The Survival and Population Response to Frequent Fires of Two Woody Resprouters Banksia serrata and Isopogon anemonifolius

Abstract

Plants of B. serrata and I. Anemonifolius resprout after fire, although the species differ in morphology (single-stemmed small tree, multistemmed low shrub respectively). If fires occur before newly established plants are fire-tolerant, populations will decline. The age of first fire tolerance was found to be lower in B. serrata (6 years) than in I. Anemonifolius (about 13 years). Rates of survival between and during fires were measured in the field along with rates of stem regrowth in fire-tolerant B. serrata juveniles. These results were used to predict rates of population decline under repeated fires sufficiently closely spaced to prevent the survival of newly established genets. In both species, juveniles were more prone to death than adults in fires and high-intensity fires caused most deaths. In B. serrata, adult stems (>2.0 cm d.b.h.) are mostly fire-tolerant, but fires less than 10 years apart can prevent many juveniles which survive from reaching adulthood. This restriction is less likely in I. Anemonifolius. As a result stands of B. serrata may decline more rapidly than I. Anemonifolius under 5-year fire cycles. I. Anemonifolius populations, however, may be more prone to decline when the interval between fires is slightly longer (e.g. 10 years) because lignotubers in young juveniles develop at a slower rate than in B. serrata. Extinction or substantial depletions of adult numbers may be approached in stands of either species after 50 years under some repeated 5- or 10-year fire cycles. The rate of such declines will depend directly on the structure of populations (proportions of adults and juveniles). Declines in populations of these resprouters may be likely under current fire regimes within the Sydney region of New South Wales, although these species are more likely to persist through long runs of frequent fire (<lo year interval) than some cohabiting species of obligate seeders.