Fire Increases Invasive Spread of Molinia Caerulea Mainly Through Changes in Demographic Parameters

Abstract

Abstract. We investigated the effects of fire on population growth rate and invasive spread of the perennial tussock grass Molinia caerulea. During the last decades, this species has invaded heathland communities in Western Europe, replacing typical heathland species such as Calluna vulgaris and Erica tetralix. M. caerulea is considered a major threat to heathland conservation. In 1996, a large and unintended fire destroyed almost one-third of the Kalmthoutse Heide, a large heathland area in northern Belgium. To study the impact of this fire on the population dynamics and invasive spread of M. caerulea, permanent monitoring plots were established both in burned and unburned heathland. The fate of each M. caerulea individual in these plots was monitored over four years (1997)(1998)(1999)(2000). Patterns of seed dispersal were inferred from a seed germination experiment using soil cores sampled one month after seed rain at different distances from seed-producing plants. Based on these measures, we calculated projected rates of spread for M. caerulea in burned and unburned heathland. Elasticity and sensitivity analyses were used to determine vital rates that contributed most to population growth rate, and invasion speed. Invasion speed was, on average, three times larger in burned compared to unburned plots. Dispersal distances on the other hand, were not significantly different between burned and unburned plots indicating that differences in invasive spread were mainly due to differences in demography. Elasticities for fecundity and growth of seedlings and juveniles were higher for burned than for unburned plots, whereas elasticities for survival were higher in unburned plots. Finally, a life table response experiment (LTRE) analysis revealed that the effect of fire was mainly contributed by increases in sexual reproduction (seed production and germination) and growth of seedlings and juveniles. Our results clearly showed increased invasive spread of M. caerulea after fire, and call for active management guidelines to prevent further encroachment of the species and to reduce the probability of large, accidental fires in the future. Mowing of resprouted plants before flowering is the obvious management tactic to halt massive invasive spread of the species after fire.

Contributions of demography and dispersal parameters to the spatial spread of a stage‐structured insect invasion

“…Strong effects of dispersal parameters on invasion speed are a highly consistent result across taxa and modeling approaches (e.g., Kot et al 1996, Neubert and Caswell 2000, Buckley et al 2005, Jacquemyn et al 2005, Shea and Skarpaas 2007. This is rather bad news from a management perspective because manipulating movement behavior is exceedingly difficult.…”

Fire Effects on Demography of the Invasive Shrub Brazilian Pepper (Schinus terebinthifolius) in Florida Pine Savannas

“…Our model did not include natural mortality from senescence at advanced age because we did not observe any in our populations ( Figure 2); however, mature stands of Brazilian pepper have been shown to persist for at least 35 years (Ewel et al 1982). The corresponding increase in the average reproductive output of this cohort as individual stems grew would be expected to translate into increased population growth, especially in the absence of non-fire, background mortality (Jacquemyn et al 2005). A simulated 16-year fire-return interval ( Figure 4B) resulted in substantial mortality after the first fire, but the initial cohort recovers between fire events.…”

“…Fire may create opportunities for colonization and subsequent invasion by removing preexisting vegetation, but it may also cause mortality or otherwise suppress population growth of non-native species (D'Antonio 2000). Therefore, demographic responses to fire by non-native plants are important in determining their potential invasion success under a specific fire regime (Jacquemyn et al 2005;Lockwood et al 2007). A species can invade a fire-prone community if its population growth is enhanced by fire relative to the native community (Buckley et al 2007), for example, through greater post-fire survival (Bond and Midgley 1995;Rossiter et al 2003) or by increased fecundity after fire (i.e., through serotiny; Richardson et al 1990).…”

Non-indigenous species management using a population prioritization framework

“…Permanent monitoring plots must be established to track long-term changes in the dynamics of a population (Blossey 1999;Buckley et al 2003;Jacquemyn et al 2005;Dodson and Fiedler 2006). A method of quantifying NIS population invasiveness in terms of change in density and spatial extent, using data collected annually from permanent monitoring plots has been developed by Lehnhoff et al (2006).…”