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Forests and �Watersheds

The interconnection of water supply and forests

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Big Chico Creek (Ótakim Séwi) �Watershed Forest Ecosystem

Valley oak

Quercus lobata

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The Valley Oak (Quercus lobata) grows into the largest of North American oaks. It ranges over the hot interior valleys of California where there is a water table within reach of the roots.

Understanding forest structure is important for:

Water supply
Plant, animal, and human health
Land management
Community protection

Oak woodland forest ecosystem

If you have samples of valley oak leaves, etc., have students pass them around.

The interconnection of trees, water or streams and creeks, other vegetation, and wildlife habitat is called a food web, or an ecosystem. The study of these systems is ecology. The study of forest ecosystems and the resources that humans obtain from them is called forest ecology, and the resources are ecosystem services. Finally, the study of the role that fire plays in these ecosystems is called Fire Ecology.

Valley oaks are usually the second most abundant species of tree in the Big Chico Creek watershed. The valley oak leaf is lobed and singular. Many early explorers that passed through the Big Chico Creek watershed even thought the blackness of the bark indicated that valley oaks had survived fires. Make a quick sketch of a valley oak leaf in the box labelled “Valley Oak” on your worksheet. Give students time to draw their leaves.

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What types of forests are in CA?

Let’s try to narrow down this ecosystem’s distribution. Using this “satellite view,” draw a boundary around where you think oak woodlands are found. Keep in mind how ecosystems/biomes change across these three states. The satellite image shows biome variations and transitions that might be helpful. Since trees are an important component of the Big Chico Creek watershed, knowing where trees can be found could be helpful. Feel free to use what you already know about biomes! Be sure to respond to the prompts beneath the map concerning the evidence and reasoning you used. After students have a minute to come up with their range maps, have them compare with their colleagues’. Now, take a moment to compare your map with your neighbors’. How are your maps matching up? Now let’s see how well your maps compare with those of experts.

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Land Use & Vegetation in the Big Chico Creek Watershed

Source: https://sacriver.org/explore-watersheds/eastside-subregion/big-chico-creek-watershed

In this aerial view, distinct Big Chico Creek watershed systems are separated by roads. What type of system (forest, woodland, savanna, prairie) is found in area “1”? The canopy cover in area “1” appears to be very dense, so this would be categorized as a forest. How about areas “2” and “3”? Depending upon where the observation is made, area “2” could probably be considered a woodland or savanna, and area “3” would probably be called a woodland. Since these three areas are found so close together, they receive the same precipitation and temperature variations. Therefore, other factors must be causing their differences. We’re now going to take a look at a factor that contributes to such variation within the Big Chico Creek watershed. This factor is a naturally occurring disturbance.

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Big Chico Creek watershed – Forest types

Forest types:

Riparian, grasslands - Valley
Oak woodlands – Valley & Foothills
Conifers (pine cones!) – Foothills & Mountains
Mid elevation mixed conifers
High elevation – alpine! (skiing!)

Here’s an area of forest in the Big Chico Creek watershed. Ecologists have ways of distinguishing forests and woodlands. One approach is to determine the canopy cover. A forest ecosystem has a canopy cover of 80-100%. To estimate percent canopy cover, ecologists have developed a variety of tools. A classic tool is the densiometer which uses a spherical mirror to quickly estimate percent canopy cover. A more modern approach is a digital camera equipped with a fisheye lens combined with computer software which can help reduce human error and/or bias. You can imagine the results from either to look something like this. So, what do you think the term “canopy cover” means? Give students a moment to attempt to define the term. Canopy cover can be defined as the proportion of the forest floor covered by the vertical projection of the tree crowns. So looking at the spherical image, can you visualize that the canopy would cover 80-100% of the ground when projected vertically downward? Reproduce this spherical image on your student worksheet in the “Variation in the Big Chico Creek watershed” section. Include “Forest” as the name, “80-100%” as the % Canopy, and, for the Description, include a few of this forest’s characteristics as seen in the images. Don’t worry about “Fire Frequency” in the box. This will be covered later. Here’s an example to help with your first entries. Give students time to complete the first box in the “Variation in the Big Chico Creek watershed” on their worksheet.

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Big Chico Creek watershed – Valley oak grassland, or ‘Savanna’

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Fire in the Big Chico Creek watershed

Fire. The presence of this naturally occurring disturbance ensures a variety of plant species which results in a greater overall biodiversity in the Big Chico Creek watershed. All ecosystems are subject to changes from disturbance – fires, floods, drought, wind events, and even avalanches. Change and growth following ecosystem disturbance is called, ‘ecological succession’. The disturbance or impact resulting from disturbance, such as wildfire, maintains fuels from open areas within the Big Chico Creek watershed where grasses and forbs can thrive. This broadens the types of habitats available. Succession and subject to change increases forest resilience. For this very reason, the fires pictured were set on purpose. Prescribed fires, or good fire, have specific management goals and are only conducted under “prescribed” weather conditions with adequate personnel and equipment to reduce the chance of impacts outside of the burn unit.

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Fire in the Big Chico Creek watershed

Every

Year

Every

2 Years

Every

3 Years

Never

Burned

Fire frequency can result in significant differences in dominant vegetation types. If an area has fire pass over it every year, woody vegetation may be reduced to such an extent that it’s unnoticeable. Most native vegetation in the Big Chico Creek watershed, such as the valley oak, is fire tolerant. Fire-tolerant species can resprout, or grow back, from undamaged belowground biomass. Fire every two years usually allows some woody vegetation to survive and, perhaps, grow into larger trees. When a fire occurs every three years, woodlands are the dominant ecosystem. In most parts of the Big Chico Creek watershed, when fire has a frequency greater than 3 years or does not occur at all, forests will take over as trees begin to exclude other vegetation. Return to the “Variation in the Big Chico Creek watershed” section of the worksheet. In each of the systems’ descriptions, include the fire frequency usually associated with each. Give students time to include the fire frequency for each ecosystem category.

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Big Chico Creek watershed function

What services do forests provide in the watershed and ecosystem?
Are these services biotic, chemical, or physical? Or all the above? Why?

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Fire in the Big Chico Creek watershed

2. What type of Big Chico Creek watershed system(s) would you expect to encounter if an area were burned every 3+ years? Why?

Source: Chico Enterprise-Record

Prescribed burn at Bidwell Park, June 22, 2023. Burned again on March 11, 2025.

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Forests and Watersheds

PPT Sourced from:

Forest structure within watersheds provides:

Water supply
Plant, animal, and human health
Biological habitat, recreation, fisheries
Community protection from catastrophic wildfire when fire intervals and recurrence are understood.