- Author: Nathan Van Schmidt
After five years, the northern Sierra Nevadas have finally been moved out of the “severe drought” category by the US Drought monitor following a promisingly rainy start to the 2017 water year. This is not only good news for our agricultural community, but it's also good news for our wetlands, which depend on steady water flow to stay saturated and perform their ecological functions. The gold country region of the Sierra Nevadas has over 1,500 wetlands, which can provide many important benefits including water quality control and purification, runoff reduction, aesthetic value, and wildlife habitat. The Beissinger lab has been working with SFREC and local landowners to study these wetlands since 2002, originally just to track a secretive, understudied bird species: the California Black Rail (Laterallus jamaicensis coturniculus). Our recent research has expanded to study how the wetlands function as a “coupled human and natural system,” affected by both ecological processes (rainfall and natural water flows) and human processes (our irrigation infrastructure and water use).
First, we've been tracking how these wetlands changed over time with a time series of historical aerial photographs stretching back to 1947. We first made a comprehensive map of all wetlands in the region, then selected a subset of 283 wetlands and tracked them back through time. Coupled with field visits, seeing what they were like under different historic irrigation regimes allowed us to determine the water sources for each wetland. Based on that study, we estimated that nearly 9 in 10 foothill wetlands are fed by irrigation water, and roughly 2 in 3 are entirely irrigation-dependent. Some of those wetlands were intentionally created: state wildlife areas use irrigation to create new wetlands and supplement existing ones, and private landowners on the edge of the Sacramento Valley create wetland impoundments for waterfowl hunting. But over half the irrigated wetlands of the foothills are fed apparently unintentionally by excess water, forming from runoff or leaks from irrigation infrastructure.
During times of drought, these wetlands are one of the most vulnerable ecosystems because they are characterized by the presence of relatively small amounts of water saturating the surface. We were interested in figuring out how wetlands fared during the drought, and especially if irrigated wetlands and natural wetlands behaved differently. To determine this, we carried out field visits to 270 wetlands up to 12 times during the 2014 drought. At each visit our technicians walked throughout the wetland with a map and estimated the percent of the wetland surface that was saturated (either surface water or spongy mud). We found that wetlands fed by irrigation water were both wetter on average and more stable over time than natural wetlands during the drought. Natural wetlands showed strong fluctuations in saturated area, with over half drying completely at least once during the study period, compared to only a third of irrigation-only sites and only 15% of sites that had both irrigated and natural water sources. While some drying during the summer dry season is normal, this degree of seasonality was exceptional compared to what our lab had seen in pre-drought years.
Irrigation water may thus be even more important during drought for wetland species' habitat. Concurrent studies conducted by our lab have found that natural wetlands had very high levels of local extinction for California Black Rails over the course of the drought: no natural wetland occupied by the species in one breeding season remained occupied in the next, and in the last two years of the drought no California Black Rails were detected in any natural wetlands. Irrigation water use in the foothills has thus not only dramatically increased the number of wetlands in the foothills, but has increased their function by keeping them saturated year-round. This has created a unique win-win scenario where private, chiefly agricultural water use has created substantial ecosystem benefits.
However, this increased resilience to drought could lead to sudden severe impacts if drought becomes any more severe than already seen. If irrigation water is removed from the wetlands at the same time as natural water—either via cutbacks in response to more severe drought, transferring water out of the foothills, or efforts to fix leaks and reduce runoff—it may create “cliffs” where wildlife populations, bolstered by water sources resilient to mild drought, decline rapidly when faced with sudden reductions in both natural and irrigated water sources. The next step for our lab is to assess whether such dynamics might occur, using computer simulation studies to link the results of our field research together and examine how the system might respond to hypothetical scenarios.
To learn more about the Black Rail, join us on February 18th.
- Author: Lauren Hallett
- Author: Katharine Suding
Over the last few years Californians have grappled with how to manage lands during times of both drought and plentiful rainfall. At SFREC and on Central Valley rangelands, one question is whether management that promotes high forage in wet years alters ecosystem resilience in dry years. For example, promoting highly productive grasses is a common goal. While drought years can negatively affect productive grasses, less productive species, particularly forbs like filaree, do relatively well in drought years due to decreased competition. Over the last several years the Suding lab and SFREC crew have been building ever-larger drought manipulations to test how different management practices, and associated species mixes, affect forage across good and bad rainfall years.
In the first iteration of this project, we looked at how grazing practices and rainfall interact to affect forage over dry and wet years. We hypothesized that grazing practices that maintained a diverse mix of grasses and forbs would promote more stable forage across wet and dry conditions. To test this, we first varied grazing intensity over four years within a pasture to describe how grazing alters grass and forb abundances (Figure 1a). Second, we implemented rainout shelters and irrigation over three years to create “dry” and “wet” plots within areas of different grazing histories (Figure 1b). We found that moderate grazing practices maintained a diverse mix of grass and forb species. This mixture better maintained vegetation cover and biomass across rainfall conditions compared to low-grazed areas dominated only by grasses (Figure 2) (Hallett, Stein, Suding conditionally accepted, Oecologia).
In the second iteration of this project, we are exploring how rainfall timing alters grassland diversity and forage production. We hypothesized that early-season drought will alter which species recruit that year, with higher forb abundance in dry falls and higher grass abundance in wet years, whereas late-season drought would reduce overall production. To test this, we have implemented large shelters with roofs that are pulled in place to create early-season, late-season and continuous drought as well as a control (Figure 3). We are finding that periodic early-season drought helps to maintain forb diversity in California rangelands. Working with Dr. Whendee Silver, we are also testing the effect of rainfall timing on nutrient cycling and greenhouse gas emissions. We are finding that previous-season rainfall as well as current season alters greenhouse gas emissions, which may be important for managing rangelands for multiple ecosystem services going into the future.
- Author: Dan Macon
One of the most obvious signs of systemic stress, at least to me, are the water levels in our foothill reservoirs. After the first three years of this drought, we went into last winter with depressingly low water levels in most of our man made lakes. These reservoirs are critical for storing water for irrigation, human consumption, and downstream wildlife habitat. In normal years, they allow us to capture snow runoff and save it for use during the dry summer months. The winter of 2014-2015, however, brought virtually no snow to the Sierra Nevada – and consequently no spring runoff. I thought our reservoirs were low last summer; this summer is even worse. Last weekend, I drove across the Parrotts Ferry bridge over New Melones Reservoir (on the Stanislaus River between Calaveras and Tuolumne Counties). I was shocked to see that the water level had dropped below the old Parrotts Ferry bridge – I'd ridden across it as a kid, but didn't think I'd ever see it again once the New Melones Dam was built. Perhaps even more shocking – I could see the Stanislaus River flowing under the bridge.
Closer to home, the oak trees in Auburn and at the Sierra Foothill Research and Extension Center are starting to turn color as if autumn were already here. When deciduous trees experience extremely dry conditions, they'll often shed their leaves early as a survival mechanism. The blue oaks and black oaks at SFREC are dropping leaves earlier this year than most of us can remember. Some of the trees are in full color; they make the hillsides seem like we're already in October. In addition to turning color and dropping leaves, we've seen more trees dropping entire branches (and some are even falling down entirely).
According to the National Weather Service, one of the strongest El Niños ever measured seems to be shaping up in the Pacific Ocean. Many in the media are reporting this phenomenon as if it's a sure bet – our drought is all but over! Unfortunately, the impacts of El Niño aren't so certain – Northern California is just about as likely to experience dry conditions as wet weather in an El Niño year. I'll believe we're having a wet winter when I'm still wearing my mud boots next April! In the meantime, I'll keep an eye out for additional signs of stress.
- Author: Dan Macon
This year, we have four distinct groups of cattle at SFREC. Each group is part of one or more research projects:
- We have cow-calf pairs that belong to the UC Davis Animal Science Department. These are fall-calving cows. In normal years, the calves are weaned in late May, and the cows are grazed on dry forage during the summer and fall. Currently, this herd is split into 3 groups – older cows with calves, second-calf heifers with calves, and open cows with calves.
- We have bred heifers also belonging to the UC Davis Animal Science Department. These heifers are typically grazed on irrigated pastures during the summer and through fall calving.
- We have outside heifers that are part of a foothill abortion vaccine trial. These heifers will be preg-checked in mid-April. Normally, the open heifers would be kept at SFREC until late May.
- We have steers that are part of a long term adaptive management and targeted grazing research project. Like the heifers, these steers would be kept at SFREC until late May in a normal year.
But this year is anything but normal! After a very promising fall (with normal germination of our annual grasses and near-normal forage growth through the end of December), we are now coping with a fourth year of drought. Since January 1, we've measured just 2.43 inches of precipitation (average for January-March is 11.69 inches). With the lack of rainfall, forage growth has slowed (total production through April 1 was 1400 pounds per acre, which is about 100 pounds less than normal for this time of year). Total production doesn't tell the whole story, however; the pastures that we've grazed since the first of the year haven't recovered as expected (which means we haven't returned to these pastures as expected). My colleagues who have worked at SFREC for a number of years tell me that the vegetation is at least 30 days ahead of schedule – in other words, our annual rangeland looks more like mid-May than early April. All of this means that this week's rain will help in some pastures, but it's “too little, too late” in others. Our peak standing crop (the total amount of forage grown during this growing season) will likely be far below our long term average of 3000 pounds per acre.
Based on this year's reality, we started fine-tuning our drought plan in early March. One of the key steps in our drought planning is to establish a critical date – a date by which we'll make some stocking decisions if we don't receive rainfall. In early March, we decided that if we hadn't received at least an inch of precipitation by April 1, we'd need to start taking action. Here are the steps we're looking at taking in the next 30 days (by May 1):
- Ship the open foothill abortion heifers 7-10 days following preg-check. This will allow us to take as many as 150 heifers off the pastures at SFREC.
- Ship some of the steers (at least those in pastures where feed is not re-growing) by early May. If we do happen to get some late-spring moisture, this would allow some regrowth for next fall. This week's rain may be enough to get us through to the end of May.
- Ship open cows and calves. There are only 13 pairs that fall into this category, but every little bit helps!
- Wean early. Some of the Animal Science calves already weigh more than 500 pounds. Another large group is between 450 and 500 pounds. Weaning the calves now and shipping them off SFREC, will reduce the nutritional demand on the cows, and will reduce the forage demand (both from cows and from big calves) on our rangeland.
For more information on long-term weather and forage production trends in the Sierra Foothills click here. If you are interested in getting more information managing through low rainfall/forage years SFREC has a number of videos and publications that explore this topic.
To get more information about how producers can benefit from forage production data, click here.
- Author: Megan G Osbourn
As precipitation more frequently departs from the historical range of variability, maintaining stability in forage production will be a critical management priority in Californian rangelands. A key mechanism that can lead to stability in forage production is compensatory dynamics, where plant functional groups respond differently to climate fluctuations (e.g.,taprooted forbs like Erodium tolerate drought, annual grasses are highly productive in non-drought conditions).
Researchers hypothesize that trade-off among functional groups should buffer the response of overall forage production to climate variability and better retain soil nutrients in dry-wet up cycles. The specific objectives are to: 1) quantify relationships among the fate and retention of nitrogen, soil moisture dynamics, and species compensatory dynamics in drought and non-drought conditions; and 2) incorporate these relationships into process-based models of nitrogen retention and forage production in rangelands.
This project will ultimately lead to more informed decision-making for ranchers interested in optimizing forage production and nutrient retention in the face of a highly variable future climate. It addresses an often overlooked but critical component to the stability of ecosystem processes: functional diversity of forage groups.
Researcher, Lauren Hallet explains the preliminary progress of this project in detail in the below video. Stay tuned for more information as samples are taken this spring.
Principle Investigator: Dr. Katherine Suding, ESPM, UC Berkeley