Understanding the regeneration niche: Microsite attributes and recruitment of eucalypts in dry forests

Abstract

Lack of eucalypt recruitment is a key factor in the decline of forest and woodland remnants in low rainfall agricultural regions in Australia. Key to effective management of these forests is an understanding of the requirements and conditions that promote seed germination and seedling establishment (recruitment niche) and the persistence of lignotuberous sprouts (juvenile persistence niche). Recruitment is limited by the availability of safe microsites that are suitable for the germination and establishment of seedlings. The objective of this study was to investigate the microsites of established eucalypt seedlings and lignotuberous sprouts in healthy dry forests burnt in the previous 2–6years in the Tasmanian Midlands. The recruitment niche differed significantly to the juvenile persistence niche while the juvenile persistence niche had characteristics similar to the general forest floor. Seedling microsites were characterised by: canopy gaps and ashbeds (95% of seedlings surveyed); a predominantly northerly aspect (75% of microsites); over 220° shelter with the average distance from a sheltering object being less than 30cm and 80% of seedlings being sheltered by coarse woody debris; soil that was significantly softer (3.8 vs. 5.0kgf/m2) and less water repellent (moderate vs. severe repellency) than the forest floor; and low cover of grass. These characteristics of seedling safe sites all affect moisture availability. Our results have important implications for the management of dry forest in order to facilitate eucalypt recruitment and persistence, suggesting the need for retention of coarse woody debris and the judicious use of fire.