Leaf traits combinations may explain the occurrence of savanna herbaceous species along a gradient of tree encroachment

Abstract

In savanna environments, plants have specific leaf traits to deal with high irradiance. These traits allow plants to show high carbon assimilation capacity. However, under encroachment, reduced light availability may act as a filter on traits of plants established under typical savanna conditions. Here we studied morpho-physiological traits of species exclusively found in typical and forested savanna conditions to evaluate how encroachment selects for specific leaf traits in such environments. We also evaluated if species occurring in distinct encroached situations would show plasticity to deal with light variations. We studied two species exclusively found in typical savanna (TS, open condition), two species exclusively found in forested savanna (FS, encroached condition) and two species growing along a gradient of tree encroachment (typical, dense and forested savanna). We measured specific leaf area (SLA), maximum photosynthetic rate in an area basis (A max), stomatal conductance (g s), water use efficiency (WUE), leaf carbon (C) and nitrogen (N) concentrations. We found that herbaceous species exclusively found in TS possess higher A max , g s , WUE and C in comparison with plants from forested savanna. Such strategies are necessary to thrive under environments with elevated irradiances. In turn, species from FS showed elevated SLA and foliar N concentration, strategies linked to capture diffuse light in forested environments. Species capable of thriving in sites with distinct degrees of encroachment changed their leaf traits according with light availability. We conclude that differences in leaf traits between typical and forested savanna species may explain the non-occurrence of typical savanna species when their environment become encroached. Only those species capable of showing a certain degree of plasticity may survive under such distinct encroached states.

Effect of Dichrostachys cinerea encroachment on plant species diversity, functional traits and litter decomposition in an East‐African savannah ecosystem

“…Indeed, under the open savannah condition, low leaf area and SLA values, and high LDMC, reflect the plants' strategy to invest in leaf thickness to deal with high irradiance and evaporation. However, under the encroached condition, communities readjusted their leaf strategy to cope with the diffused availability of light (Rossatto and Franco, 2017;Carlos and Rossatto 2017). This community trait shift likely reflects the community composition shift from graminoid-dominated grassland towards a forb-rich dominated understorey vegetation (Pinheiro et al, 2016).…”

Why woody plant modularity through time and space must be integrated in fire research?

“…In woody savannas, the taller and more continuous woody canopy creates a more shaded environment when compared to open savannas ( Fig. 2 ; Carlos and Rossatto 2017 ; Pilon et al . 2021a ).…”

Woody plant encroachment constrains regeneration of ground‐layer species in a neotropical savanna from seeds

“…These environmental shifts induced by woody plant encroachment seem to act as filters for the persistence of typical savanna species and may affect their survival since they may alter both resource availability (Carlos & Rossatto 2017;Rossatto et al 2018) and aspects related to the regenerative ability (Hoffmann et al 2004;Abreu et al 2017). Savanna species persist and regenerate through seed germination and recruitment, vegetative spread, and/or resprouting after disturbance (Pilon et al 2021a).…”

“…These environmental shifts induced by woody plant encroachment seem to act as filters for the persistence of typical savanna species and may affect their survival since they may alter both resource availability (Carlos & Rossatto 2017; Rossatto et al . 2018) and aspects related to the regenerative ability (Hoffmann et al .…”