Grass Competition Limits Tree Growth in Savannas

Strategic Insights -

Savannas, characterized by the codominance of trees and grasses, cover a significant portion of the Earth's land surface and play a crucial role in global ecosystems. However, the mechanisms that allow trees and grasses to coexist in these ecosystems are not well understood. A recent study by researchers from Princeton University has shed light on this question, finding that grass competition can strongly suppress tree growth. The study, published in the journal Ecology, involved removing grass around trees of various sizes in a Kenyan savanna and observed a significant increase in tree growth and survival rates.

Key Takeaways:

  • Grass competition can limit tree growth in savannas, particularly in nutrient-rich environments.
  • Tree growth and survival rates increased significantly when grass was removed around trees of various sizes.
  • The study suggests that grass competition may be as important as herbivory and fire in determining tree demography in savannas.
  • The findings have implications for understanding tree-grass coexistence and savanna dynamics.
  • The study highlights the need to incorporate grass competition into savanna models to accurately predict tree growth and survival rates.
  • Acacia drepanolobium trees were used in the study, which showed significant growth and survival increase after grass removal.

Statistics:

  • 20% of the world's land surface is covered by savannas (source: study introduction).
  • Grass competition can suppress tree growth by doubling the probability of transitioning to the next size class over two years (source: study results).
  • Tree growth doubled after grass removal for even the largest trees studied (source: study results).
  • 2 years was the duration of the study (source: study introduction).
  • The study was conducted in an Acacia drepanolobium savanna in Laikipia, Kenya (source: study location).

Sources:

  • C. Riginos et al. (2009) "Grass competition suppresses savanna tree growth across multiple demographic stages." Ecology, 90(2), 335-340.
  • Ecology (journal) - Ecological Society of America, 1990 M Street NW, Ste. 700, Washington, DC 20036, USA.