SGER: Ecosystem Recovery Following Three Centuries of Livestock Grazing in Central New Mexico

Sevilleta LTER研究地点已成为一场围绕完全放牧(避难所)是否损害多样性和初级生产力的辩论的区域焦点。虽然在塞维莱塔正在进行详细的研究，但很少有关于毗邻的牧场或最近从放牧压力中释放出来的土地的比较研究。目前的Sevilleta LTER方案是在一个地点进行的，该地点本身可能正在经历从三个多世纪的集约化牲畜放牧中释放出来的连续性变化。必须隔离和了解塞维莱塔地貌放牧后的变化，以便确定未来长期生态系统变化的来源；如果不分离放牧影响，将可观察到的生态系统变化归因于气候变化或人为因素等其他原因的努力将会混乱。塞维莱塔国家野生动物保护区成立于1973年，同年竖起了牲畜排斥栅栏。1972年夏天，也就是牲畜转移的前一年，是一个异常潮湿的时期，在1972-73年冬春期间，紧随其后的是一场强烈的厄尔尼诺现象。一个非常潮湿的夏天和一个潮湿的春天的组合可能只有20年的频率模式。鉴于水分制度对干旱生态系统功能的重要性，1973年塞维莱塔的先前条件可能培育了一条不同寻常的“演替轨迹”，即使不是不可能，也很难在实地进行实验模拟。然而，由于1991-92年发生在新墨西哥州中部的异常潮湿的天气模式，进行这样的实验的机会已经出现。塞维莱塔在1991年经历了一个极其潮湿的夏天。塞维莱塔目前正处于一场强烈的厄尔尼诺现象中，这种现象正在产生冬末和春季的湿气。目前的天气条件已经为模拟1973年后塞维莱塔上发生的过渡的研究奠定了基础。这种气候事件的组合可能很少发生(每几十年一次)，重要的是立即启动研究，以利用这些不寻常的情况。该SGER项目的基础是：(1)需要关于牲畜转移对生态系统影响的特定地点的基本信息，再加上(2)与近20年前非常相似的天气条件的巧合发生。

Sevilleta LTER study site has become a regional focal point in a debate centered on whether total release from grazing (a refuge) is detrimental to diversity and primary productivity. While detailed studies are occurring on the Sevilleta, there are few comparative studies on adjoining grazed land or land recently released from grazing pressure. The current Sevilleta LTER Program is being conducted on a site that may itself be undergoing successional changes following release from over three centuries of intensive livestock grazing. It is imperative to isolate and understand the post-grazing changes on the Sevilleta landscape in order to identify future sources of long-term ecosystem changes; without a separation of grazing influences, efforts to attribute observable ecosystem changes to other causes, such as climate change or anthropogenic factors, will be confounded. The Sevilleta National Wildlife Refuge was established in 1973, and livestock exclusion fences were erected in that year. The summer of 1972, one year prior to livestock removal, was an unusually wet period, and was followed by a strong El Nino during the winter-spring of 1972-73. The combination of a very wet summer followed by a wet spring may have only a 20 year frequency pattern. In view of the importance of moisture regimes on arid ecosystem functioning, the antecedent conditions on the Sevilleta in 1973 may have fostered an unusual "successional trajectory" that would be difficult, if not impossible, to simulate experimentally in the field. However, an opportunity to perform just such an experiment has arisen as a result of the unusually wet weather patterns that have occurred in central New Mexico in 1991-92. The Sevilleta experienced an extremely wet summer in 1991. The Sevilleta is presently in the midst of a strong El Nino that is producing late winter and spring moisture. The current weather conditions have set the stage for studies that could simulate the transition that occurred on the Sevilleta after 1973. This combination of climatological events may occur only rarely (once every few decades) and it is important to initiate studies immediately to take advantage of these unusual circumstances. This SGER project is based on (1) the fundamental need for site- specific information on ecosystem effects of livestock removal, coupled with (2) the coincidental occurrence of weather conditions that are very similar to those of nearly 20 years ago.