Browsing Journal of Range Management, Volume 48, Number 6 (November 1995) by Subjects
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Ecosystem changes associated with grazing intensity on the Punta Ninfas rangelands of Patagonia, ArgentinaChanges in the vegetation and soil surface were assessed along a grazing intensity gradient on rangelands of the Punta Ninfas area in southern Argentina. Thirty-two transects were sampled in areas with different grazing intensity. Bray-Curtis polar ordination and simple correlation were used to display changes in community composition and measure association between different community attributes. The first axis expressed the changes in species composition along a gradient of grazing intensity. The extremes of the gradient were represented by shrub and grass steppes. Shrub steppes dominated in heavily grazed areas close to permanent water points, while grass steppes dominated in lightly grazed areas in the extremes of the paddocks. A significant negative relation (r = -0.81, P<0.05) between grass and shrub cover suggested that grasses decreased as shrub increased. Flechilla (Stipa tenuis Phil.) and fiechilla negra [Piptochaefirrm napostaense Speg.) Hackel ap Stuckert.] were the main decreaser grasses while quilembai (Chuquiruga avellanedue Cav.) was the main shrub invading the grass steppes. Uneroded soil surface conditions decreased, and the size and frequency of crusted and desert pavement areas and mounds increased with shrub cover. Three states or stages of range degradation were identified along the gradient of grazing intensity. Grass steppe represented the most desirable state in term of livestock production and soil stability, while shrub steppe represented the most degraded and least productive state.
Invasive potential of ashe juniper after mechanical disturbanceReinvasion 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.
Plant response to soils, site preparation, and initial pine planting densityThis study described the effects of soils, site preparation, and initial pine regeneration spacings on tree growth and the associated understory woody and herbaceous plant succession. Although Sawyer soils appeared more productive than Ruston soils before the harvest and regeneration treatments, woody and herbaceous plant differences were not apparent between the soils after regeneration. During the first 3 years after treatment, the mechanical site preparation method (shear-windrow-burn) reduced woody plant heights more than the underplant-release method; however, these height differences disappeared by the 6th year of post-treatment. Woody plant densities decreased initially, increased by the 6th year after treatment, and decreased to pretreatment levels by the 10th year. Herbage yields increased significantly after site preparation and pine regeneration through the 3rd year, decreased by the 6th year, and declined to levels below pretreatment by the 10th year. initial pine planting densities did not significantly influence the understory herbage yields during the first 10 years as a result of the confounding effects of the other woody plant growth.
Technical Note: Root-plowing effects on nutritional value of browse and mast in south TexasLeaf and mast material was collected from mesquite (Prosopis glandulosa Torr.), huisache (Acacia smallii Isely), granjeno (Celtis pallida Torr.), and hog plum (Colubrina texana (T.& G.) Gray) on both root-plowed and untreated sites in south Texas. Forages were analyzed for nitrogen (N), neutral detergent fiber (NDF), and in vitro dry matter digestibility (IVDMD). Forages differed among species for N, NDF, and IVDMD. Leaf IVDMD of huisache and hog plum was higher on untreated sites. Huisache mast was higher in N and NDF concentrations, but not IVDMD, on untreated sites. Browsers on root-plowed sites may be forced to use forages of fewer digestible nutrients than on untreated sites. The cause of changes in browse quality following brush manipulation should be examined.