Why Tree Shade is Critical for Grazing Animals
Animals, like people, have a zone of thermal comfort, beyond which it is difficult to thrive. This narrow window of temperatures — known as the “thermoneutral zone”— varies depending on species, age, breed, and relative humidity, but generally does not exceed 77 degrees F for most livestock. In a warming world, summer highs will continue pushing the boundaries of this window of tolerance, threatening animal welfare, productivity and farm income. To mitigate these losses, producers are looking to trees: the protective shade they cast, the fodder they provide, and the economic and ecological benefits they offer the landscape. A widespread resurgence of silvopasture– the ancient practice that integrates trees and livestock– is underway, as farmers and ranchers recognize the need for shade in the landscape.
The Importance of Shade and Wind Protection for Grazing Animals
Animal scientists estimate that heat stress will result in $39.94 billion in losses per year by the end of the century, compared to $2.4 billion in annual losses incurred at present (Thornton et al, 2022; St. Pierre et al, 2003). From California to India, producers self-report 15-30% declines in dairy production during the sweltering summer months, and even in some cases livestock dieoffs from heatwaves. With global average temperatures estimated to rise by 3.6 degrees F above pre-industrial averages by the end of the decade, that old adage – “the best time to plant trees was 10 years ago, the second best time is now” – takes on new heft.
But do the benefits associated with trees justify the costs? For many silvopastoralists, the answer is a resounding yes. In general, trees improve productivity through:
Reduced Heat Stress: By intercepting solar radiation, shade can reduce heat loads on cattle by 30% (UK). Reductions will depends on the Temperature Humidity Index (THI) of your region, which can be gleaned here [link to article], and the percent effective shade provided by trees.
Increased Weight Gain and Milk Production : Studies suggest that shade can increase weight gain by 1.25 lb per day for cows, 0.41 lb per day for calves, and 0.89 lb per day for steers. Similarly, cows with access to shade produce 9lb more milk per day than cows without shade (Higgins et al, 2024).
Wind and Cold Protection: By providing wind protection, trees also increase cattle weight gain by an estimated .24 lbs per day, cutting the direct cold effect by 50 percent or more while reducing wind velocity by up to 70 percent (Smith et al, 2021; USDA, 2008). Interestingly, integrating conifers into a silvopasture system can also potentially extend the grazing season by increasing ambient air temperatures (Feldhake 2002).
Improved Fertility: Research from Florida and Missouri suggests that cows with access to shade access conceive at 20-40% higher rates than their heat stressed counterparts (Higgins et al, 2024).
Improved Forage Production and Quality: Contrary to the popular belief that shade decreases forage production by intercepting sunlight, many cool season grasses perform better in dappled summer shade. University of Missouri’s Center for agroforestry writes that “fescue and orchardgrass production has been shown to be greater under a 35-year old walnut canopy than in open pastures.” The silvopastoralists at Trees for Graziers describe a “goldilocks zone” of shade – around 55% – that actually improves forage growth during summer slumps by letting morning dew seep into the otherwise drought-stressed pasture.
Animal Health: Reduced veterinary bills are another ancillary benefit of shade. As animals adapt to heat stress, immune function is lost, making animals more susceptible to disease (Edwards-Callaway et al, 2021). Though few studies examine this in detail to our knowledge, we’ve heard growers report reductions in pink eye when their herd has access to adequate shade.
The Role of Tree Crops in Providing Shade
Before diving into the nitty gritty details of silvopasture design, aligning your goals with the holistic context of your farm is a critical first step. For many silvopastoralists, shade provision for improved animal welfare and productivity is a common goal. Secondary goals might include stockpiling feed for winter, revenue diversification though tree crops, fodder production, and even improved forage growth during hot, water-limited summer slumps.
If your primary goal is shade, it’s important to remember that not all shade is created equal. In general, cattle prefer shade from trees to artificial shade, as trees enable better airflow beneath the canopy and evapotranspirative cooling through their leaves, which further reduce surrounding temperatures. In exposed pastures, cattle are notorious for congregating beneath the single tree in the field, causing soil compaction, nutrient imbalances in the pasture, and even tree death. This means designing silvopasture with shade distribution and movement is critically important. The placement and growth habit of trees will influence these factors, therefore the goal of tree placement and species selection should be to distribute shade (and nutrients) evenly across the pasture, and to optimize forage production during summer slumps.
Ideal characteristics for silvopasture trees include:
An open canopy, late leaf-out, and early leaf-drop, which maximize light penetration to the forage understory;
Deep root structures and drought tolerance, which reduce competition with forages;
And production of additional products for human or animal consumption, be it nuts, fodder, timber, or fruit.
There is no perfect silvopasture species, so silvopasture designers often combine species in diverse planting mixes to achieve their goals.
Trees species to Optimize Shade
Black Walnut: Tall growth means shade moves more across the pasture. The late to leaf out, open canopy allows for dappled shade that optimizes cool season forage growth, while its deep root structure reduces competition with grasses such as orchardgrass, Kentucky bluegrass, and tall fescue, which are unaffected by juglone, the allelopathic compound produced by walnut tissues (Johnson, 2011). Walnuts can be harvested for human consumption, integrated into value added products like nocino, or harvested for timber (black walnut is among the highest value timber species in the US).
Honey Locust: Like black walnut, the tall growth habit and open, late-leafing canopy provide optimal shade and shade movement within silvopasture systems, increasing cool season forage production and cattle movement within a paddock. The deep root structure and drought tolerance of this species also means it competes less intensively with forages. Accordingly, research has demonstrated increased forage production and forage nutritive value in honey locust silvopasture (Johnson, 2011). A masting species, the trees produce sugary pods – approximately 40-150 lbs per tree (Gold, 2019) – biennially in autumn that can serve as a stockpile of winter feed, reducing supplemental feed costs.
Black Locust: Related to the honey locust (sans pods, but with nitrogen fixation as an added, confirmed benefit), black locust is known for its fast growth rates and adaptability to a wide range of soils and environmental conditions. Dappled shade through the porous canopy, late-leaf out, and timber revenues make this another high value species integrated into a silvopasture mix. Brett Chedzoy of Cornell Cooperative Extension writes that locust is one of the best silvopasture species on his 500 acre grazing operation.
Other trees often integrated into silvopasture mixtures include persimmon, oak, apple, willow, poplar, and mulberry.
Year Round Benefits: Trees for Wind Protection
Protection from cold and wind in the winter months is another benefit of silvopasture, though trees planted explicitly for protection vary from those planted for shade.
A dense planting of fast growing deciduous trees like poplars and black locust (which can be thinned for posts) or densely planted shrubs such as willow and mulberry (which can double as fodder) make for a decent windbreak, but integrating conifers makes for better year-round protection. If combining conifers with deciduous species, Virginia Tech recommends planting a row of conifers on either side of the hardwood block (Fike et al, 2023).
An interesting emerging option that stacks the benefits of year-round wind protection with the cost savings and nutritional improvements of fodder is river cane, a group of native woody grasses endemic across the Eastern US. Trees for Graziers writes that canebreaks “formed the backbone of grazing in the south for generations until it was cleared for cotton and other crops,” (TFG Species Profile 2023) though its resurgence since this systematic removal is only just beginning.
Case Studies
Most research into the benefits of silvopasture focus on cattle and sheep, though other species including poultry, goats, and hogs can benefit from the shade and protection offered by trees. Our farmer partners at Handsome Brook Farms, a US leader in pasture raised eggs, worked with our team to implement silvopasture in Kentucky, landing on elderberries, chestnuts, persimmons, mulberries, and willows for integration in the pasture. Our team streamlined implementation by leading system design, suitability analysis, site-prep, planting, alongside other services. We’ve designed and planted out acres of silvopasture from the Northeast to the Midwest, including fodder, shade, and windbreak plantings.
Interested in learning more?
Propagate’s Farm Services team supports landowners, farmers, and graziers who are looking to unlock the benefits of shade on their farms. Our team, alongside our network of technical service providers and nursery suppliers, can work with you wherever you’re at in your transition.
Works cited:
Edwards-Callaway, L. N., Cramer, M. C., Cadaret, C. N., Bigler, E. J., Engle, T. E., Wagner, J. J., & Clark, D. L. (2021). Impacts of shade on cattle well-being in the beef supply chain. Journal of Animal Science, 99(2). https://doi.org/10.1093/jas/skaa375
Feldhake, C. M. (2002). Forage frost protection potential of conifer silvopastures. Agricultural and Forest Meteorology, 112(2), 123-130. https://doi.org/10.1016/S0168-1923(02)00058-8
Gold, M. (2019). Species spotlight: Honeylocust. Green Horizons, 23(1), Winter. Center for Agroforestry. Retrieved August 14, 2024, from http://agebb.missouri.edu/agforest/archives/v23n1/gh9.php
Johnson, J. W. (2011). Honeylocust and black walnut tree products within a temperate Appalachian silvopasture (Master’s thesis). Virginia Polytechnic Institute and State University. Defense date: February 4, 2011. Retrieved August 14, 2024 from https://vtechworks.lib.vt.edu/server/api/core/bitstreams/569e1326-96fc-4ca0-838f-a20db2ea2949/content
St-Pierre, N. R., Cobanov, B., & Schnitkey, G. (2003). Economic losses from heat stress by US livestock industries. Journal of Dairy Science, 86(Supplement), E52-E77. https://doi.org/10.3168/jds.S0022-0302(03)74040-5
Smith, M. M., Bentrup, G., Kellerman, T., MacFarland, K., Straight, R., & Ameyaw, L. (2021). Windbreaks in the United States: A systematic review of producer-reported benefits, challenges, management activities and drivers of adoption. Agricultural Systems, 187, 103032. https://doi.org/10.1016/j.agsy.2020.103032
Thornton, P., Nelson, G., Mayberry, D., & Herrero, M. (2022). Impacts of heat stress on global cattle production during the 21st century: a modelling study. The Lancet Planetary Health, 6(3), e192-e201. https://doi.org/10.1016/S2542-5196(22)00002-XUniversity of Kentucky. The importance of shade and water. Retrieved August 14, 2024, from https://grazer.ca.uky.edu/importance-shade-and-waterUSDA National Agroforestry Center. (2008). Working trees: Silvopasture, an agroforestry practice. USDA. Retrieved August 14, 2024, from https://www.fs.usda.gov/nac/assets/documents/workingtrees/brochures/wts.pdf Higgins, S. F., Agouridis, C. T., & Wightman, S. J. (2024). Shade options for grazing cattle (AEN-99). University of Kentucky Cooperative Extension Service. Retrieved August 14, 2024, from https://publications.ca.uky.edu/files/aen99.pdf 