Riparian Corridors: Rich Biodiversity

August 2nd, 2022

What are riparian corridors and why are they important? This is an important topic to be talking about at this point in the summer because looking out at the mitigation lands, it is the riparian corridors that are green and relatively lush with plant life right now. When I am out walking the valley lands, it is the riparian areas that I seek out for respite from the intensity of the sun and heat. This of course is what all the animals are doing, using the cool shaded, wet corridors through the valley for traveling, hunting, resting, hiding, and drinking. Setting up the video cameras on any wet place will surely be the best for understanding the biodiversity of these areas.

So, what is the definition of a riparian corridor? A riparian corridor is a unique plant community consisting of the vegetation growing near a creek, river, stream, lake, lagoon, or other natural body of water. This is according to a google search which seems like an oversimplification of a complex system of soil, water, and vegetation types. The common tree species along our riparian corridors in the valley – Baechtel, Broaddus, Berry, Outlet, Mill, Davis, and Upp Creeks – are White Alder, Rhombus rhombifolia, Black Cottonwood, Populus trichocarpa, Red Willow, Salix laevigata, Pacific Willow, Salix lasiandra, and quite a few other species of willow. Other important riparian species include Big Leaf Maple, Acer macrophylla, Northern California Black Walnut, Juglans hindsii, and Oregon Ash, Fraxinus latifolia. These trees are native species that evolved to live along streams and are adapted to survive high-water events during winter storms and dry hot summers where the water can disappear altogether. In other words, resiliency, being a resilient species, is important. In the last ten years, many riparian tree species have died or have displayed physical effects of the drought. The Northern Black Walnut is a tree that has been planted by farmers and ranchers further south of us and has since become established further north of its natural range along the creeks here.

The birds use the riparian corridors for nesting, shelter, food sources, and resting. Besides the variety of water birds such as Common Mergansers and Wood Ducks, there are many species of herons – Great Blue, Green, and the Night Heron. Plus, there are two species of Egrets – the Snowy and Great. There are many passerine birds that depend on riparian habitats for foraging and nesting, some of them neotropical migrants such as the Lazuli Bunting and Yellow-breasted Chat. Others are residents such as Song Sparrows, Belted Kingfishers, and Downy and Hairy Woodpeckers. More than two hundred and twenty-five species of birds, mammals, reptiles, and amphibians depend on riparian habitats. Right now, it is the habitat that seems the most alive with birds and insects out in the valley.

The American Beaver families that live along the riparian corridors in this valley have been working hard to maintain water in Outlet Creek for the last few years and appear to have made a positive impact on the quality and amount of water retained in the pools. This is accomplished by a beaver paying attention to what is happening to the water flow and constructing dams that are strategically placed to slow and hold it. The area in front of the dam is dug out by mouth and very small paws and then patted down to form a waterproof barrier.

This creates a paradise of deep pools where other animals such as salmonids, turtles, waterbirds, insects, and other species can survive our long dry periods. It has truly been an honor to watch what these engineers can accomplish.

The beauty of the Willits Valley resides in the riparian corridors that cross the fields, fed by the watersheds above the valley floor. These rich and diverse habitats add ecological value to the surrounding watershed, allowing our aquifer of valley water to replenish and stabilize. It is an extremely important ecosystem function that we should not ignore.