The relationship between community diversity and exotic plants: cause or consequence of invasion? - Invasive Plants: Ecological and Agricultural Aspects - page 86

Case-studies: Lonicera japonica and Rosa multiflora

The limited temporal duration of most studies constrains our understanding of
the causes and consequences of exotic plant invasions [5, 8, 66, 95-97]. While
most plant invasions occur over time periods of decades or longer, most exper-
imental studies of invasions are brief, lasting only 1-2 years. Similarly, obser-
vational sampling studies frequently only capture a single snapshot of com-
munity associations, yielding little information on how these associations
developed. Even studies that have incorporated time spans matching the scale
of invasions frequently have only a few sample periods, typically only before
and after invasion [65, 97-99] and do not capture the complex dynamics dur-
ing the intervening period.
To explore the utility of our conceptual framework for understanding the
community dynamics that shape the relationship between exotic species and
diversity, we use long-term data of species invasions in abandoned agricultur-
al land from the Buell-Small Succession Study (BSS). This study has record-
ed the presence and percent cover of all species occurring within permanent
plots in 10 abandoned agricultural fields since 1958 [100]. The fields vary in
crop prior to abandonment (hay versus row crops) and in the year of abandon-
ment (1958-1966). Each field contains 48, 0.5

2.0 m plots that were sam-
pled annually from 1958-1976 and in alternate years since 1976. This long-
term data has provided a unique opportunity to study the function of exotic
plant species within dynamic communities [22, 72, 94]. Individual plots can be
followed over the course of an invasion to simultaneously determine the fac-
tors that regulate community invasibility and the community impacts of the
invasion [72].
The two most common and abundant exotic species within the study are
Lonicera japonica and Rosa multiflora . We use these two species to examine
patterns of invasion and impacts on species richness over the course of the
invasions. Both of these species are problematic at a regional scale and are typ-
ical of the plant species that are the focus of diversity/invasion studies in that
they are widely believed to be detrimental to native ecosystems [14]. Lonicera
japonica is a bird-dispersed liana that is native to Asia and has become wide-
spread throughout the eastern United States [101]. This species has been
shown to compete strongly with native tree species [74]. Rosa multiflora ,a
bird-dispersed shrub, also native to Asia, was purposefully introduced as a liv-
ing fence and as erosion control [102].
We analyzed data from years 5-15 and 10-20 post-abandonment for L.
japonica and R. multiflora , respectively. These periods represent the beginning
and midpoint of the species invasions within the study (Fig. 3). We document-
ed three basic patterns for each species to assess the relationship between inva-
sion and diversity: 1) the relationship between invader cover and species rich-
ness as a general pattern at a single point in time, 2) the relationship between
species richness and invasibility, and 3) the relationship between invasion and
subsequent species loss.

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