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Nutrient cycling and competition for belowground resources

I spent my PhD-student days camped out in a far flung part of Venezuelan Amazon rain forest. It is customary when writing about tropical rainforests to allude in the first paragraph to their staggering biological diversity and to the profusion of foliage that makes light such a scarce resource on the forest floor that regenerating trees are limited. Yet not all tropical forests are highly diverse or deeply shading; Amazonian caatinga, found over millions of hectares of white-sand soils in the Guianas, has relatively low diversity and an open canopy. Having characterised the ecology of this forest type1, I proceeded to test experimentally whether competition for below-ground resources might be limit growth on the forest floor of such a nutrient poor system2. Sure enough, removal of root competition by cutting trenches to isolate saplings from taller neighbours led to an acceleration of their growth - one of the first publications to show that competition for nutrients can be important for forest regeneration in the tropical lowlands. This result encouraged Professor Peter Grubb (my supervisor) and I to theorise about the types of woody system in which might you expect below-ground competition to be important - our paper in Ecological Monographs sets out these ideas and tests them by viewing the experimental literature. My reputation as an excellent digger-upper of roots led to collaborations in New Zealand, this time looking a Nothofagus regeneration in the Southern Alps. Once again, competition for nutrients proved to be strong4.

  1. Coomes, D.A. & Grubb, P.J. (1996) Amazonian caatinga and related communities at La Esmeralda, Venezuela: Forest structure, physiognomy and floristics, and control by soil factors. Vegetatio, 122, 167-191. click
  2. Coomes, D.A. & Grubb, P.J. (1998) Responses of juvenile trees to above- and belowground competition in nutrient-starved Amazonian rain forest. Ecology, 79, 768-782. click
  3. Coomes, D.A. & Grubb, P.J. (2000) Impacts of root competition in forests and woodlands: A theoretical framework and review of experiments. Ecological Monographs, 70, 171-207. click
  4. Platt, K.H., Allen, R.B., Coomes, D.A., & Wiser, S.K. (2004) Mountain beech seedling responses to removal of below-ground competition and fertiliser addition. New Zealand Journal of Ecology, 28, 289-293. click
  5. Tanentzap, A. J., Lee, W. G., & Coomes, D.A. (2012) Soil nutrient supply modulates temperature-induction cues in mast-seeding grasses. Ecology, 93, 462-469.