ecosystems. The invasive plant's effects may persist after its removal thus exerting a “legacy” that influences community composition or the ecosystem properties or both over some ensuing period. Here, we review evidence of such legacy effects on plant and soil communities, soil chemistry, and soil physical structure. We discuss this evidence in the context of efforts to restore community composition and ecosystem function in invaded habitats. Legacies are especially likely to develop in cases where invasive species cause local extirpations of resident species, alter resource pools, and interact with other aspects of global change including land-use changes, atmospheric N deposition, acid rain, and climate change. In cases where legacies of invasive plants develop, the removal of the nonnative species must also be accompanied by strategies to overcome the legacies if restoration goals are to be achieved.
Article
Full-text available
Restoration in Mediterranean-climate grasslands is strongly impeded by lack of native propagules and competition with exotic grasses and forbs. We report on a study testing several methods for exotic plant control combined with planting native grasses to restore prairies in former agricultural land in coastal California. Specifically we compared tarping (shading out recently germinated seedlings with black plastic) once, tarping twice, topsoil removal, herbicide (glyphosate), and a control treatment in factorial combinations with or without wood mulch. Into each treatment we planted three native grass species (Elymus glaucus, Hordeum brachyantherum, and Stipa pulchra) and monitored plant survival and cover for three growing seasons. Survival of native grass species was high in all treatments, but was slightly lower in unmulched soil removal and control treatments in the first 2 yr. Mulching, tarping, and herbicide were all effective in reducing exotic grass cover and enhancing native grass cover for the first 2 yr, but by the third growing season cover of the plant guilds and bare ground had mostly converged, primarily because of the declining effects of the initial treatments. Mulching and tarping were both considerably more expensive than herbicide treatment. Topsoil removal was less effective in increasing native grass cover likely because soil removal altered the surface hydrology in this system. Our results show that several treatments were effective in enhancing native grass establishment, but that longer term monitoring is needed to evaluate the efficacy of restoration efforts. The most appropriate approach to controlling exotics to restore specific grassland sites will depend not only on the effectiveness, but also on relative costs and site constraints.
Article
Full-text available
Resolving conflicting ecosystem management goals-such as maintaining fisheries while conserving marine species or harvesting timber while preserving habitat-is a widely recognized challenge. Even more challenging may be conflicts between two conservation goals that are typically considered complementary. Here, we model a case where eradication of an invasive plant, hybrid Spartina, threatens the recovery of an endangered bird that uses Spartina for nesting. Achieving both goals requires restoration of native Spartina. We show that the optimal management entails less intensive treatment over longer time scales to fit with the time scale of natural processes. In contrast, both eradication and restoration, when considered separately, would optimally proceed as fast as possible. Thus, managers should simultaneously consider multiple, potentially conflicting goals, which may require flexibility in the timing of expenditures.
Article
Plant invasions are a serious threat to natural and managed ecosystems worldwide. The number of species involved and the extent of existing invasions renders the problem virtually intractable, and it is likely to worsen as more species are introduced to new habitats and more existing invaders move into a phase of rapid spread. We contend that current research and management approaches are inadequate to tackle the problem. The current focus is mostly on the characteristics and control of individual invading species. Much can be gained, however, by considering other important components of the invasion problem. Patterns of weed spread indicate that many species have a long lag phase following introduction before they spread explosively. Early detection and treatment of invasions before explosive spread occurs will prevent many future problems. Similarly, a focus on the invaded ecosystem and its management, rather than on the invader, is likely to be more effective. Identification of the causal factors enhancing ecosystem invasibility should lead to more-effective integrated control programs. An assessment of the value of particular sites and their degree of disturbance would allow the setting of management priorities for protection and control. Socioeconomic factors frequently play a larger part than ecological factors in plant invasions. Changes in human activities in terms of plant introduction and use, land use, and timing of control measures are all required before the plant invasion problem can be tackled adequately. Dealing with plant invasions is an urgent task that will require difficult decisions about land use and management priorities. These decisions have to be made if we want to conserve biodiversity worldwide.
Article
Invasive species can threaten the conservation of biodiversity and natural resources and incur considerable economic losses. Invasive species management programs therefore aim to reverse or mitigate the impacts of invasion, but these programs can have severe negative impacts on native species and ecosystems ( 1 , 2 ), because invasive species integrate into their new ecosystems and can assume ecological functions previously carried out by native species. Indirect effects of management are likely to become more common as existing invaders form new interactions and new species continue to be introduced. On page 1028 of this issue, Lampert et al. report an optimal management model that shows how invasive species control can be combined with other ecosystem goals ( 3 ).
Article
Conservation goals at the start of the 21st century reflect a combination of contrasting ideas. Ideal nature is something that is historically intact but also futuristically flexible. Ideal nature is independent from humans, but also, because of the pervasiveness of human impacts, only able to reach expression through human management. These tensions emerge in current management rationales because scientists and managers are struggling to accommodate old and new scientific and cultural thinking, while also maintaining legal mandates from the past and commitments to preservation of individual species in particular places under the stresses of global change. Common management goals (such as integrity, wilderness, resilience), whether they are forward looking and focused on sustainability and change, or backward looking and focused on the persistence and restoration of historic states, tend to create essentialisms about how ecosystems should be. These essentialisms limit the options of managers to accommodate the dynamic, and often novel, response of ecosystems to global change. Essentialisms emerge because there is a tight conceptual coupling of place and historical species composition as an indicator of naturalness (e.g., normal, healthy, independent from humans). Given that change is increasingly the norm and ecosystems evolve in response, the focus on idealized ecosystem states is increasingly unwise and unattainable. To provide more open-ended goals, we propose greater attention be paid to the characteristics of management intervention. We suggest that the way we interact with other species in management and the extent to which those interactions reflect the interactions among other biotic organisms, and also reflect our conservation virtues (e.g., humility, respect), influences our ability to cultivate naturalness on the landscape. We call this goal a natural practice (NP) and propose it as a framework for prioritizing and formulating how, when, and where to intervene in this period of rapid change. Desarrollo de una Práctica Natural para Adaptar Objetivos de Conservación al Cambio Global Resumen Los objetivos de conservación al inicio del siglo XXI reflejan una combinación de ideas contrastantes. La naturaleza ideal es algo que está intacto históricamente y que es flexible futurísticamente. La naturaleza ideal es independiente del humano, pero por causa de la dominación del impacto humano, sólo puede expresarse por medio del manejo humano. Estas tensiones emergen en el actual razonamiento de manejo porque los científicos y los administradores luchan por acomodar el pensamiento científico y cultural viejo y nuevo bajo el estrés del cambio global, mientras mantienen los mandatos legales del pasado y los compromisos de preservación de especies individuales en lugares particulares. Los objetivos comunes de manejo (como la integridad, lo silvestre del terreno, la capacidad de recuperación), ya sea que miren hacia el frente y estén enfocados en la sustentabilidad y el cambio, o miren hacia atrás y estén enfocados en la persistencia y restauración de los estados históricos, tienden a crear esencialismos sobre cómo deben ser los ecosistemas que limitan las opciones de los administradores para acomodar la respuesta dinámica, y comúnmente novedosa, de los ecosistemas hacia el cambio global. Esto es porque hay un emparejamiento conceptual entre el lugar y la composición histórica de especies como indicador de la naturalidad (p. ej.: normal, sana, independiente del humano) que está grabado en las metas. Dado que el cambio es cada vez m´s la norma y los ecosistemas evolucionan en respuesta, el enfoque sobre los estados idealizados de los ecosistemas es imprudente e inalcanzable. Para proporcionar más objetivos sin restricciones, proponemos que se ponga mayor atención a las características de la intervención del manejo. Sugerimos que el modo en el que interactuamos con otras especies en el manejo y la extensión a la cual esas interacciones son similares a las interacciones de otros organismos bióticos y cómo reflejan nuestras virtudes de conservación (p. ej.: humildad, respeto) influye sobre nuestra habilidad para cultivar la naturalidad en el paisaje. A esto lo llamamos práctica natural y sugerimos que puede contribuir a un marco de trabajo para priorizar y formular, cómo, cuándo y dónde intervenir en este periodo de cambio rápido.
Article
QuestionsHow is natural regeneration of a patchy landscape affected by within-patch species interactions and among-patch dispersal after an extreme disturbance? Do landscape dispersal processes facilitate the invasion of native-dominated patches by exotic species in adjacent patches? LocationIrvine Ranch Natural Landmark, Irvine, California, USA. Methods We monitored plant community composition in paired grassland patches that were initially dominated by native or exotic grasses at eight sites. We followed recovery of native and exotic grassland species over time, starting in a record drought year prior to an intense fire, and then for 3 yr with more typical rainfall patterns after the fire. Additionally, we compared seed rain of native and exotic species across native and exotic patches, quantifying how seed rain influenced species abundance in the following year. Multivariate and regression analyses were used to assess the potential homogenization of the landscape. ResultsFollowing the extreme drought/fire disturbance, the exotic annual grasses quickly recovered in abundance in patches that they dominated prior to the disturbance. However, the native grass, Stipa pulchra, was not able to recover in the patches it once dominated. As the exotic grasses gradually increased in the native patches, the paired patch types became more similar in composition over time. Exotic grasses produced up to 28 times more seed than the native dominant grass, Stipa; even in the patches initially dominated by Stipa, exotic seed rain was equivalent or greater than the native. Seed rain was positively correlated with the following year's abundance for both exotic and native species. Conclusions After an extreme disturbance, recovery of native patches can be stalled by an influx of propagules from neighbouring exotic patches. This exotic seed rain can allow the invasion of areas once dominated by natives, thus inhibiting regeneration. The matrix surrounding remnant native stands can be a critical factor in determining whether an extreme disturbance enhances native diversity vs. increasing its susceptibility to invasion.
Article
Nutrient-poor, serpentinitic soils in the San Francisco Bay area sustain a native grassland that sup- ports many rare species, including the Bay checkerspot butterfly ( Euphydryas editha bayensis ). Nitrogen (N) deposition from air pollution threatens biodiversity in these grasslands because N is the primary limiting nu- trient for plant growth on serpentinitic soils. I investigated the role of N deposition through surveys of butter- fly and plant populations across different grazing regimes, by literature review, and with estimates of N dep- osition in the region. Several populations of the butterfly in south San Jose crashed following the cessation of cattle grazing. Nearby populations under continued grazing did not suffer similar declines. The immediate cause of the population crashes was rapid invasion by introduced annual grasses that crowded out the larval host plants of the butterfly. Ungrazed serpentinitic grasslands on the San Francisco Peninsula have largely re- sisted grass invasions for nearly four decades. Several lines of evidence indicate that dry N deposition from smog is responsible for the observed grass invasion. Fertilization experiments have shown that soil N limits grass invasion in serpentinitic soils. Estimated N deposition rates in south San Jose grasslands are 10-15 kg N/ha/year; Peninsula sites have lower deposition, 4-6 kg N/ha/year. Grazing cattle select grasses over forbs, and grazing leads to a net export of N as cattle are removed for slaughter. Although poorly managed cattle grazing can significantly disrupt native ecosystems, in this case moderate, well-managed grazing is essential for maintaining native biodiversity in the face of invasive species and exogenous inputs of N from nearby ur- ban areas.
Article
Most ecosystems are now sufficiently altered in structure and function to qualify as novel systems, and this recognition should be the starting point for ecosystem management efforts. Under the emerging biogeochemical configurations, management activities are experiments, blurring the line between basic and applied research. Responses to specific management manipulations are context specific, influenced by the current status or structure of the system, and this necessitates reference areas for management or restoration activities. Attempts to return systems to within their historical range of biotic and abiotic characteristics and processes may not be possible, and management activities directed at removing undesirable features of novel ecosystems may perpetuate or create such ecosystems. Management actions should attempt to maintain genetic and species diversity and encourage the biogeochemical characteristics that favor desirable species. Few resources currently exist to support the addition of proactive measures and rigorous experimental designs to current management activities. The necessary changes will not occur without strong input from stakeholders and policy makers, so rapid information transfer and proactive research-management activities by the scientific community are needed.