• 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.
    • Technical Note: Datalogger control of environmental chambers for variable-temperature germination experiments

      Hardegree, S. P.; Burgess, M. D. (Society for Range Management, 1995-11-01)
      Environmental conditions in the seedbed are much more variable than have historically been simulated in laboratory germination experiments. This paper describes a laboratory control system for real-time simulation of seedbed temperature regimes. The system is composed of a set of small refrigerators that have been enhanced with incandescent and fluorescent lights, fans and electrical-resistance heaters. The germination chambers are regulated by an electronic data acquisition/control system that allows each chamber to vary internal temperature on a continuous basis. Field temperatures can be transmitted to the laboratory and the germination chambers programmed in near-real-time for simultaneous laboratory germination/field emergence studies.