Trees and the Watershed

Here, in Bozeman, Montana, we reside in the Lower Gallatin Watershed, and our water flows to the mouth of the Gallatin River where it joins up with the Madison and Jefferson to form the Missouri River.

Have you ever stopped to think about all the wonderful things that trees do for us? The people and critters of our watershed depend on trees. All the things that trees do to keep us safe, healthy, and happy are called ecosystem services. Trees provide shade and increase wildlife habitat. Trees are also carbon sinks, pulling CO2 from the atmosphere and storing it deep in the soil. Trees benefit public health by improving air quality and increasing access to green space, which can, in turn, reduce stress and mental fatigue. Robust urban forests provide critical social and cultural benefits that strengthen community resilience to climate change.

Water Supply

Our water supply is finite and shared with all people, plants and animals. Trees are like sponges–they naturally filter, clean, and store water, keeping our rivers healthy and helping prevent floods and drought. Leaf canopy and branches help to slow the movement of rain and stormwater. Trees absorb water through their leaves and also push water down through their roots. A mature evergreen can intercept almost 4,000 gallons of water per year! Root growth and plant litter also improve soil structure, which allow more rainwater to soak back into the soil and replenish groundwater. Healthy forests can decrease evaporative losses from the soil by tempering wind velocities and shading the ground surface from the hot sun. Trees help us hold on to our limited water supply for as long as possible, reducing floods in the spring and preventing drought in the summer.

 

Water Quality

We all need clean water— to drink, to grow food, for plants and wildlife, and to swim, fish, and boat in. Nutrients like nitrogen and phosphorus normally occur at low concentrations relative to what aquatic plants need, but excess nutrients can pollute our rivers and streams. Excess nutrients can come from fertilizers on lawns and farm fields, animal waste, and discharge from poorly maintained septic systems. This is called non-point source pollution.

Trees play a huge role in keeping our water clean. Trees decrease the amount of stormwater runoff and pollutants that reach our local waters. Root growth and tree residue improves soil structure and filters contaminants more effectively. When water is intercepted by a tree, harmful levels of nutrients and sediment are removed.

 

Aquatic Habitat

A riparian area is the vegetated transition between upland and a river, stream, or lake. Complex and messy riparian areas play a critical role in a healthy watershed. The woody roots of trees like willows and cottonwoods stabilize soil and prevent streambank erosion. Their branches above trap windblown dust and sediment before it enters our waterways. Fish and aquatic wildlife depend on the detritus and debris from trees for food and habitat. When stormwater and flooding flow through healthy riparian areas, the array of stems, roots, and branches dissipates energy and slows the flow. This tamed current is less destructive, sediment can settle out of solution, and water can infiltrate into the ground. Groundwater then seeps into our rivers and streams long after spring run-off and maintains a base flow throughout the summer, which is especially helpful in times of drought.

Additionally, shade from riparian trees reduces and regulates stream temperature. High water temperatures reduce levels of dissolved oxygen which can have negative impacts on aquatic life. Consistently warm temperatures in rivers can quicken chemical reactions and release excess nutrients. In Bozeman, the fish and wildlife have evolved to depend on especially cold, clean water, so even slight changes in temperature and water quality can be disruptive.

 

Doing our Part

In our watershed, we are doing our part to enhance watershed health and our urban forest. Every action across the landscape ultimately impacts water and influences our neighbors downstream, both human and animal alike. With the help of Gallatin Watershed Council and the City of Bozeman Forestry Division, Oboz will be planting 50 trees this Arbor Day. Our vision is an urban forest that promotes a healthy, resilient and equitable future for all.