Competing Vegetation in Ponderosa Pine Plantations

📖 The Scoop

Planted ponderosa pine (Pinus ponderosa Dougl. ex Laws. var. ponderosa) seedlings in young plantations in California are at a disadvantage compared with competing shrubs, forbs, and grasses. In many instances, roots of competing plants begin expanding and exploiting the soil earlier and in greater numbers, thereby capturing the majority of available resources and lowering pine survival and growth. Competition thresholds or "how much is too much?" are: for treatments where a cleared radius is prescribed, no weeds are acceptable within the space needed for maximum growth of pine seedlings during the establishment period; for treatments involving the entire area, crown cover values of 10 to 30 percent seem to be the level beyond which shrub competition significantly affects pine growth. Methods for preparing the site, which include mechanical and chemical methods, use of fire, and combinations of treatments, show the interaction of site and ensuing vegetation. Techniques for controlling competing vegetation from seed include preventing such plants from getting started by use of preemergent herbicides or mats (collars). To prevent sprouting, hardwood trees and large shrubs can be pushed over, thereby getting the root crown out of the ground, or if still in the soil, grinding it out with a machine. Once present, the effect of weeds from seed can be minimized by grubbing or spraying when young, by grazing plants with cattle or sheep, or by introducing plants of low competitive ability. Once sprouting weeds are present, their effect can be minimized by spraying with chemicals, or if palatable, by grazing with cattle or sheep. Costs range from as low as $10 per acre ($25/ha) for aerially applying herbicides to $711 per acre ($1757/ha) for grinding out tanoak stumps.

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