Relationships between leaf-litter traits and the emergence and early growth of invasive Pinus radiata seedlings

Summary: Pinus radiata is an invasive weed in Australia that spreads from plantations and establishes in surrounding native eucalypt woodlands. To determine factors linked to the invasiveness of P. radiata, we compared emergence and growth traits of P. radiata seedlings at five different depths of leaf litter under pine needles, native eucalypt leaves and an equal mix of the two. Seedling emergence, height, survival and establishment were significantly reduced as leaf-litter depth increased. Seedlings had lower root:shoot ratios and higher specific leaf area (SLA) under deeper litter treatments, shifts linked to the provision of more surface area for light capture and greater light access by seedlings. Total seedling dry weight was highest in treatments with 1 cm of litter cover due to greater moisture retention provided by a small amount of leaf litter outweighing the costs of seedling penetration through leaf litter. Importantly, we found that at any given depth of leaf litter, there were no significant differences in emergence and growth traits between pine, eucalypt or mixed leaf-litter treatments. The ability of P. radiata seedlings to succeed equally well under a range of different leaf-litter types is undoubtedly an important trait linked to its invasiveness. Given ethical concerns of introducing highly invasive species, such as P. radiata into remnant native woodland in field-based studies, glasshouse research is highly desirable and invaluable in elucidating important factors underpinning the invasiveness of weed species such as P. radiata. © 2010 The Authors. Weed Research © 2010 European Weed Research Society