Collaborative Research: Linking models to data to investigate patterns and process in savannas

稀树草原是由草地基质中分散的树木组成的生态群落。导致草和树共存以及稀树草原群落长时间持续存在的机制尚不清楚。相反的生态学理论要么预测了生态位划分导致的平衡稀树草原群落，要么预测了由反复干扰（如火灾）导致的非平衡稀树草原群落。该项目将考虑另一种模型来解释稀树草原的结构，其中稳定性源于火灾干扰和植被之间的反馈。它将检验这样一个假设，即易燃的热带稀树草原植物导致更频繁或更强烈的火灾，而这些火灾反过来又促进了热带稀树草原植被的生长和建立。热带稀树草原植被和火灾之间的这种正反馈可以使树木的密度保持在无树草原和封闭林冠的极端之间。该项目将进一步探索飓风等频率较低的周期性扰动是否会与火灾产生相互作用，从而引发植被-火灾反馈，并将稀树草原从森林状态中拯救出来。干扰反馈模型的基本假设和预测将使用从过去30年研究的地点收集的经验和实验数据进行检验，这些地点包括佛罗里达州南部、乔治亚州西南部和路易斯安那州东部，这些地点广泛代表了美国东南部的松树稀树草原。由扰动反馈模型预测的人口和空间格局将与实地观测和实验数据进行比较，以确定模型的有效性。这种稀树草原动态的替代模型将有助于对世界范围内各种环境中稀树草原结构过程的一般理解，并将有助于预测稀树草原对气候变暖和景观破碎化等干扰的反应。了解热带稀树草原对扰动的响应具有广泛的意义，因为热带稀树草原占全球陆地面积的八分之一，提供必要的生态服务，是生物多样性的重要储存库。该项目的成果也将广泛适用于美国各地生态系统的生态恢复和管理。该项目将资助一名博士后学者，并在路易斯安那州研究地点附近的一个营地为研究生和本科生以及女童子军提供研究培训。

Savannas are ecological communities comprised of scattered trees in a grassland matrix. The mechanisms leading to the coexistence of grasses and trees and the persistence of savanna communities over long time periods are unclear. Opposing ecological theories have predicted either equilibrium savanna communities that result from niche partitioning or non-equilibrium savannas that result from repeated disturbances such as fire. This project will consider an alternative model to explain the structure of savannas, in which stability results from feedbacks between fire disturbance and vegetation. It will test the hypothesis that flammable savanna plants result in more frequent or intense fires and that these fires, in turn, promote the growth and establishment of savanna vegetation. Such positive feedbacks between savanna vegetation and fire could maintain the density of trees between the extremes of treeless prairies and the closed canopy of forests. The project will further explore whether less frequent, periodic disturbances such as hurricanes could have interactive effects with fire that could initiate vegetation-fire feedbacks and rescue savannas from a forest state. The underlying assumptions and predictions of a disturbance-feedback model will be tested using empirical and experimental data collected from sites that have been studied for the past 30 years in southern Florida, southwestern Georgia, and eastern Louisiana, and that broadly represent pine savannas in the southeastern United States. Demographic and spatial patterns predicted by a disturbance-feedback model will be compared to field observations and experimental data to ascertain the validity of the model.This alternative model of savanna dynamics will contribute to a general understanding of the processes that structure savannas across a wide range of environments worldwide, and will facilitate predictions of savanna responses to disturbances such as climate warming and landscape fragmentation. Understanding savanna responses to perturbations is of broad significance as savannas comprise an eighth of the global land surface, provide essential ecological services, and are important reservoirs of biodiversity. Results from this project will also be broadly applicable to ecological restoration and management of ecosystems across the United States. This project will support a postdoctoral scholar and provide research training for graduate and undergraduate students, and Girl Scouts at a camp near the study site in Louisiana.