THE AUTHORS 



ROGER D. HUNGERFORD is a research forester 

 at the Intermountain Research Station's Forestry Sciences 

 Laboratory in Missoula, MT. His current research includes 

 forest micrometeorology and forest ecology. 



RONALD E. BABBITT is an electronics technician at the 

 Intermountain Station's Forestry Sciences Laboratory in 

 Bozeman, MT. His duties included development of instru- 

 mentation for environmental monitoring. He is currently 

 working on systems to monitor logging operations and to 

 measure ground water. 



RESEARCH SUMMARY 



Timber harvesting and residue reduction practices that 

 alter shade, surface thermal properties, and moisture influ- 

 ence energy balance and heat transfer on the site, signifi- 

 cantly influencing temperatures. Because the problems of 

 mortality to seedlings due to high temperature and insuffi- 

 cient moisture are potentially widespread and expensive, it 

 is crucial to be able to identify problem sites during the 

 planning process. 



Following alternative overstory removal and residue 

 reduction treatments at three location's, ground surface 

 temperature maximums increased and minimums declined 

 significantly as the amount of overstory removal increased. 

 Potentially lethal high temperatures (>133 °F) occurred fre- 

 quently on all sites, while potentially lethal minimum tem- 

 peratures (<25 °F) occurred on two sites. Potentially lethal 

 temperatures occurred more frequently under treatments 

 involving greater overstory removal. Similar relationships 

 between treatment intensity and maximum and minimum 



temperatures were observed among alternative surface 

 conditions resulting from residue treatments. In general, 

 maximum and minimum temperatures of burned and litter 

 surfaces in clearcuts were not different, but mineral soil 

 surfaces were significantly different from the litter surfaces 

 under a shelterwood cutting. Temperatures of a chip sur- 

 face included maximums significantly cooler than that of 

 burned and litter surfaces. Observed mortality of planted 

 seedlings on study sites was consistent with the pattern of 

 potentially lethal temperatures measured on the units. 



Clearcutting significantly increased soil temperatures at 

 depths to 16 inches compared to the uncut treatment. 

 Humus temperatures in a shelterwood were intermediate 

 between the clearcut and uncut treatments. Surface con- 

 dition also significantly altered temperatures at 2 to 

 16 inches deep. Average temperatures under burned, litter, 

 and chip surfaces were all different; those under burned 

 surfaces were warmest and those under chips were 

 coolest. In general, the pattern of treatment differences in 

 the soil is the same as at the surface. Overstory treatment 

 did not influence air temperature. 



If high temperatures or frosts are expected on a site, 

 varying the amount of overstory removal or providing 

 shade by leaving more residues on the surface may re- 

 duce the potential for seedling mortality. Scarification of 

 the surface to provide for a mineral soil seedbed will also 

 reduce the potential for high temperatures and, thus, seed- 

 ling mortality. It is important to be aware of the thermal 

 properties of the surface materials and understand the 

 consequences of leaving plant litter, branches, charcoal, 

 loosened soil, and other materials on the surface. Where 

 the potential for frost pockets exists, cutting units should 

 be laid out so cold drainage is not blocked. Overstory 

 canopies can be effective in reducing the occurrence of 

 midsummer frosts. 



The use of trade or firm names in this publication is for 

 reader information and does not impiy endorsement by the 

 U.S. Department of Agriculture of any product or service. 



March 1987 



Intermountain Research Station 

 324 25th Street 

 Ogden, UT 84401 



