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Tree–grass competition along a catenal gradient in a mesic grassland, S outh A frica
Author(s) -
Tedder Michelle,
Kirkman Kevin,
Morris Craig,
Fynn Richard
Publication year - 2014
Publication title -
grassland science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.388
H-Index - 19
eISSN - 1744-697X
pISSN - 1744-6961
DOI - 10.1111/grs.12034
Subject(s) - shading , grassland , competition (biology) , agronomy , grazing , biomass (ecology) , soil water , plant ecology , sowing , biology , environmental science , productivity , ecology , art , macroeconomics , economics , visual arts
The interaction, both above and belowground, between tree saplings and the surrounding grass sward is dependent on solar radiation, temperature, rainfall, soil depth, tree species and sward composition. These factors, as well as level of sward defoliation, influence whether the system will remain as savanna or move towards a woodland or grassland state. The effects of above‐ and belowground competition between grasses and two A cacia species and the effects of soil depth on these interactions were examined by planting A . karroo and A . nilotica seedlings into a natural sward on three different soil depths. Three aboveground treatments: full shading, reduced shading by tying back the neighboring grasses and reduced shading by clipping, and two belowground treatments: full and no belowground competition, were used. Plant size increased with increasing soil depth, while belowground competitive intensity was unaffected. Removing belowground competition increased sapling biomass by half ( P < 0.05) on all soil depths. By contrast, reduced shading had little effect at all soil depths, whereas sward clipping increased sapling biomass (47%) on shallow soils only ( P = 0.027), indicating that encroachment on shallow soils may result from factors that decrease root vigor of the surrounding grasses rather than light competition. Irrespective of soil depth, root competition appeared to be the major factor influencing sapling growth rates, thus grazing management practices that reduce grass root productivity are expected to result in woody encroachment.