Competitive effects of grasses and woody plants in mixed-grass prairie

Peltzer, DA Kochy, M

Da. Peltzer et M. Kochy, Competitive effects of grasses and woody plants in mixed-grass prairie, J ECOLOGY, 89(4), 2001, pp. 519-527

72

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

89

4

2001

519 - 527

ISI

0022-0477(200108)89:4<519:CEOGAW>2.0.ZU;2-6

1 Variation in the competitive ability of plant species may determine their persistence and abundance in communities. We quantified the competitive ef fects of grasses and woody plants in native mixed-grass prairie on the perf ormance of transplant species and on resources. 2 We separated the effects of grasses, shrubs and intact vegetation contain ing both grasses and shrubs by manipulating the natural vegetation using se lective herbicides to create four neighbourhood treatments: no neighbours ( NN), no shrubs (NS), no grasses (NG) and all neighbours (AN). Treatments we re applied to 2 x 2 m experimental plots located in either grass- or shrub- dominated habitats. The effects of grasses and shrubs on resource availabil ity (light, soil moisture, soil available nitrogen) and on the growth of tr ansplants of Bouteloua gracilis, a perennial tussock grass, and Elaeagnus c ommutata, a common shrub, were measured over two growing seasons. 3 Resource availability was two- to fivefold higher in no neighbour (NN) pl ots than in vegetated plots (NS, NG, AN) with grasses and shrubs having sim ilar effects. Light penetration declined linearly with increasing grass or shrub biomass, to a minimum of about 30% incident light at 500 g m(-2) shoo t mass. Soil resources did not decline with increasing neighbour shoot or r oot mass for either grasses or shrubs, suggesting that the presence of neig hbours was more important than their abundance. 4 Transplant growth was significantly suppressed by the presence of neighbo urs, but not by increasing neighbour shoot or root biomass, except for a li near decline in Bouteloua growth with increasing neighbour shoot mass in pl ots containing only shrubs. Competition intensity, calculated as the reduct ion in transplant growth by neighbours, was similar in both grass- and shru b-dominated habitats for transplants of Bouteloua, but was less intense in shrub-dominated habitats for the shrub Elaeagnus. Variation in the persiste nce and abundance of plants in communities may therefore be more strongly c ontrolled by variation in the competitive effects exerted by neighbours tha n by differences in competitive response ability.