Given the sheer number of invasive species in New Zealand and the difficulties that we have with them it often feels like things couldn’t get much worse for our native ecosystems. Of course things can always get worse and there are some prominent invasive pest species in other parts of the world that we don’t have, thankfully, here in New Zealand. One of these is the weed shrub lantana (Lantana camara). Although this South and Central American species is a major problem in various parts of the world, all I knew about it was that it was good at invading bush edges and regularly disturbed environments, hard to get rid of and was the title of a very good movie featuring Geoffrey Rush. Thanks to our new plant ecology lecturer, Tim Curran, I now know a great deal more.
Tim recently moved to our Department of Ecology from a field station in northern Queensland where he was part of the School for Field Studies at the Centre for Rainforest Studies. Lantana is a problem species in this part of Australia and Tim and colleagues have just published a paper in Weed Research on a potentially insidious aspect of this species. Lantana often invades dry rainforest (yes a strange combination but an important habitat nevertheless!) where it dominates the understory. One of the suggested problems that this invasion causes is in changing the fire regime, such that these habitats become more prone to fire. This change could be the result of chemicals in lantana that make it more ignitable (and therefore fires are more likely to start) or, by changing the structure of the understory, more fuel may accumulate that would aid in the spread and duration of fires (making them more damaging).
Tim and his undergraduate students went to field sites in Forty Mile Scrub National Park and measured fuel bed depths, leaf litter depths, % cover of fuels in areas with and without lantana. They also took lantana specimens back into the lab and measured how much dry matter the leaves and twigs had as well as burn durations.
The results were reasonably clear-cut. Lantana was not found to be particularly ignitable. In fact, lantana burnt faster than many native plants, which would usually decrease the damage from a fire moving through a forest. However, measurements of fuel loads in dry rainforest found that fuel cover was significantly greater in areas with lantana and fuel bed depth changed from 9 cm without lantana to 66 cm with lantana. So, lantana added significantly more fuel to burn in the habitat (so fires would burn longer and more intensely in an area) and also allowed greater access to the canopy layer of the forest (so that parts of the habitat not normally at risk were affected).
This research helps to show why lantana is such a successful weed species. It is a species that is very good at colonising disturbed habitats and this study shows that lantana can cause further disruption of the habitat, allowing itself to become even more competitive. This study suggests that removing lantana from forest edges near frequently burned savannas should be a high conservation process. All in all, this is certainly one species we can do without here in New Zealand!