• Invasive potential of ashe juniper after mechanical disturbance

      Owens, M. K.; Schliesing, T. G. (Society for Range Management, 1995-11-01)
      Reinvasion of mechanically disturbed juniper communities is possible through contributions from the soil seedbank, seed rain, and the juvenile seedling bank. We compared spatial distribution of the seedbank and seed rain of undisturbed communities to sites where trees were deliberately left as single trees, small mottes of less than 5 trees per group, or large mottes of 5-10 trees per group. Seed density in the litter layer ranged from 1,197 to 1,436 seeds m-2 and in the soil layer from 318 to 617 seeds m-2. Seed rain ranged from 275 to 366 seeds m-2 over all tree arrangements. The treatment associated with single trees caused the litter layer to be removed resulting in the removal of that portion of the seedbank, consequently most seeds (>80%) were found under the canopy of mature, seed-producing trees. Soil disturbance was less severe in small and large motte arrangements, so only 65% of the soil seed bank was under mature trees. In undisturbed communities, the seed population was distributed evenly under tree canopies and in interspaces. Viability and germinability within the seedbank were low (4% and 0%, respectively). Viability of new seed was 47% and germinability was approximately 5%. The juvenile seedling bank contained a sufficient number of seedlings (408 seedlings ha-1) for ashe juniper to regain dominance on the site through growth. There was no advantage to any spatial pattern of tree distribution in terms of invasive potential when fewer than 10 trees ha-1 were left on a site. However, when 20-50 trees ha-1 are left on a site, tree spatial arrangement has a significant effect on reinvasion rates.
    • Observations on spread and fragmentation of blue grama clones in disturbed rangeland

      Samuel, M. J.; Hart, R. H. (Society for Range Management, 1995-11-01)
      Establishment of blue grama (Bouteloua gracilis [H.B.K.] Lag ex. Steud.) depends on adequate precipitation at critical times and on reduced competition from associated vegetation. These conditions rarely occur on Central Plains rangelands. Therefore, rapid vegetative spread of new seedlings is desirable for colonizing disturbed rangeland. Blue grama genotypes selected for rapid spread would also be desirable for rangeland seeding. For 6 years, we followed the rate of spread of 19 blue grama clones originating from seedlings which emerged in 1980 and grew under natural competition. We observed a 4.5-fold difference in basal area and a 16.3-fold difference in above-ground biomass of these clones, perhaps because of genetic differences among clones and varying levels of competition. Clones must be tested under uniform competition with clonal replication to obtain reliable estimates of their capacity to spread.