Fire is an environmental filter that selects for woody species able to survive or recruit and grow quickly in the post-fire environment. Those that survive fire maintain their location in the habitat, which is predicted to convey an advantage over recruiting from seed in fire-frequented habitats, especially when time-to-reproduction exceeds the historic fire frequency. Although resprouting is predicted to be advantageous, differences in mode of resprouting (i.e., resprouting from aerial or underground buds) should affect competitive interactions following fire and result in additional filtering. For those habitats that are invaded by invasive species, it is necessary to know the mode of regeneration after fire for native and invasive species, because this will predict whether the reintroduction of periodic fire will filter out invasives and successfully restore the native community. To determine the effects of restoration using fire on eight natives and one invasive native to Asia, Lonicera maackii, we reintroduced fire into fire-suppressed forests of central USA. Plots with coexisting native and invasive species were established during the summer of 2011 and burned or unburned during January 2012. Demographic measurements were taken during the summers of 2011-13, including growth, reproduction, survival, recruitment, and post-fire regeneration mode.
Results/Conclusions
We found that the invasive had significantly higher survival than any of the native species. It also had a different mode of post-fire regeneration; natives resprouted from root crowns and the invasive resprouted from aerial buds and were reproductive the first season following the burns. Although many of the natives were reproductive prior to burning, very few produced seeds in the first two years following fire. Seedlings of the natives and invasives were rarely observed after fire indicating that resprouting is the main regeneration mode for all species. Overall, burning had no significant effect on the population growth rate of the invasive, but negatively affects those of the natives. Lonicera maackii has been shown to outcompete native plants by blocking light attenuation; it grows quickly and spreads, allowing very little light to reach the forest floor. Burning may enhance this advantage because L. maackii is able to maintain its location in the shrub canopy while native species become restricted to the shrub understory. Fire acts as a filter that can quickly and dramatically alter the competitive balance between natives and invasives, and thus it should be used with caution unless post-fire regeneration modes and demographic responses are known in advance.