With proper planning and management, trees can provide numerous benefits to our horse properties.
Shade - One obvious benefit of trees is, of course, shade. Just as we humans enjoy shade on a hot day, horses too benefit from this natural, living shelter. Man-made structures such as barns or run-ins can certainly provide shade; however, as prey animals that evolved to see predatory threats in large, open spaces from great distances, horses will often prefer the open shade of trees. Existing trees also provide the benefit over man-made structures of incurring little to no added cost to the farm owner.
While trees can provide excellent shade, this ability is reliant on the age and size of the available trees. A field that provides access to smaller saplings is not a good choice, as horses may be more likely to damage saplings than use them for what little shade they provide. Hence, planting young trees in the hopes of providing shade might not be feasible, as certain tree species only reach maturity at 25, 50, or 75 years of age. If one decides to plant young trees, care must be taken to ensure they are not destroyed by the horses or by natural events. Fencing off the young trees within the pasture, or planting them outside the pasture along the fence line will help protect the trees as they grow. Additionally, it is important to select native species that grow quickly to receive maximum benefit.
Another benefit of shade from trees is lower sugar content in pasture grass. One review paper shows that grasses grown in shade have lower sugar content than those grown in full sun, which can reduce the risk of a horse developing laminitis. This benefit can be utilized by planning some pasture areas located adjacent to an existing stand of trees. Be aware that if given the option, horses may selectively graze un-shaded areas, as horses have shown preference for higher sugar content grasses. However, just as a child may prefer to eat a hot fudge sundae to brussels sprouts, a horse’s grazing preference is not an indicator of better nutritional health. As such, use cross fencing to confine grazing access within these “shaded” areas, and incorporate them into an overall rotational grazing strategy that includes other pastures that receive full sun. The lower sugar content of shaded pastures can also provide a better turnout option for horses with insulin resistance than pastures that receive full sun. Ultimately, you should consult with your veterinarian regarding a proper turnout protocol for a horse with insulin resistance or one that is prone to laminitis.
Environmental benefits - Beyond shade, trees can provide other benefits on your horse farm. Trees play an important role in protecting water quality, especially when incorporated into a riparian buffer strip. A riparian buffer allows for any water runoff from pastures to be naturally processed and filtered, removing excess nutrients—an important consideration given the volume of manure that horses can create as well as the need to periodically fertilize pastures. It is critical that horses be fenced completely out of these buffer strips, but with proper planning they can double as a shade source in pasture areas along fence lines. Your local Soil and Water Conservation District or local Natural Resource Conservation Service agency can provide help and resources when planning riparian buffers and the trees they should contain.
Additionally, trees provide important habitat features to a range of wildlife, but particularly birds and bats. These creatures rely on trees for their habitats, but can also benefit from the manure that horses leave behind. These droppings can contain parasites and provide a breeding ground for flies and other insects, providing a food source to the birds and bats, which in turn help reduce the insect populations in a field.
Concerns and Risks
Reading the above, it can seem that trees provide an ideal natural resource for a horse pasture. However, for all the benefits above, the wrong type of trees – or inadequate management practices -- can present risk to the horses that live amongst them. As such, important factors must be addressed prior to planning a new pasture or paddock, or when managing an existing one.
Toxicity - The first and most immediate concern with trees is toxicity. While the majority of trees are generally safe for horses and from horses, a single toxic tree can have extensive, costly, and sometimes deadly impact on a horse. Below is a list of common toxic trees, with links provided to detail the trees for identification purposes.
- Yew (Taxus sp.). There are several species of yew. Some are native and some were introduced as ornamental species due to the bright evergreen leaves and red berry-like structures that ripen in fall. All parts of the plant are highly toxic.
- Oleander (Nerium oleander). Technically a shrub, but a common introduced ornamental that is highly toxic and worthy of noting due to extensive planting.
- Red Maple (Acer rubrum). A common maple, turning brilliant red in fall. Often planted, but grows wild as a mid and understory tree.
- Black Cherry/Plum/Peach (Prunus spp.). Cherry trees, plum trees, and peach trees all contain cyanide compounds, a deadly toxin. Both native and introduced species are widespread.
- Black Walnut (Juglans nigra). A large growing tree, often associated with wetlands. Produces fragrant nuts that are good for humans to eat, but all parts of the tree are toxic to horses.
- Black Locust (Robinia pseudoacacia). A mid to large tree, often growing in recently cleared areas, that is covered in sharp thorns and produces white flowers in spring.
- Horse Chestnut (Aesculus hippocastanum). A large introduced tree, producing glossy brown nuts that emerge from spiky green seed capsules.
- Acorns/Oaks (Quercus spp.). Oaks vary widely in average size, leaf shape, and range of growth. Of primary concern are the acorns, leaves, and buds, which are toxic to horses.
- Russian Olive (Elaeagnus angustifolia). A highly invasive, non-native species, introduced for ornamental purposes, due to its silvery-green leaves and fragrant flowers.
This list is by no means exhaustive, but serves to highlight common trees that present a threat. Several sites include full lists of toxic trees -- and plants (TheHorse.com, ASPCA, NCSU). Any toxic trees should be removed from pastures or any other area where a horse can have unsupervised access. Tree removal services can provide help in determining the safest, most effective way to remove any toxic trees from an existing pasture, and proper planning of a new facility can work to avoid existing stands of toxic trees and to ensure that any planted species are safe. Additionally, some of these trees are valuable commercially for timber or ornamentals, so well grown specimens might be able to be harvested for other uses, which a local forester can assist with.
Aside from the risk of ingesting toxic tree material, there are also concerns with the overall health of the trees in a pasture. Trees should be monitored for signs of rot and weakened areas, which might result in a branch falling in even a gentle breeze or mild storm. Old trees and/or branches should be removed to ensure that they do not present a falling hazard.
Girdling - Horses can easily strip bark from trees, and if the damage is extensive enough, this can kill a tree through girdling. This occurs when the cambium and xylem, the “transport tubes” for the tree, are severed, which cuts off the leaves from the roots. The risk is worst for younger saplings, but if the damage is consistent and extensive, even the oldest tree can be dispatched through investigative chewing. Any new plantings within a field should be fenced off for protection, as should any trees showing signs of abuse. Fencing should be placed far enough from the tree to keep a horse from reaching the tree with its neck, and added distance is ideal for very young trees that need their leaves and branches protected.
Impacts on grass growth - Similarly, while shade-grown grass has benefits we highlighted earlier, too much shade might result in poor grass growth or even stand loss from too little sun or rain. Be aware that some grass varieties will perform better in shade. Orchardgrass is one example – whose name derived from its ability to grow well under trees. When seeding in shaded areas, select shade tolerant grass types such as orchardgrass. Occasional thinning of trees and removal of falling leaves and pine needles will aid in grass growth.
Certain trees may also negatively impact local soil chemistry with respect to suitability for grass to grow. If your grass is looking thin in areas around trees, it could be due to the soil chemistry, and could be worth testing to determine if a nutrient deficiency or acidification event is preventing grass growth.
Soil compaction - Finally, if only a single or a couple of trees are the source of shade for the horses, soil compaction is a risk if horses crowd the base of the tree(s), and will result not only in killing the grass, but impacting the health of the tree as well. Providing multiple shelter options can help reduce stress on these areas.
Keep in mind that, as a general rule of thumb, horses are more likely to negatively impact, or be negatively impacted by, trees under scenarios in which a horse is bored, such as when grass or hay grazing is not available, or when horses are kept in isolation from each other. Horses and trees co-located in smaller confined areas such as a dry lot also present a greater risk and should typically be avoided. Even under optimal conditions, however, fallen leaves and seeds can be ingested accidentally as part of regular grazing.
In conclusion, trees provide a wide array of benefits to a pasture, as a potentially free source of shade, beneficial wildlife habitat, and water filtration. However, care must be taken to ensure that such trees are not toxic or hazardous to the horses that live amongst them, and that the trees are in turn protected from curious nibbling. Hopefully, with the above resources, you will be better able to plan and manage your pastures through the use of existing trees, or with addition of planted trees, to keep your horses and the environment happy and healthy.