Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Forestry, Wildlife, and Fisheries

Abstract

Prescribed burning for hardwood control in young southern pine stands has been limited by inability to predict the safety and efficacy of burns of specific intensities. In this study I quantified the effects of various fire intensity levels on girdling, scarring, and subsequent-year growth response of loblolly pine (Pinus taeda L.), water oak (Quercus nigra L.) and sweetgum (Liquidambar styraciflua L.) saplings between 3 and 10 cm diameter at ground line (dgl). Two hundred saplings of each species in four dgl classes were treated at five fire intensity levels, 0, 36, 64, 80, and 98 kJ/s/m, with a propane-fueled backfire simulator during winter 1985. The following variables were measured and tested for inclusion in logistic regression models of probability of girdling: temperature exposure (area under the temperature x time curve, $\sp\circ{\rm C}\ast{\rm s})$ at four locations around the base of the trees, maximum temperature outside bark, duration of lethal temperatures, dgl, diameter at breast height (dbh), bark thickness, bark moisture content, air temperature, bark temperature, and relative humidity. Mean temperature exposures varied between 4,960 and $60,460\sp\circ{\rm C}\ast{\rm s},$ mean temperature maxima ranged from $139\sp\circ$C to $718\sp\circ$C, and mean lethal temperature durations varied from 141 s to 275 s, depending on propane flow rate and thermocouple position relative to wind direction. Of 200 trees in each species, 10 loblolly pines were girdled (out of 35 scarred), 98 water oaks were girdled (143 scarred), and 95 sweetgums were girdled (142 scarred). Logistic regression models I developed from these data to predict girdling in 3-10 cm dgl stands of loblolly pine, water oak, and sweetgum by backfires with fire intensities of 0-98 kJ/s/m are: (1) Loblolly Pine. P$\sb{\rm p}$ = (1 + e$\sp {-(5.1302-0.4361({\rm dgl})+0.00021({\rm mte}))}$) $\sp{-1}$;(2) Water Oak. P$\sb{\rm o} = $ (1 + e$\sp{-(-0.9480-0.0653({\rm dgl})+0.00019({\rm met}))}$) $\sp{-1}$; (3) Sweetgum. P$\sb{\rm g}$ = (1 + 3$\sp{-(2.3597-0.0901({\rm dgl})+0.00030({\rm mte}))}$) $\sp{-1}$; where: P$\sb{\rm p,o,g}$ = Probability that an individual stem of loblolly pine (P$\sb{\rm p})$, water oak (P$\sb{\rm o})$, or sweetgum (P$\sb {\rm g})$ will be girdled; dgl = stem diameter (mm), 3 cm above mineral soil; mte = mean temperature exposure based on four thermocouple measurements at the base of the stem, $\sp\circ{\rm C}\ast{\rm s}.$.

Pages

116

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