Something strange is happening to grasshoppers at the Konza Long-Term Ecological Research site in Kansas – they’re disappearing a little at a time. For the past 25 years, their populations have declined 2% per year. That doesn’t seem like much, but as Michael Kaspari, a research professor at the University of Oklahoma says, “It’s like compound interest. You add that up over 25 years and we’re talking about a significant decline in one of the most important insects on the prairie.”
Why are they disappearing? After looking at two decades of datasets for grasshopper population numbers and grass production, along with nutritional analysis of thousands of grass samples from the last 40 years, Dr. Ellen Welti had an answer. The grasses they eat no longer have the nutrition they need to thrive.
In an interview with Brian Grimmett of KMUW news, Welti explains it this way:
“At first, it looks like there’s overall more food availability for grasshoppers. But when we got back the plant chemistry, what we could see is that this increase in plant biomass really corresponded to decreases in the quality of the biomass.”
It’s something known as nutrient dilution and it’s affecting more than just grasshoppers. A twenty-year study by Texas A&M researchers found that forage digestibility and crude protein quality were declining. Their research estimates that it costs producers an additional $1.9 billion annually to meet the U.S. cattle herd’s protein needs with supplemental feeds.
Recent research by the USDA Agricultural Research Service indicates that as atmospheric CO2 continues to rise, future cattle weight gains will decrease by 12.5% or 30 pounds per animal. In addition, over time, this reduced gain could lead to increased time for breeding and/or reduced conception rates.
But isn’t more CO2 good for plants?
When I first published a story about declining forage quality, readers weighed in with their opinions that it wasn’t a result of CO2 but rather a result of poor grazing management. But, while management can impact forage quality, what we’re seeing today is simply a matter of how plants function.
It’s something that scientists have known about plants for a long time. When atmospheric CO2 levels are higher, every time a plant takes in air as part of photosynthesis, it takes in more carbon than ever before. They put all this carbon into their cell walls, which can become thicker and more lignified. That means more plant tissue, so it seems like we have more forage. But, because the nutrients in the soil don’t change, we end up with larger, more fibrous plants.
The limiting factor for ruminants is nitrogen. Their rumen microbes need a certain level of nitrogen (N) to do their job of converting forage into nutrition for the animal. When forage values fall below that level, graziers have two choices – recognize that gains will be reduced, or provide a protein supplement to feed the rumen microbes so they can convert poor quality forage into good nutrition for weight gains. Either choice impacts the bottom line.
Finally, scientists have found that in a higher CO2 environment, leaves become thicker – as much as one-third thicker. As James Urton writes, “This changes the ratio of surface area to mass in the leaf, and alters plant activities like photosynthesis, gas exchange, evaporative cooling and sugar storage.” The result is plants can’t sequester as much carbon as before.
Is there something we can do about this?
I’ll start with the management implications from the USDA ARS research paper on the topic. They focus on using grazing to keep plants in a vegetative state:
“How can livestock managers implement adaptive management strategies to reduce or offset weight gain losses associated with declining forage quality?
Grazed grasses regrow leaves with increased protein and reduced cellulose and lignin concentrations compared to ungrazed grasses in rangelands worldwide, and specifically in the western Great Plains. Thus, given our projections of increased forage production, reduced forage quality, and declining weight gain per animal in the coming decades, a clear solution is for producers in the North American Great Plains, where plants are well adapted to ungulate grazing, is to adaptively increase stocking rates to match forage availability. Increased stocking with increased forage production would maintain the grazing pressure index (and grazing efficiency) at current levels, thereby either maintaining or increasing total mass gain per unit area.”
Because we can’t be sure what a given year will look like, they remind us that stocking rates should be flexible and adaptive to drought and other weather fluctuations. Other strategies they suggest to mitigate declining forage quality include:
Providing protein supplements protein supplements.
One benefit of protein supplements on large landscapes is that they can be used to move livestock across the landscape for better grazing distribution and forage use.
Interseeding with legumes.
We’ve written a lot about this at On Pasture. Here are some resources for you.
Matching graze periods with changes in when plants grow and to encourage grazing invasive plants.
Thanks to the Lilac Network and the National Phenology Network, we know that spring is arriving earlier every year, about 2 weeks earlier on average. The National Phenology Network, predicts spring each year based on a spring leaf index. You can check in at their website for what to expect in your area.
Knowing when spring is helpful to planning early grazing, especially in areas where you’re trying to manage invasive grasses. Here’s an example of that for you.
Patch-burning to manipulate forage quality and livestock grazing distribution
Patch-burning is known for improving forage quality of regrowth and is also an excellent tool for improving wildlife habitat. Here are three On Pasture articles to help you explore this idea more:
More frequent, tactical monitoring of forage quality and quantity to guide stocking rate adjustments and other adaptive management strategies.
One of the quickest ways you can do this without actually sending forage off for analysis is to check what’s coming out of the back end of your livestock. For cattle producers, here’s a manure scoring method from the Noble Foundation.
Nitrogen fertilization of rangeland at rates low enough to avoid invasion of undesired plants
This suggestion – fertilizing pastures – coincides with the information we have about compost as a means of improving forage production while pulling CO2 from the atmosphere and turning it into long-term sequestered soil carbon. This practice is covered in this month’s Grazier’s Focus. To that you can add your own Carbon Farming Plan. And, to scale the practice up to a local region or state, check out ______ for ideas.
To keep up with applied science on climate and grazing, follow the Working Lands Innovation Center. Though they’re focused on California work, practices can be adapted for other regions too. I
You can also learn more about what we know about what’s happening with plants from this summary from Nature. And if you’re interested in how all this might impact the nutritional values of the foods we eat, this piece from Civil Eats is quite good.