Compositional decoupling of savanna canopy and understory tree communities in Serengeti

Anderson, T. M., Morrison, T. , Rugemalila, D., Holdo, R. and Ward, D. (2015) Compositional decoupling of savanna canopy and understory tree communities in Serengeti. Journal of Vegetation Science, 26(2), pp. 385-394. (doi: 10.1111/jvs.12241) (PMID:AGR:IND601)

Abstract

Questions: What is the pattern of compositional similarity for woody plants across the demographic bottleneck (i.e. canopy trees >2 m vs understorey trees <2 m) commonly observed in savannas? Does compositional similarity between woody plants in the canopy and understorey change across environmental gradients, and if so, which resource or disturbance factors explain the pattern? Finally, does disturbance history, i.e. whether individuals are newly established seedlings or top‐killed resprouts, help to explain the compositional similarity between canopy and understorey woody plants across sites? Location: The Serengeti ecosystem, Tanzania, East Africa. Methods: We compared the observed similarity to that expected from a simulated null model, and investigated the association between compositional similarity and soil bulk density, mean annual rainfall, fire return interval and elephant damage using a model selection approach. Moreover, we asked if disturbance history, i.e. whether individuals were newly established seedlings or top‐killed resprouts, helped explain compositional similarity between the canopy and understorey. Results: The composition of canopy (>2 m) and understorey (<2 m) trees was surprisingly distinct: Acacia robusta (37.9%) and Acacia tortilis (23.7%) dominated the canopy, while Ormocarpum trichocarpum (43.0%) and Dichrostachys cinerea (19.6%) dominated the understorey. Compositional similarity between canopy and understorey woody plants generally decreased with soil bulk density, while for top‐killed individuals there was support for an increase in compositional similarity with fire return interval. Conclusions: Our results suggest that the similarity between the canopy and recruitment communities is primarily associated with soil factors. Our results also suggest that long fire return intervals (i.e. infrequent fires) lead to increased similarity between the composition of the canopy and the recruitment pool, suggesting that disturbance promotes heterogeneity in the community across demographic bottlenecks. Despite the prominent role that megaherbivores and disturbance play in driving structural changes in savannas, our results suggest that previously unreported but pervasive species decoupling across demographic bottlenecks is primarily driven by resource availability or other bottom‐up constraints.

• Item Type: Articles
• Additional Information: This research was funded by NSF DEB grant 1145861 and 1145787 awarded to T.M. Anderson and R.M. Holdo.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Morrison, Dr Thomas
• Authors: Anderson, T. M., Morrison, T., Rugemalila, D., Holdo, R., and Ward, D.
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: Journal of Vegetation Science
• Publisher: Wiley
• ISSN: 1100-9233
• ISSN (Online): 1654-1103
• Published Online: 15 November 2014