PART IX — TERRESTRIAL ECOSYSTEMS 



parently, the population of soil or- 

 ganisms recovers rapidly after burn- 

 ing and is associated with the increase 

 in nitrogen. In the top four centi- 

 meters of mineral soil in the South 

 Carolina study, over four grams of 

 nitrogen per hectare per day were 

 fixed in the burned plots while only 

 0.2 grams were fixed in the unburned 

 plots. However, the individual sam- 

 ples from the burned plots ranged 

 from no nitrogen fixation up to 61 

 grams per hectare per day, for rea- 

 sons that were not evident. 



Disease — A survey throughout 

 the South showed less Fomes annosus 

 root rot on burned areas. This dis- 

 ease spreads by growth of mycelia 

 in the forest floor, or aerially by 

 spores from the fruiting bodies. Con- 

 sequently, fire may tend to retard the 

 spread of the disease. 



Use of Prescribed Burning 

 in the Timber Industry 



Prescribed fire has been recom- 

 mended and widely used in the lob- 

 lolly pine range for control of under- 

 story hardwoods, site preparation for 

 seeding or planting, and for fire- 

 hazard reduction. 



Prescriptions for safe burning have 

 been reasonably well developed by 

 research and experience. Favorable 

 conditions are: relative humidity of 

 40 to 60 percent; a wind steady in 

 direction but under ten miles per 

 hour at four feet above ground; and 

 litter moisture content of 5 to 20 

 percent. Burning is safest when these 

 conditions are first reached after a 

 rain of half an inch or more. 



Backfires are preferred for areas 

 with heavy fuel because they burn 

 more slowly and less intensely. 

 Headfires are used where fuel is 

 light. Igniting the entire perimeter 

 of the area is poor practice, since 

 "hot spots" occur where fires from 

 different directions meet, resulting 

 in crown scorching and sometimes 

 killing trees. 



For Understory Control — Because 

 the hardwood understory is a major 

 obstacle to re-establishment of the 

 pine stand after harvest, its control 

 has received a great deal of attention. 

 If hardwoods are allowed to grow 

 unchecked throughout a pine rota- 

 tion, site preparation for regenera- 

 tion is difficult and costly; often 

 requiring use of heavy machinery. 

 Periodic burning during the rotation 

 holds this understory in check, with 

 the burning interval determined by 

 the growth rate of the understory 

 sprouts. A prescribed fire will burn 

 hardwood stems up to about two 

 inches in diameter back to the 

 ground. Thus, the burning interval 

 may range from a few years up to 

 ten years, depending on site quality, 

 overstory density, and the species in 

 the understory. 



Periodic burning for understory 

 control is usually done in the winter. 

 Summer burns are more difficult to 

 control with several years' fuel ac- 

 cumulation, and winter burning usu- 

 ally fits better into the over-all 

 schedule of seasonally determined 

 forestry operations. Winter fires do 

 not kill the rootstocks, so the popu- 

 lation of understory plants is not 

 reduced; in fact, the number of 

 sprouts is usually greater during the 

 first few years after the fire than 

 before. 



In contrast to winter fires, summer 

 fires reduce the understory popula- 

 tion. When the parent stem is killed 

 or cut in the summer, especially near 

 the end of the spring flush of growth, 

 the sprouts are much weaker than 

 those arising from winter-killed 

 stems. Plants that are not vigorous 

 often die. Thus, two or three suc- 

 cessive annual summer fires virtually 

 eradicate the understory. This effect 

 can sometimes be used to prepare 

 loblolly pine stands for regeneration. 

 The first burn is made in winter to 

 lower the fuel level to the ground 

 and make subsequent summer burns 

 safe. Then, two or three summer 

 burns reduce the understory popula- 

 tion and leave a favorable seedbed. 



With an adequate supply of seed, a 

 new stand is virtually assured. 



Prescribed burning for understory 

 control apparently has no detrimental 

 effect on the growth of the overstory 

 pine stand. In South Carolina, even 

 ten successive annual summer fires 

 did not cause any reduction in growth 

 of the overstory. With heavier sur- 

 face soil, or on slopes where more 

 water would be lost through in- 

 creased runoff following burning, 

 growth of the overstory might be 

 reduced. 



For Site Preparation — Fire is also 

 often used after harvest cutting for 

 site preparation. Logging breaks up 

 the litter and exposes mineral soil 

 on an appreciable portion of the 

 harvested areas, but much of the 

 forest floor and the understory re- 

 main undisturbed. Fires for seedbed 

 preparation after logging are most 

 effective in late summer, before pine 

 seedfall, because pine seedlings have 

 an even start with the competing 

 hardwood sprouts the following 

 spring. 



Other benefits are realized from 

 periodic burning. The stand is es- 

 sentially "fire-proofed." Because of 

 greater ease of movement, the costs 

 of timber inventory, tree marking, 

 logging, and timber-sale supervision 

 are reduced. Perhaps more important, 

 the habitat for wildlife, particularly 

 deer, is improved. Without fire, the 

 browse plants grow beyond reach of 

 deer early in the life of the stand. 

 With periodic burning, especially in 

 winter, the browse supply is repeat- 

 edly replenished as the understory 

 is killed back to the ground and 

 promptly resprouts. 



Use Outside the South — Pre- 

 scribed burning has been most widely 

 practiced in the South but is now 

 coming into use in other sections of 

 the country. In the Lake States, it 

 is used as a site-preparation measure 

 for jack- and red-pine regeneration 

 and for understory control in red 

 pine. The effects on vegetation seem 



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