SGER: The Interactions of Nitrogen Eutrophication and Fire on Invasive Annuals in California Coastal Sage Shrublands

在过去的40-50年里，艾伦外来的一年生植物以越来越快的速度入侵了加州南部的灌木丛。 一些因素可能是负责的入侵，包括前，人为氮沉降，土壤扰动，放牧和破碎。 在这些潜在的原因中，氮沉积没有得到关注，频繁的火灾的影响才刚刚开始被认识到。 南加州灌木地的空气氮沉降率高达30公斤/公顷/年，与农业和城市化地区的距离较低的利率。 许多定居的一年生植物可能是喜氮的，例如，随着氮的增加，它们的生长速度也很高。 相比之下，我们假设，本地灌木有相对较小的响应增加N。火灾本身就可以解释一些地方杂草增加和灌木覆盖减少的原因，但在30-40年没有被烧毁的地区，外来物种增加。 主要包括雀麦属、大麦属和燕麦属的一年生禾本科植物。 最容易受到杂草入侵的原生植被是沿海鼠尾草灌木丛，这是一种范围有限的类型，受到城市化的威胁，并拥有一些敏感的物种。 我们的目标是研究火灾和氮沉降对植物生长的相互作用。 我们通过SGER计划申请资金，以利用加州最近的火灾。 我们已经找到了两个网站，在11月被烧毁，一个高，一个低N沉积。 我们建议在每个站点设置一个析因实验，燃烧和未燃烧与施肥和未施肥的地块。 我们假设，一年生草的生长将增加更多的灌木生长后，氮施肥，火加速转换从原生灌木林到一年生草地。 该研究对沿海鼠尾草灌丛的保护具有重要意义。 减少火灾周期将是重要的，以防止迅速转换为杂草一年生植物，但我们也可能建议减少人为N沉积。

9408079 Allen Exotic annuals have been invading southern California shrublands at increasing rates over the past 40-50 years. A number of factors may be responsible for the invasion, including fore, anthropogenic nitrogen deposition, soil disturbance, grazing, and fragmentation. Of these potential causes, N deposition has received no attention, and the effects of frequent fire are just beginning to be realized. Southern California shrublands are subject to aerial N deposition rates as high rates as high as 30 kg/ha/yr, with lower rates at a distance from agricultural and urbanized areas. Many of the colonizing annuals are probably nitrophilous, e.g., they have high rates of growth with added N. By contrast, we hypothesize that the native shrubs have relatively little response to increased N. Fire alone can explain the increased weediness and decrease in shrub cover in some sites, but areas that have not been burned in 30-40 years have and increase in exotics. These include primarily annual grasses in the genera Bromus, Hordeum, and Avena. The native vegetation that is most subject to weed invasion is the coastal sage scrub, a type that is limited in extent, is threatened by urbanization, and harbors a number of sensitive species. %%% Our objective is to examine the interaction between fire and nitrogen deposition on plant growth. We request funding through the SGER Program to take advantage of the recent fires in California. We have located two sites that were burned in November, one with high and one with low N deposition. We propose to set up a factorial experiment at each site, with burned and unburned vs. fertilized and unfertilized plots. We hypothesize that annual grass growth will be increased more than shrub growth after N fertilization, and that fire hastens the conversion from native shrubland to annual grassland. This research has important implications for the conservation of coastal sage shrub. A reduction in the fire cycle will be important to prevent a rapid conv ersion to weedy annuals, but we may also recommend a reduction in anthropogenic N deposition.