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

Sevilleta LTER研究地点已成为一场辩论的焦点，焦点是放牧（避难所）的完全释放是否会损害多样性和初级生产力。虽然对塞维莱塔进行了详细的研究，但对毗邻的牧场或最近摆脱放牧压力的土地进行的比较研究很少。目前的塞维利亚ltr计划正在一个地点进行，该地点本身可能正在经历三个多世纪的集约化放牧后的连续变化。为了确定长期生态系统变化的未来来源，必须隔离和了解塞维莱塔景观的放牧后变化；如果不分离放牧的影响，将可观察到的生态系统变化归因于其他原因（如气候变化或人为因素）的努力将是混乱的。塞维利亚塔国家野生动物保护区成立于1973年，并在那一年竖起了牲畜隔离围栏。1972年夏季，牲畜被清除前一年，是一个异常潮湿的时期，随后在1972-73年冬春期间出现了强烈的厄尔尼诺现象。一个非常潮湿的夏天接着一个潮湿的春天的组合可能只有20年的频率模式。鉴于湿度制度对干旱生态系统功能的重要性，1973年塞维利亚河之前的条件可能形成了一种不寻常的“演代轨迹”，即使不是不可能，也很难在实地进行实验模拟。然而，由于1991年至1992年新墨西哥州中部出现了异常潮湿的天气模式，进行这样一个实验的机会出现了。塞维利亚在1991年经历了一个极其潮湿的夏天。塞维利亚目前正处于强厄尔尼诺现象的中心，产生了冬末和春季的水分。目前的天气条件为模拟1973年后塞维利亚塔发生的转变的研究奠定了基础。这种气候事件的组合可能很少发生（每几十年一次），重要的是要立即开展研究，以利用这些不寻常的情况。该SGER项目基于(1)对牲畜移除对生态系统影响的特定地点信息的基本需求，以及(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.