Responses of tropical tree seedlings in the forest–savanna boundary to combined effects of grass competition and fire

Hamza Issifu*, Philippine Vergeer, George K.D. Ametsitsi, Jelle Klijn, Paolo Sartorelli, Millicent Tanson, Hypolite Bayor, Vincent Logah, Frank van Langevelde, Elmar Veenendaal

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Co-occurring tree functional types (TFTs) within forest–savanna transitions may differ in seedling responses to grass competition and fire in savannas. We performed a common garden experiment in the Guinea savanna of Ghana to test hypotheses related to competition effects on growth, allocation to root storage reserves, and subsequent survival responses to dry season fire for savanna-transitional TFT (i.e., species occurring both in forest and savanna) and forest TFT. The experiment included factorial combinations of TFT, comprising four species each of forest versus savanna-transitional trees, wet season grass competition (grass competition vs. grass no-grass competition), and dry season fire (burn vs. no-burn). Partly consistent with prediction, we found that grass competition suppressed tree seedling growth and caused a 17% reduction in root non-structural carbohydrates concentration [NSC] but had no effect on direct survival regardless of TFT at the end of the wet season. Post-fire survival averaged 6% for forest versus 91% for savanna-transitional TFTs across competition treatments. In contrast to our prediction on how grass competition influences post-fire seedling survival, a history of grass competition did not result in lower post-fire survival regardless of TFT, although plant mass, root mass fraction, and root [NSC] at the end of the dry season were lower for tree seedlings with a history of competition. Our results demonstrate that grass competition suppresses tree seedling growth and root storage reserves irrespective of TFT, and that competition alone (without fire) may not preclude the establishment of forest seedlings in savannas close to forests.

Original languageEnglish
JournalBiotropica
DOIs
Publication statusE-pub ahead of print - 4 May 2021

Keywords

  • fire
  • forest trees
  • functional traits
  • herbaceous vegetation
  • root non-structural carbohydrates
  • savanna trees
  • seedling survival

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