Differential response to fire in the germination of an invasive shrub and the native plant community explains invasion success

Background/Question/Methods Positive feedbacks between fire and invasive species have been reported worldwide with important implications for community invasibility and ecosystem processes. We studied a Fabaceae shrub that has been widely reported as invasive in temperate regions (Teline monspessulana (L.) K. Koch). We tested for differences in the response of this shrub and native plants to fire in south-central Chile. We used simulated fire conditions in small container (10 by 15 cm) containing soil collected in the field with added T. monspessulana seeds and placed in greenhouse for two months. In addition, we added T. monspessulana seeds to soil samples collected under native forests. Half of these samples were experimentally exposed to a low-severity fire by burning the leaf-litter covering each sample. Finally, we studied the response of germination of T. monspessulana seeds heated in oven, between 80 and 180°C.

Results/Conclusions We found that after a simulated wild fire T. monspessulana germination increases significantly, being the heating of seeds the most important factor above the destruction of litter cover. We found an optimal temperature range between 90 and 100 ºC, above 140 C all seeds died. In the controlled burns, temperatures similar to the optimal for germination are reached at 2 cm of depth. Although, this area of the soil profile does not have the highest concentration of seeds, the large seed densities (ca. 7000 seed/m²) sustain an intense regeneration after fire. In low severity fire treatments, the seedling emergence of T. monspessulana was not different from the control. However, this fire treatment decreased both the mean number of native species emerged and the mean number of native seedlings emerged. We believe that this difference among the invasive shrub and the native plants is responsible for the success of the species, especially given the high rate of human-induced fires in the area. Funding provided by Fondecyt 1070488, ICM P05-002 and PFB-23.