Slightly more serious notes to future George

I wanted to go back to one of our first lectures in the course where Scott Mangan talked with us about negative plant-soil feedback mediated by soil biota. Through field (aboveground and below ground enemies present) and greenhouse experiments (only below ground enemies present), Scott was able to show some very interesting patterns:

  • It was mostly the belowground soil biota, not the aboveground enemies, that were leading to these negative feedback patterns.
  • Species in the experiments that showed stronger negative feedbacks were the less common forest species. Those species that showed weaker negative feedbacks were the more common forest species.

Scott and his colleagues use these patterns to explain (or at least partially explain) the extreme diversity seen in tropical forests.

These findings and their implications are especially interesting to me. This upcoming semester, I will be working in a system where I will be trying to uncover the causes of the opposite phenomenon. Instead of wondering why the tropical forests host such an incredibly diverse tree community, I will be considering the formation of ectomycorrhizal monodominant tree stands…a phenomenon seen in highland tropical forests all around the world, but not well understood. This questions doesn’t align with Scott’s study as ectomycorrhizae have been added to the story, but nonetheless, I’ve been wondering if Scott’s work may help to inform the way I think about the formation of these monodominant stands.

Interestingly enough, reading through the dissertation of Aridana Corrlales who has already done quite a bit of work on this question at Fortuna, it doesn’t seem to be that these EM monodominant tree species are resistant to belowground pathogens or that EM fungi are able to form some sort of network that creates linkages between trees. If either of these two things were to have been true, you could say that the EM species forming these monodominant stands had created their own system of positive feedback. Instead, Adri found evidence for an altered Nitrogen economy in the EM stand soils, creating an environment beneficial to EM associated trees and subsequently making it hard for other AM species to compete. This is a theory that has been seen in various different systems and makes sense from some angles…but there are endless uncertainties associated with it.

When I think about Adri’s findings in connection with Scott’s, a few questions/thoughts come to mind…maybe they will help me as I figure out how I want to go about studying this system in the upcoming years:

  • If the system of negative-feedback is “beatable” (EM monodominant trees seem to have “beat” it), why isn’t this strategy seen more often? You would think it would be every trees goal to become dominant; the trees certainly aren’t consciously deciding on a more diverse ecosystem.
  • Also, even though this monodominancy is occurring, its span is very limited. There are very few species showing this strategy and the monodominant plots aren’t taking over the forest. What is stopping them from asserting dominance on a larger scale?
  • What is it that separates the EM monodominant species from the others. Although the EM mycorrhizae seems to be the clear distinction, through what mechanisms is it working?
  • I would assume that the system by which these EM trees are establishing monodominancy is much more complex than “because the mycorrhizae”…so maybe we can see important effects in soils as Scott was able to do.
  • Maybe I should think about if/how transplant experiments may be informative for my questions.
  • What would findings mean in the context of forest formation and nutrient cycling on a larger ecosystem scale?!


Mangan, Scott A., et al. “Negative Plant–Soil Feedback Predicts Tree-Species Relative Abundance In A Tropical Forest.” Nature 466.7307 (2010): 752-755. Academic Search Complete. Web. 22 Jan. 2017.

Dissertation of Adriana Corrales


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