Mediterranean type ecosystems globally are projected to become progressively warmer and drier through the remainder of this century, and fire to become more frequent. Shortened fire interval threatens many fire-killed woody plant species with increased immaturity risk, while warming and drying climate reduce both post-fire recruitment and inter-fire rates of plant survival, growth and reproduction. The interactive impacts of these three drivers are proposed to lead to 'interval squeeze', the marked narrowing of the fire interval within which many woody plant species will be able to persist. We present evidence for interval squeeze for fire-killed, serotinous woody plant species of Mediterranean type ecosystems based on comparison of plant demographic information collected for the same species in the same sites 20 - 40 years ago and today.
Results/Conclusions
Plant size and serotinous (canopy) seed stores for plants of the same age (time since last fire) are lower for 2 of 4 species for which sufficient data were available. Seed store in one species was today less than half that for the same species in the same site 30 years ago and requires at least a 50% increase in fire-free interval to ensure self-replacement after the next fire. Data for the other 2 species showed no change in demographic parameters compared with 20 - 40 years ago. Data are required for more species, but preliminary evidence suggests that interval squeeze will compromise the ability of some, including iconic, species to maintain population size as climate and associated fire regimes change over coming decades. Interval squeeze will likely lead to key species losses and ecosystem state changes in some instances.