Fire season and intensity affect shrub recruitment in temperate sclerophyllous woodlands

Abstract

The season in which a fire occurs may regulate plant seedling recruitment because of: (1) the interaction of season and intensity of fire and the temperature requirements for seed release, germination and growth; (2) post-fire rainfall and temperature patterns affecting germination; (3) the interaction of post-fire germination conditions and competition from surrounding vegetation; and (4) the interaction of post-fire germination conditions and seed predators and/or seedling herbivores. This study examined the effects of different fire intensities and fire seasons on the emergence and survival of shrubs representing a range of fire response syndromes from a summer rainfall cool climate region. Replicated experimental burns were conducted in two seasons (spring and autumn) in 2 consecutive years and fuel loads were increased to examine the effects of fire intensity (low intensity and moderate intensity). Post-fire watering treatments partitioned the effects of seasonal temperature from soil moisture. Higher intensity fires resulted in enhanced seedling emergence for hard-seeded species but rarely influenced survival. Spring fires enhanced seedling emergence across all functional groups. Reduced autumn recruitment was related to seasonal temperature inhibiting germination rather than a lack of soil moisture or competition. In Mediterranean-type climate regions, seedling emergence has been related to post-fire rainfall and exposure of seeds to seed predators. We think a similar model may operate in temperate summer rainfall regions where cold-induced dormancy over winter exposes seeds to predators for a longer time and subsequently results in recruitment failure. Our results support the theory that the effect of fire season is more predictable where there are strong seasonal patterns in climate. In this study seasonal temperature rather than rainfall appears to be more influential.

Campo rupestre recém-queimado na Chapada Diamantina, Bahia, Brasil: plantas de rebrota e sementes, com espécies endêmicas na rocha

“…A parte aérea de muitos indivíduos é dizimada pelo fogo, mas devido ao predomínio de ervas e arbustos com tecidos meristemáticos nos órgãos perenes, a regeneração da cobertura das plantas do campo rupestre é relativamente rápida após distúrbios por fogo, ao contrário das fi sionomias com muitas árvores, que possuem grande quantidade de tecido lenhoso a ser substituído (Horn 1989;Hoffman 1999), ou em locais montanhosos mais altos (Bilbao et al 2009;Horn & Kappelle 2009 Miranda et al 2009). Outro fator que também poderia aumentar a diversidade seria a competição menos intensa no início da sucessão depois do incêndio (Knox & Clarke 2006).…”

Combining community-level spatial modelling and expert knowledge to inform climate adaptation in temperate grassy eucalypt woodlands and related grasslands

“…Fire played an important role in the dynamics of TGE prior to European settlement (Lunt et al 2012), influencing recruitment and composition of the dominant woodland trees (Vesk and Dorrough 2006), shrubs (Knox and Clarke 2006;Watson et al 2009) and herbaceous plant species (Morgan 2001;Prober et al 2007), and contributing to maintenance of their open grassy structure (Lunt et al 2012). In productive TGE (i.e.…”

The evolution of growth rate, resource allocation and competitive ability in seeder and resprouter tree seedlings

“…For seeders to reach adulthood, they must thrive (or at least survive) through a seedling stage in a potentially competitive post-disturbance environment. Common wisdom suggests that there should be a competitive release for survivors after a fire event (e.g., Keith and Bradstock 1994), and competitive interactions are not often important in controlling survivorship in tree seedlings, at least not at the earliest stages of development (e.g., Moles and Westoby 2004;Knox and Clarke 2006). However, post-fire seedling germination and establishment can be dramatic, and competitive interactions can limit seedling growth (Sardans et al 2006).…”