Arboreal Invasion

The Sierra Nevada’s vanishing mountain meadows


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.

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? WE_bug_web

  • James H.

    I do not believe that there is anything about the life cycle of trees that would substantially diminish the organic matter in the soil. Most trees, even needle leafed trees, drop leaves, and contribute to the Organic matter. I’ve been in a white pine forest where the needle duff was so thick it was almost like walking on a soft springy mattress. The second point is that if it really is true that meadows would be mechanically harmed (water retention) by the invasion of trees, then perhaps it is in the interest of the benefiting people to actively manage those meadows to retain the form and function that is currently “enjoyed”. The third point is that all things change over time, and it might be unreasonable to expect that these meadows should stay meadows forever. Why, for example, are the twisted remains of trees being found in the mountains emerging from underneath retreating glaciers? It is because those areas, long before the machinations of mankind, were warm enough for long enough to support forests of mature trees.

  • Robert F..

    With the recent drought in California and the mass die-off of trees due to the drought and beetle infestations it is likely that we will see area that were once forested become meadows again and areas that were once meadows become forest. It is a balance that plays out that is as old as time. This is not a unique experience. Put simply it is the “Law of Conservation” at work. The forces of nature through wildfire, erosion, transport, and deposition will ensure that these areas will not be lost. They will just migrate to a new area where the conditions are right.

    If you look at an aerial of Lake Tahoe you can see along the western shore that it is in a depositional phase and that area of the lake will become meadow at some point. Just as with any lake that receives inflow from streams and hills surrounding them. They will fill in along the fringes and it will eventually become meadow and then eventually forest. The point is there will not be a net loss. Mother Nature will find a way to maintain her Forests and Meadows.

    • Laura S.

      Hi Robert. Thank you for sharing these insights. I find them both comforting and hopeful.

  • Daniel Dempsey.

    I have to concur with James H’s commentary. Any self-respecting mountain geographer will inform the reader that alpine meadows are comparatively, short-lived “geofeatures” within their respective environments. This doesn’t discount their importance to or influence on mountain hydrology or the myriad biosystems they support and enable. But to claim that the encroachment (a.k.a. succession) of alpine tarns by meadows to forests is a source of alarm is absurd. In fact, as a California community college educator myself, I’m having a difficult time understanding the motivations behind the UC Merced’s study if it’s for any other reason than to support the claims and caveats of ensuing climate change. The focus of the article should emphasize the realities of anthropomorphic-induced global warming; and the fact that the unfettered consumption/burning of fossil fuels for human objectives has glaringly obvious and negative ramifications regardless what deniers continue to tell our progeny!


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