Invasive Species: Some Science and Some Questions
> FEBRUARY 15, 2011
> in INVASIVE PLANTS<http://www.ecolandscaping.org/category/invasive-plants=
/>
>
> *by Jono Neiger*
>
> *=93Man is part of nature, and his war against nature is, inevitably, a w=
ar
> against himself.=94 *Rachel Carson, *Silent Spring, 1962***
>
> Invasive species, the new species on the block, have been taking heat for
> ecosystem changes for several decades. And yet, many of our commonly held
> assumptions about invasive species are not entirely correct. The science
> backing up heated claims is increasingly coming into question. As ecologi=
cal
> designers, land managers and landscapers we rely on the information we ge=
t
> to inform and direct our work.
>
> Many of us spend large amounts of time getting plants established,
> maintaining plants, or managing woodlands, edges, and meadows. This is ha=
rd
> work and not made any easier by the tough plants that may already be
> occupying that space. Observation of invasive species where we live and w=
ork
> seems to confirm our suspicions that they are rapidly taking over.
>
> *Early Control Strategies*
>
> I first took up the cause of fighting invasive species while restoring
> riparian forest for The Nature Conservancy on the Sacramento River in
> California in the early 1990s. Establishing forests in flood prone
> agricultural fields was difficult but rewarding. Like farming crops,
> establishing riparian species required controlling the weeds. We took tha=
t
> task seriously and used mowing and hand removal, but mostly we used an AT=
V
> spray rig to apply Roundup along the rows of plants. These weren=92t just=
any
> weeds; we had star thistle, bane of the west; Johnson grass with 6=92-lon=
g
> rhizomes; and numerous others. After several years I had been inoculated
> with the fervor of fighting the battle to get our plants in, and the bad
> ones out.
>
> <http://www.ecolandscaping.org/wp-content/uploads/2011/02/neiger-photo-1.=
200.jpg>
> The Nature Conservancy restoration project on the Sacramento River 18 yea=
rs
> later.
>
> These projects were very successful. I recently had the chance to visit t=
wo
> of the fields we planted about 18 years ago. Our plantings of seeds, star=
ts,
> and cuttings are now a forest. The stately valley oaks are now big enough
> that my 13-year-old son could climb them. We saw the massive ten feet tal=
l
> elderberry bushes and towering willow and cottonwood trees over 30 feet
> tall. I was moved to see the results of our sweat and toil. A deer ran fr=
om
> us as we climbed over fallen wood and worked through brush and limbs. I
> found drip line still there, though the rows were now hard to make out
> through the new growth established among the intentional plantings.
>
> But the strategies we used were very expensive and energy intensive. They
> relied on a complete domination of the land the same as the farming
> practices we mimicked. Since that time much of the project focus has been=
to
> buy up floodplain land and allow natural systems and succession to establ=
ish
> floodplain forest.
>
> In the years since planting that forest, I have spent many hours trying t=
o
> understand the feelings that grew in me while we fought the weeds and
> established =93our=94 plants. When I left the project, I had a passion an=
d
> fervor for native plants that remains with me. I also had adopted a
> missionary zeal fueled with anger. In my desire to help natural systems, =
I
> found myself at war with a part of it. In the war to heal nature, I felt
> that invasive plants were the problem.
>
> *Reassessing and Questioning*
>
> I lost this zeal and anger several years later when a teacher kindly and
> persistently kept asking what those plants had done to me personally. I w=
as
> ripping out Scotch broom from a planting we had completed to diversify an
> orchard into a forest garden. (My teacher kept replanting them=85.) The
> proverbial light bulb went off as I saw myself angrily pulling those plan=
ts
> out, believing I knew better how to heal the disrupted landscape we worke=
d
> in. Suddenly, I felt less sure of myself and full of questions.
>
> <http://www.ecolandscaping.org/wp-content/uploads/2011/02/neiger-photo-2.=
200.jpg>
> The Nature Conservancy project revisted.
>
> Those questions sent me looking to better understand restoration work, th=
e
> ecology of disturbed landscapes, the ecology of invasive plants, and the
> reason these newly arrived species are so different. As a pioneer species=
,
> the Scotch broom in the forest garden we planted was fixing nitrogen and
> stabilizing the poor, clayey soils. How was this process different than
> succession in the woods nearby? Why didn=92t it belong there? Was it a pr=
oblem
> or a solution? Did succession still operate here and what about disturban=
ce
> ecology? Were other species helped or harmed by the Scotch broom?
>
> I have since come to have more questions than answers about invasive
> species. Questions like: How do we separate invasive species effects from
> climate change, habitat loss, development, sprawl and human population
> impacts? What objective ecological criteria identify =93alien species=94 =
or
> =93invaders=94? What are the temporal and spatial scales included in the
> definitions? What protocols will determine the conservation value of new
> species populations that have moved outside their =93historical ranges=94=
?
> Should we consider the mere existence of an allegedly nonnative species
> sufficient evidence for control or extermination? On what factual basis c=
an
> we take this position?
>
> Close observation and good research is required to understand the
> ecological implications of the changed ecosystems around us. I=92ve also
> looked closely at the emotional reactions of myself and others to the
> changes in species and ecosystems. The changes we humans are witnessing (=
and
> causing) are vast. There is no doubt that we are losing species and habit=
at;
> that the climate is changing, getting more extreme; that soils are eroded=
,
> compacted, and made toxic; that waterways are polluted; that wells are
> drawing precious groundwater up faster than it can be replenished; that
> species are being moved far from where they originated; and that the grou=
nd
> itself is covered over, sealed in a casing of asphalt and concrete.
>
> *Defining the Battle Against Invasive Species*
>
> It=92s change on a scale we can=92t imagine. And of course we want to fin=
d a
> way to stop it. And find who or what is responsible. Enter the battle
> against Invasive Species.
>
> Charles Elton wrote *The Ecology of Invasions by Animals and Plants *in**=
1958,
> using colorful language and metaphor. He essentially started the field of
> Invasion Biology writing this book. Elton conceived the introduction and
> spread of non-native species as ecologically distinct from native species
> dispersal and colonization. After defining invasion biology this way, the
> field has retained the concepts of invasive species as different and of t=
he
> invasion process as different from succession ecology and disturbance
> ecology. Forty-three years later, Davis, Thompson, and Grime looked at
> research citation practices and concluded that the field of Invasion Biol=
ogy
> had dissociated itself from succession ecology and other ecological
> sub-disciplines (Davis et al. 2001). This distinction between native
> colonizers and introduced invaders is likely spurious and a hindrance to
> further understanding the processes of introduced species.
>
> There is no disputing that newly arrived species can, and in many cases d=
o,
> bring dramatic and alarming changes to ecosystems. Islands like Guam and
> Hawaii have been hard hit from the brown tree snakes and goats, pigs, rat=
s,
> and cows respectively. Thousands of species have been moved long distance=
s
> and are changing ecosystems in known and unknown ways. Many scientists ar=
e,
> however, finding the ecosystem picture far from black and white. Early
> observations and conclusions are not proving out. Not all interactions ar=
e
> negative and many are positive.
>
> As an example, zebra mussels colonized the great lakes and Hudson River
> estuary in the early 1990s. Predictions were dire and indeed they have co=
st
> industry money to clear intake pipes and outfalls. But the ecological
> impacts are harder to gauge and continue to unfold over time. Numerous
> studies show the mussels have dramatically changed water quality paramete=
rs,
> reducing chlorophyll and phosphorous levels and increasing transparency i=
n
> these highly polluted waters (for instance Fahnenstiel 1995). A cascade o=
f
> changes in the aquatic food web has ensued. Though phytoplankton levels a=
re
> down, many reduced fish stocks have returned. In Long Point Bay, Ontario
> researchers found the introduced mussels are providing food for three duc=
k
> species increasing waterfowl activity 10-fold (Strayer 2006). These aquat=
ic
> systems were in a state of decline from decades of eutrophication, water
> contamination, and species loss. Some species have rebounded, but others
> still struggle. The ecological effects of the zebra mussel are not all ba=
d.
> Ecological systems are profoundly dynamic and in many places newly
> introduced species are adding to the change in ways that can be hard to
> understand.
>
> *The Extinction Quandary*
>
> One commonly held (and perpetuated) claim about invasive species is highl=
y
> questionable. The claim is that =93Invasive species are the second leadin=
g
> cause of extinctions=94. This declaration was made in an assessment of da=
ta
> sets and personal interviews by David Wilcove and others and published in=
a
> 1998 paper titled =93Quantifying Threats to Imperiled Species in the Unit=
ed
> States=94. The assessment had serious limitations including partial avai=
lable
> data; use of anecdotal accounts; and inclusion of Hawaii, whose distinct
> conditions greatly skewed the data. The authors themselves stated the
> limitations to their data. But the paper is widely cited in other scienti=
fic
> papers (over 700 times in the ten years following publication), research
> proposals, and college classes. In the media the claim of invasive specie=
s
> as the second leading cause of extinctions is presented as fact (sometime=
s
> attributing invasive species to extinctions globally), and often the link=
to
> where it came from is left off completely. Several authors have reassesse=
d
> the data and found the link between invasive species and species extincti=
on
> lacking:
>
> *=93The link between species invasions and the extinction of natives is
> widely accepted by scientists as well as conservationists, but available
> data supporting invasion as a cause of extinctions are, in many cases,
> anecdotal, speculative and based upon limited observation.=94 (*Gurevitch
> and Padilla 2004)
>
> A study in Canada analyzing extinction threats found introduced species t=
o
> be the least important of the six categories analyzed: habitat loss,
> over-exploitation, pollution, native-species interaction, introduced
> species, and natural causes such as stochastic events like storms and
> limited dispersal ability (Venter 2006).
>
> Many questions about invasive species need to be answered. Are naturaliz=
ed
> species the drivers or passengers of change? Are the long-term effects
> negative? Do human-caused invasions differ significantly than =93natural=
=94
> invasions? How do we measure harm and how is harm different from change? =
How
> do we separate invasive species effects from climate change, habitat loss=
,
> development, sprawl, and human population impacts? Scientists are grappli=
ng
> with these questions. Notably, Dr. James Brown, Distinguished Professor o=
f
> Biology at the University of New Mexico and Dr. Dov Sax, Assistant Profes=
sor
> at the University of Georgia=92s Institute for Ecology, have wrestled wit=
h the
> relationship of invasive species and ecosystems.
>
> *=93We don=92t know how serious the threats of alien invaders are to our
> native flora and fauna; these are scientific questions. And, as is often =
the
> case in science, the answer is less clear than reports in the popular pre=
ss
> about the devastating impacts of gypsy moth, zebra mussels, and purple
> loosestrife might imply=85. Although we often accuse invasive species of
> damage to the structure and function of ecosystems, there is usually litt=
le
> hard scientific evidence of such negative impacts.=94 *(Brown et al. 2007=
)**
>
> *An Ongoing Discussion*
>
> At the ELA Conference on March 3rd, I will participate in a panel
> discussion that allows time to delve into more of the research and differ=
ing
> perspectives on invasive species as well as what land management approach=
es
> we might take. I hope to engage people in discussion that will bring more
> consideration to this difficult topic. I know that many people have stron=
g
> feelings about invasive species. Some feel certain in their approach and
> others are searching for more understanding. There are no easy answers.
>
> Undoubtedly, we are responsible for the cataclysmic changes we=92ve wroug=
ht,
> and we can=92t place the blame anywhere else. In the years since I plante=
d
> trees on the Sacramento River I have learned that we can be a positive pa=
rt
> of this process. We need clear thinking, solid research with quality peer
> review to help direct our management activities. Anything less is wasting
> our time and efforts and imperiling fragile ecosystems.
>
> Copyright =A9 2011, Jono Neiger
>
> *About the Author*
>
> *<http://www.ecolandscaping.org/wp-content/uploads/2011/02/jono_neiger.10=
0.jpg>Jono
> Neiger* worked as a restoration biologist with the Nature Conservancy for
> several years, establishing riparian forest on the floodplain of the
> Sacramento River in California. Jono is an ecologist/land manager/landsca=
pe
> designer, teaches permaculture design at the Conway School of Landscape
> Design, and operates a design and implementation firm, Regenerative Desig=
n
> Group in Greenfield, Massachusetts.
>
> Jono, William Cullina, and Peter Del Tredici will engage in a panel
> discussion entitled =93Native, Introduced, Invasive, and Endangered Plant=
s in
> the Landscape: Untangling the Roots of the Problem=94 on March 3 at the E=
LA
> Conference <http://www.ecolandscaping.org/conference/>& Eco-Marketplace.
> Jono may be found at http://regenerativedesigngroup.com.
>
> *References:*
>
> Brown, J. H., D. F. Sax, D. Simberloff, M. Sagoff 2007. =93Aliens Among U=
s.=94
> *Conservation Magazine*, (8)2:14-21.
>
> Colautti, R.I., and H.J. MacIsaac 2004. =93A neutral terminology to defin=
e
> =91invasive=92 species.=94* Diversity and Distributions*, (10):135-141.
>
> Davis, M., K. Thompson, and P. Grime 2001. =93Charles S. Elton and the
> dissociation of invasion ecology from the rest of ecology.=94*Diversity a=
nd
> Distributions, *(7):97-102
>
> Davis, M. 2009. =93*Invasion Biology*=94 Oxford University Press.
>
> Fahnenstiel et al. 1995. =93Effects of zebra mussel (*Dreissena polymorph=
a*)
> colonization on water quality parameters in Saginaw Bay, Lake Huron.=94 *=
Journal
> of Great Lakes Research*, (4):21
>
> Gurevitch, J. and G. Padilla 2004. =93Are invasive species a major cause
> of extinctions?=94 *Trends in Ecology and Evolution*, (19):9
>
> Strayer et al. 2006 =93Understanding the long-term effects of species
> invasions=94, *Trends in Ecology and Evolution*, (21):11
>
> Venter, B. et al. 2006. =93Threats to endangered species in Canada.=94*
> Bioscience*, (56):903-910
>
> Wilcove et al. 1998. =93Quantifying threats to imperiled species in the
> United States: Assessing the relative importance of habitat destruction,
> alien species, pollution, overexploitation, and disease.=94*BioScience*,
> (48):8. 607-615
>
> Zavaleta et al. 2001 =93Viewing invasive species removal in a whole-ecosy=
stem
> context.=94 *Trends in Ecology and Evolution, *(16):454-459
>
--=20
******************
Jono Neiger
Regenerative Design Group
308 Main St, 2C
Greenfield, Ma 01301
413-658-7048
www.regenerativedesigngroup.com
Conway School of Landscape Design
Graduate Program in Sustainable Landscape Planning & Design
www.csld.edu
PINE; Permaculture Institute of the Northeast
www.thepine.org