INVASIVE POTENTIAL OF ASHE JUNIPER AFTER MECHANICAL DISTURBANCE

Reinvasion of mechanically disturbed juniper communities is possible t hrough contributions from the soil seedbank, seed rain, and the juveni le seedling bank, We compared spatial distribution of the seedbank and seed rain of undisturbed communities to sites where trees were delibe rately left as single trees, small mottes of less than 5 trees per gro up, or large mottes of 5-10 trees per group. Seed density in the litte r layer ranged from 1,197 to 1,436 seeds m(-2) and in the soil layer f rom 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 tr ees caused the litter layer to be removed resulting in the removal of that portion of the seedbank, consequently most seeds (>80%) were foun d under the canopy of mature, seed-producing trees, Soil disturbance w as less severe in small and large motte arrangements, so only 65% of t he 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 germinabi lity was approximately 5%, The juvenile seedling bank contained a suff icient 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 potenti al 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.