Milchunas D G, Lauenroth W K, Chapman P L
Department of Range Science, and Natural Resource Ecology Laboratory, Colorado State University, 80523, Fort Collins, CO, USA.
Statistics Department, Colorado State University, 80523, Fort Collins, CO, USA.
Oecologia. 1992 Dec;92(4):520-531. doi: 10.1007/BF00317844.
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.
在添加种子后，对五种机会性“杂草”的出现、后续存活和生长情况进行了监测，实验设置了长期放牧处理（包括当年放牧或不放牧）、长期禁牧处理以及旨在消除现有多年生植物竞争的去除处理，其中去除处理又分为保持植被和土壤结构不变或进行扰动两种情况。这些处理应用于高地和低地，以评估宏观非生物环境与植物竞争的相对影响。大型食草动物对幼苗初始出苗的长期影响大于去除竞争的影响。在实验期间进行放牧或禁牧的长期放牧处理中，很少有个体出苗。长期禁牧处理中出苗的个体数量大于或等于无竞争且未扰动处理中出苗的个体数量，但无竞争且受扰动处理中出苗个体数量最多。长期放牧且当年放牧处理中的播种个体没有一个存活到生长季结束。与放牧但未落叶处理相比，长期禁牧处理中播种物种的季末生物量略高，达到生殖状态的种群百分比也略高，并且在两种无竞争处理中，播种物种的存活率、生物量和生殖比例都非常高。幼苗附近的植被类型影响了发芽和存活，但不同物种和处理的影响有所不同。即使长期受保护地点的地上产量远高于长期重度放牧处理，但长期重度放牧处理对当年食草动物的补偿作用相同。生产力随地形变化，但很少有地形主效应或与播种物种的种群变量发生相互作用，这表明与放牧和植物竞争相比，宏观非生物效应的重要性较小。
