Forage production under thinned Douglas-fir forest
In the Pacific Northwest, trees may take up to 60 years to mature for harvest. This ties up land for other commercial purposes. Depending on tree species, commercial thinning opens up the tree canopy to reduce competition among trees. In Douglas-fir forests, commercial thinning reduces the tree density per acre from 450 to 200. Under the trees, the space created by thinning allows desirable forages for livestock to thrive. These forages can be invigorated by applying nitrogen in early spring and the resultant feed used for grazing or hayed to support livestock. This study investigated how much forage could be produced under 25-year old and 55-year old Douglas-fir thinned forest when fertilized with nitrogen (N) at 75 lbs/acre in early spring. Cumulative forage dry matter yields averaged 2.14 and 1.27 tons/acre for forages growing under 25- and 55-year old trees, respectively. Cumulative forage grown on open space with similar treatments yielded 4.15 tons/acre dry matter which is 27% higher than estimates from the USDA soil survey of 3 tons/acre in similar soil and climatic conditions. Currently, animal stocking rate is one beef cow/calf to two acres. If woodland owners adopted silvopastoral systems like this one, a new animal stocking rate of 4 and 6.5 acres per cow/calf unit under the 25- and 55-year silvopastoral systems respectively, is recommended. This, however, will depend on location and aspect of the land. Using thinned forestland for forage production is another way to diversify agriculture and increase income for forest landowners.