Introduction and General Information about Invasive Exotics

About this project—

Invasive exotic species are organisms artificially introduced from their natural geographic range into a new area where they expand both their population and distribution range and significantly alter the structure and function of the new system (Cronk, 2001). They may pose lasting and pervasive threats by establishing self-sustaining populations in otherwise natural environments and competing with indigenous species for essential resources. If left unchecked, invasion by exotics may severely alter the ecological and economic value of infested areas (McNeely, 2001). Invasive exotics are thought by many to have one of the most detrimental impacts on natural biodiversity globally, second only to habitat loss, which is why their presence on the University of Richmond campus is of great interest (Luken, 1997).

This research is intended to inventory the myriad invasive exotic plant species at the University of Richmond, and its immediate vicinity, in order to provide baseline data useful in determining how the problem develops and modifies vegetation on campus. The Virginia Department of Conservation and Recreation lists nearly two-hundred species of invasive exotic plant species known to be in Virginia. This state-wide list was narrowed down to roughly eighty species that could potentially be on campus based on climate, terrain, and prior knowledge. The eighty plant species were extensively researched using various botanical manuals and then located on campus and nearby areas based on their preferred habitat information.  Documentation of each plant species included the following elements: the location where the species originated; a brief physical description; its geographic range within the United States as well as its preferred habitat; where it may be found on campus; its threats to ecological systems; its degree of invasiveness (more about the invasiveness rankings from VDCR); and one or more photographs.  This website was completed by Bethany Shewmaker and guided by Dr. W. John Hayden, Professor of Biology at the University of Richmond.

Distinction between indigenous and exotic plant species 

A species is known as indigenous to a particular area if it originates naturally without having been either intentionally or inadvertently introduced.  Indigenous species have well-established ecological niches within their natural ranges, and are well adapted to local abiotic and biotic factors, such as climate, soil, and species interactions (Cronk, 2001). 

Exotic species are those artificially introduced from their natural geographic range to a new area where they may become invasive, significantly altering the structure and function of the new system by naturally expanding both their population and distribution range (Cronk, 2001).  Deliberate establishment of exotics is often motivated by the aesthetic or agricultural utility of the plant introduced, and includes plants such as corn, wheat, and rice.  Unintentional introductions generally result from contaminated imports, such as tussock grass, which was introduced from South America as a seed crop contaminant (McNeely, 2001).  Invasive exotics pose lasting and pervasive threats, establishing self-sustaining populations in natural areas, often out-competing with and otherwise harming indigenous species (Cronk, 2001). 

Invasive exotics should not be confused with weeds, which may also be native species that invade agricultural and highly disturbed habitats, or transient plants, which do not successfully establish lasting populations (Cronk, 2001).  Although invasive exotics can display many of the characteristics of weedy species, it is their ability to invade undisturbed natural communities that distinguishes invasive exotics from the weeds of agriculture and horticulture (Cronk, 2001).

How a plant species can become invasive—

With enhanced global trade and travel, plant species are being relocated to new areas, offering revolutionary possibilities for international markets (Luken, 1997).  Not all exotic species are disadvantageous when translocated into a new environment.  Many play important ecological roles—as photosynthesizing agents that also help impede global climate change, in recovery after ecosystem disturbances, and as substitutes for extirpated native species—while others play a crucial economic role—as foundations of critical horticultural and agricultural systems as well as subsistence and pharmaceutical resources.  Many such useful exotic plant species show little tendency to spread and establish themselves outside of cultivation.  However, natural selection is inexorable and exotic plants in cultivation are not immune to its effects.  Thus, subtle genetic changes occurring over time may be sufficient to allow previously “well-behaved” cultivated species to escape and become problematic invasives (McNeely, 2001).


Other species become exotic when inadvertently moved from native ecosystems into foreign areas as stowaways on transportation and shipping vessels and imports, as well as by the effects of changes in global climate and land use patterns that allow species to expand their natural ranges, usually invading areas disturbed by nature or human activity and infrastructure (Cronk, 2001). 

Without the natural controls (predators, competitors, parasites, diseases) inherent in their native regions that keep their populations in check, exotic species become invasive because of their tendency towards rapid growth and maturity, prolific seed production and dispersal over large areas, and highly successful germination and colonization.  They are thus able to displace native plants by out-competing for essential resources (Cronk, 2001).

The significance of invasive exotic plant species—

Invasive exotics are thought by many to have one of the most detrimental impacts on natural biodiversity globally, second only to habitat loss (Luken, 1997).  Invasion by exotics results in an explosion that floods a native ecosystem, which if left unchecked may severely and irrevocably alter the biological function and economic value of a particular area by displacing native vegetation, decreasing productivity, altering nutrient cycling and soil structure, and disrupting natural disturbance and succession patterns.  The magnitude of the problem is underscored by the myriad plant species whose populations have become seriously threatened (Cronk, 2001). 

The control of invasive exotic plant species— 

There are two ways to control the spread of invasive exotics—prevention and eradication—both of which are extremely difficult and costly (McNeely, 2001).  General awareness about the scale of the problem is pivotal in eliciting action, which must be garnered internationally in order to generate essential legal, institutional, and technical cooperation (Rubec, 1997).  So little is currently known about potential invaders and efficacious removal techniques that large-scale education, monitoring, and regulation must emerge at the forefront of global environmental policy in order to protect the quality of native ecosystems (Rubec, 1997). 

The problem of invasive exotic plant species on campus 

Approximately eighty of the nearly two-hundred species of invasive exotic plants known to be in Virginia can be found on or immediately surrounding the University of Richmond campus, where the large amount of disturbance constitutes prime area for their spread.  Many of the invasive exotics have been planted as cultivars, while some have presumably spread from nearby regions, and others almost certainly remain undetected, in the nascent stages of spreading.