Ecologically Case

PURPOSE

Overview

As you learned in Chapter 1, ecosystems are a complex and delicate balancing game. The addition or removal of any species affects many other species that might compete for or provide food. These interspecific interactions are further influenced by human impacts on the environment such as habitat fragmentation. Chapter 4 noted how disturbances associated with deforestation and urban sprawl alter environmental conditions in ways that can both shift competitive outcomes in ecosystems and threaten human well-being.

In this lab you will apply the scientific method to examine how thresholds of land use changes such as deforestation and urban sprawl can impact communities, predator/prey relationships, species diversity, and quality of life in human communities.

Scenario

The imaginary forest town of Pinchot, California is facing a land use planning battle. Conservationists and the local outdoor recreation industry want to protect at least 75% of Pinchot's surrounding forest reserve to maintain the town's natural heritage, including its unique biodiversity and valuable ecosystem services. Developers, however, want to expand the town's neighborhoods and shopping malls and insist that protecting 25% of the reserve is all that is needed to sustain the forest's biodiversity and economic value.

You have been appointed to a select team of scientists tasked with using the scientific method to evaluate the impacts of fragmentation on the forest reserve and community. Your objective is to determine the percent of intact forest that must be maintained to protect the reserve's biodiversity and ecosystem services.

To achieve this objective, your team has developed a computer model based on decades of plant and animal population data collected by the Dept of Fish & Wildlife and local land trusts. Your modeling has also incorporated population data from the forest reserves of three nearby towns, which are 25%, 50% and 75% fragmented, respectively.

By comparing how fragmentation has impacted four ecologically important species within these four forest reserves, your team aims to answer the question of whether 25%, 50% or 75% fragmentation will be "sustainable" for Pinchot's forest in terms of sustaining its biodiversity and ecosystem services. The science-based hypothesis that you are testing, using this computer model, is that neither 50% nor 75% fragmentation will achieve this goal.

About the Species

The four ecologically important species that your study focuses on include:

1. Spiny firegrass (SFG): a fictional Eurasian invasive annual grass. It is dangerous because as an annual that dries out in the summer, it increases the risk of dry-season wildfire in habitats that it invades. Elk do not eat SFG unless they are starving. SFG prefers disturbed sites such as roadsides and clearings, and does not do well in the shady environment of a closed forest. It flourishes in direct sunlight. Its effects on human communities include harm to pets and livestock - where it invades, it gets lodged in their noses and mouths, causing serious injury. Its spread also increases the risk of wildfire to homes and businesses.

2. Bluebunch wheatflower (BBWF): a fictional native perennial plant that is a habitat generalist, but is most competitive in moist forest interiors and least competitive in direct sunlight. In all habitats except direct sunlight, it is able to outcompete SFG and prevent the weed's spread. As the preferred food of elk, it is particularly efficient at outcompeting the annual grass when wolf populations are large enough to moderate herbivore populations.

3. Elk: Elk eat BBWF, but do not find SFG palatable. Their preferred habitat is edges between the forest and clearings. At high numbers, elk eat BBWF, which otherwise suppresses the spread of SFG. When their population is high, elk pose the safety and economic threat of collisions with vehicles, which cause expensive and sometimes deadly damage.

4. Wolves: eat elk. Preferred habitat is intact forest. Wolves are highly sensitive to human disturbance and habitat fragmentation due to (a) getting hit by vehicles and (b) getting shot at by ranchers. They tend to avoid contact with humans, but occasionally prey upon livestock and pets.

The Importance of Forest Ecosystem Services to Your Findings

Your scientific team noted that several citizens of the town with a 50% fragmented forest reserve expressed concern about an increase in flood danger. They told the team that since 50% of the forest was removed and much of the land paved over for development, flood waters in the stream running through town have risen strikingly higher during major precipitation events.

Land trust officials of the town with a 75% fragmented forest reserve reported similar observations. They said that the stream running through town recently flooded the business district for the first time in history, causing millions of dollars in damage. In fact, the mayor told the team that the development the city had allowed seems to have exceeded a threshold of sustainability: it was not only unsustainable for maintaining their forest's biodiversity, but also for maintaining the forest's valuable ecosystem service of acting as a sponge that helps mitigate floods.

OBJECTIVES

Investigate the effects of habitat fragmentation associated with deforestation and urban sprawl on forest food webs and ecosystem processes.

Learn how to use the scientific method to address questions in environmental science and apply scientific findings to recommend management solutions.

Determine the percent of intact forest that must be maintained in order to protect the Pinchot Forest Reserve's biodiversity and ecosystem services.

PROCEDURE

Literature Review

First, review course readings relevant