Lexicon terms: spontaneous vegetation, weeds and invasive species

Spontaneous vegetation, weeds and invasive species are three overlapping terms that refer to plants that were not intentionally cultivated at a given site by humans but not considered to grow there naturally, either.  The term “weeds” is used to refer interchangeably to spontaneous vegetation and invasive species.

Spontaneous vegetation

Spontaneous vegetation is associated with urban areas.  It may be native or non-native, but is often negatively associated with an absence of care.  Del Tredici and Kuehn emphasize that spontaneous vegetation can have ecological and social services that are often on recognized or undervalued.  Where funding for landscape maintenance is unavailable, spontaneous vegetation may hold potential as a landscape strategy requiring minimal maintenance.  Kuehn describes methods by which spontaneous vegetation might be made more aesthetically appealing.  Kuehn also describes spontaneous vegetation as “authentic and always appropriate to the site conditions”, and even evocative of a site’s past use.

Del Tredici, Peter “Wild Urban Plants of the Northeast: a field guide” Ithaca, NY: Cornell University Press, 2010

“Given that cities are human creations and that the original vegetation that once grew there has long since disappeared, one could argue that spontaneous plants have become the de facto native vegetation of the city.  Indeed, a basic premise of this book is that the ecology of the city is defined not only by the cultivated plants that require ongoing maintenance and the native species that are restricted to protect natural areas, but also by the plants that dominate the neglected interstices of the urban environment.  This ‘wasteland’ flora occupies a significant percentage of the open space in many American cities, especially those with faltering economies.  Recent research indicates that if such vegetation is left undisturbed long enough to develop into woodlands, it can provide cities with important social and ecological services at very little cost to taxpayers (Zipperer et al. 1997; Kowarick and Koerner 2005; Weiss et al. 2005; Mauratet 2007).”  (1)

Kuehn, Norbert “Intentions for the Unintentional: Spontaneous Vegetation as the Basis for Innovative Planting Design in Urban AreasJOLA autumn 2006

“Spontaneous vegetation is a characteristic component of the urban environment.  It occurs at no financial cost, is authentic and is always appropriate to the site conditions.”  (46)

“However it is generally considered to be ‘weeds’ and is seen by many people as the indicator of a site that has been left to fall into decay or is poorly cared for.  In order to use spontaneous vegetation properly, it needs to be ‘improved’, to be ‘put on display’ – but how many this be achieved?”  (47)

“To intervene in spontaneous vegetation to improve it aesthetically may seem as a contradiction: ‘spontaneous’ means that which occurs by chance, without conscious design intent.  ‘Intervention’ means well-intended design work and creates more or less sophisticated new types of plantings that include some spontaneous vegetation.  Essentially, there are four ways of dealing with spontaneous vegetation:

1. Maintaining the current state (status quo) through appropriate measures (for example, maintaining a meadow by mowing);

2. Allowing succession to proceed naturally (no intervention takes place: a new kind of wilderness will be created);

3. Effecting changes in succession through interventions (for example, creating an open grove-like effect by removing branches and shrubs in a mature stand);

4. Improving the aesthetic value by changing the species composition.”      (48)

“The results of the use of spontaneous vegetation in urban planting design have more than just economic advantages.  Vegetation can also tell us something about the historical uses of a site.  A way of working with spontaneous vegetation has developed from this idea – a way of managing parks that have been established on former industrial sites.  There the vegetation is seen, together with structural ruins, as a clue to the industrial culture and is incorporated as a sign of the decline and transformation of the landscape.

“When the vegetation and the structures are intentionally left as they are, the residents are confronted with the industrial past of the site.  They may build a relationship to it and develop a pride in the history of the place and perhaps in their own history as well.  The public may be motivated to become involved.”  (51)

Invasive species

Invasive species are non-native species that are well-adapted to disturbance and often seed prolifically.  These species are assumed to degrade the environment by edging out native species, but Sogge et al, Brown and Sax, and Sagoff argue that relatively little is known about the true impact of these species.  So-called invasive species may be filling an open-niche – not actively competing with a native species for resources, but replacing one where climate change or other environmental factors have impacted native species distribution and health.  Sogge et al argue that to birds, it may matter very little whether a species is native or non-native – and that the removal of invasive species does not guarantee that native species will return.  Removal of invasive plant species may mean habitat loss for native birds.

Del Tredici argues that context influences our impression of these plants – aesthetic or security (visibility) concerns may cause us to devalue them.

Warren offers a geographer’s view of the native/alien species debate.  He cites globalization and McDonaldization as causes of concern – ecosystems as well as cultures are becoming increasingly similar world-wide.  Warren rejects the “native” and “alien” species labels as an outgrowth of the discredited nature/culture dichotomy: human action has influenced all aspects of the natural environment, including species distribution.

Sogge, Mark K; Sferra, Susan J.; and Paxton, Eben H. “Tamarix as Habitat for Birds: Implication for Riparian Restoration in the Southwestern United States” Restoration Ecology vol 16, issue 1 mar 2008

“The structure of vegetation, native or exotic, may be more important to birds than the actual species composition (Hausner et al. 2002; Jones & Bock 2005), and different species of birds will respond differently (Gjerde & Saetersdal 1997). The complexity of responses by bird communities to exotics in different ecosystems around the world suggests that negative impacts by exotics cannot be universally assumed; rather, evaluation of impacts should be conducted species by species with attention to geographic differences.” (146-147)

Brown, James H. and Sax, Dov F. “Do Biological Invasions Decrease Biodiversity?” Conservation Magazine vol 8, no 2 april-june 2007 http://www.conservationmagazine.org/2008/07/aliens-among-us/

Authors argue that little is known about invasive species or their impact on ecosystems.  Invasives are replacing species that were already threatened by human action.  The argument that invasive species contribute to a loss of biodiversity may not be true – species distributions are changing, but in the US we have gained more species than we have lost.

Sagoff, Mark “Are nonnative species harmful?” Conservation Magazine vol 8, no 2 april-june 2007 http://www.conservationmagazine.org/2008/07/aliens-among-us/

Impact of native species depends on your perspective.  Zebra mussels have been very effective at filtering phytoplankton and suspended material in Great Lakes.  Their ecological services include cleaning up water and re-establishing native grasses and fishes – but mussels have also clogged up intake valves and filtration plants.

Warren, Charles R “Perspectives on the ‘alien’ versus ‘native’ species debate: a critique of concepts, language and practice” Progress in Human Geography 31:427 2007

Native species – “autocolonized an area since a selected time in the past”

Alien species – “introduced by humans, intentionally or otherwise” – transfer of species has been going on for millennia, but pace is increasing with technology

Alien species have real costs (may be invasive) but real benefits as well (food, economics, etc)

Williamson’s “tens rule” – 10% of introduced species appear in the wild, 10% of those become established, and only 10% of those become pests (.1% of all imports)

Native and alien are really just relative terms – the whole environment is shaped by human action, and picking a spot on the continuum to call native or alien is pretty arbitrary.  Question of temporal and spatial scales.

Functional and cultural natives – introduced species that are now considered native or characteristic of a place

Some concerns over alien species associated with xenophobia

Warren suggests that native/alien labels are an outgrowth of modernism – and in a postmodern age, we should accept species from across the spectrum,  “In a similar vein, Jamieson (1995: 340) suggests provocatively that ‘a celebration of alien plants and surprising biological juxtapositions may be more in tune with the postmodern world than attempts to protect native species’. Far from promoting nativity and pure-bloodedness, postmodernity celebrates hybridity, a stance which runs directly counter to the ‘McDonaldization’ fears described above but which chimes with postcolonial arguments that globalization does not automatically dilute distinctiveness (O’Brien, 2006). In today’s postpolarity, postnatural, postmodern context, the native/alien dualism thus appears antiquated (if appealing) in its naïve simplicity and certainty,and it clashes violently with contemporary social ethics. It has little hope of surviving when the old, bipolar dogmas on which it rests are themselves collapsing amid these conceptual reconfigurations.

The abandonment of a polarized conception of native and alien thus coheres well with wider conceptual trends. In common with many former polarities, it is dissolving into an entangled, mixed-up continuum.”  (440)

Tuhus, Dubrow “Don’t Sweat the Invasion: Why foreign plants and animals may not be that bad.” Slate Nov 4, 2009 http://www.slate.com/id/2234605/pagenum/all/

Del Tredici, Peter “Wild Urban Plants of the Northeast: a field guide” Ithaca, NY: Cornell University Press, 2010

“From a biological perspective, weeds are plants that are adapted to disturbance in all its myriad forms, from bulldozers to acid rain.  Their pervasiveness in the urban environment is simply a reflection of the continual disruption that characterizes this habitat.  Weeds are the symptoms of environmental degradation, not its cause, and as such are poised to become increasingly abundant within our lifetimes.”  (3)

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