Bird Loss Limits Recruitment of New Zealand’s Large-Seeded Trees
The widespread extinction of fruit-eating birds (frugivores) was always thought to potentially limit regeneration and dispersal options for fleshy-fruit producing plants, but only now has the link been proven.
In research recently published in the prestigious journal Proceedings of the Royal Society B researchers Debra Wotton (Landcare Research) and Dave Kelly (University of Canterbury) have established the serious consequences for plants of the breakdown in this ecological partnership.
Drs Wotton and Kelly used an experimental approach to show that two large-fruited native tree species (taraire and karaka) are seriously affected by reduced bird densities, with regeneration over two years falling by 57-84%. Bird dispersal not only gave better seedling growth and survival, but also protected seeds and seedlings from predatory introduced mammals. This shows that protecting birds is important for the conservation of forest plants. At the research sites (one near Auckland and the other near Whangarei) dispersal of both species is dependent on a single frugivore and many fruits remain uneaten.
“This research demonstrates the importance of seed dispersal for local plant population persistence and validates concerns about the consequences of frugivore declines”, Dr Wotton said.
The research demonstrated that trees with large-fruits (> 14mm wide) lost most of their progeny unless the fruits both passed through a bird and established well away from the parent plant. Such massive regeneration failure limits the ability of these trees to respond to changing environments.
Although declines of large-bodied frugivores are well documented, the effects on plant recruitment have rarely been demonstrated and remain poorly quantified. At one extreme, dispersal failure might prevent regeneration completely, leaving forests full of ‘living dead’ adult trees amd eventually, depending on tree longevity, leading to the collapse and successional replacement of mature forest stands.
However, because plant regeneration is sometimes surprisingly robust in the face of disperser loss, Drs Wotton and Kelly wanted to determine the specific mechanisms and effects for any potential declines in tree regeneration.
For more information:
Dr Debra Wotton
Landcare Research
P: 03 321 9605
Posted: 05/04/2011