|This is the second in a series of newsletter articles which respond to commonly-asked questions about western juniper woodland management and science. For this issue, the question is: What happens after the decision is made to thin or partially cut a western juniper woodland parcel?|
For the purpose of this discussion, it is assumed landowners have already defined their primary objectives (for example, improving wildlife habitat or forage for domestic animals), and decided how the woodland should look once this phase is finished. It is also assumed the landowner has determined the amount and extent of residual grasses and forbs on-site, and whether seeding is needed.
It is desirable, though not critical, that trees are cut in autumn or early winter, so that down material can cover the ground during the first winter. This helps reduce the amount and depth of frozen soil, and should result in better capture and retention of winter snow if the majority of the limbs are disposed of in the manner suggested below.
To Limb or Not to Limb
In most cases, it is important to limb fallen trees, whether they are cut with a chainsaw or knocked over by a bulldozer. Limbs should then be scattered across the site as best you can. Juniper limbs are basically the only material available on-site with which to institute good watershed management principles: Moisture capture (rainfall or snow), moisture storage (subsurface, for example), and beneficial release of moisture (such as at lower temperatures and over a longer period of time).
Specifically, scattered limbs will:
If juniper is simply cut, or pushed over and left in place, it will take two to three years for needles to fall off. During that time, ground vegetation under the cut trees is often shaded too severely to survive, which results in slow recovery of desirable plants. And even though the influence of juniper on the water cycle is reduced, due to less transpiration (water uptake and loss by the tree) and interception, desirable new vegetation may not develop to the fullest extent possible.
Whole Tree Removal vs Removal of Bole Only
If the entire tree is removed (such as might be the case in "whole tree" chipping, or when everything is piled and burnt), nutrient cycling and protection benefits of the scattered limbs will be lost. On sites which have little or no understory, the one opportunity you may have to increase and improve understory vegetation, and protect soil from erosion, will probably be lost, perhaps forever.
Removal of only the tree trunks or boles for firewood, streamside riprap, or commercial products, will probably not significantly impact nutrient cycling. Only 20% or so of the site's nutrients are tied-up in the bole wood and branches, and these do not decompose rapidly enough to be considered available. Harvest or removal layout and timing can also be planned to maintain emphasis on good watershed principles.
Reintroduction of Grazing or Fire
The first priority after cutting and scattering limbs is to promote recovery of residual and seeded grasses and forbs. Before using fire to control remaining young juniper trees and new seedlings, existing perennial grasses should be given sufficient time to develop viable new plants. Time is needed for seed production, germination, and seedling establishment, and for new plants to become reproductive. Good perennial plant cover will also inhibit spread of undesirable annuals. Research is currently being conducted to determine how long we should leave cut juniper limbs in place to ease harsh site conditions.
Once new plants have had an opportunity to become reproductive, resulting forage can be safely grazed. Grazing should be timed to benefit desirable plants. New plants cannot be expected to tolerate season-long grazing.
Just remember, in some circumstances, you can make juniper your friend!
For more information, contact Michael M. Borman, Rangeland Resources Extension Specialist, Oregon State University, (541) 737-1614.