Does above‐average rainfall stimulate a recruitment pulse in semi‐arid woodlands of southeastern Australia?

Abstract

AbstractQuestionsRegeneration success of semi‐arid and arid regions worldwide is episodic and often linked to large rainfall events in consecutive years. It is also influenced by past and current land use, seed availability and herbivore grazing. This is particularly true for four dominant canopy trees — Allocasuarina luehmannii (Buloke), Casuarina pauper (Belah), Callitris gracilis (Slender Cypress Pine) and Myoporum platycarpum (Sugarwood) — within southeastern Australia semi‐arid woodlands. These species also apply hedge‐betting when responding to resource pulses with mass germination while low‐level background recruitment continues. We asked if drought‐breaking rainfall stimulated a germination pulse of these species and if it did, how did other external factors (grazing pressure from rabbits/hares, seed source, suitable seedbed) influence seedling abundance. We also asked if evidence of continuous recruitment had occurred during 14 years of drought by exploring trends in juvenile abundance.LocationVictorian Mallee semi‐arid woodlands, southeastern Australia.MethodsWe recorded seedling and juvenile abundance of the four dominant canopy species at 310 1‐ha sites within semi‐arid woodlands. Seedling presence was explored in relation to rainfall, tree density, ground cover and herbivory. Juvenile presence was explored in relation to rainfall, seedling and tree density, total plant cover and herbivory.ResultsSeedling and juvenile abundance were positively correlated with more mature trees, higher rainfall and no herbivory. Juvenile abundance was also positively correlated with more seedlings. There were more seedlings and juveniles at sites where rabbits/hares were present.ConclusionsAbove‐average rainfall was positively correlated with initiation of recruitment; however, there was limited net recruitment of the four dominant canopy species indicating other factors are influencing germination (e.g. seed viability) or that seedlings are not surviving. The long‐term survival of these semi‐arid woodlands is in jeopardy without a concerted effort to maintain and improve their condition through revegetation works, weed removal and herbivore management.