Assessing the roles of seed bank, seed dispersal and historical disturbances for metapopulation persistence of a pyrogenic herb

摘要

Seed bank, seed dispersal and historical disturbance are critical factors affecting plant population persistence. However, because of difficulties collecting data on these factors they are often ignored. We evaluated the roles of seed bank, seed dispersal and historical disturbance on metapopulation persistence of Hypericum cumulicola, a Florida endemic. We took advantage of long-term demographic data of multiple populations (22 years; ~11 K individuals; 15 populations) and a wealth of information on burn history (1962-present), and habitat attributes (patch specific location, elevation, area and aggregation) of a system of 92 patches of Florida rosemary scrub. We used previously developed integral projection models to assess the relative ability of simulations with different levels of seed dormancy for recently produced and older seeds and different dispersal kernels (including no dispersal) to predict regional observed occupancy and plant abundance in patches in 2016-2018. We compared a simulation with this model using historical burn history to 500 model simulations with the same average fire regime (using a Weibull distribution to determine the probability of ignition) but with random ignition years. The most likely model had limited dispersal (mean = 0.5 m) and the highest dormancy (field estimates x 1.2 %) and its predictions were associated with observed occurrences (67% correct) and densities (20% of variance explained). Historical burn synchrony among neighbouring patches (skewness in the number of patches burned by year = 1.79) probably explains the higher densities predicted by the simulation with the historical fire regime compared with predicted abundances after simulations using random ignition years (skewness = 0.20 + SE = 0.01).Synthesis. Our findings demonstrate the pivotal role of seed dormancy, dispersal and fire history on population dynamics, distribution and abundance. Because of the prevalence of metapopulation dynamics, we should be aware of the significance of changes in the availability and configuration of suitable habitat associated with human or non-human landscape changes. Decisions on prescribed fires (or other disturbances) will benefit from our knowledge of consequences of fire frequency, but also of location of ignition and the probability of fire spread.