Silviculture and Harvesting Methods
At MRC and HRC, we manage our forestlands with a long term goal of restoring the forest to a well-stocked condition with a large variety of sizes and ages of trees. To that end, neither company uses traditional clearcutting as a harvesting method. All harvested stands retain elements that provide perpetual, multi-aged stand structure, and maintain critical ecological refugia (e.g., patches of retained trees, snags, downed woody debris, and undisturbed soil). Silviculture is the science of managing a forest stand for the establishment, growth, and composition of trees to meet the needs of a particular land manager. There are two major classifications of silvicultural management regimes, even-aged and uneven-aged management, with explanations to follow. You may also view this informative video regarding our Harvesting Process.
Where our forestlands have well-stocked conifer (redwood and Douglas-fir) forest, our foresters maintain the forest in a well stocked condition. Hardwood competition is kept in check naturally with the overstory dominance of the conifers. Any harvest is balanced with growth using various selection silvicultures and harvesting methods. These methods include harvest of single trees or small groups of trees depending on the species, sizes and ages of the trees. Over time, uneven-aged management will develop and maintain a stand of trees with a wide variety of different ages and sizes. Redwood forests grow particularly well using this regime because they can regenerate and grow in some shade.
Single Tree Selection: Single Tree Selection silviculture is used primarily to thin conifer-dominated stands of redwood or Douglas-fir, or very young stands of redwood and Douglas-fir. Redwood (at any age), and young Douglas-fir (up to around 60 years old) will respond well to a stand thinning and “release.” As trees are thinned and the forest canopy is opened around a tree, that tree will increase its annual growth. This increased growth continues until the forest canopy closes again. Periodic Single Tree Selection harvest (every fifteen to twenty years) will maintain steady individual tree growth while allowing for smaller trees to fill in from beneath.
Group Selection: In some areas, especially towards the eastern and southern warmer parts of our forestlands, stands of pure Douglas-fir can be found. Unlike redwood, Douglas-fir cannot successfully regenerate under a heavily shaded canopy. Douglas-fir needs more light to reach maturity. The tree crowns will thin out to a point at which photosynthesis is dramatically reduced. Consequently in pure Douglas-fir stands or areas dominated by Douglas-fir, small group openings are created with Group Selection harvest methods to provide light for growth. If designed correctly, this Group Selection method will maintain a successful stand of uneven-aged trees. Group selection is also used in mixed redwood and Douglas-fir forest stands to create larger openings for regeneration. We also use Group Selection when clumps of tanoaks are located in a conifer-dominated stand. The tanoak groups are managed and the areas are then planted with conifer. Group Selection involves harvest of groups of trees ranging from 1/4 to 2 acres.
Transition: Transition silviculture is a selection system used to develop an un-even aged stand from an even-aged stand with unbalanced or irregular stocking. Transition silviculture involves removal of trees individually or in small groups to create a balance of different stand structure and natural reproduction.
The use of even-aged silviculture and harvesting systems on MRC land is used as a transitional strategy and may still occur occasionally on HRC land where restoration harvests are needed. Once tanoak-dominated stands are restored to redwood and Douglas-fir stands, the need for even-aged silviculture will be limited across both companies.
The California Forest Practice Rules (CFPR) require the Registered Professional Forester (RPF) preparing the plans to designate and describe what cutting prescriptions are to be used in areas proposed for harvest. MRC and HRC use a special silvicultural prescription known as Variable Retention (although the CFPRS consider variable retention to be a special prescription – it is generally classified as an even-aged management technique). Variable Retention methods differ significantly from traditional clearcutting in that the retention left in place ensures meeting our goal of reestablishing multiple age classes. The following even-aged silviculture prescriptions are used by both companies.
Variable Retention: MRC began using Variable Retention as a harvesting method four months after we started in business on the advice of Dr. Jerry Franklin (Professor of Ecosystem Analysis, University of Washington, Seattle, WA) and the Pacific Forest Trust. Variable retention harvesting retains between 10% and 40% of the original stand in both rolling and permanent pockets of retained trees and critical refugia. This 10-40% of the forest that is retained is composed of tanoaks, Douglas-fir and redwood, as well as other hardwood and conifer species specific to the site. This silviculture regime provides post-harvest ecological structure while creating sufficient opportunity to plant and naturally regenerate redwood and Douglas-fir, as well as restore historical conifer dominance to the forestland. Generally, the use of this silviculture is limited to poorly stocked, tanoak-dominated stands which need forest restoration.
Shelterwood and Seed Tree: Much of MRC and HRC lands have been harvested at least once in the last century, some acreage two or three times. In the past, foresters depended largely upon natural regeneration from seed drop verses planting trees to reestablish the conifer stocking following harvest. Towards that goal, a small portion of trees were left behind to produce seed for new stands of trees. This method was intended to be accomplished in steps including re-entry into the stand to remove the residual seed and shelterwood trees. In some cases, regeneration from the seed and shelterwood trees was unsuccessful. MRC and HRC re-enter some of these areas to harvest some of the residual trees and to rehabilitate those acres that did not successfully regenerate with manual planting. Additionally, the younger stands, below the residuals, are often thinned to alleviate overcrowding and maintain healthy growing conditions. In cases of re-entry with Shelterwood or Seed Tree silviculture, trees are always retained across the spectrum of sizes and ages including a percentage of the residual trees.