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Shade alters savanna grass layer structure and function along a gradient of canopy cover
Author(s) -
Pilon Natashi A. L.,
Durigan Giselda,
Rickenback Jess,
Pennington R. Toby,
Dexter Kyle G.,
Hoffmann William A.,
Abreu Rodolfo C. R.,
Lehmann Caroline E. R.
Publication year - 2020
Publication title -
journal of vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 115
eISSN - 1654-1103
pISSN - 1100-9233
DOI - 10.1111/jvs.12959
Subject(s) - species richness , ecosystem , canopy , biology , ecology , agronomy , leaf area index , environmental science
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 ≈ 1 as being critical to cerrado grassy layer conservation.