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

在过去的40-50年里，外来的一年生植物正以越来越快的速度入侵南加州的灌木丛。许多因素可能对入侵负责，包括人为氮沉积、土壤扰动、放牧和破碎化。在这些潜在的原因中，氮沉积没有受到重视，而频繁火灾的影响才刚刚开始意识到。南加州灌木地的氮沉降速率高达30公斤/公顷/年，离农业和城市化地区较远的地区氮沉降速率较低。许多入侵的一年生植物可能是亲氮的，例如，随着n的增加，它们的生长率很高。相比之下，我们假设本地灌木对n的增加反应相对较小，仅火可以解释某些地点杂草增加和灌木覆盖减少，但30-40年未被烧毁的地区对外来植物的影响和增加。这些主要包括一年生草属的凤尾草属、凤尾草属和凤尾草属。最容易受到杂草入侵的原生植被是沿海鼠尾草灌丛，这种类型的范围有限，受到城市化的威胁，并庇护了许多敏感物种。我们的目的是研究火和氮沉降对植物生长的相互作用。我们请求通过SGER项目提供资金，以利用加州最近发生的火灾。我们找到了两个11月被烧毁的地点，一个是高氮沉降，一个是低氮沉降。我们建议在每个地点设置一个因子试验，用燃烧和未燃烧的地块与施肥和未施肥的地块。我们推测，施氮后，禾本科的年生长量比灌丛的年生长量增加得更多，而火烧则加速了原生灌丛向一年生草地的转变。本研究对沿海鼠尾草灌丛的保护具有重要意义。减少火循环对于防止向杂草丛生的一年生植物的快速转变将是重要的，但我们也可能建议减少人为氮沉降。

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.