ROOT DEVELOPMENT OF PITCH PINE, WITH SOME COM- PARATIVE OBSERVATIONS ON SHORTLEAF PINE ' By WILLIAM EVERETT MCQUILKIN 2 Formerly field assistant, Allegheny Forest Experiment Station,^ Forest Service^ United States Department of Agriculture INTRODUCTION The development of the root systems of trees constitutes a rela- tively unexplored field of botany. Most of the older references to this subject have been based on casual observations of exposed roots along roadside cuts and eroded stream banks, or of the upturned roots of wind-thrown trees. Hence, descriptions of the root systems of trees generally have been incomplete, if not actually inaccurate. The extensive investigations of the roots of herbaceous and shrubby plants, particularly those by Cannon (5) ^ and Weaver (26, 27, 28), led naturally to a greater interest in the roots of trees. However, the relatively large amounts of time and labor required have tended to discourage work in this field. Problems arising in the nurseries and the relative facility with which small plants can be studied havß directed research mostly toward the seedling stages. Toumey described and classified the seedHng root systems of many of the more important eastern species {25) and stimulated many other investiga- tions of a similar character. A few studies of the roots of older trees have been carried out in this country. In general, the work done thus far has been of a preliminary character, and gives neither a complete picture of the root growth of a species from seedüng to maturity on any particular site nor an adequate account of the root reactions of a species to the various sites on which it may grow. Woodroof's studies {30, 31) on the pecan constitute an exception to this statement. Somewhat more work has been done in the north-European coun- tries. The German work has been summarized by Büsgen and Munch (4). Perhaps the most complete study of any one species was carried out by Laitakari {17) in Finland on Scotch pine {Finns sylvestris L.). The species chosen for the present investigation was pitch pine {Pinus rigida Mill.), because of its wide distribution throughout the Eastern States and its remarkable tolerance of a wide range of unfavor- able situations. Particidarly because of this latter quality, the species promises to assume increasing importance in the forestation programs of the future, although it is not an important timber tree at present. Pitch pine is prominent among the botanically interesting flora of the pine barrens of New Jersey. The abiUty of the species to with- stand fire evokes the wonder and admiration of all who know that unique section. 1 Received for publication Aug. 20,1935; issued February, 1936. 2 Completion of this study was made possible through fellowships granted by the Morris Arboretum and the University of Pennsylvania. Acknowledgment is due E. T. Wherry, H. H. York, and K. D. Doak for helpful criticism and suggestions. 3 Maintained at Philadelphia, Pa., in cooperation with the University of Pennsylvania. * Reference is made by number (italic) to Literature Cited, p. 1015. Journal of Agricultural Research, Vol- 51, no. 11 Washington, D. C. gee. 1,1935 Key no. F~74 45695—36 3 (983) 984 Journal of Agricultural Research voi. si, no. ii Definite root studies of pitch pine have apparently never been made. Harshberger {10) made some general statements concerning the root development of the species, and pubhshed a small drawing of a tree with its root system. His observations obviously were of a most cursory character, and his figure is entirely inadequate as a portrayal of a root system. IlUck and Aughanbaugh {15) mention the strong taproot of pitch pine seedlings and the fact that this root becomes relatively less significant in older trees. They measured the upturned root mass of a wind-fallen tree, recording 18 feet as the diameter of the root system of a specimen 82 feet tall. Such figures are of questionable value; probably not more than one-fourth of the actual diameter of that root system was represented in the mass torn from the earth when the tree fell. The observations of Harshberger and of lUick and Aughanbaugh are representative of the available information on the roots of pitch pine, and of most other tree species. More precise knowledge of the root habits of trees is requisite for the judicious planning of foresta- tion programs. ^ In this investigation, the major objective was to study, on one site, a developmental series of root systems of pitch pine from the seedling stages to maturity. Secondary objectives included comparative observations of the root systems of normal and weak trees, of trees growing on different sites, and of pitch pine and shortleaf pine {Pinus echinata Mill.) growing on the same site. FIELD WORK DESCRIPTION OF SITE The major part of the field work was done on the tract of the Allegheny Forest Experiment Station in the Lebanon State Forest in New Jersey. Some data were obtained from the Ockanickon area of the experiment station near Medford, N. J., and from the Mont Alto State Forest in southern Pennsylvania. Both of the locations in New Jersey are in the pine barrens, the ecology of which has been treated in some detail by Harshberger {10), The site of most of the excavations on the Lebanon forest was an area of about 40 acres which, being traversed by a low ridge, varies from level to gently sloping. Drainage is good; excavations as deep as 9 feet did not encounter water, even on the lower ground. The soil of the ridge is typical Lakewood sand; on the lower ground it tends somewhat toward the Sassafras types. At a few places, a slightly harder, dark-colored layer was encountered below the A horizon, suggestive of the St. Johns series, but it was not well de- veloped. These minor variations in sou did not seem to exert any appreciable direct effect on the behavior of the pine roots. A recent paper by Lutz {^0) gives detailed data on the sous of the section and a quantitative expression of their poor quality. His determinations show that the pine-barren soils are characterized by: (1) High percentage of sand; (2) low percentages of clay and total colloids; (3) low content of organic matter; (4) low contents of nitrogen and phosphorus; (5) high carbon-nitrogen ratio; (6) high acidity; (7) excessive leaching, and varying degrees of podsolization; (8) low water-holding capacity; and (9) periodic occurrences of low per- centages of available moisture—the moisture content may fall below the wilting coefficient during periods of drought. Dec. 1,1935 Root Development of Pitch Pine 985 The forest cover is a mixture of white, black, and chestnut oaks {Quercus alba L., Q. velutina Lam., Q. prinus L.) with pitch and short- leaf pines. ^ The oaks are mostly sprout growth averaging 4 to 5 inches in diameter breast high,^ and represent the growth since the last cutting for charcoal. The pines are of all sizes up to 12 inches d. b. h. Some of the larger ones are approaching, or perhaps exceed, 100 years of age. Apparently the area has not suffered severe burning for some time, as seedling and sapling pines of various sizes are fairly abundant. The ericaceous ground cover, typical of the section, is sparse on the ridge, and composed mostly of dry-land blueberry (Vaccinium vaciU lans Kalm). Lower down on the slopes, black huckleberry (Gaylus- sacia baccata (Wang.) C. Koch) becomes predominant, with dangle- berry (G. frondosa (L.) Torrey and Gray) appearing also on the lowest flats. A dense ground cover of the huckleberries rather eflFectively excludes pine seedlings. The natural inference is that saplings and older trees growing among them got started following a ground fire which had temporarily checked the huckleberries. The majority of the pines in seedling stages are now found on the higher and less densely vegetated parts of the area. METHODS The root systems were exposed by the dry method. The first step in the case of trees larger than sapUng size was to uncover the root crown to a depth of 1 foot or more and radially about 3 feet. This operation was, of necessity, largely done by hand in "badger'' fashion. With the root crown thus revealed, the most suitable position for making deeper excavations with the least destruction of roots could be determined. A hole of sufficient size to allow a man to stand in it and use a spade was then dug alongside the stump. Its ultimate depth and the size necessary to permit spading movements and pre- vent caving of the walls were determined, of course, by the depth of the taproot. By careful caving of the wall toward the stump, the root crown and taproot could be clearly exposed without serious muti- lation. With the bases of the lateral roots thus revealed, represen- tative ones could be selected and followed in any degree of detail desired. Exposure of the laterals also was largely a hand process, although a trowel and small hand ax were useful. An ice pick was helpful in freeing the finer roots from the soil. Excavation of vertical branches of the large laterals necessitated digging a hole in the same manner as for the taproot. The dry method has several advantages over the alternative wet method, in which the roots are washed from the soil with a stream of water under pressure. The former can be used by an investigator working alone, it does not require proximity to a source of water or to a road by which water may be hauled, and it requires only the simplest outlay of equipment.