Green Horizons

The research program at the University of Missouri Center for Agroforestry (UMCA) consists of eleven research clusters, which bring scientists, collaborators and faculty together in focused, collaborative studies. The Silvopasture Cluster conducts experiments at the University of Missouri Horticulture and Agroforestry Research Center, New Franklin; the Wurdack Farm, Cook Station; and the Beef Research Farm, Columbia. Focus areas include the response of cattle and trees in pastures with planted trees, extending the grazing season with early/late season forages and the influences of management-intensive grazed cattle upon forages and trees. In this article, UMCA collaborators and staff share preliminary information gleaned from current studies and plans for future silvopasture research projects.

Silvopasture is the intentional combination of trees, forage and livestock managed as a single integrated practice. In a typical silvopasture practice, perennial grasses and/or grass-legume mixes are intentionally combined with trees to create unique livestock pastures in one of two ways: (1) between established rows of trees or (2) in appropriately managed natural forests. The proper integration of trees and pasture allows for the management of light and moisture, critical factors related to forage production. The trees not only provide a long-term investment in nut crops or a timber harvest, but also provide the animals shade in the summer and shelter in the winter. In turn, the forage base provides feed for beef cattle which ultimately provides livestock sales for short-term income. A silvopasture practice diversifies farm income, minimizes the need for chemical or mechanical vegetation control and can reduce hay and feeding costs for livestock. (Note: Allowing livestock to graze in a natural woodland area without tree and forage management is not considered silvopasture. Unmanaged forest grazing is never recommended.)

Cattle graze among white oak in a thinned forest with a select forage established. In the background is a unthinned forest from which cattle are excluded. (Research on University of Missouri Wurdack Farm)

Resolving Silvopasture challenges by Rob Kallenbach
Silvopastoral management creates an environment where trees, forage, and livestock can be developed to their full economic potential. Ideally, the tree species selected for a silvopastoral practice should be marketable - this includes both the wood itself and other products such as nuts or fruit, offering another source of income in addition to livestock. In a rotational grazing system, a successful silvopastoral practice requires understanding forage growth and managing the timing and duration of grazing to avoid browsing of young tree seedlings and specifically, their elongating shoots. Precautions should be taken, such as adding fencing, to prevent trampling or rubbing of the young trees as well as over-grazing and soil compaction.

Potential of Silvopastoral Prac-tices in Beef Grazing Systems by Monty Kerley
The primary focus area of silvopastoral research has been the use of forage for hay production or grazing, with a twofold emphasis: the effects of the forage on tree growth, and the effect of the tree on forage growth and nutritive quality.

Silvopasture research indicates that managed forage production (whether used for hay or rotationally grazed for pasture) has little effect on tree growth, while continuous grazing has been shown to reduce tree growth. As expected, new or young tree plantings have little consequence on forage production since they have little impact on light intensity reaching the forage plant. However, when light intensity is altered due to the tree canopy, forage growth and nutritional quality can be affected. Many cool season grasses and legumes show growth that is not reduced when grown in partial shade and their nutritional quality (crude protein content and digestibility) is improved longer into the summer. The extrapolation of these data show that forage quality is better longer into the summer grazing season when forage is grown under shade, as in a silvopastoral practice.

With more than 13 million acres of pasture lands dedicated almost entirely to beef production, Missouri is in a position to greatly benefit from the economic and environmental benefits of silvopasture. While silvopasture seems like a natural choice for many producers in Missouri, growing perennial forages for livestock pasture with trees requires careful matching of tree, forage, and animal species. Interactions among all three of the biological systems must be in concert with each other to make the system work. For instance, if the system is not managed well, competition from many forage species reduces tree growth. This is most likely to be a problem in the early phases of tree establishment. Later in the production cycle, the opposite can be true, where shading and competition from trees can reduce forage growth and thus, livestock feed. Another problem that producers observe is that when young trees are not protected from livestock, the trees can be damaged, reducing growth. Still another challenge in silvopasture is that the allelopathic compounds produced can inhibit the growth of susceptible forages and/or trees. Sounds like a lot to worry about, doesn’t it? In reality, these challenges are very manageable and are overshadowed by the benefits of the practice.

Silvopasture in a managed forest. When thinning a forest to establish the silvopasture practice, or planting trees in a pasture, always remember tht light will drive forage production.

There has been little research conducted studying the effect of silvopastoral practices on the grazing animal. Specifically, what are the effects of a silvopastoral practice on reduced heat stress in the summer and reduced cold stress in the winter? Cattle typically seek shade in the summer to alleviate the heat load created from exposure to direct sunlight. Likewise, cattle seek windbreak shelter in the winter to reduce the additional cold stress caused by wind. This can be particularly important for cows that are calving where the need is to reduce the cold exposure on the newborn calf. For these reasons, there are few pastures that don’t provide access to some form of tree structure that offers shelter. While most pastures provide access to such shelters, almost none of these shelters are managed to provide maximum benefit to the animal, the tree and the forage. It is our hypothesis that silvopastoral practices could be implemented to provide the shelter component to the grazing animal, while simultaneously managing the timber to increase its value and shelter functionability and the forage for grazing and soil cover.

It is our plan to implement silvopastoral practices at the University of Missouri Beef Research Farm in Columbia, Missouri, to study the effects of silvopastoral practices on grazing animal production. Research will be implemented by converting existing unimproved timber to silvopastoral practices and by incorporating tree plantings into open pasture. In addition, we plan to position the silvopastoral areas to facilitate animal waste deposits in the grazing area, specifically emphasizing the prevention of uneven distribution of waste in the pastured area, thus preventing the deposits from being near points of erosion or water movement. This research is expected to provide us data not only on the tree - forage interaction, but also on the animal interaction with the tree and forage components.

Silvopasture on the Wurdack Farm by Dusty Walter
To produce multiple products from a single land area, as in a silvopasture practice, it is necessary to match plant species to both landowner goals and the ability of a specific site to grow a tree or forage species. When planting 10trees to a pasture, or managing and thinning a forest, select and favor trees recommended for that site.

Arguably, the most important interaction between the tree and the forage crop is the trees’ direct influence on the light available for forage growth. This can be controlled by selecting appropriate tree species and spacings. For example, tree species such as black walnut have a leaf configuration that allows for a filtered light to pass through and will produce less shade than a white oak. Under forested conditions, we often find trees growing offsite. By this we mean that the tree is not growing on a site where we would expect it to perform best. If the appropriate tree species are selected for your site and soil, you are then free to manage spacing between your trees in order to create the best shade/light environment for forage production and livestock benefits.

Rotational pasture management is always recommended in the silvopasture practice. When establishing trees into existing pastures, space tree rows to allow for their growth and development. In this photo, the rows of trees are 30 feet apart.

One of the best examples of hardwood silvopasture is located on the University of Missouri Wurdack Farm in south central Missouri. This is the third year since the establishment of an experimental silvopasture practice in an Oak-Hickory forest type. To establish the silvopasture, we chose 25 acres of forested land on north-facing slopes, then thinned the forest to approximately 50-percent light/shade levels and seeded appropriate cool-season forages (Kentucky 31 Tall Fescue, red clover, annual lespedeza). Proper forage management allows us to identify the effects that controlled grazing of cattle may have on tree growth. When implementing the thinning, we applied a slightly modified version of a practice known as crop tree release (CTR). In CTR, emphasis is placed on selecting the best trees on a given site and thinning/removing all other competing trees around them. We also designed removal of competition based on the crown size of each crop tree, resulting in 40-60 percent shade. White oak was favored on the sites.

A great deal of skepticism exists on the impact controlled grazing may have on the remaining trees. Critics of this practice have some valid concerns. In the past, continuous grazing of, and access to, woods by livestock was shown to have a very negative impact on soil erosion and the regeneration (seedlings) of the forest. However, at this time the use of management intensive grazing (rotational grazing) has resulted in a forage stand that is continuous, and we have not seen any erosion problems. Additionally, we are not relying on natural reproduction (which in many unmanaged forests is lacking to begin with), but have planted improved white oak seedlings and placed a welded wire cage around each of them. This allows us to place seedlings in selected locations (looking toward their future shade value) and helps assure their survival and growth by providing protection from livestock and deer browsing.

Although the final numbers have not yet been calculated, we hope the Wurdack Farm will illustrate the advantages a properly managed silvopasture practice can provide to Missouri land and livestock owners. We fully expect that the enhanced growth of the high value white oak trees remaining following our harvest/thin, in conjunction with regular forage and beef production, will provide long-term positive income to the farm.

University of Missouri Center for Agroforestry (UMCA) collaborators Rob Kallenbach, associate professor, Agronomy; Monty Kerley, professor, Animal Science; and Dusty Walter, UMCA Research and Technology Transfer Specialist