Summary
The emergence and subsequent survival and growth of five opportunistic “weeds” were monitored after seed additions to long-term grazing treatments with or without current-year grazing, long-term ungrazed treatments, and removal treatments designed to eliminate plant competition from existing perennials while either leaving vegetation and soil structure unaltered or disturbed. The treatments were applied on both uplands and lowlands to assess the relative influence of macroabiotic environment versus plant competition. The long-term effects of large herbivores on the initial emergence of seedlings were greater than the effects of removing competition. Very few individuals emerged on the long-term grazed treatments that were either grazed or ungrazed during the experiment. Numbers of individuals emerging on the long-term ungrazed treatments were greater or equal to those emerging on the no-competition-undisturbed treatments, but numbers were greatest on no-competition-disturbed treatments. None of the seeded individuals on the long-term grazed, currently grazed treatments survived to the end of the growing season. There was a slightly greater end-of-season biomass of seeded species and percentage of the total population reaching reproductive status on the long-term ungrazed compared with grazed-nondefoliated treatments, and very high survival, biomass, and proportions of reproductives on both no-competition treatments. Cover types in the immediate vicinity of seedlings influenced both germination and survival, but the effects differed between species and treatments. Equal compensation to current-year herbivory occurred on long-term heavily grazed treatments even though above-ground production was much greater on long-term protected sites. Productivity varied with topography, but very few topographic main effects or interactions occurred with demographic variables of seeded species, suggesting that macroabiotic effects were of minor importance compared with grazing and plant competition.
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References
Auerbach M, Shmida A (1987) Spatial scale and the determinants of plant species richness. TREE 2:238–242
Chippindale HG (1948) Resistance to inanition in grass seedlings. Nature 161:65
Coffin DP, Lauenroth WK (1988) The effects of disturbance size and frequency on a shortgrass plant community. Ecology 69:1609–1617
Connell JH (1990) Apparent versus “real” competition in plants. Pages 9–26 in JB Grace and D Tilman (eds.) Perspectives on Plant Competition. Academic Press, San Diego
Cook SJ (1980) Establishing pasture species in existing swards: a review. Trop Grassl 14:181–187
Coughenour MB (1985) Graminoid responses to grazing by large herbivores: adaptations, exaptations, and interacting processes. Ann Mo Bot Gard 72:852–863
Crawley MJ (1983) Herbivory. University of California Press, Berkeley. 437 pp
Daubenmire R (1940) Plant succession due to overgrazing in the Agropyron bunchgrass prairie of southeastern Washington. Ecology 21:55–64
Detling JK (1988) Grasslands and Savannas. In: Pomeroy LR, Alberts JJ (eds) Regulation of energy flow and nutrient cycling by herbivores. Concepts of Ecosystems Ecology: A Comparative View. Springer ES #67, New York, pp 131–148
Dunnett CW (1980) Pairwise multiple comparisons in the homogeneous variance, unequal sample size case. J Am Stat Assoc 75:789–800
Fenner M (1980) Seedlings. New Phytol 106:35–47
Goldberg DE, Werner PA (1983) The effects of size of opening in vegetation and litter cover on seedling establishment of goldenrods (Solidago spp.). Oecologia 60:149–155
Great Plains Flora Association (1986) Flora of the Great Plains. University Press of Kansas, Lawrence
Grime JP (1973) Control of species density in herbaceous vegetation. J Environ Man 1:151–167
Harper JL (1977) The influence of density on form and reproduction. Pages 195–235 in Population biology of plants. Academic Press, London
Harper JL (1977) The recruitment of seedling populations. Pages 111–147 in Population biology of plants. Academic Press, London
Hixon MA, Brostoff WN (1983) Damselfish as keystone species in reverse: intermediate disturbance and diversity of reef algae. Science 220:511–513
Hogenbirk JC, Reader RJ (1989) Biotic versus abiotic control of plant density: studies of Medicago lupulina L. on a topographic gradient. J Biogeogr 16:269–277
Joyce LA (1989) An analysis of the range forage situation in the United State: 1989–2040 USDA-Forest Service Gen. Tech. Rep. RM-180. Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO., USA. 136 pp
King J (1971) Competition between established and newly sown grass species. J Br Grassld Soc 26:221–229
Lauenroth WK, Laycock WA (1989) Secondary succession and the evaluation of rangeland condition. Westview Special Studies in Agriculture Science and Policy. Westview Press, Boulder, 163 pp
Mack RN, Thompson JN (1982) Evolution in steppe with few large, hooved mammals. Am Nat 119:757–773
McNaughton SJ (1984) Grazing lawns: animals in herds, plant form, and coevolution. Am Nat 124:863–886
Milchunas DG, Lauenroth WK (1989) Three-dimensional distribution of plant biomass in relation to grazing and topography in the shortgrass steppe. Oikos 55:82–86
Milchunas DG, Sala OE, Lauenroth WK (1988) A generalized model of the effects of grazing by large herbivores on grassland community structure. Am Nat 132:87–106
Milchunas DG, Lauenroth WK, Chapman PL, Kazempour MK (1989) Plant communities in relation to grazing, topography, and precipitation in a semiarid grassland. Vegetatio 80:11–23
Milchunas DG, Lauenroth WK, Chapman PL, Kazempour MK (1990) Community structure relationships along a perturbation gradient encompassing different types of disturbances in the shortgrass steppe. J Veg Sci 1:375–384
Montgomery DC (1991) Design and analysis of experiments, 3rd ed. John Wiley & Sons, New York, pp 649
Oesterheld M, Sala OE (1990) Grazing effect upon seedling establishment: the role of seed and safe-site availability. J Veg Sci 1:353–358
Paine RT (1966) Food web complexity and species diversity. Am Nat 100:65–75
Pyke DA (1987) Demographic responses of Bromus tectorum and seedlings of Agropyron spicatum to grazing by small mammals: the influence of grazing frequency and plant age. J Ecol 75:825–835
Rauzi F, Smith FM (1973) Infiltration rates: three soils with three grazing levels in northeastern Colorado. J Range Man 26:126–129
Senft RL, Rittenhouse LR, Woodmansee RG (1985) Factors influencing patterns of cattle grazing behavior on shortgrass steppe. J Range Man 38:82–87
Snaydon RW, Howe CD (1986) Root and shoot competition between established ryegrass and invading grass seedlings. J Applied Ecol 23:667–674
Silvertown JW, Wilkin FR (1983) An experimental test of the role of micro-spatial heterogeneity in the co-existence of congeneric plants. Biol J Linnean Soc 19:1–8
Solbrig OT (1980) Demography and natural selection. In: Solbrig OT (ed) Demography and evolution in plant populations. Univ. California Press, Berkeley pp 1–20
Van Haveren BP (1983) Soil bulk density as influenced by grazing intensity and soil type on a shortgrass prairie site. J Range Man 36:586–588
Tremlett M, Silvertown JW, Tucker C (1984) An analysis of spatial and temporal variation in seedling survival of a monocarpic perennial, Conium maculatum. Oikos 43:41–45
Williamson SC, Detling JK, Dodd JL, Dyer MI (1989) Experimental evaluation of the grazing optimization hypothesis. J Range Man 42:149–152
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Milchunas, D.G., Lauenroth, W.K. & Chapman, P.L. Plant competition, abiotic, and long- and short-term effects of large herbivores on demography of opportunistic species in a semiarid grassland. Oecologia 92, 520–531 (1992). https://doi.org/10.1007/BF00317844
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DOI: https://doi.org/10.1007/BF00317844