Native grass, sedge and legume establishment and legume-grass competition at a coal mine in the Rocky Mountains of southeastern British Columbia

ABSTRACT

Seed establishment and seedling persistence of seven native high elevation legume, twelve grass and two sedge species on coal mine spoil were studied over a period of five years. Three separate direct seeding experiments were established: (1) native legume, (2) native grass and sedge and (3) native legume - agronomic grass competition.

In the legume experiment, field seed germination percentages ranged from 41- 65% percent. At die end of the recording period, survivorship ranged from 20% (Hedysarum sulphurescens) to 58% (Oxytropis podocarpa and Oxytropis sericea). Percent cover increased each year for all species and ranged from 10 - 38% at the end of the fifth growing season. Recruitment from seed was small for each Species (n<15).

In the grass/sedge experiment, field seed germination percentages ranged from 5 - 61%. At the end of the recording period, abundances ranged from 3% (Festuca scabrella) to 74% (Festuca brachyphylla). Seedling mortality varied with species but, in general, declined after three years. Percent cover increased each year for all species and ranged from 5 - 48% at the end of the fifth growing season. Recruitment from seed ranged from 4% (Festuca scabrella) to 24% (Festuca brachyphylla) individuals.

Competitive dominance or exclusion of the native legumes by agronomic grasses was also studied. Legume co-existence was not constrained in the agronomic bunchgrass - native legume sward but was constrained in the rhizomatous grass sward - native legume sward. The amount of above-ground biomass production constrained the growth of the lower relative growth rate (RGR) native legumes. Oxytropis sericea, Astragalus alpinus, Astragalus bourgovii and Astragalus vexilliflexus var. nubilus were least constrained by the higher densities of grasses.