During the "silvopasture day course" trainings last August, we expressed the need to reduce forest stand stocking levels to about 60 sq. ft./acre of basal area (approximately 50% relative density, depending on the stand type) in order to achieve "good" forage productivity of the more shade tolerant cool season grasses. For more information on this, refer to the .pdf file attachment titled "Creating Quality Silvopastures" from the August blog post on the day courses - or read the section on thinning in the "Guide to Silvopasturing in the Northeast", available at: www.forestconnect.info (publications page).
With that said, a forester member of this forum noted that in some of the recently posted pictures the silvopastures appear to have been thinned signficantly below 60 ft2 of basal area/acre. The reason that these silvopastures were thinned more heavily (~ 25 to 50 ft2/acre) is because they were understocked with trees of good vigor, value and quality that were worth leaving (foresters refer to this as "acceptable growing stock", or AGS). In each of these areas, a decision was made to remove all "unacceptable growing stock" (UGS) - or trees that had no hope of producing more than firewood or pulpwood now or in the future. Consequently, only AGS were left, opening up the silvopasture more than might be necessary to simply achieve acceptable forage growth.
Even though it might seem logical to remove all trees that don't have sawtimber potential (current or future) to allow even greater levels of sunlight to reach the ground, there are a number of reasons why we may want to retain higher stocking levels - even if it means leaving some UGS. Examples include: to reduce epicormic branching, sunscald or thinning shock on crop trees (AGS), reduce incidence of windthrow, to hold excess firewood/pulp trees until a more appropriate opportunity to harvest, or to reduce overall thinning costs or workload. Shading is also another very important benefit that trees provide to grazing livestock in silvopastures, so we want to leave enough shade - even if the trees don't necessarily fit our criteria for AGS.
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