J. Ecol. https://doi.org/10.1111/1365-2745.12933 (2018)
In grasslands, fire is less an occasional catastrophe and more a regular occurrence. Plant species have evolved to survive fires and even control it by tuning traits such as flammability to promote particular fire regimes. However, ecosystem properties are sensitive to disturbance by invading exotic species, as is shown by a 25-year study in New Zealand's south-eastern South Island. By changing the overall flammability of the grasslands, invading plants probably alter the patterns of fires that take place, which can have dramatic effects on subsequent plant community structure.
The researchers investigated the morphology and flammability of plant species found along 103 transects across Canterbury and Otago in South Island, New Zealand. These transects were surveyed three times between 1982 and 2007. Of the 334 species found, 51 accounted for more than 86% of the ground cover and were considered the dominant components of the ecosystem. Samples of these species were placed on a ‘plant barbecue’ at ~150 ºC before being lit with a blowtorch. The time taken to ignite, the temperature of the flame produced and the length of time that the samples burned were all recorded.
Combining the make-up of the communities with the traits of individual species gave a measure of the flammability of the ecosystems over time. In those locations where significant alien invasions had occurred, the general level of flammability decreased, mainly due to highly flammable native tussock grasses being replaced by lower-growing and less-flammable exotic mat-forming forbs. This could act as a positive feedback by changing the fire regime in favour of fewer, shorter and lower-intensity fires that in turn may make further invasions by less fire-tolerant non-native plants easier.