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S. A. McCullough A. T. O’Geen M. L. Whiting D. A. Sarr K. W. Tate 《Environmental monitoring and assessment》2013,185(7):5563-5576
Quaking aspen (Populus tremuloides Michaux) stands are important for biodiversity in conifer-dominated forest landscapes. Our goal was to quantify the consequences of conifer succession on understory diversity and litter quality, as well as associated changes in aspen stand condition. We studied aspen stands on national park land in the transition zone between the northern Sierra Nevada and southern Cascade mountain ranges. We field-measured ten metrics of aspen stand condition in 29 aspen stands. Along a gradient of increasing current conifer cover, we observed decreases in herbaceous species diversity and richness and an increase in forest floor O horizon depth. We interpreted aerial photos from 1952 and 1998 to determine whether directional changes in conifer cover had occurred in the stands over the past half century, and used regression modeling to associate succession with the observed range of aspen stand condition. From the period 1952 to 1998, we found that conifer encroachment occurred in half the sampled stands, with an average increase in conifer cover of 1 % a year. Aspen were persistent in the remaining stands. Stand cover dynamics and percent total canopy cover interacted to influence species richness, diversity, aspen sprouting, and litter quality. In stands with conifer encroachment, both understory species richness and diversity declined. Although aspen sprouting increased, aspen establishment declined and the relative mass of woody to fine soil litter increased. 相似文献
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Riparian livestock exclosure research in the western United States: a critique and some recommendations 总被引:1,自引:1,他引:0
Sarr DA 《Environmental management》2002,30(4):516-526
Over the last three decades, livestock exclosure research has emerged as a preferred method to evaluate the ecology of riparian
ecosystems and their susceptibility to livestock impacts. This research has addressed the effects of livestock exclusion on
many characteristics of riparian ecosystems, including vegetation, aquatic and terrestrial animals, and geomorphology. This
paper reviews, critiques, and provides recommendations for the improvement of riparian livestock exclosure research. Exclosure-based
research has left considerable scientific uncertainty due to popularization of relatively few studies, weak study designs,
a poor understanding of the scales and mechanisms of ecosystem recovery, and selective, agenda-laden literature reviews advocating
for or against public lands livestock grazing. Exclosures are often too small (<50 ha) and improperly placed to accurately
measure the responses of aquatic organisms or geomorphic processes to livestock removal. Depending upon the site conditions
when and where livestock exclosures are established, postexclusion dynamics may vary considerably. Systems can recover quickly
and predictably with livestock removal (the “rubber band” model), fail to recover due to changes in system structure or function
(the “Humpty Dumpty” model), or recover slowly and remain more sensitive to livestock impacts than they were before grazing
was initiated (the “broken leg” model). Several initial ideas for strengthening the scientific basis for livestock exclosure
research are presented: (1) incorporation of meta-analyses and critical reviews. (2) use of restoration ecology as a unifying
conceptual framework; (3) development of long-term research programs; (4) improved exclosure placement/design; and (5) a stronger
commitment to collection of pretreatment data. 相似文献
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Sy Ibrahima Cissé Birane Ndao Babacar Touré Mory Diouf Abdoul Aziz Sarr Mamadou Adama Ndiaye Ousmane Ndiaye Youssoupha Badiane Daouda Lalou Richard Janicot Serge Ndione Jacques-André 《Environmental science and pollution research international》2022,29(55):83365-83377
Environmental Science and Pollution Research - The Sahelian zone of Senegal experienced heat waves in the previous decades, such as 2013, 2016 and 2018 that were characterised by temperatures... 相似文献
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用槐叶苹象甲对塞内加尔河水面的槐叶苹进行有效生物控制 总被引:1,自引:0,他引:1
Arnold H. Pieterse Marianne Kettunen Sara Diouf Ismael Ndao Khady Sarr Anne Tarvainen Sandra Kloff Seppo Hellsten 《Ambio-人类环境杂志》2003,32(7):458-462
1999年,在毛里塔尼亚和塞内加尔的塞内加尔三角洲下部,槐叶苹(Salvinia moesta)的侵入对当地居民的社会经济状况以及湿地生物多样性构成严重的威胁.分别于2000年5月在塞内加尔和毛里塔尼亚及2001年4月在塞内加尔的河面引进槐叶苹象甲(Cyteobagous salviniae),最终实现了对槐叶苹的有效生物控制.2001年10月,象甲起到的作用已非常明显.植物的颜色由绿色变为深褐色或黑色,槐叶苹最终沉入水底.2001年11~12月对槐叶苹象甲扩散的监控证实了生物控制结果的真实性.至2002年4月已有结论,塞内加尔河畔槐叶苹不再成为问题. 相似文献
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Pieterse AH Kettunen M Diouf S Ndao I Sarr K Tarvainen A Kloff S Hellsten S 《Ambio》2003,32(7):458-462
The invasion of Salvinia molesta in the Lower Senegal River Delta in Mauritania and Senegal in 1999 posed a serious threat to the socioeconomic conditions of the local people as well as to wetland biodiversity. Eventually, an effective biological control of S. molesta was obtained by means of the weevil Cyrtobagous salviniae, which was introduced in the river in Senegal and Mauritania in May 2000 and in Senegal in April 2001. In October 2001, it became apparent that the weevils were doing a magnificent job. The color of the plants was turning from green to dark-brown or black, and subsequently the plants started to sink to the bottom. Detailed monitoring of the dispersal of C. salviniae in November-December 2001 confirmed the visual observations of the outcome of biological control. In April 2002, it could be concluded that S. molesta was no longer a problem in the Senegal River. 相似文献
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Long-term monitoring programs emphasize power analysis as a tool to determine the sampling effort necessary to effectively document ecologically significant changes in ecosystems. Programs that monitor entire multispecies assemblages require a method for determining the power of multivariate statistical models to detect trend. We provide a method to simulate presence-absence species assemblage data that are consistent with increasing or decreasing directional change in species composition within multiple sites. This step is the foundation for using Monte Carlo methods to approximate the power of any multivariate method for detecting temporal trends. We focus on comparing the power of the Mantel test, permutational multivariate analysis of variance, and constrained analysis of principal coordinates. We find that the power of the various methods we investigate is sensitive to the number of species in the community, univariate species patterns, and the number of sites sampled over time. For increasing directional change scenarios, constrained analysis of principal coordinates was as or more powerful than permutational multivariate analysis of variance, the Mantel test was the least powerful. However, in our investigation of decreasing directional change, the Mantel test was typically as or more powerful than the other models. 相似文献
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