Theme 1: Grassland Ecology
Description
Woody plant encroachment threatens ecosystem services and functions, thereby reducing herbaceous plant population persistence and community stability. Consequently, woody plant control projects are implemented in South Africa to restore herbaceous vegetation. Because persistent seeds drive passive restoration and vegetation trajectories, management following woody plant control entails examining soil seed bank (SSB) size and composition. However, a knowledge gap exists regarding how SSB characteristics respond along a woody plant removal gradient. This study was conducted at Roodeplaat in Gauteng Province of South Africa to assess the impact of woody density reduction [hereafter woody plant removal intensity (WPRI)] on SSB density, composition, diversity and richness. Selective tree removal was applied to downscale woody density (4065 plants ha-1) of the control (0% WPRI) to 10, 20, 50, 75 and 100% WPRIs in four blocks, resulting in four replicates per WPRI. A total of 120 soil samples (n = 20 per WPRI) collected at 5-cm depth were examined using germination method. Fifty-one species, mainly forbs (n = 26) and grasses (n = 16) were recorded from 32 237 seeds. The SSB densities of grasses increased from 649 to 6000 seeds m-2 from 0 to100% WPRI whilst sedges and forbs exhibited differential declining trends along WPRI gradient. Cyperus rotundus accounted for more than one-third of the SSB densities at 0 and 10% WPRIs, whereas Panicum maximum contributed nearly half (46%) to the SSB density at 100% WPRI. Woody removal increased SSB diversity (H') and richness, but diversity peaked at 20% WPRI (H' = 1.78); thereafter it declined. Increased SSB size and species richness of grasses at 100% WPRI indicated that complete woody clearing is key for restoration of woody- encroached rangelands. However, this means that savanna will be converted completely to a grassland, leading to a loss of other important savanna ecosystem services. Thus, on account of conserving the ecosystem services of the savanna, a research is warranted to test other woody density proportions to determine a potential optimal woody density.
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Soil Seed Banks Along a Woody Plant Removal Gradient in a Semi-arid Savanna of South Africa: Implications for Restoration
Woody plant encroachment threatens ecosystem services and functions, thereby reducing herbaceous plant population persistence and community stability. Consequently, woody plant control projects are implemented in South Africa to restore herbaceous vegetation. Because persistent seeds drive passive restoration and vegetation trajectories, management following woody plant control entails examining soil seed bank (SSB) size and composition. However, a knowledge gap exists regarding how SSB characteristics respond along a woody plant removal gradient. This study was conducted at Roodeplaat in Gauteng Province of South Africa to assess the impact of woody density reduction [hereafter woody plant removal intensity (WPRI)] on SSB density, composition, diversity and richness. Selective tree removal was applied to downscale woody density (4065 plants ha-1) of the control (0% WPRI) to 10, 20, 50, 75 and 100% WPRIs in four blocks, resulting in four replicates per WPRI. A total of 120 soil samples (n = 20 per WPRI) collected at 5-cm depth were examined using germination method. Fifty-one species, mainly forbs (n = 26) and grasses (n = 16) were recorded from 32 237 seeds. The SSB densities of grasses increased from 649 to 6000 seeds m-2 from 0 to100% WPRI whilst sedges and forbs exhibited differential declining trends along WPRI gradient. Cyperus rotundus accounted for more than one-third of the SSB densities at 0 and 10% WPRIs, whereas Panicum maximum contributed nearly half (46%) to the SSB density at 100% WPRI. Woody removal increased SSB diversity (H') and richness, but diversity peaked at 20% WPRI (H' = 1.78); thereafter it declined. Increased SSB size and species richness of grasses at 100% WPRI indicated that complete woody clearing is key for restoration of woody- encroached rangelands. However, this means that savanna will be converted completely to a grassland, leading to a loss of other important savanna ecosystem services. Thus, on account of conserving the ecosystem services of the savanna, a research is warranted to test other woody density proportions to determine a potential optimal woody density.
