Disappearing Sierra Meadows

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maverick
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Disappearing Sierra Meadows

Post by maverick » Tue Nov 28, 2017 5:48 pm

By Water Deeply:
Why Disappearing Sierra Nevada Meadows Are Bad News for Water

Meadows play an important role in water storage and flood prevention. But a new study shows that warming temperatures and resulting tree encroachment could doom these landscapes, except at very high elevations.

Cattle grazing in meadows, can harm meadow health by compacting the soil and may contribute to encroachment by lodgepole pine trees.
Mountain meadows are starting to get some respect. For over a century, meadows were the first alpine environments targeted for development, grazing and farming, because they tend to be flat and packed with rich soil and nutritious plants. But we’re starting to understand that meadows have a much more important role to play for society at large.

Meadows, it turns out, are water banks. As winter snows melt, the runoff flows into meadows, where deep organic soil holds the moisture like a sponge and then releases it slowly. This helps minimize downstream flooding during spring. Meadows release that runoff over a longer period, helping stretch valuable water supplies through the long, dry summer months.

Efforts are underway to restore meadows, which have lost some of their water-holding ability as they’ve been compacted and eroded by grazing, logging and other activity. Unfortunately, a new threat has emerged: climate change.

A new study by researchers at University of California, Merced, found that Sierra Nevada meadows are shrinking due to encroachment by trees – primarily lodgepole pines. And not just some meadows, but virtually all meadows throughout the Sierra Nevada.

Warmer temperatures are likely to blame, according to the study, creating conditions more favorable to trees. As a result, lodgepole pines are creeping into areas that have been historically meadow environments, sinking deeper roots that create a new year-round water drain on meadow environments.

And the future doesn’t look good. As temperatures warm further due to climate change, more trees are expected to encroach on meadows. The authors reach a startling conclusion: By the end of this century, the average meadow will shift entirely to forest. Eventually, meadows may only be found in sparse locations at high elevation, where lodgepole pines can’t thrive.

What are the implications for biodiversity, for water supply and flood prevention? A lot of these answers aren’t yet known. But to find out more, Water Deeply recently talked to Lara Kueppers, a co-author of the study and a research scientist at the Sierra Nevada Research Institute, based at U.C. Merced.

Water Deeply: What’s unique about this study?

Lara Kueppers: I think the main thing is the extent of ground-based observations that we did. When you are in the field observing just a single meadow or a small number of meadows, you can sort of draw conclusions about those few meadows you looked at. But we were really after a large area and wanting to understand: Is this phenomenon something that’s widespread across a big section of the Sierra? So we surveyed meadows across a pretty broad area, from Sequoia-Kings Canyon National Park on up to the Lake Tahoe area.

The other way people try and cover a lot of ground is usually by using satellite images. But we were interested in the number of trees that were coming into these meadows that might be smaller and difficult to detect remotely. So being on the ground enabled us to do that.

I think in the end we surveyed over 340 meadows. Not all with the same level of intensity.

Lara Kueppers is a research scientist at the Sierra Nevada Research Institute, based at U.C. Merced, and co-author of a new study about disappearing meadows in the Sierra Nevada.

Water Deeply: Are meadows really likely to disappear by the end of the century?

Kueppers: The conclusion isn’t that all meadows will disappear. The conclusion is that the average meadow will disappear. Basically, what we were finding is that many meadows are experiencing encroachment. There are some that aren’t, however, and those may continue to be resistant to encroachment in the future.

So, for example, in some meadows at higher elevations, where lodgepole pine isn’t abundant, you don’t see the same kind of encroachment as you do at lower elevations. But anyone who hikes in the backcountry of the Sierra has surely noticed trees creeping into meadows, if you return over time.

That’s why we say the “average” meadow, because a lot of those meadows that are out there are experiencing encroachment. It may not be full encroachment by the end of the century, but it will have experienced some encroachment.

Water Deeply: Your results show that climate change is a major reason for meadow shrinkage. How did you reach that conclusion?

Kueppers: If by climate change you mean human-caused climate change, we actually didn’t examine that question. What we were focused on is figuring out what are the causes of encroachment we see in terms of specific factors. So we looked at landscape factors like topographic position, elevation, what are the tree species around the meadow. Then we also looked at climate factors.

We found that climate factors are important drivers of the patterns we’re seeing, but we didn’t really try to quantify whether past human-caused climate change was complicit in that. We don’t really conclude the encroachment we’ve seen so far has been caused by human-caused climate change. Our conclusion is that climate is an important driver of encroachment. And then we said, let’s look to the future and projections of climate change.

Given what we know about factors that seem to lead to tree recruitment in these meadows, that’s what led us to the conclusion that future climate change is going to be a really strong contributor to encroachment. For example, temperature is one of the important factors that explains variability in the number of [tree] recruits in a meadow in any given year. So when we look at future temperatures increasing, we see that drives an increase in the number of trees in the meadows.

Water Deeply: How does snowpack affect meadow encroachment?

Kueppers: High snowpack actually promotes encroachment. We think that’s in part because, if there’s low snowpack, over winter these young trees can be exposed to very cold temperatures, and that can be detrimental to their ability to grow and survive. So when you have high snowpack, the really young juvenile trees are buried in snow, and protected over the winter. Then they can emerge and grow really strong in the summer.

The other thing snowpack is important for is a sustainable source of water in the drier meadows during spring and summer. These meadows are collecting meltwater, not just from the meadow itself but from the surrounding watershed, because the meadows are in topographically low locations. Again, when these trees are young and getting established, if the meadow dries out they’re going to have a hard time making it through the summer. But if there’s a high snowpack, there’s that sustained input of water and they’re less liable to dry out.

Meadows in the Toiyabe National Forest south of Lake Tahoe, are at risk of encroachment by lodgepole pine trees as temperatures warm over the decades ahead, according to a new study.

Water Deeply: How big of a role do meadows play in water storage?

Kueppers: They’re an integral part of the hydrology of the High Sierra. A big role that many meadows play is sort of as a regulator in the water system. They collect snowmelt from the surrounding slopes and they store it and sort of release it slowly over the spring and summer season. They can absorb a large amount of water and then release it. Some is coming from surface runoff, but other water is coming underground through cracks in the rock and then emerging in the meadows.

The soil, especially in the wettest part of meadows, is very organically rich. That’s because, over time as these grasses and other sedges and wildflowers that are well adapted to the meadows grow and die, the organic matter decomposes very slowly because there’s so much water around. So this organic matter just builds up, and more organic-rich soil can hold more water. And they release that water slowly over the summer.

Water Deeply: What are the water-supply implications of shrinking meadows?

Kueppers: We don’t fully know what the full-sum impact might be. There are a couple different ways that trees encroaching into meadows could alter hydrology. One explanation we have would be that trees typically use more water than the meadow grasses and wildlife. As a consequence, as trees become more abundant and larger, they would use more of the water coming into meadows, which means less water would flow downstream.

Another is that as the meadows dry, if the trees are using more of the water, there would be faster decomposition of organic matter, and that organic matter wouldn’t necessarily be replaced in kind by the trees.

If there are fewer roots with the trees than there were with the grasses and forbs, then the amount of organic matter flowing might not keep up with the losses from the drying conditions. So you would lose that sponginess in the soil, and it would weaken its ability to absorb and release that water over time.

Water Deeply: Will the Sierra look different in future?

Kueppers: I think there will still be some meadows. There will still be areas that remain wet. You just might have to look harder. You probably will have to go higher to get to them. Maybe not over our lifetimes, but in our children’s lifetimes. Luckily for us, changes happen very slowly. So while we can see signs of this process underway, at least all of us can still enjoy the meadows for what they are right now.

Water Deeply: What can we do to reverse this trend of meadow loss?

Kueppers: Our simple modeling exercise suggests that supporting solutions to climate change is a really important part of slowing meadow encroachment, because the critical factor driving encroachment overtime is the temperature increase. Another thing we can do is really limit the direct effects on meadows, such as trampling by grazing animals, because that just contributes to impacts on these meadows.
https://www.newsdeeply.com/water/commun ... -for-water


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Re: Disappearing Sierra Meadows

Post by rlown » Tue Nov 28, 2017 5:53 pm

I saw some of this on the upper meadow area near the waterbars on the way to Vogelsang. It looked completely different from 9 years ago; trees were working their way towards the trail on the North side. Lots of new, young trees nearing the trail, and the outlet stream from Evelyn was now completely forested.

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Re: Disappearing Sierra Meadows

Post by LMBSGV » Tue Nov 28, 2017 6:11 pm

A prime example is Tuolumne Meadows. If one compare photos from 30-40 years ago with recent photos, the lodgepole encroachment is obvious. Or, in my case, I remember being able to walk over the open meadow in places that are now groves of lodgepoles. I expect many of us have favorite meadows, large and small, that have been shrinking or even almost disappearing over the last twenty years.

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Re: Disappearing Sierra Meadows

Post by Tom_H » Tue Nov 28, 2017 11:06 pm

Not in the Sierra, but I noticed the same thing happening in all the meadows on the west slope of Mt. Whittenberg in Pt. Reyes.

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Re: Disappearing Sierra Meadows

Post by Jimr » Wed Nov 29, 2017 10:14 am

Seems to me that other than the grazing aspect that heavily impacts meadow health, the rest is just describing the natural evolution of a meadow. They don’t last forever. Shallow lakes slowly silt in to become a meadow, then slowly become forest as trees fill in from the perimeters.
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Re: Disappearing Sierra Meadows

Post by dave54 » Wed Nov 29, 2017 5:11 pm

We had a meadow enhancement project near Child's Meadow, south of LAVO. Part of the project was building small check dams across a V gulley, the ponds created behind the dams would raise the water level. This would encourage more riparian and mesic vegetation and inhibit tree encroachment. Another part of the project was removal of large fir and pines that had already encroached.
This is where is gets bizarre. The trees were commercial sized and could have been sold, offsetting the cost of the project, possibly financing similar projects or sent to the U.S. Treasury. But... this was in a No Logging zone. No commercial sales allowed for any reason. Because it was now a wetlands the logs and slash could not be burned on site. Likewise could not leave for personal use fuelwood, as woodcutters would drive on the newly created meadow. So (and this is hair pulling frustrating and sad) the logs were bucked into manageable pieces, Calfire inmate crews loaded the cut-up logs into a dumptruck, and all taken to a landfill. The only legal method of disposal under the law.
Just one example of misguided and poorly written environmental laws creating a waste of commercially valuable resources and unnecessary expense to the taxpayers.
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Re: Disappearing Sierra Meadows

Post by robow8 » Wed Nov 29, 2017 10:07 pm

Does fire play any part in this process? Seems like a little burning would kill the encroaching seedlings.

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Re: Disappearing Sierra Meadows

Post by dave54 » Wed Nov 29, 2017 10:39 pm

Fire is a minor factor. Lodgepole is a thin barked species, so is fire sensitive, and soil moisture in meadows would conduct the heat down to the roots. However, the herbaceous live green vegetation does not carry fire easily, and then only at very low intensity. High water table/soil moisture seems to be the primary inhibiting factor. Lodgepole tends to tolerates higher soil moisture than other species so encroachment favors lodgepole.
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Re: Disappearing Sierra Meadows

Post by Tom_H » Thu Nov 30, 2017 12:05 am

Jimr wrote:Seems to me that other than the grazing aspect that heavily impacts meadow health, the rest is just describing the natural evolution of a meadow. They don’t last forever. Shallow lakes slowly silt in to become a meadow, then slowly become forest as trees fill in from the perimeters.
Any flat meadow that you find in a valley/bowl is indeed a eutrophicated lake. We've all seen lakes that are almost full of sediment, and are a flat marsh, right at the transition point between lake and meadow. But not all meadows used to be lakes, however. There are plenty of meadows near the tops of mountains as well as downsloping valleys with rolled sides where erosion and decomposition have filled in topsoil, but they never were a lake.

The first type tends to have a more well formed aquifer in the old lake bed that retains moisture in the ancient bowl below. The second type has a bedrock bottom which is sloped in one direction and groundwater tends to flow downhill and seep into the stream via springs. I think the type described in the article is primarily the eutrophicated lake type, though those I mentioned at Pt. Reyes are the other type and the trees a different species.

As far as fire, we know Native Californians used to regularly burn areas to suppress forestation by conifers and to maintain meadows surrounded by and interspersed with oaks. They were not in the absolute total harmony with nature to the degree many people think, but in cases like this really managed the environment to their own purposes.

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Re: Disappearing Sierra Meadows

Post by dave54 » Thu Nov 30, 2017 6:00 pm

Tom_H wrote:
Jimr wrote:...As far as fire, we know Native Californians used to regularly burn areas to suppress forestation by conifers and to maintain meadows surrounded by and interspersed with oaks. They were not in the absolute total harmony with nature to the degree many people think, but in cases like this really managed the environment to their own purposes.
Heavily depends on the meadow. Dry meadows burn, wet meadows not as much.

Also native American burning may have been accidental as much as deliberate. There are great differences in fire effects depending upon the season of the burning. Spring burning tends to promote the forbs and grasses favored in many traditional uses and leaves the woody growth. Late Summer and Fall burning does not stimulate herbaceous growth as much, but does get rid of woody plants. Fire scar data shows very few fires early in the year (Spring) and most fires in the Sierra Nevada were mid Summer to Fall. Assuming the Native Americans were observant enough to realize the difference between burning in Spring versus Fall, they would have burned more in the Spring. The data does not show they did.
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