Author: Sam Angima
Publish Date: Winter 2007
Agroforestry combines agriculture and forestry technologies to create a more integrated, diverse, productive, profitable, healthy, and sustainable land-use system that is especially beneficial to the small scale farm. In the Pacific Northwest, the best combination integrates woody perennials like conifers and hardwoods with improved forage species and pastures for grazing animals in what is called silvopasture. Sheep or goats are most suitable due to the quantity of forage biomass available with time as the trees mature. Since forests take longer to mature, adoption of this technology can increase profitability, reduce overall risk, and increase environmental benefits from overall land management.
Most people who want to practice silvopasture usually start by asking which species of trees are suitable for the technology to work. Virtually all trees can work, but the linear arrangement of these trees will vary. Douglas fir, ponderosa pine, red alder, black walnut, black locust, maple, cherry and poplar can be used depending on your local ecology and climate. For forage species, orchard grass, tall fescue and perennial rye along with legumes such as white clover and subclover in a mixed pasture system work very well. The clovers provide high quality feed plus needed nitrogen for the grasses. At the same time, adjacent trees benefit from this nitrogen, often maturing quicker than conventional forest systems. In deeper soils, tall fescue and white clover are better choices to extend growth throughout the season when competition for moisture is strong during the drier months; whereas, orchard grass and subclover are better choices than perennial rye grass for shady conditions. For dry sites, perennial ryegrass and subclover are preferred, although total forage yields are lower.
If you are interested in starting this silvopasture system, you might ask which ones should I plant first; the trees or the forages. It will be more meaningful to plant trees into existing or recently seeded pasture so that you start with a known good stand of preferred pasture species. Due to variations in available moisture for tree use, it is advisable to have 20-30% of the planting area be weed free for the first 3-4 years of starting this system especially on drier climates. This is equivalent to a vegetation free zone of 4-6 feet wide around the tree seedlings.
The tree pattern or design sets distinguishes agroforestry practices from conventional forestry. On most commercial timber farms, trees are planted 300-600 trees/acre, thus taking care of loss due to death and commercial thinning. However, in silvopasture systems, trees are planted at lower initial densities of 200-300 trees/acre, and in this case, all the trees are nurtured to grow to maturity or harvest time.
A grid pattern is used where you maximize competition between trees and ground vegetation but minimize competition between trees. Trees are arranged into single rows or multiple rows/clusters so that wide open alleys (dependant on size of your farm equipment) for forage production are created to allow grazing, haying, fertilizing, spraying, and hay harvesting. Grouping trees into double rows or clusters creates a local forest effect enhancing growth that produces good quality timber. Usually tree species such as Doug fir trees are combined with hardwoods to take advantage of their different growth habits and nutrient requirements.
When you finally introduce livestock, there is a high chance of trees being browsed by animals. This does not kill the tree but will slow growth, especially conifers that have a strong terminal leader. At this time, it is advisable to hay the forage for the first 1-4 years to give trees a chance to root and develop. However even after the initial years, it might be a good idea to protect your seedlings with a mesh or solid tube or electric fencing. It is most important to use rotational grazing in a silvopasture system to get good forage utilization and reduce tree browsing.
Lastly, it is advisable to prune trees to increase the value saw logs and reduce tree/pasture competition while improving movement within the system. Pruning the trees also will reduce competition for water resources by the complex system. Studies have shown that tree growth will exceed 10% when forages are managed properly to balance water relationships in a silvopasture system.
[Agroforestry information: Dr. Steven H. Sharrow, Professor, & Rick Fletcher, Professor, Oregon State University]