Growth dynamics and leaf quality of the stinging trees Dendrocnide moroides and Dendrocnide cordifolia (Family Urticaceae) in Australian tropical rainforest: implications for herbivores

Abstract

Leaf growth dynamics and leaf quality of Dendrocnide moroides (Wedd.) and Dendrocnide cordifolia (L.S.Sm.) Jackes and Hurley varied widely with age, season, plant height and habitat. Althoughleaves were produced continuously, growth rates varied seasonally. Leaf moisture and nitrogen content increased in spring and summer and decreased with age, while toughness increased with age. All leaf growth attributes varied with height, with the majority of activity occurring on mid-sized plants. Leafgrowth rates and proportions of different leaf age classes were similar for both species. Leaves were larger and lived longer in shade. Size and longevity responded rapidly to changing light conditions, reflecting their ability to survive in small rainforest gaps. Leaves of all ages were highly nutritious and the exceptionally nutritious young leaves were abundant throughout the year making them susceptible to herbivore attack. However, immature stinging tree leaves were densely covered with painful stinging hairs and hair density decreased with age. Further to causing pain, stinging hairs of D. moroides and D. cordifolia are shed continuously and may deter mammalian herbivores by causing allergic reactions. However, the leaves of stinging trees appeared better suited to the rapid colonisation of rainforest gaps, than in fending off or avoiding herbivore damage.