# The Journal of Indian Botany/Volume 2/September 1921/Forest Formations and Successions of the Sat Tal Valley, Kumaon Himalayas

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FOREST FORMATIONS AND SUCCESSIONS OF THE SAT TAL VALLEY, KUMAON HIMALAYAS
By
L. A. Kenoyer, M.A., Ph.D.
Allahabad Agricultural Institute, Allahabad.
Location and Climate.
The Himalayan range, the highest mountain range of the world, deserves far more attention from the ecological standpoint than it has received. It is given merely a passing notice by such authors as Schimper (10) and Warming (12). This survey of a limited area is given with the hope that it may stimulate the botanists of India to further researches in this most fruitful field.
Sat Tal is in the Kumaon Division, United Provinces, India, at a latitude of 29° 23' north and a longitude of 79° 32' east. It takes its name from the existence some time ago of seven lakes, probably produced by the blocking of the drainage by landsides. Three of these lakes remain, one of them being over 90 and another over 80 feet in depth.
The region included in this study is the drainage basin of these lakes which almost coincides with the Sat Tal estate and has a length from north to south of one mile and a width from east to west of one-half mile. This valley lies just behind the outer range of the Himalayas, the drainage to the south of it going rather directly to the plains. The lowest lake has an altitude of about 4160 ft. and the highest peak, that at the north end of the valley, of 5860 ft. Some of the observations, particularly those related to biotic factors, were made outside the above-mentioned area.
This valley was selected for this study because it is at the altitude in which the prevailing formations of the lower Himalayas
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The average rainfall in the Sat Tal valley as recorded by Mr. A. 0. Evans, proprietor of the estate, for the eight years from June, 1913 to May, 1921 was 85.02 inches. This corresponds pretty closely with the figures in the Naini Tal Gazeteer for the rainfall at Kathgodam at the foot of the outer range, 91.27 inches, and at Naini Tal about five miles from Sat Tal to the north-west and at an altitude of about 7000 feet, 97.49 inches (8). These places all lie in a general way on the outer slope of the outer range, for the highest peak of Sat Tal is at the north of the valley. The inner valleys of the Himalayas have considerably less precipitation.
The altitude above which frost is severe enough to affect vegeta- tion is approximately 4000 feet. Sat Tal has an occasional hoarfrost, but the temperature rarely gets down to the freezing point.
Seasonal Periodicity of Vegetation.
The distribution of the rainfall by months is shown in Fig. II, 84 per cent, of the rain falls in four months — June, July, August and September. Hence there is in all the formations a striking seasonal periodicity based on the water supply. This is most marked in the lower or monsoon forest formation where the effect of the dry period is most intense. At the beginning of June, vegetation is at a compa- ratively low ebb, the monsoon forest trees being leafless and herbs being not much in evidence. With the first rains there is a marked revival of activity. The trees which have to this time remained leafless burst into leaf, a wealth of annual and fleshy rooted perennial herbs spring up, and there is germination of many tree seeds upon the forest floor, e.g., those of the Bauhinias.
With the close of the rainy season much of the herbaceous vegetation ripens its seeds and dies to the ground. October brings a wealth of composite and labiate herbs, including goldenrods, asters and groundsels, which remind one of the forest floor of a climax oak forest in Europe or America. Already some of the monsoon forest trees such as Bombax malabaricicm, Qaruga pinnata, and Erythrina suberosa are losing their leaves. Winter deciduous trees of the oak forest, such as Primus pucldum and Pyrus pashia, become leafless about the same time. No part of the winter is too cold for the vege- tative activities and even for the flowering and fruiting of much of the vegetation. Prinsepia utilis, a widespread pioneer rosaceous shrub of the oak forest, has festoons of blossoms in midwinter. About Feb- ruary the candle-like spikes of Sapium insigne appear.
From March to May is the hot season. Trees blossom profusely during the early part of this season, conspicuous among them being
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apple tree. Erythrina suberosa dots the woods with scarlet, Jndigo- fera atropurpurea and Ougeinia dalbergioides with lavender, and Caesal- pinia sepiaria with golden yellow. A number of early blooming herbs, such as geraniums and violets now come out. The deciduous trees of the oak forest develop their leaves until the beginning of the mon- soon while the trees of the monsoon forest become increasingly leafless until about the same time. The highest recorded temperature is 92° in May, 1921.
The herbaceous vegetation at this level may be considered as constituting three fairly distinct seasonal groups. With the spring rise of temperature come mainly representatives of temperate zone families, such as Ranunculaceae, Gruciferae, Caryophyllaceae, Viola- ceae, Geraniaceae, Bosaceae, Crassulaceae, and Compositae. With the monsoon come mainly representatives of tropical families, such as Begoniaceae, Gesneriaceae, Orchidaccae and Scitaminaceae. In the cooler and less humid conditions following the monsoon come repre- sentatives of families which largely constitute the autumnal vegetation of the temperate zone, such as Compositae and Labiatae.
Monsoon Forest (Shorea and Bauhinia) Formations.
The monsoon forest grows over the whole area from the foot of the hills up to the crest of the ridge, about 4500 ft. high, which borders the Bhim Tal and Sat Tal lake valleys on the south, and occupies many of the exposed slopes and ridges within the valley. This is the typical forest described by Schimper (10) for tropical dis- tricts with pronounced dry seasons.
There are two types of this formation determined by altitude. From the base of the hills to about 3000 feet is a forest dominated by Shorea robusta, but having as important elements Semecarpus anacar- dium and Bassia butyracea> This type does not extend to the altitude of Sat Tal valley. It contains a good number of tree species, but Shorea is the climax form, producing r an almost pure forest of tall straight black-barked trees which is able to hold its own against in- vaders. From 2500 to 4500 (in suitable exposures as high as 5500) feet the climax forest is marked by three species of Bauhinia. B. va- riegata is a spring-blooming tree, B. retusa an autumn blooming tree and B. Vahlii, the elephant creeper, a gigantic woody twiner. There is a good sprinkling of other legumes such as Erythrina, Indigofera. Oligemia, Dalbergia, and Caesalpinia. This might be called the Le- gume forest or better, since the Bauhinias occupy a climax position, the Bauhinia forest. It contains numerous other deciduous trees such as Grewia, Nyctanthes, Mallotus, Sapium, Odina. This forest is found ​only on the sunny faces of the Sat Tal valley, south, east, and west, and is with the exception of a few scattering outliers entirely absent from the higher valleys. Its upper limit is roughly 4000 feet, on north facing slopes and 5500 feet on south facing slopes.
The factors which induce the shedding of the old leaves and the development of the new deserve careful investigation. The end of May, 1921 was an unusually dry time in the Western Himalayas. At Sat Tal the rainfall for the eight dry season months ■ October, 1920 to May, 1921 inclusive, was 6*29 inches and was limited to two of these months. The rainfall for the corresponding period 1918-19 was 17'17 inches and was distributed through seven of the eight months. A com- parison of notes on the vegetation in May of the two years shows that in almost all Species of the deciduous forest the shedding of the old leaves occurred earlier in 1921 than in 1919. Hence it seems appa- rent that the shedding of the foliage is hastened by lack of humidity. On the other hand observations show that the putting out of new foli- age by no means awaits the beginning of the monsoon rains. Schim- per (10) says that the trees of monsoon districts renew their foliage at or immediately before the commencement of monsoon rains, but he throws no light on the nature of the stimulus which causes leafing in anticipation of rain. The chief surprise that the writer has met in his observation of the monsoon forest on the plains of India is the fact that many, indeed most, species go through the exceedingly severe heat and drought of May and June with young tender foliage. At Sat Tal there were no showers in May, 1921 to indicate the coming of the monsoon, yet the leafing of the monsoon trees had proceeded further than in 1919 when such showers did occur. The species latest to put forth their foliage are Nyctanthes arbortristis, Grewia tiliaefolia&nd Euphorbia Boyleana, yet in numbers of Grewia trees and in one Euphorbia leaves were coming out before the end of May. Instead of being a benefit to the tree, preparing it to profit from the rains without loss of time, this early leafing seems in some cases a real detriment, for the drying of the tender foliage has gone on to such an extent as to threaten the life of trees and shrubs of several species.
It may be that the development of leaf buds requires a certain period of incubation. In some cases greater insolation seems to induce earlier leafing. Temperature-controlled experiments or ob* servations checked with a thermograph are most desirable to test this point. The way in which temperature most probably acts upon leafing is by hastening the maturation of the fruit. In at least twenty of the monsoon forest species, notable among which are the tree Bauhinias, Erythrina suberosa, Oligemia dalbergioides, Odina Wodier, ​Sapium insigne, the Stercufunalias, and Nyctanthes arbortristis the leaf buds do not open until the fruit is mature. Evidence for this is found in the fact that young non-fruiting trees often develop their leaves before the fruiting ones do so, that pollarded non-fruiting branches on fruiting trees are the first to leaf out, that the male trees of such dioecious species as Odina begin to leaf while the female trees bearing immature fruit show no signs of leafing, that trees which for any other reason are less cumbered with fruit are more prompt to leaf. Another example which might apply here is that Bauhinia retusa, which blooms in the autumn and matures its fruit early in the spring, is in full leaf before Bauhinia variegata, which blooms in the spring and matures its fruit later, has commenced to leaf.
An exposed hillside generally has a strikingly less leafy appearance in May than has a sheltered hillside or a ravine. Examination shows that this is because the floral population of the exposed hillside is made up mainly of such trees as Grewia, Nyctanthes, and Euphorbia, which are tardy in leafing, while the sheltered area has a larger number of evergreens and of early-leafing deciduous trees such as Bauhinia retusa. It is a matter of survival, for evergreens and Bau- hinia retusa could not persist in a place of severe exposure.
Almost all the vegetation is to a high degree deciduous. The leaf fall occurs irregularly, as compared with that of the temperate zone winter deciduous forest. Some of the trees are bare in October and others retain their leaves until just before the rains.
Broad-leaved Sclerophyllous (Quercus incana) Formation.
This forest is made up largely of evergreen trees and shrubs, but with an admixture of winter deciduous forms. Roughly about 60% of the species belong to the former and 40% to the latter class. The dominating tree is Quercus incana which is easily distinguished from the other Himalayan oaks by the silvery white lower surface of the leaves. It is the lowest of three altitudinal oak zones, and extends from the upper limit of the Bauhinia forest to about 8,000 feet. Quercus dilatata extends from 7,500 to 9,000 and Quercus semecar- pifolia from 9,000 to 11,000. The latter forms occur at altitudes higher than that of the Sat Tal valley. Q. incana renews its leaves in March and April, the other species somewhat later. At no time are the trees entirely bare, as the new leaves appear while the old ones fall.
Associated with the oak are three members of the Laurel family which occupy stream depressions and are probably hydrarch pioneers. Bhododendron arboreum and Pieris ovalifolia of the Heath family ​are characteristic trees of the climax oak forest. They .'require more shaded and moist situations than does the oak, hence in this valley they are found only on north slopes.
The distribution of the oak forest is evidently determined by the degree of protection against dessication. Its moisture requirement is greater than that of the Bauhinia forest for it occurs in depressions, stream valleys, north slopes, and other sheltered aspects. The ridge which forms the watershed to the west of the valley at one place is in- terrupted by a flat shelf which receives the seepage from the higher portions of the ridge. The adjoining portions of the ridge are occupied by Bauhinia forest but this shelf has a small oak grove. The altidudinal distribution of the oak may be a matter of humidity. As I have pointed out the rainfall on the south slopes of the first high range varies but little with altitude. But, because of the lower temperature, the relative humidity, hence the moisture effective for vegetative growth, is greater at the higher altitudes.
Coville (5) has found that in many cases the trees and shrubs of cold climates will not resume growth after dormancy without a certain amount of chilling. The necessity for chilling probably deter- mines why many of the cold region plants, as for example the apple, will not grow to advantage in the tropical regions. One wonders then to what extent temperature itself is a factor in determining the altitudinal range of the hill vegetation.
Broad-leaved sclerophyllous woodlands, according to Schimper (10), are characteristic of warm temperate regions with moist winters and dry summers. Except within the range of a mountain climate they are found only in certain coastal regions. In these regions vegetation is subject to short and irregular periods of rest which may be due either to the cold of winter or to the drought of summer. The winter is not altogether favourable to plant growth because of the low temperature neither is the summer altogether favourable because of the low water supply. By constant retention of leaves the trees of these forests are able to take advantage of the favourable periods in either season.
The climate of the region occupied by this forest in the Himala- yas differs from the climate of a typical sclerophyllous region in the fact that the rainy season does not coincide with the winter. Never- theless the fact remains that there are at all seasons periods which are favourable to plant activity. It would be a loss to the plant to enter these short periods without foliage.
Bulbous and tuberous plants, such as are common in the coastal sclerophyllous regions, are also abundant here. But unlike the former regions this Himalayan formation contains a profusion of ​woody climbers and of epiphytic mosses, lichens and ferns, and seed plants such as the Orchidaceae and Peperomia refleta of the Piper- aceae. The presence of epiphytes would indicate a dry season of less severity than is found in the coastal xerophyllous regions.
Pinus longifolia Formation.
Pinus longifolia occurs in almost pure forests in an altitudinal zone slightly lower than that of Quercus incana. On the steep north slope of the canyon separating Sat Tal from Naini Tal there are a few pines at 2,000 feet. Very little pine forest is seen, however, until 4,000 feet is reached, where it continues upward to about 6,500 feet. Hence it will be seen that it overlaps a small margin of the Bauhinia formation and over half of the oak formation. It however occupies an edaphic situation distinct from that of the oak. It occurs on the hilltops and ridges and more exposed flanks of the hills. On the north slope of the Sat Tal valley it descends from the crest to meet the oaks. On other hill slopes it descends from the crests along the ridges into the Bauhinia forest in much the same manner as the oaks ascend from the valley base along the stream channels. On peaks between 4,000 and 6,500 feet in height it is usual to find pines occupy- ing the highest and most exposed position. Higher peaks, such as are found a few miles further to the northeast, have pines only on the ridges, the summits being occupied by oaks.
Pinus longifolia is a strikingly xerophytic species. In May old leaves have mostly fallen while the new are appearing, so that the tree is almost bare. Much sun reaches the ground between the trees, and pine seedlings flourish, so the forest renews itself freely. The ground is covered most of the time by a layer of fallen pine leaves, which seem to prevent the extensive development of herbs and grasses. Shrubs are limited to such xerophytic pioneers as Aechman- thera. Other ^pecies of trees found sparingly mixed with the pines in the more sheltered parts of the forest are Englehardtia spicata, Castanopsis tribuloides and Myrica Nagi.
Factors Determining Distribution of Formations.
Clearly the monsoon forest is adapted to extremes of seasonal humi- dity and to a temperature which does not descend below freezing. The pine forest is adapted to dry exposures within certain altitudinal, hence temperature, limits. The Quercus incana forest is adapted to humid situations within altitudes slightly higher, hence temperature limits slightly lower, than those which make the upper and lower boundaries of the pine forest. ​ It is the task of dynamic ecology to point out the order of succession by virtue of which existing formations come into being. Cowles (6) and Clements (4) have done much toward the elucidation of this problem on the western continent. But little has been done in India. Dudgeon (7) has pointed out the probable succession in the Upper Gangetic plain, beginning with pond vegetation. He feels that the intense human competition prevents vegetation from reach- ing the climax stage which would otherwise occur. The inquiry arises what would be the order of succession of these formations at Sat Tal if they were left to themselves. Here, as in the plains, the human disturbance is great and increases the difficulties in the solu- tion of the problem. Sat Tal valley has been protected, but not for a long enough period to enable us to read the whole story.
In the narrow altitudinal zone, 4,000 to 5,000 feet, where all three formations are found, the pine and the Bauhinia seem to be xerarch pioneers and the oak the climax toward which the former two tend. Evidences were found in my study that the oak invades the pine regions. Oak seedlings could be seen frequently along the borders of the pine. On the other hand pine seedlings do not thrive in the oak forest because of the continual shade. In such situations could be found pines thirty years of age which do not exceed 10 feet in height. In this particular altitude the oak forest seems to be encroaching on the Bauhinia. When oaks become established it is probable that their shade is too dense for the establishment of Bauhinia seedlings, which germinate in the sunny Bauhinia forest at the very beginning of the rains. In other words, the oak appears to be the climatic climax in the Sat Tal valley. It must be remembered, however, that the Bauhinia formation is the climax one for the altitudinal zone just adjoining and below that in which the oak is climax. In the zone of the Bauhinia, the oak occurs as an edaphic hydrach pioneer in stream valleys, lake depres- sions and shaded slopes and tends, as the contour becomes more level to give way to the Bauhinia. As between the pines and the Bauhinias it is probable that the latter invades the former in edaphic situations favorable to Bauhinias. The pine forest is, as has been stated, singularly free from other plants, not excluding epiphytes and lianas. But at times one can see a pine tree overgrown and weighted down by Bauhinia Vahlii. The pine, then, seems to be mainly restricted to well-drained and exposed situations above the altitudinal range of the Bauhinia and to situations which, although within the altitudinal range of the latter, are on north exposures and hence probably subject to low temperatures for periods too long to permit Bauhinia to get a foothold. ​
Successions within the Formations
The three formations whose interrelations we have noted are themselves advanced stages in the topographical succession. At many places in and about this valley may be seen plant groups which do not fit into any one of the three but which form an initial stage leading to one of the three. As a topography tends to advance from a rough tract to a plain, the hills being levelled by erosion and the valleys filled by deposition, so plant societies tend to advance from those of extreme dry or extreme wet situations to the climax form which occupies a situation of moderate water supply.
I. Xerarch Topographical Successions.
A topography may be dry because, —
(a) It is so located that it receives a small amount of rainfall.
(b) It is so located a3 to be subject to a large amount of evapo- ration. (c) The slope is such as to permit rapid drainage of water. {d) The substratum is impervious to water.
Much work could with profit be done toward the determination of the local distribution of rainfall in the Himalayas. Certain places such as Naini Tal have a high rainfall because a funnel-shaped valley catches the incoming clouds and conveys them into a pocket surround- ed by hills. Interior valleys receive less rainfall than the outer slopes because the air has given up a large proportion of its water vapor by the time it is forced over the crest of the outer range. It is most interesting during the monsoon'to see how almost every day the clouds pass through gaps in the outer ridge to move almost on a level until they strike higher elevations further within the system. As the hills became eroded and the valleys 'filled there would of course be changes in the precipitation and with these we might expect vege- tational changes. But the course of these changes is so slow that we can get little direct evidence regarding them.
A striking difference is observable whenever the north slope and the south slope of a valley are compared. The former is well wooded, while the latter is often an expanse of grassland with a little forest of a xerophytic type in ravines and sheltered places. This difference becomes more marked in the Himalayas as one goes westward to sections having less rainfall. In the Chakrata region, for example, the forest abruptly vanishes as the crest is reached or as the slope turns from the north to a direction of greater exposure to the sun. The ​difference here is probably purely a matter of evaporation. The south slope, being exposed to the sun more directly and for longer periods, will not retain moisture enough to permit the oak forest to become established.
A precipitious slope will in general not allow trees to get a foot- hold, with the exception of special scrambling forms such as Ficus foveolata. With time such slopes become more gentle and support a more luxuriant forest vegetation.
An exposed rock is occupied by lichens. These are followed by xerophytic mosses, herbs, grasses and sedges and finally by shrubs and trees, the trees passing from xerophytic to mesophytic.
A typical xerarch succession then would be lichens, mosses, grass- lands, Euphorbia, pine, oak. Instead of the pine there might be substituted, following Euphorbia, such semi-shrubby pioneers as Woodfordia, Flacourtia and Nyctanthcs, then the Bauhinia formation, finally the oak forest.
In parts of this valley and the neighboring region are steep slopes of shale or other soft rock which readily crumbles giving rise to landslips with well-developed talus slopes. Both the exposed rock face and the talus have contours so temporary that their occupation by plants may be prevented for years. "When finally the contour be- comes more permanently established the first plants to appear are generally xerophytic grasses and sedges with an admixture of ruderal herbs, such as Rumex hastatus and the American Tridax procumbens and Oenothera rosea. These are followed by shrubs, among which the Berber is-Rosaceae group is often prominent, and the shrubby vegeta- tion very gradually gives way to the climatic forest. If shrubs and trees which have the power of producing adventitious buds from the roots have grown previously on the slope these may contribute largely to the new population by suckering from the exposed roots on the denuded area or by the continued growth of the slumping vegeta- tion on the talus slope.
Euphorbia royleana, the most extreme xerophyte among the trees of this region, is admirably fitted for the place it fills. Its fleshy angled cactus-like stems hold large quantities of water and do the greater part of the synthetic work, the leaves being very transient.
The shrubby formation of Woodfordia, Nyctanthes and Flacourtia occupies considerable areas on the south-facing slope at the north end of the valley. It is for the most part a relatively dense growth, difficult of penetration, but the individual members are low, usually not over twice the height of a man. Woodfordia is a pioneer which is often met with on bluffs and even in stream valleys in the plains as well as in the lower hill country. ​
II. Xerarch Biotic Successions.
Man's influence shifts vegetation from the mesophytic to the xerophytic level. Forests are burnt, cut, grazed or cleared for cultivation with the result that the land becomes more exposed to sunshine, the moisture-retaining undergrowth largely disappears, the moisture-absorbing humous soil often becomes less abundant and in general the plants which require considerable humidity give way to those which can endure more rigorous conditions so far as water supply is concerned.
Fires were wide-spread during the drought of May, 1921 and caused an appalling destruction of vegetation. The hill villager habit- ually burns the dry grass so that the fresh grass may get a better start at the outset of the monsoon. Fires started intentionally or acci- dentally spread through all three of the forest types and, helped along by the high winds, the dryness of the vegetation, and the large quan- tity of fallen leaves, were exceedingly difficult to conquer. The diffi- culty was greatest and the destruction most marked in the pine forest because of the greater inflammability of fallen leaves and twigs as well as of standing trees.
The young trees are damaged but older ones escape. Hence it is that we frequently find in the pine forest large trees with an under- growth of young trees of a uniform age, the intermediates having been killed by fire just following which the young ones come from seed. Osmaston (9) says that no fire, unless helped by trimmings at the base of the tree can kill Pinus long i folia which is over 100 feet high. These large trees will reseed the area. Champion (3) says that in burnt areas pine seedlings grow to one foot in four years while in unburnt areas they take six years to attain this size. This he attributes to (a) manuring by ashes, {b) diminished competition of herbs, (c) increased light due to thinning of covering crown. Smithies (11) says " The intense light-demanding nature of the chir {Pinus longifolia) is too well known to require comment. Nevertheless the shade of a mature chir forest is never sufficient to stop the young seedlings from spring- ing up and establishing themselves although their further development is checked unless they are completely freed of overhead cover."
So the natural course seems to be for pine seedlings to follow a fire in a pure pine forest. If it is a mixed pine and oak forest the results may be different. Champion (3) calls attention to the wonderful capa- city of oak, Rhododendron and Pieris for developing dormant buds after a fire if only a narrow strip of the bark remains alive. Such survivors, he says, will often be found where the intermingled chir has been destroyed and, if in any numbers, will remove all chances
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