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Durham University

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Publication details for Professor Stephen G Willis

Willis, SG & Hulme, PE (2002). Does temperature limit the invasion of Impatiens glandulifera and Heracleum mantegazzianum in the UK? Functional Ecology 16(4): 530-539.

Author(s) from Durham

Abstract

1. Impatiens glandulifera Royle and Heracleum mantegazzianum Sommier et
Levier are widespread, non-indigenous plant species in the UK. A
variety of correlational analyses suggest that their spatial extent is
limited by climate, although no experimental studies have tested this
hypothesis. This paper reports the first detailed experimental
examination of the impact of climate on the performance of the two
species.
2. Seeds of each species were sown, in each of 2 years, in replicated
plots along an elevational gradient (10-600 m a.s.l.) in north-east
England. Both species germinated readily at all elevations, even in
areas well above their current limits within the study area. The plants
were, however, smaller at higher altitudes. Impatiens glandulifera also
produced fewer seeds with increasing elevation.
3. Plant performance was assessed in relation to actual and
interpolated climate data along the elevational transect. For H.
mantegazzianum , the timing of germination was correlated most strongly
with the pre-emergence heat sum; for I. glandulifera this relationship
was significant in one year only. Maximum height of both species was
correlated with increasing post-emergence heat sum, as was pod
production by I. glandulifera . The biomass of second-year H.
mantegazzianum plants varied non-linearly with post-emergence heat sum.
For both species, overwinter survival of seeds was not related to
winter temperature or frost days. Overwinter survival of first-year H.
mantegazzianum plants declined with increasing frost incidence.
4. The results suggest that, of the two species, only I. glandulifera
is currently most limited by temperature, although this is not the only
factor determining the distribution of the species.