Biology Reference
In-Depth Information
Both swallow-wort species are typically found in habitats with temperature
ranges in the winter of −11 to 0.7°C and in the summer of 20.7-26.4°C, while mean
annual precipitation levels in these areas range from 776-1,206 mm (DiTommaso
et al. 2005b).
In contrast, annual temperatures in Ukraine (PSW's native range) vary from −8
to 24°C with a mean precipitation of 629 mm. Temperatures in southwestern France
(part of BSW's native range) vary from 2 to 28°C with 668 mm of precipitation and,
in northeastern Spain, the climate varies from 2 to 31°C with only 317 mm of pre-
cipitation (World Meteorological Organization 2008).
13.5 Impacts
PSW in particular has invaded sensitive and rare alvar communities both in eastern
Ontario, Canada, and in Jefferson County, NY, and has displaced endemic flora
and fauna (DiTommaso et al. 2005b). A survey in the affected areas revealed a
significant negative correlation between PSW cover and the number and diversity
of previously common grassland bird species (DiTommaso et al. 2005b). Ernst
and Cappuccino (2005) found fewer arthropods both dwelling on PSW plants and
ground-dwelling insects adjacent to sampled plants. The authors concluded that
the decline in old-field arthropod populations because of the invasion of swallow-
worts could negatively impact bird and small mammals that also depend on insects
for food.
Lawlor (2000) reported that habitats of the Hart's tongue fern [
Asplenium scolo-
pendrium
L. var.
americanum
(Fern.) Kartesz & Gandhi], a rare plant species native
to regions of New York, have been invaded by PSW. Similarly, PSW has invaded
sites at The Nature Conservancy's Mashomack Preserve on Shelter Island, NY
where the federally listed endangered species sandplain gerardia (
Agalinis acuta
Pennell) is found (M. Scheibel, personal communication). BSW is a relatively less
well-studied species and thus few targeted studies have been carried out to assess the
ecological impacts of its invasion. One study found that the species threatens the
survival of the endemic Jessop's milkvetch [
Astragalus robbinsii
(Oakes) A. Gray]
along the banks of the Connecticut River in Windsor, VT, one of only three locations
in which the plant is known to remain (DiTommaso et al. 2005b).
While the swallow-worts have had a substantial negative impact in a variety of
natural areas, the species pose a substantial and looming threat to New York states'
important agricultural industry. The detection of PSW plants in no-till corn and
soybean fields is problematic given the relative difficulty of controlling either of the
swallow-wort species effectively with commonly used herbicides in crop systems
(DiTommaso et al. 2005b; Lawlor 2003; Weston et al. 2005). There have been
numerous reports of landowners abandoning horse pastures due to unmanageable
infestations of PSW, possibly due to the physical obstruction posed by dense
swallow-wort stands or the suspected toxicity to mammals of plant tissues (Lawlor
2003; Weston et al. 2005). A feeding trial with fresh PSW plant material resulted
