Biology Reference
In-Depth Information
outside of the research realm (Allendorf and Lundquist 2003; Jordan et al. 2003).
The intersection of science, conflicting value systems, environmental ethics, public
policy, and articles in the popular press have given mixed messages, confusion, and
tension in the NIS theater (Lodge and Shrader-Frechette 2003). Communication
shortcomings are especially evident for audiences in the ornamental horticulture
industry and the gardening public. Ornamental horticulture personnel are generally
aware of the issue of invasive NIS; however, there is a need for the industry to grasp
the fundamental concepts of plant invasion biology and to address and formulate
strategies concerning the sale and planting of potentially invasive NIS. The nursery-
mediated spread of invasive plants is a major challenge and concern for the future
of the nursery industry (Green and Green 2003). The objective of our paper is to
convey the salient aspects of plant invasion biology that are relevant to the orna-
mental horticultural audience. We will cover the fundamental aspects of invasive
nonnative plants, the role of the nursery and landscape industry in invasive nonin-
digenous plant species, the reasons why the ornamental horticulture industry should
care about NIS, and recommendations for the ornamental plant industry to mitigate
its role in dispersing invasive, nonnative plant species.
9.2
Fundamental Aspects of Invasive NIS
9.2.1
What is Plant Invasion?
Biological invasion is a phenomenon that is old as life itself (Drake 2005). However,
the rate of invasion has greatly accelerated in the past century due to anthropogenic
factors such as removal of dispersal barriers, international travel, and enterprise
(Drake 2005). The process of invasion (area occupied vs. time) exhibits the pattern
of a sigmoidal curve in which the initial slow growth, exponential growth, and the
flattening of the curve represent introduction, colonization, and naturalization,
respectively (Radosevich et al. 2003). Radosevich et al. (2003) state that a species
is naturalized “when it successfully establishes new self-perpetuating populations,
is dispersed widely throughout a region, and is incorporated into the resident flora.”
The time from first arrival to the rapid occupation by the naturalizing species is
termed
lag time
and may occur in years or decades (Kowarik 1995). Lag time dura-
tion can be influenced by environmental factors of the recipient habitat that improve
conditions for the invading organism, detection, invasion pressure, dispersal path-
ways, introduction of new pollinators, or genetic changes that improve fitness of the
organism (Bryson and Carter 2004; Crooks and Soule 1999; Mack et al. 2000). Lag
times for woody plants can exceed 100 years (Kowarik 1995); however, lag times
for herbaceous perennials are believed to be much shorter than for woody plants
(Reichard and White 2001). Detection of invaders and quantification of their inva-
siveness is a function of human perception. Species may be cryptic and widespread
and therefore go unnoticed for years until people start to look for them.
