One of the highlights of an early-summer hike is when one rounds the corner of a trail to see a meadow in full bloom. In the Sierra Nevada, a diversity of meadow and wetland types offer the opportunity to admire beautiful and fascinating plants from spring through fall. The secret to that diversity lies primarily in the varied geomorphology, or ways the earth’s surface was formed, and hydrology of our area.
Due to our dry summer climate in the Sierra Nevada, many plants experience their greatest growth and flowering period during the wet spring and into early summer, when soils are still damp due to snow melt. However, in some shallow depressions and seemingly random pockets on hillsides, the lush green of spring seems to persist well into summer. If you have spotted this phenomenon, you may very well have seen a fen.
Fens are a type of wetland. Wetlands are ecosystems in which the water table is at or just below the surface of the ground, resulting in soils saturated with water and plant species tolerant of the wet soil conditions. Fens are a particular kind of wetland fed primarily by groundwater. This distinguishes fens from bogs, which are peat-producing wetlands primarily fed through atmospheric precipitation and are therefore not found in the dry summer climate of the Sierra Nevada. The existence of a groundwater source allows fens to persist in verdant lushness throughout the Sierra’s dry summers.
Fens can often be found within or alongside meadows, of which there are two primary types in the Sierra Nevada: wet and dry. Wet meadows are wet for at least one month of the summer, and they can be difficult to visually distinguish from fens. Beneath the roots of the plants, however, the difference is distinct. The groundwater that keeps a fen green throughout the summer saturates the soil, limiting aerobic decomposition of plant materials. These materials instead accumulate and over time, developing into spongey, carbon-rich peat. In wet meadows, the soil gradually loses moisture throughout the summer, and fallen plant materials can decompose.
Fens and wet meadows can co-occur with dry meadows (meadows that are only wet during the spring melt of the snowpack), forming a matrix of habitat types with transition zones rather than clear borders. This matrix is known as a meadow complex. In a broad alpine valley, for instance, ponds may persist throughout the summer at the lowest points, surrounded by fen. A matrix of wet and dry meadows fill out the lower topography, transitioning on the shallow slopes to upland plant species, shrubs, and eventually, forest.
The meadow that greets you as you round a corner on the trail is not simply a meadow, as it turns out, but an ever-shifting mosaic of habitats whose existence is in constant flux with the seasons and the water cycle.
To learn more about the ecosystem services provided by fens and wet meadows and SYRCL’s work to restore them, please visit our Meadow Restoration page. And remember, as you explore this spring and summer, please stay on established trails in order to preserve our important and fragile ecosystems.