Arboreal Invasion

Oct. 5, 2017

Meadows are a pastoral paradise. Beyond their verdant beauty, however, they are essential to vital environmental systems. If you were to look under the surface—beneath the grasses, the clover, the primrose, and the yarrow—you would see that important hydrologic processes are taking place.  

Mountain meadows play a crucial role in water regulation. A new study that surveyed more than 340 meadows in California’s Sierra Nevada indicates that warming temperatures and the resulting intrusion of tree species could mean the end of these grassy clearings, except at very high elevations.

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Within the past decade, researchers have outlined the importance of meadows to the hydrology of the High Sierras. These basins collect snowmelt from the surrounding slopes and store it for release during summer months. Meadow soils, experts explain, are rich in organic material and nutrients from the decomposition of grasses, enabling them to hold more moisture than forested areas.

“This helps minimize downstream flooding during spring,” writes Matt Weiser for Water Deeply. “Meadows release that runoff over a longer period, helping stretch valuable water supplies through the long, dry summer months.”

Researchers at the University of California, Merced recently found that meadows in the Sierra Nevada are being invaded by trees—most notably, the lodgepole pine. The study found that warmer conditions are ideal for tree species, and that as they take root in meadowland, the areas are less capable of water retention.

“Temperature is one of the important factors that explains variability in the number of [tree] recruits in a meadow in any given year,” explains study co-author Lara Kueppers. The data that she and her team collected pointed to climate change as one of the primary drivers of the tree encroachment patterns. The UC Merced researchers further predict that as temperatures continue to warm, more trees will occupy meadow clearings, shifting the landscape of the Sierra Nevada.

What implications do you think this forestation might have on the area’s hydrology? Are other North American mountain ranges experiencing similar shifts? What might the ripple effects be?
About the Author

Laura Sanchez

Laura Sanchez is the editor of Distributed Energy and Water Efficiency magazines.