Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/5/2003
Publication Date: 11/3/2003
Citation: Tischler, C.R., Polley, H.W., Johnson, H.B. 2003. Effects of disturbance and soil fertility on competitiveness of weedy invaders of Texas pastures [abstract]. American Society of Agronomy Abstracts. 2003 CDROM.
Technical Abstract: Rangelands and tame pastures in Texas are invaded by both herbaceous and woody undesirable species. Previous research demonstrated that annual invaders cannot complete their life cycle in undisturbed grasslands, but perennial woody species add yearly increments of growth until they top the grass canopy. To elucidate the role of disturbance and soil fertility in facilitating invasion, we followed the fate of individual seeds of woody and herbaceous (annual) legumes in both undisturbed and disturbed sites with and without additions of nitrogen and phosphorous. The disturbed sites were kept devoid of all vegetation except target species. Without grass competition, Bagpod Sesbania and Wild Bean (annual species) flourished while in the undisturbed sites, they did not produce seed. Mesquite, Huisache, and Catclaw Acacia (woody species) exhibited greater growth in disturbed, fertilized sites than in disturbed, unfertilized sites. However, their growth was significantly less in undisturbed sites. Fertilization favored growth of the grasses in undisturbed sites and increased competition for light. These observations support the notion that overgrazing (disturbance) and depletion of soil fertility favor woody invasion of rangelands. Because woody legumes fix nitrogen, they also can more successfully compete with range and pasture grasses when soil nitrogen is low.