Chapter Xxiv.[183]

THE RECOGNITION OF CHARACTER OF SOILS FROM THEIR NATIVE VEGETATION; MISSISSIPPI.

Climatic and Soil-Conditions.—Next to climatic conditions, chief among which are temperature and moisture, the physical and chemical nature of the soil and subsoil is the most potent factor in determining the natural vegetation of any region. The limitations we observe in the adaptation of cultivated lands to certain crops, even with artificial help, must be much more strongly pronounced when no such aid is given, and the struggle for the survival of the fittest is continued, subject only to seasonal variations, for thousands of years. It is obvious that within the limits of the regional flora, the natural vegetation of any tract represents the best adaptation of plants to soils, in the results of long periods of the struggle for existence between competing species; the survivors being those best adapted to the entire environment.

The special object of this chapter as a whole has seemed to the writer to require a repetition of much that is already said in the preceding chapters.

In countries uninhabited by man the chief conditions outside of the direct influence of climate and soil that may materially affect the results of the competition are connected with the animal creation; and within the latter, insects are probably the most influential, beneficially in the part they play in the fertilization of flowers, injuriously in their role as parasites. Since in the absence of man, the effects of fire would ordinarily be conditioned upon the occurrence of thunderstorms, its effects would then properly come under the head of climatic influences. But while these and some other disturbing factors must not be forgotten in considering the relations of soils to the natural vegetation borne by them, the common consensus of mankind has long recognized the intimate connection existing between the two, and has everywhere made it the basis of at least a general estimate of the agricultural value of the land concerned.

NATURAL VEGETATION THE BASIS OF AGRICULTURAL LAND VALUES IN THE UNITED STATES.

In countries long settled, as in Europe, where the nature of the original forest is unknown or a matter of tradition only, the adaptations of the several kinds of land to culture plants and forest trees has been gradually ascertained by cultural experience, and their designations, values and uses determined accordingly. In the United States, the character of the original forest growth is mostly in evidence, or is definitely known by tradition, even in the older states. West of the Alleghenies, there is as yet little difficulty in this regard, partly because even where the original forest growth has disappeared its character remains on record, the assessed land values being very commonly based upon the tree growth of the wild land. In the Southern States especially, the classification of uplands into “pine lands” and “oak lands” is universal, and is associated with certain limits of valuation, both by assessors and purchasers. Within each of these two classes, however, there are well-defined gradations of cultural value according to the kind (species) e. g., of pine or oak that occupies the ground, either alone, or in intermixture with other trees whose presence or absence is considered significant. In the case of “bottoms” or alluvial lands, corresponding distinctions and classifications obtain; we hear of hickory, beech, gum, and cherry bottoms, hackberry hammocks, etc. each name being associated with certain cultural values or peculiarities of soil, well understood by the farming population.

See above, pp. 313 to 315, chapter 18.

INVESTIGATION OF CAUSES GOVERNING THE DISTRIBUTION OF NATIVE VEGETATION.

It seems singular that such well and widely understood designations and important distinctions should not long ago have been made the subject of careful investigation and precise definition by agricultural investigators. For apart from their practical importance as guides to the purchaser of land, or settler, this correlation of land-values and natural vegetation is of the utmost interest in offering an opportunity for researches on the factors which determine the choice of these several trees and the corresponding shrubby and herbaceous growths. Moreover, the cultural results and adaptations corresponding to certain natural growths being known from experience, a thorough knowledge of the soils so characterized should enable us to project into new lands, where experience is lacking, the benefits of experience already had; even in cases where, from some cause, the natural vegetation is different, or absent. Only very fragmentary and casual observations in this line are on record thus far, almost the only generally recognized chemical characterization of plant habit being that of calciphile (lime-loving), and calcifuge (lime-repelled) ones, but with few attempts at more than local application. Yet, to ascertain by the physical and chemical examination of soils what are determining factors of certain natural vegetative preferences, which are invariably followed by certain agricultural results, should not be an unsolvable problem, and its practical importance should justify its most active investigation.

Investigations in Mississippi.—In his explorations connected with the Geological and Agricultural Survey of the State of Mississippi, as well as, later on, in similar researches carried on in other states, the writer was forcibly struck with the close correspondence of the limits of geological formations with those of vegetative zones; so much so that he was led to rely very largely on the latter as indicative of the probable occurrence of outcrops that otherwise, in a level country, would have passed unperceived.

These observations upon the correlations between virgin soils and their native vegetation having originally been made by the writer, in great detail, in the state of Mississippi, from 1855 to 1872, and that state being from natural causes a peculiarly cogent illustration of such correlation: it seems advisable to describe first, somewhat in detail, the facts observed there, and subsequently to compare them with what has been observed elsewhere by him or others.

No claim is made to an even approximately exhaustive presentation of the whole subject, even within the United States; nor is it intended to give complete lists of vegetation. The object is to give such facts as have been fairly well established by observation, hoping that more thorough investigations in the same line will thereby be stimulated.

Such lists, so far as the State of Mississippi is concerned, may be found in the writer’s Report on the Agriculture and Geology of Mississippi, 1860. See also Plant Life of Alabama, by Charles Mohr.

VEGETATIVE BELTS IN NORTHERN MISSISSIPPI.

The diagram below is a sketch-map of the most northern part of Mississippi, showing the narrow parallel belts of successive geological formations or terranes running north and south, which bear the varying zones of vegetation characteristic of each one, as indicated in the legend beneath.

SOIL REGIONS OF NORTHERN MISSISSIPPI, SHOWING CHANGES FROM EAST TO WEST, AND LIME PERCENTAGES IN SOILS.

|Lime, p.c.| Soil Character.| Vegetation. | | | 1. | .40— .60|Clay loams, clay. |Oaks, sweet gum, tulip tree, | | | walnut, red cedar, ash, | | | hickories. | | | 2. | .05— .14|Sandy loams, sands.|Short-leaf pine, post, scarlet | | | and black-jack oaks, black gum, | | | chestnut. | | | 3. |1.00—1.40|“White lime” |Red cedar, crab-apple, Chickasaw | |prairie; clays and | plum, sturdy post and black-jack | |clay loams. | oaks, honey locust. | | | 4. | .30— .50 |Mellow red loams of|Oaks, hickories, walnut, tulip | |“Pontotoc ridge.” | tree, ash, cherry, umbrella | | | tree. | | | 5. | .08— .18 |Heavy gray clay |Scrubby post and black-jack oak, | |soils, some gray | short-leaf pine. | |sands. “Flatwoods.”| | | | 6. | .15— .25|Sandy ridges and |Post, black-jack, scarlet and | |uplands, broken. | upland willow oaks, small; some | | | chestnut. | | | 7. | .25— .35 |Mellow clay loams |Fine black, red, post, Spanish | |of “Table lands.” | and black-jack oaks, hickories, | | | sweet gum. | | | 8. |2.00—5.00|Calcareous sandy |Oaks as above, tulip tree, ash, | |silt, “Bluff loess”| honey locust, linden, sassafras, | |“Cane Hills.” | umbrella tree, cane. ---+----------+-------------------+--------------------------------- 9. | .40—1.10 |Mississippi Bottom.|Basket, white and black oaks, | | | ash, tulip tree' 9a.| 1.12— |Yazoo backland |honey locust, pecan, shell-bark | |buckshot clay. | hickory, walnut, hackberry, | | | cane. 9b.| .40 |Sandy alluvium, |Sweet gum, maple, willow oak, | |“Frontland.” | elm, hackberry. ---+----------+-------------------+--------------------------------- 10.| .26— .40 |Light sandy loam of|Dogwood, sweet gum, holly, ash, | | “Dogwood ridge.” | sassafras, prickly pear. | | | ---+----------+-------------------+---------------------------------

Limestone Belt.—beginning on the east we have, first, a narrow belt of limestones of the carboniferous formation, on which there is a fine growth of various oaks, with walnut, hickory, sweet gum, tulip tree and red cedar, and a very productive soil.

“Pine Hills.”—Next adjoining on the west comes a belt of sandy, non-calcareous beds of the lower Cretaceous formation, about 18 miles wide. It has a hilly surface, and outside of the narrow valleys, the prevalent timber is short-leaved pine and scrubby black-jack oak, with some post oak and small black gum, and a few large chestnut trees.

“Prairie” Belt.—Westward of this belt we descend into a level “prairie” region, six to twelve miles wide; the “white lime country,” having heavy black clay soils, underlaid by the cretaceous “rotten limestones;” which are profusely productive. The sparse tree growth consists of stout, vigorous and dense-topped post and black-jack oaks, with clumps of crab-apple, Chickasaw plum thickets, and an occasional red cedar.

Pontotoc Ridge.—West of the prairie belt we ascend into a ridgy hill country, twelve to fourteen miles wide; the “Pontotoc ridge,” formed of the soft limestones and marls of the upper cretaceous formation, and covered with a deep red soil, which bears a rich growth of oaks, with hickory interspersed, and black walnut, umbrella and tulip tree even on the ridges. This is one of the finest agricultural regions of the State.

Flatwoods.—From the Pontotoc ridge and its fine lands and timber we descend to westward into the “Flatwoods” belt, three to eight miles wide; a level country underlaid by heavy gray non-calcareous clays of the tertiary formation, from which most of its soil is directly formed. It bears a pretty dense growth of the same species of oaks that characterize the prairies farther east, but the form, habit and size of the trees is so different that many of the inhabitants believe them to be different species. The black-jack oak looks like small, dense-topped apple trees; the post oak, on the contrary, has an open top of the form of a short-handled, spreading broom. The soil is poor and unthrifty, as are the few disappointed settlers, who bought the land on the strength of its oak-tree growth. (See page 500).

Brown Loam Region. Table Lands.—Adjoining the Flatwoods on the west is a broad upland region, with a brownish-yellow soil and subsoil, extending nearly to the edge of the Mississippi bottom. In its eastern portion it is rather broken and hilly, with sandy ridge soils, a mixed growth of oaks and short-leaved pine, and occasional chestnuts; a fair farming country only. To westward the ridges become lower and broader, assuming a plateau character. The pine disappears, and black, Spanish, red and white oak, with much hickory, largely replaces the black jack and post oak; thus characterizing the fertile brown-loam “table-lands” that extend through western Tennessee and Mississippi into Louisiana, and have long been noted for their high production of fine upland cotton.

Cane Hills.—On the western border of the table-land region, and here forming a strip only a few miles wide along the edge of the Mississippi bottom, but from 70 to 450 feet above it, lies the remnant of what farther south constitutes a wide and important agricultural belt; the Bluff or Loess formation, locally known as “the Cane Hills.” The soil is largely composed of grains of sand and silt cemented by lime carbonate; it is therefore calcareous, and as on the Pontotoc ridge, described above, we find here the black walnut, the tulip tree, ash and others, elsewhere restricted to the alluvial “bottoms,” on the ridges themselves, from sixty to a hundred feet above the stream beds.

Mississippi Bottom.—At the western foot of this bluff there lies the great Mississippi Bottom, with its rich soils and varied forest growth. This also, however, subdivides into at least three distinct soil and vegetative zones, viz., the sandy “Frontlands,” which lie on the immediate banks of the great river and its main branches, and the heavy clayey “Back-land” areas, whose soils are partly the product of modern swamp deposits from backwaters, partly result from the disintegration of strongly calcareous clays constituting the lower part of the Bluff or Loess formation. A third natural subdivision is the “Dogwood ridge,” a narrow belt of slightly elevated land, mostly above ordinary overflows, which extends diagonally from the Mississippi river to the Yazoo bottom, and seems to be the continuation of “Crowleys ridge” in Arkansas. Each of these soil belts has its own characteristic forest growth, as indicated in the table below the map.

We have here along an east-and-west line of about 200 miles, eleven markedly distinct zones of vegetation, readily recognized as such by every farmer, and each underlaid by a distinct geological terrane. It does seem as though a close study of these and of the soils overlying them should lead to some definite results showing the physico-chemical causes of these differences.

Lime apparently a governing Factor.—The connection of some of these changes in vegetation with the calcareous nature of the corresponding formation has already been referred to. As regards four of the eleven divisions, this is obvious even to the casual observer, and is well known to the population, who speak of the “lime country” or belts being, as a matter of common knowledge, the best land; in full accord with what, in Kentucky and elsewhere, has passed into a popular maxim.

“A lime country is a rich country.”

Taking as a guide the trees and plants which characterize the obviously calcareous lands, our next step should be to verify, if possible, the fact that wherever these occur naturally, lime is abundant in the soil in comparison with those lands in which such vegetation does not occur naturally, or perhaps even fails to flourish when planted without special fertilization. This the writer has sought to do, first in connection with the survey work of the state of Mississippi, and subsequently in the wider field that has since come under his observation.

SOIL BELTS IN SOUTHERN MISSISSIPPI.

In Mississippi, the general conclusions derived from the observations made on the northern cross section, are corroborated many times over in other portions of the state. Aside from the cretaceous prairie region, there runs across the middle of the state a belt of varying width, of calcareous tertiary beds, which also give rise to more or less extensive tracts of “black prairie” lands, interspersed with non-calcareous, mostly sandy ridges, the lower slopes of which, influenced by the calcareous beds, bear an oak and hickory growth, while the higher portions have only pine, and usually remain uncultivated. Southward of this “central prairie” belt lies the long-leaf-pine forest area of the state, underlaid throughout by sandy, non-calcareous formations, with poor sandy soils, save here and there in patches, which can be at once recognized by the replacement of the long-leaved pine by a vigorous oak growth; as is also the case where the pine area abuts against the calcareous “Cane Hills” on the west. The bottom soils of this region are largely “sour,” and bear the gallberry (Prinos glaber), bay galls (Persea Carolina), ti-ti (Cliftonia monophylla), candleberry (Myrica cerifera), various whortle-berries, the pitcher plants (Sarracenia), yellow star grass (Aletris), sundews, Xyris, Eriocaulon, and other plants of similar habits.

Vegetative and Soil Features of the Mississippi Coast Belt.—South of the long-leaf pine area lie the coast flats, with sour, sandy soils underlaid by stiff clays. On these “pine meadows” of the Mississippi coast occur some of the most striking cases of modifications of vegetation due to physical and chemical causes.

As is well known, the long-leaved pine habitually belongs to the dry sandy uplands of the Gulf States; the deciduous cypress, on the other hand, is most characteristic of the swamps, where its roots are permanently submerged in water. But on the pine meadows of the Mississippi coast we see these two incongruous trees growing side by side, though sadly worsted by their mutual concessions; their heights usually ranging from 12 to 15, rarely as much as 18 feet. Yet both preserve their characteristic forms, the cypress being an exact miniature reproduction of the usual level-topped swamp form, except as to the “knee” feature; while the pine differs only in stature from its giant brethren of the pine hills, from which it can be traced down through all grades of transition. The soil on which this growth occurs is a sour, sandy one, one and a half to three feet in depth, underlaid by a solid, impervious gray clay, above which is usually found several inches of coffee-colored bottom water, which drains slowly into the sluggish water-courses, themselves carrying brownish, sour, but very clear waters. Analysis shows the soil to be sour and extremely poor, especially in its lime and phosphates (see chapter 19, p. 352); its herbaceous vegetation consists exclusively of very small-seeded, “calcifuge” plants (sedges, orchids, Juncus, Hæmodoraceæ, Xyris, Polygala, etc.). This land is wholly unproductive and affords but indifferent pasturage, except the first season after burning-over; probably because of the effect of the minute amount of ashes so added. As the coast is approached, the clay subsoil has an increasing depth of sandy soil-mass above it, and on these “sand hammocks” the long-leaved pine gradually assumes more and more of its usual stature; the cypress disappears, and the Cuban pine (here called pitch pine) gradually comes in; while the sedgy vegetation diminishes and finally disappears. On this land crops may be grown as in the long-leaf-pine uplands.

R. M. Harper, who has graphically described the vegetative features of the coastal plain of Georgia (Contr. from the Dep. of Bot. Colum. Univ. Nos. 192, 215, 216, 1902-05; also Bull. Torr. Bot. Club 29-32), claims the deciduous cypress of the wet pine-barrens and ponds therein, the vegetation of which greatly resembles that of the pine meadows of the Mississippi sea-coast, to be a distinct species, Taxodium imbricarium, the leaves of which are imbricated, instead of two-ranked and with spreading leaflets. He supports this distinction mainly by the differences in habit from the Louisiana swamp cypress, and the fact that the imbricated form occurs wholly on non-calcareous land, while the other is at home in the calcareous alluvial areas. The imbricated form has been observed and commented on before, as a mere ecological variation, and in the writer’s opinion this is all that can be claimed, in view of the much greater differences in the form of other trees, notably oaks, illustrated below, caused also by lime. There would, à fortiori, be reason for claiming at least three different species of post oak and black-jack (and two of willow oak), which differ not only in tree form but also in the form and number of leaf lobes, and yet can be traced into one another by innumerable transition forms. If new species are to be established on such grounds, it is hard to see where the variations manifestly due to environment are to come in.

But on the immediate coast, evidently under the influence of the aboriginal “shell mounds,” the yellow sandy soil becomes blackish from the (humus-forming) effect of the lime thus supplied; and concurrently the coast live-oak (Q. virens), grape vines, the Hercules club (Aralia spinosa), “l’herbe a trois quarts” (Verbesina sp.), and numerous leguminous plants (which are wholly absent from the pine meadows) take possession of the land, which is very productive and has been specially utilized in the growing of Sea Island cotton. Here the clay stratum is 15 to 20 feet below the surface, and roots penetrate to great depths in the pervious soil, whose great thickness makes up for its low percentage of plant-food (see table below). This land is distinctly limited by the extent of the shell heaps, past or present, and shows a respectable percentage of lime.

The annexed schematic profile (fig. 78) illustrates these changes of soil and vegetation, which furnish a striking example of the effective modification of vegetative features by physical and chemical soil-conditions.

It would be difficult to find a more striking exemplification of the effect of lime carbonate, not only upon the vegetation but also upon the physical and chemical characters of the hopelessly unproductive soil of the sand hammocks and pine meadows; no longer brown and sour, but jet black and neutral, modifying favorably every physical quality. Humus likewise nowhere shows its benefits more strikingly.

Table of Lime-Percentages.—The table below shows the average lime percentages observed in most of the several vegetative areas mentioned above. To meet the objection sometimes made that the vegetative changes noted may be due to the larger amounts of phosphoric acid and potash frequently found in calcareous lands, the percentages of the latter are also given. Considering the origin of limestones, such a connection is not unexpected, but it is far from constant. On the contrary, the frequent co-occurrence of much lime and high production with small percentages of phosphoric acid and potash leads to the conclusion, already discussed (see chapter 19, p. 365), that in presence of abundance of calcic carbonate, smaller percentages of phosphoric acid may be considered adequate than when lime is deficient, on account of greater availability. Almost the same may be said of potash; and it is quite possible that the presence of large amounts of lime tends to prevent the leaching-out of this base, in consequence of greater facility for the formation of zeolites. Illustrations of this kind have already been given (chapters 3, 22).

Definition of “Calcareous Soils.”—It will be noted that the very obvious and important changes of vegetation are brought about by comparatively slight differences in lime-content. In fact, only two of the soils enumerated above would, according to the estimates usually given in books on soil composition, be considered as properly calcareous. But the decisive feature in this matter must evidently be the native vegetation, which expresses the nature of the land much more clearly and authoritatively than any arbitrary definition or nomenclature can possibly claim to do. A soil must be considered as being calcareous whenever it naturally supports the vegetation characteristic of calcareous soils.

TABLE SHOWING NATIVE FOREST GROWTH, POPULAR ESTIMATE OF DURABILITY AND INITIAL PRODUCTION, AND PERCENTAGES OF LIME, PHOSPHORIC ACID AND POTASH, IN MISSISSIPPI LANDS. ===+==========+============================+======================= No.| Name. | Natural Vegetation. | Production Per Acre. | | | ---+----------+----------------------------+----------------------- | Black |Mainly sturdy black-jack and|400 lbs. cotton lint, 172| Prairie | post oak, red cedar, crab | decreasing to 200 lbs. | Soil. | apple and honey locust. | in 30 years. | | | ---+----------+----------------------------+----------------------- | Pale |Scarlet, post and Spanish |200 lbs. cotton first 164| Yellow | oak, small. | year, tailing off | Ridge | | to 75 to 100 lbs. | Loam. | | by 5th year. ---+----------+----------------------------+----------------------- | Pontotoc |Oak, hickory, walnut, sweet |350-400 lbs. cotton 226| Ridge |and black gum, honey locust.| lint, 300 lbs. after | Soil. | | 20 years. ---+----------+----------------------------+----------------------- | Heavy |Post and black-jack oak, |20 bushels of corn 230| Flatwood | and some short-leaved pine.| first year--then | Soil. | | nubbins only. ---+----------+----------------------------+----------------------- |Black-Jack|Black-jack oak, pine, |Unproductive. 345| Ridge | huckleberry. | | Soil. | | ---+----------+----------------------------+----------------------- | Oak and |Red and post oak, pig-nut |200 lbs. cotton lint | Pine | hickory, short-leaved pine.| at first; 100 lbs. 142| Upland | | 6-8 years. | Loam. | | ---+----------+----------------------------+----------------------- | Brown |Black, post, Spanish and |400 lbs. cotton--250 219|Table-land| black-jack oak, hickory, | lbs. after 20 years. | soil. | sweet and black gum. | ---+----------+----------------------------+----------------------- | Bluff or |Cane, black and white oak, |400 lbs. cotton, 237| Loess | tulip tree, linden, | decreasing to 250 lbs. | Soil. | sassafras. | after 30 years. ---+----------+----------------------------+----------------------- |“Buckshot”|Hickory, ash, sweet gum, |800 lbs. cotton lint, 390| Soil. | pecan, cow oak, honey | reduced to 500 lbs. | | locust, cane, crab-apple, | in 30 years | | plum. | cultivation. ---+----------+----------------------------+----------------------- | Pine |Long-leaved pine, with |20-30 bushels corn for 206| Hill | scarlet and post oak, | one year--then | Soil. | scattered small and | nubbins. Usually | | occasional pig-nut | good sweet potatoes | | hickory. | for 2-3 years. ---+----------+----------------------------+----------------------- | Pine |Dwarf long-leaved pine, |Unproductive. Bears 215| Meadow | cypress, sedges, orchids, | small-seeded “sour” | Soil. | Hæmodoracæ, etc. | vegetation. ---+----------+----------------------------+----------------------- | Shell |Live and water oak, cedar, |300 lbs. sea-island 88| Hammock | magnolia, holly, dogwood, |cotton for 15 years. | Soil. | sweet gum, hickory, | | | sassafras, grape, Hercules | | | club, etc. | ---+----------+----------------------------+-----------------------

===+==========+===============+=======+=====+=====+======+======= No.| Name. | Physical | K₂O. | CaO.| MgO.| P₂O₅.| Humus. | | Character. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Black |Heavy adhesive | | | | | 172| Prairie | dark-colored | .333 |1.367| .363| .104 | 1.25 | Soil. | clay. | | | | | | | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pale | Pale yellow | | | | |★ 164| Yellow | sandy loam. | .093 | .069| .126| .033 | .50 | Ridge | | | | | | | Loam. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pontotoc | “Mulatto” | | | | | 226| Ridge | medium loam. | .374 | .281| .234| .082 | 1.00 | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Heavy | Heavy gray | .753 | .178| .831| .052 | .305 230| Flatwood | clay. | | | | | | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- |Black-Jack| Very sandy | | | | |★ 345| Ridge | loam. | .073 | .142| .100|Trace.| .20 | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Oak and | Medium | | | | | | Pine | loam. | | | | |★ 142| Upland | | .236 | .092| .196| .091 | .50 | Loam. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Brown | | | | | | 219|Table-land| Clay loam. | .630 | .270| .450| .210 | .79 | soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Bluff or | Sandy loam. | .511 |5.921|3.278| .143 | .72 237| Loess | | | | | | | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- |“Buckshot”| Heavy | | | | |★ 390| Soil. | calcareous | 1.104 |1.349|1.665| .304 | 1.0 | | clay soil. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pine | Light sandy | | | | | 206| Hill | loam; mere | .259 | .129| .180| .030 | .35 | Soil. | sand at | | | | | | | 3 feet. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Pine | Very sandy | | | | | 215| Meadow | loam, gray | .061 | .023| .069| .021 | | Soil. | clay subsoil. | | | | | ---+----------+---------------+-------+-----+-----+------+------- | Shell | Very sandy | | | | | 88| Hammock | loam, deep. | .080 | .115| .065| .107 | .75 | Soil. | | | | | | ---+----------+---------------+-------+-----+-----+------+------- Starred values (★) are approximate.

DIFFERENCES IN THE FORM AND DEVELOPMENT OF TREES.

It will be noted that in the above table, as well as in the discussion preceding it, identical species of trees are ascribed to vegetative areas of widely different productive capacity. Perhaps the most striking example is that the cretaceous prairies and the adjoining flatwoods belt, standing respectively highest and lowest in the scale of productiveness, are yet bearing specifically identical tree-growth, to-wit, the post oak (Quercus minor) and the black-jack oak (Q. marylandica). While to the field botanist there can be no question as to the absolute specific identity of the two trees as growing on the respective areas, yet the mode of development of both is so different in the two cases, that, as before remarked they are popularly supposed to be different “kinds.”

It is a matter of regret to the writer that owing to the long distance intervening and the difficulty of securing competent and sympathetic observers for such work, it has not been possible for him to secure photographs of the tree-forms here discussed. At the time his own observations were made, photography was practically unavailable as yet, and the figures given are therefore based upon sketches made at the time, and partly upon recollection. They represent types rather than definite individuals, which were however described when fresh in mind, in the Report on the Agriculture and Geology of Mississippi, 1860, pages 254 et seq.

It has been already, and doubtless will be again and increasingly, attempted to make distinct “species” of these widely different forms of trees. But this is simply begging the question. Mere external diagnostic marks will not avail here; it would have to be shown that the seed of these different forms do not produce the other forms under changed conditions. Until this has been done, the number-less transition forms which he that runs may observe in the field, throw upon the species-makers the onus of proof of differences of specific value—if it be possible to define such value.

Forms of the Post Oak.—The post oak of the prairie lands is a tree 50 to 70 feet high, with a stout, excurrent, rather conical trunk, often somewhat curved to one side above, and densely clothed from within 12 or 15 feet of the ground with comparatively short, sturdy branches set squarely to the trunk, much crooked (geniculate), often reflexed downward; altogether forming a dense head, beneath whose thick foliage, a bird or squirrel is quite secure from the hunter’s aim.—In the flatwoods, on the contrary, the post oak has a thin, rather short trunk, divided up at 15 or 20 feet height into long, rod-like branches, spreading broom-fashion, and scantily clothed with short twigs bearing tufts of leaves; thus forming an open head, in which no creature can hide effectually. On the brown-loam table-lands, again, the post oak has a straight, rather slender, excurrent trunk with long and more or less crooked limbs projecting at a large angle, sometimes even drooping, and freely divided up into lateral, leafy branches; the trees attain from 40 to 55 feet in height. Again, on the high sandy ridges which are interspersed in the eastern portion of the brown loam area, we find, generally associated with a similarly depauperated form of the black-jack oak, and with the Upland Willow oak (Q. cinerea), a form of the post oak intermediate between that of the Flatwoods and the Table lands; twelve to fifteen feet high, with thin trunk, “sprangling” long, crooked branches, clothed with sparse tufts of leaves. These four strikingly distinct types are shown schematically, in their extreme development, in the subjoined figures.

It is hardly necessary to say that between these extreme forms there are many degrees of transition, corresponding to the transitions between the several soil-classes respectively represented by them; or they may be developed into depauperated types. Thus, for example, the forms of the post and black-jack oak found on the sandy ridges of the yellow loam region, hardly need experience in the observer to interpret them as characterizing a wretchedly poor soil.

Forms of the Black-jack Oak.—Not less striking are the characteristics of the forms of the black-jack oak as developed upon these several kinds of land. The black-jack of the prairies is a low tree with a dense rounded head, often somewhat flattened above, and a low, thick-set trunk divided up into square-set branches, so densely clad with foliage that no light penetrates into the interior, and birds can safely hide and nest within it. The height rarely exceeds 35 feet, the head being 20 to 30 feet across.

The Flatwoods form, on the contrary, rarely exceeds 15 feet in height, with a very rough bark and a small, rather dense, rounded top, giving the whole the appearance of a small apple tree. Practically the same form is seen on poor, clay ridges of “hog-wallow” land.

FIG. 79.—Extreme Forms of Post Oak (Quercus minor Marsh., obtusiloba Mich.).]

On the brown-loam lands the black-jack, like the post oak, has a rather slender, often somewhat crooked, but excurrent trunk 35 to 50 feet high, with more or less crooked limbs of moderate length, well provided with leafy branches, but forming altogether a rather open crown. A depauperated form of this type occurs on the sandy ridges of the yellow-loam region and is 12 to 15 feet high, with slender, crooked branches, clothed with scanty foliage; as shown in Figure No. 80, alongside of the other typical forms.

FIG. 80.—Extreme Forms of Black-Jack Oak (Q. marylandica Mursh, nigra Wangh).]

In all these variations of the tree forms, there is also a concomitant variation in the forms and other characters of the leaves. Thus in the compact forms of the black-jack oak, the trilobate leaf is almost completely obliterated, the leaf being simply rounded-cuneate, somewhat auriculate at base. In the sparse-branched upland forms the leaves are deeply three-lobed, and the ferruginous tomentum of the lower surface is much less pronounced. The lobation of the post oak also varies considerably both in the numbers of lobes and in their obtuseness. Similar differences prevail in the case of the black and Spanish oaks; thus in the latter, the long terminal, falcate lobe is always most pronounced on “rich” soils, while on poor ones the trilobate leaf predominates.

Of course all these forms may be found bearing acorns, so that they undoubtedly represent adult trees.

Characteristic Forms of other Oaks.—Similar general features are repeated in the case of the other species of oaks, and also more or less in other kinds of trees; though mostly less pronouncedly than with the two species above described. Among the more striking are the two forms of the willow oak (Q. phellos), which on low, undrained ground assumes the low, rounded, “apple-tree” form, while on well-drained uplands of good fertility it is a beautiful, slender tree producing almost the effect of the acacia type; it is then a sign of first-class land. The scarlet oak rather reverses these types; on good, “brown-loam” upland it is of rounded form, not very tall, with sturdy, rough-barked trunk; while on poor hillside lands its tall, smooth, white trunk stands out as a conspicuous admonition to the land-seeker to beware of a poor purchase. The black and Spanish oaks also indicate, by tall thin trunks, a deterioration of the land as compared with the lower and more sturdy growth on areas relatively richer in lime.

Sturdy Growth on Calcareous Lands.—One feature invariably repeated, not only in Mississippi but throughout the United States, is that in many strongly calcareous soils the growth of all trees, as well as of shrubs and of many herbaceous plants, is of a more sturdy and thick-set habit than that of the same species grown on thin, sandy, or generally on non-calcareous land. This effect is quite as apparent in the arid region of the Pacific Coast as in the Atlantic States, on the prairies of the Middle West, and of the Gulf Coast. The experienced farmer recognizes this habit of the tree-growth as a sign of good land, and the reverse, viz., trees of lank, tall and thin growth, as evidence to the contrary, from the Atlantic to the Pacific.

Cotton Plant.—The cotton plant affords very striking evidences of this influence of lime. On the bottom lands of a creek in Rankin county, Mississippi, the writer found a “patch” of cotton with luxuriant stalks reaching above the head of a man on horseback, but almost devoid of “squares” or blooms. The soil was very dark and rich-looking, but was derived from a non-calcareous tertiary terrane surrounding the heads of the stream. A few rods below, the latter crosses the line of a calcareous terrane, from which copious marly debris have been washed down on the bottom soil. Here the cotton was just half as high as above, and thickly covered with squares, blooms, and bolls.

Another similar example was noted on the Chickasawhay river, in Wayne county, Miss. Where that stream flows through the non-calcareous, lignitiferous area of the tertiary formation, its bottom lands bear cotton crops of medium productiveness only, the stalks being of the usual height of about three feet, and only fairly bolled. But a short distance below the point where the soft marls of the marine tertiary are cut into by the stream, the cotton plants on the bottom lands are from 18 to 20 inches high only, closely branched, and literally thronged with cotton bolls, so that the fields appear a solid mass of white. The only objection urged against this land is that to pick such cotton “breaks the backs” of the pickers. The tree growth of the bottom, of course shows a corresponding change.

Lime Favors Fruiting.—In connection with the obvious changes of form and stature caused by the presence of an abundant supply of lime carbonate in soils, there is another that has been long noted in cultivation, but is no less striking in the native vegetation. The abundant fruiting of oaks on such lands as compared with the same species on non-calcareous soils is a matter of common note in the Mississippi Valley states; and the same is true of other trees, and of herbaceous plants as well. The fruit on the lime soils is often smaller, unless much humus is present; but the statement made in Europe that cultivated fruits, and especially grapes, are sweeter on calcareous lands, is abundantly verified in the native fruits of the Mississippi Valley states as well; where the various wild berries, haws, plums, etc., are well known to the younger part of the population to be much sweeter and higher-flavored in certain (calcareous) localities than in others, besides being usually more abundant.

This is entirely in accord with the well-known fact that the application of lime checks the excessive wood and leaf growth resulting from excess of nitrogen as well as moisture; while on the other hand, the injurious effects of overdressing with lime or marl are known to be repressed by the use of stable manure, or by green-manuring. The repression of excessive wood growth by lime would seem to offer a simple explanation of the compact habit of growth on calcareous lands; and the extraordinary sweetness of fruits grown in the arid region as compared with the same in the humid, is fully in accord with the high lime-content of the arid lands.

Stunted Growth.—In practice it will be found in most cases that a stunted native growth is due not so much to lack of plant-food in the soil, as to unfavorable physical conditions. Among these, shallowness, and extreme heaviness of the soil are the most common causes. The “scab lands,” underlaid by impervious rock at a depth too slight for culture plants, as in many plateaus of the Pacific Northwest, and in rocky or mountainous regions generally, are cases in point. Strata of impervious clay often produce the same result; but in this case, should such clay be intrinsically capable of supporting plant growth, the land can often be made available for orchard purposes by blasting with dynamite (see chapter 10, p. 181).

The post oak (and black-jack) flats of the Mississippi Valley states are familiar examples of land whose dwarfed tree growth causes it to be avoided by settlers; similarly, a dwarfed growth of red elm (Ulmus rubra), hackberry and ash indicates in the flood plain of the Red river of Louisiana a heavy “waxy” red clay, or “gumbo” land, scarcely available for agricultural purposes. The gray or white “cray-fishy” bottom and bench lands of the Southwestern States, so poor in lime, phosphates and humus as to be worthless under existing conditions, are characterized by an easily recognized scrubby growth of Water and Willow Oaks (Q. nigra, or aquatica, and phellos), with low, rounded tops; while the same trees, when well developed, indicate highly productive lands.

Rep. of Geological Reconnaissance of Louisiana; New Orleans, 1873, p. 27.

Physical vs. Chemical Causes of Vegetative Features.—The extent to which the modifications of form alluded to above are referable to chemical and physical causes respectively, can be approached by the discussion of the presence or absence of certain trees from soils of extreme physical character, but otherwise normally constituted. As has been shown above, the black-jack and post oaks belong, as species, equally to the heaviest and lightest soils within the state of Mississippi; to the black and yellow “prairie” soils, as well as to the sandy ridges of the yellow-loam region; showing for these two species as such, an independence of physical conditions and an extraordinary adaptability, found in few other trees. They are frequently found either alone or associated with only a few other species of local adaptation, such as, in the prairie lands, the crab-apple, wild plum, and the juniper or red cedar. On the soils of intermediate or loam character, on the contrary, they are always associated with other oaks as well as with hickory, and in that association attain what may be considered their normal type or form.

From the fact that the dense, rounded top is formed by the black-jack oak both on the rich prairie lands and on the poor soils of the Flatwoods, it would seem that that form is the outcome of a physical cause, viz., the extreme “heavy-clay” character of both kinds of land; and we may note that exactly the reverse effect is observed in the form growing on the poor sandy ridges, as shown in fig’s 79 and 80. Yet it will also be noted that in the case of the post oak, the poor, heavy-clay soil of the Flatwoods produces an open, broom-shaped top, while the form assumed on the sandy ridges is substantially the same for both species. Care must therefore be exercised in drawing general conclusions as to the effects produced by either physical or chemical causes, alone, upon tree forms.

Lowland Tree Growth.—The variations occurring in the valleys or alluvial bottoms are less obvious to superficial observation, yet equally important and cogent to the close observer. In the properly alluvial lands, one dominant condition, that of adequate moisture supply, is almost always fulfilled, irrespective of soil quality. In addition to this, as stated in chapter 2 (see page 24), practically all the alluvial lands of the humid region may be considered as being of a more or less calcareous character, as compared with the adjacent uplands. These two important conditions dominate in a great measure the minor ones of variation in soil-texture. Yet where, as is largely the case in the southern part of the State of Mississippi, the amount of calcic carbonate is insufficient to overcome the sourness of the soil, the vegetative contrasts become extremely striking and characteristic, as explained above.

Contrast Between “First” and “Second” Bottoms.—A very striking phase of transition between the alluvial bottoms and the uplands proper in the Cotton States are the second bottoms or hammocks of the streams, whose soil and tree-growth in most cases differ markedly from those of the first bottom; and these being usually closely adjacent, often afford a very striking contrast to the latter. From some antecedent geological cause not fully understood, these hammocks, usually elevated from 4 to 10 feet above the present flood plain, have almost throughout soils of a fine sandy, pulverulent or silty nature, frequently in strong contrast to heavy clay soils in the first bottom.

They seem, moreover, to have been at some time subject to prolonged maceration under water, resulting in the reduction of the ferric oxid, and its accumulation in the lower portion of the deposit in the form of bog-ore spots or “black gravel.” Since such a process always results in the abstraction of phosphoric acid from the general mass of the soil, to be accumulated in the bog ore in an inert condition, these hammock soils, usually whitish or gray in color, are almost throughout poor in phosphates as well as in lime; the latter having been definitively leached out. The resulting vegetation, as may be imagined, is widely different from that of the bottom proper, as well as, frequently, from that of the adjacent uplands; and though level and fair to see, these hammocks are usually unthrifty and last but a short time under exhaustive cultivation. Accordingly, their forest growth is prevalently that of the poorer class of uplands, viz., small-sized post and black-jack oaks, and in the low ground depauperated water oak, or less commonly willow oak, of the low, stunted type indicative of a soil of inferior productiveness. The luxuriant growth of the present alluvial bottom is often seen within a few feet of the unthrifty vegetation of these hammocks. It is usually only in the limestone regions, and in the lower course of the larger streams, that the hammocks or second bottoms are found to be of good fertility.

See Chapter 2, p. 24.

The Tree Growth of the First Bottoms. The Cypress.—Among the trees occupying the low ground of the first bottom in the southern Mississippi states, the deciduous cypress (Taxodium distichum) deserves special mention as an example of extreme variation in form. In sloughs and swampy tracts, as is well known, the cypress grows with roots submerged throughout the season, excepting only the excrescences known as “knees,” which project above the water, probably performing some function in connection with the aeration of the root, which is essential to the root functions in all plants. The trunk rising from the water is supported by numerous projecting buttresses for from 8 to 15 feet above the water; higher up it becomes cylindrical for a height of from 40 to 70 feet, then divides up into a few widely spreading, thick, almost conical branches, whose twigs and foliage form an almost level surface to the head. This level-topped forest growth characterizes at once the submerged areas of the river and coast swamps.

But the cypress is by no means confined to the swamps and sloughs; it is also found occupying the better class of hammock lands, 12 or 15 feet above water level. In this case, however, the tree assumes a shape and growth so wholly different from that described above as to lead to a popular assertion of a difference of species. As a matter of fact, however, the cones of these upland cypresses, when dropping into the water below them, reproduce exactly the common swamp form. The extraordinary difference in the aspect of the tree under these different conditions is best seen in the subjoined diagram, showing the upland cypress to assume the form of the tall willow oak, with which it is sometimes locally associated.

FIG. 81.—Forms of Deciduous Cypress on overflowed and on bench-land.]

The trees from which the annexed sketch is taken grew within thirty feet of each other, on Yellow creek, a small tributary of the Tennessee river, in Tishomingo county, Miss. The soil stratum is underlaid by a shaly limestone, and bears lime vegetation.

The fact that the deciduous cypress grows without difficulty on the moister class of lowlands in California, 12 or 15 feet above bottom water, is of interest in this connection. It then assumes the upland form shown in the figure above, although not growing quite as tall. The calcareous nature of these soils is probably an important factor in this apparently incongruous adaptation of a subtropical swamp tree to arid conditions. In its swamp form the cypress usually grows in rather shallow, heavy clay soil, into the dense subsoil of which the roots penetrate but little.

Other Lowland Trees.—The lowland hickories, like their brethren on the highlands, seem on the whole to prefer the lighter or loamy bottom soils to those of a heavier character. This is especially true of the Pecan. The latter, as well as the shell-bark hickory, is especially indicative of the highest class of bottom soils. The black walnut, while apparently also best suited in loamy soils, is also more or less found on heavy bottom lands, provided they are sufficiently calcareous; and the same is measurably true of the tulip or white-wood tree. The most frequent occupants of heavy bottom lands, however, are the black gum and sweet gum, so that “gum swamps” are usually found to be of that character. But in the prairie region, where the bottom soils are very calcareous and heavy, as well as in corresponding soils of the “buckshot” lands of the great Mississippi Bottom, the chestnut-white (cow- or basket-) oak sometimes occupies such ground almost exclusively. Among the accompanying trees are especially the honey locust, the crab-apple, mulberry and sweet gum, as well as ash.

Hence perhaps the vernacular name “gumbo” for heavy, adhesive clay soils in the north central states; which may also, however, be derived from a comparison with the “gummy” pods of the cultivated okra or gumbo plant.

General Forecasts of Soil Quality in Forest Lands.—While the oaks and pines mentioned as forming the bulk of the timber constitute in the cotton states the primà facié evidence, as it were, of the general character of the land, there are numerous other trees and plants which serve the discriminating land-seeker as a guide for the quality of the soils in different localities. While everywhere, well-developed black, red, Spanish and white oaks are considered as signs of a high quality of land, the tall, thin scarlet, the upland willow, and the barrens scrub oak are considered as indications detracting materially from the producing value wherever they prevail. The various hickories are throughout considered as indicating good land when mixed with the oaks, or by themselves; while the presence of walnut, linden and tulip tree will usually raise the estimate of uplands to the highest class. On the other hand, the occurrence of small black-gum trees and short-leaved pine, with low huckleberry, among the oaks of whatever kind, accompanied as they usually are by the disappearance of the black, white and Spanish oaks, will materially depress the land-values.

The appearance of well-formed oaks, as well as of hickory, is therefore at once welcomed as an evidence of soil improvement, while that of low huckleberry bushes and small black gums indicates the reverse. An increase in the thickness and retentiveness of the soil stratum is also usually indicated by the occurrence of short-leaved pine in the long-leaf-pine areas.

The black, red, white, and Spanish oaks belong altogether to soils of medium physical constitution, only their size upon such lands depending upon the relative richness in plant-food; but without such changes producing any notable variation in their form. Clearly then, these species are intolerant of extreme physical conditions, and are practically restricted to soils of “loamy” character and easy cultivation.