Complex and Dynamic Effects of an Extreme Low Temperature Weather Event on Invasive Plant Populations and Resident Communities.

Whilst it is often assumed that invasive plant species may benefit more from climate change than native species, there is little empirical data on how they, and the communities they invade, respond to extreme weather events (EWEs). Here, we show that the effects of a low temperature EWE can result in a dramatic reduction in both vegetative and reproductive growth of invasive populations of Gunnera tinctoria, although a significant recovery was found within 1 year after its occurrence. Whilst the EWE decreased both the leaf/petiole numbers of mature plants, the major impact was on leaf expansion and a decrease in the size/number of inflorescences. Concomitant with the reduction in growth of G. tinctoria, there was a 5-fold increase in the number of resident species emerging in invaded areas, which largely persisted after the recovery of the invasive populations. Although the growth of G. tinctoria seedlings was also reduced, this was relatively small, and growth and development resumed almost immediately after the EWE. In comparison, the resident plant community was largely unaffected by the EWE either due to the later initiation of growth and/or because of their greater resilience to episodic low temperature events. Our results show that an EWE of this magnitude can have complex time-dependent effects on plant invasions and invaded communities, with a greater impact on the established invasive plants compared to newly recruited seedlings. Based on an assessment of historical climatic data, these long-lived populations have been exposed to EWEs of a similar or greater magnitude in the past, which have not constrained their spread or compromised recruitment. Given the likelihood of an almost complete absence of low temperature EWEs of similar magnitude in the future, any temporary restrictions on the growth of invasive G. tinctoria and other similar invasive species populations are likely to be small.