Tree seedling establishment among C4 grasses
- Published
- Accepted
- Subject Areas
- Ecology, Plant Science
- Keywords
- Seedling establishment, savanna, below ground, resource competition., above ground
- Copyright
- © 2016 February et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2016. Tree seedling establishment among C4 grasses. PeerJ Preprints 4:e2080v1 https://doi.org/10.7287/peerj.preprints.2080v1
Abstract
The coexistence of leguminous trees and C4 grasses in African savanna remains poorly understood. Trees are able to establish among grasses despite grasses being competitively superior for below ground resources. Here we test the hypothesis that trees are only able to establish when grass biomass has been reduced. We do this at four locations in Limpopo Province South Africa where we locate young seedlings of Senegalia nigrescens. Where we found seedlings we determine grass species composition as well as grass percentage canopy cover, height above ground, and root length. We also make determinations of grass characteristics at two locations where we found no seedlings. For seedlings we determine rooting depth, plant height and stem diameter. To confirm that these are indeed young seedlings, less than a year old, we compare root length and plant height with that of seedlings germinated and grown for 77 days in a greenhouse. Our results show that where seedlings are present grasses are dominated by short-lived species such as Aristida congesta and Enneapogan cenchroides. These species are often found in disturbed soils and would increase with overgrazing. On those sites with no seedlings grass species composition is dominated by perennial species such as Panicum maximum, Panicum coloratum and Cenchrus ciliarus that would decrease with overgrazing and/or repeated burning. The perennial species have a 90-100% canopy cover while the short-lived species have a much lower canopy cover of less than 50%. Within 77 days of germinating tree seedlings are able to develop a root system that is deeper than the short-lived grasses but not deeper than the perennial grasses. These results demonstrate that tree seedlings are only able to establish among grasses if there are gaps in both grass canopy and root mass resulting from increased herbivory, frequent fire or extended drought.
Author Comment
This is a submission to PeerJ for review.