Shade alters savanna grass layer structure and function along a gradient of canopy cover

Author(s)

Pilon, Natashi A. L. ^{[1, 2]} ; Durigan, Giselda ^{[3, 2]} ; Rickenback, Jess ^{[4, 1]} ; Pennington, R. Toby ^{[1, 5]} ; Dexter, Kyle G. ^{[4, 1]} ; Hoffmann, William A. ^[6] ; Abreu, Rodolfo C. R. ^{[6, 7]} ; Lehmann, Caroline E. R. ^{[4, 1]}

Affiliation

^[1] Royal Bot Garden Edinburgh, Edinburgh, Midlothian - Scotland

^[2] Univ Estadual Campinas UNICAMP, Inst Biol, Caixa Postal 6109, BR-13083865 Campinas, SP - Brazil

^[3] Inst Florestal, Floresta Estadual Assis, Lab Ecol & Hidrol Florestal, Assis - Brazil

^[4] Univ Edinburgh, Sch GeoSci, Edinburgh, Midlothian - Scotland

^[5] Univ Exeter, Dept Geog, Exeter, Devon - England

^[6] North Carolina State Univ, Dept Plant & Microbial Biol, Raleigh, NC - USA

^[7] Univ Fed Rural Rio de Janeiro, Dept Ciencias Ambientais, Seropedica, RJ - Brazil

• Document type: Journal article
• Source: JOURNAL OF VEGETATION SCIENCE; v. 32, n. 1 OCT 2020.
• Web of Science Citations: 0

Abstract

Aim In savannas, a grass-dominated ground layer is key to ecosystem function via grass-fire feedbacks that maintain open ecosystems. With woody encroachment, tree density increases, thereby decreasing light in the ground layer and potentially altering ecosystem function. We investigated how light availability can filter individual grass species distributions and whether different functional traits are associated with response to a shade gradient in a landscape experiencing woody encroachment. Location Savanna-forest mosaic in the Cerrado domain, southeastern Brazil. Methods Along an encroachment gradient of increasing tree leaf area index (LAI) and shade, we determined how changing light availability alters grass diversity and ground layer structure relative to grass cover and grass functional traits (photosynthetic pathway, underground storage organs, bud protection and traits related to grass shape, size and leaf dimensions). Results Increasing shade led to a decrease in grass cover and grass species richness, and also compositional and functional changes. We found that where tree LAI reached 1, grass cover was reduced by 50% and species richness by 30%. While C-4 grass species abundances decreased with increasing shade, the opposite pattern was true for C-3 grasses. There were only small differences in light preferences among C-4 subtypes, with phosphoenolpyruvate carboxykinase (PCK) species tolerating slightly more shaded conditions. Persistence of some C-4 species under more shaded conditions was possible, likely due to an ability to store starch reserves via underground storage organs. Conclusions Woody encroachment changes diversity and structure of the grassy layer that is critical to the functioning of savanna ecosystems, highlighting the dependence of the diverse grass layer on open and sunny conditions. Our results suggest a threshold of tree cover close to LAI approximate to 1 as being critical to cerrado grassy layer conservation. (AU)

• FAPESP's process: 16/17888-2 - Effects of prescribed burning and frost on plant diversity and structure in Cerrado ground layer
• Grantee: Natashi Aparecida Lima Pilon
• Support Opportunities: Scholarships in Brazil - Doctorate