Science Behind the Scenery: Vegetation Mapping

Point Reyes National Seashore


[waves washing ashore]

[Dave Schirokauer] This part of the Bay Area is considered one of the top areas in the world for biodiversity. We have an incredible diversity of plant species here. We have over 600 native plant species and over 300 non-native ones. In order to map plant communities, one first has to define them. So, one of the first steps that we have to undertake in figuring out how to map the plant communities was to describe them,...plant communities being the combination of plant species that occur in any one given area.

[Pam van der Leeden] When you have two plant communities that are growing next to each other, they sort of flow into each other. There isn't a sharp line, usually, where you can say the end of one and the start of the next one. What you'll usually see is, for example, something like, if you were to look at a coyote brush shrubland, you would see an area with really, really dense coyote brush, that would be, maybe, hard to walk through, and then it would get sparser and sparser. And then you would see more grasses. And then, gradually, you would have a grassland. Somewhere along that boundary a line that needs to be drawn to label one as a coyote brush shrubland and one as a grassland.

[Dave] And the next step, after deciding what the composition of those plant communities are and assigning preliminary names to them, was to design a key—a key that field crews could take out and quickly use to identify the plant community they were standing in on the ground.

The photointerpreters have a incredible responsibility in this project. They actually have to look at aerial photos that were taken from about 10,000 feet and discriminate subtle differences in the vegetation patterns they see on the image. They have to apply labels to each polygon that they draw on an aerial photo.

The photointerpreter is using a stereoscope. This allows them to view the aerial photos in three dimensions. And it makes discriminating the plant communities a lot easier.

It's often the arrangement of plant communities on the landscape that drive how wildlife interact with the landscape and how disturbance processes, such as fire, interact with the landscape.

This map is a tool to help us target areas of non-native species to remove.

Another important application of the vegetation map is to simulate the potential effects of fire on the landscape. There's a software package that we can actually apply fire on the virtual landscape, inside the computer, and watch how it burns. The vegetation map is an absolutely essential component of that process because each vegetation type burns differently. We have a lot of detailed data that we can now use to simulate fire.

Having one vegetation map is really useful as far as its application for fire management, tracking invasive species, mapping wetlands, describing wildlife habitat.

Fifteen years from now, when we have another vegetation map, we'll be able to study the effects of global climate change on our plant communities. We'll be able to look and see if new invasive species from other parts of the world have taken over areas that used to be occupied by native species. And we'll be able to...we'll be able to study the effects of how our management, specifically in regards to fire, has changed the juxtaposition of plant communities on the landscape.


The eighth part of the ten-part Science Behind the Scenery documentary featuring GIS (geographic information system) biologist Dave Schirokauer and GIS botanist Pam van der Leeden talking about how aerial photos are converted to vegetation maps to study the effects of how land management has changed the juxtaposition of plant communities on the landscape.


4 minutes, 18 seconds


Pacific Coast Science and Learning Center

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