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Individual Highlight

Long-term Thinning Alters Ponderosa Pine Reproduction in Northern Arizona

Photo of Sign at entrance of Fort Valley Experimental Forest where this research occurred. U.S. Department of Agriculture Forest Service.Sign at entrance of Fort Valley Experimental Forest where this research occurred. U.S. Department of Agriculture Forest Service.Snapshot : This study tested the relationship between overstory density and seedling survival in ponderosa pine forests. They used a long-term ( more than 50 years) experiment in northern Arizona to investigate impacts of repeated stand thinning that maintained different growing stock basal areas on early seedling survival, growth, and microenvironment. Long-term maintenance of lower overstory density created favorable conditions for ponderosa pine seedling establishment.

Principal Investigators(s) :
Moser, W. Keith 
Research Location : Northern Arizona
Research Station : Rocky Mountain Research Station (RMRS)
Year : 2016
Highlight ID : 966

Summary

Building upon existing long-term studies in the Taylor Woods of the Fort Valley Experimental Forest, this Forest Service study tested the relationship between overstory density and seedling survival in ponderosa pine forests. The scientists used a long-term (more than 50 years) experiment in northern Arizona to investigate impacts of repeated stand thinning that maintained different growing stock basal areas on early seedling survival, growth, and microenvironment. Seedling survival for the first two years after germination (2013–2015), which had above-average precipitation, was higher than reported in several earlier studies and ranged between 4 percent and 21 percent among all basal areas. Seedling density exhibited a negative quadratic relationship with basal area and was positively associated with litter cover. Growing stock levels that fostered the highest seedling survival and density were those with a low density of overstory trees, low canopy cover, high cone production, coverage of soil by a thin layer of litter, and high soil water content at a depth of 15–30 centimeters (5.9-11.8 inches). Overstory basal area was positively associated with seedling height but negatively associated with seedling diameter. During this relatively wet period, all basal area treatments supported higher average seedling densities than those previously recommended to produce a multi-aged stand or pre-settlement structure in the southwestern United States. Long-term maintenance of low to intermediate growing stock levels over the past 50 years created a favorable microenvironment for early seedling establishment of ponderosa pine. Stand thinning that creates a stage to facilitate future ponderosa pine regeneration in the rare years when sufficient seed production coincides with favorable weather may be warranted. This study provides valuable information that will guide forest managers in incorporating regeneration goals into forest management plans.

Forest Service Partners

External Partners

 
  • John B. Bradford, U.S. Geological Survery, Co-PI
  • Kelsey Flathers, Northern Arizona University, M.S. student and Co-PI
  • Kristen M. Waring, Northern Arizona University, Co-PI
  • Tom Kolb, Professor, Northern Arizona University, PI

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