The flora of the district includes the vast range found in the Himalayas, varying from the sub-tropical species which grow in the outer ranges of low hills to the rich Alpine flowers in the north. Still, it can reasonably be termed to consist of mostly such trees as grow in its forests because large tracts of the land-surface in the district constitute forests. The chir, the oaks, the conifers, the sal, the deodar, the haldlu. the yew, the cypress, the rhododendron, the birch, the horse chestnut, the cycamore the willow, the alder and various types of fruit trees like the cornel, the figs, the kaiPhal, the mulberry, the kingora, the raspberry, the blackberry, currants, medlars, gooseberries, hazelnuts, apples, pears, cherries, apricots, plums, peaches, oranges, limes, bananas, pomegranates and walnuts are found in the district besides a variety of herbal plants bushes, scrubs and grass.
The flora of the district may be divided into six main botanical divisions : (1) the tropical dry deciduous forests, (2) the sal forests (3) the chir forests, (4) the deodar, fir and spruce forests, (5) the oak forests and (6) the Alpine pastures.
Tropical Dry Deciduous Forests-
These forests occur mostly near the confluence of the Yamuna and the Aglar and on foothills and extend up to the altitudes of 1,200 m. The predominant species are kuri, kemela, jhingan, and mandar. The chief undergrowths are the dhaula, binda, basingha and the gandela.
These forests exist up to the altitude of 1,066 m., their best growths being found in the valley of the Chandan Rao in tehsil Devaprayag and in the valley of the Bandal in tahsil Tehri. Small tracts of the sal forests may also be seen in the neighbourhood of Muni ki Reti and Shivpuri in tahsil Devaprayag. Sal is highly gregarious. The upper limit of Sal is regulated to a great extent by frost. In excessively dry localities, it gives way to more xerophytic species. It does not extend beyond the outer ranges of the Himalayas even though the main river valleys in the northern part of the district are much below the maximum elavation at which this species may grow. It is commonly found up to the altitude of 762 m. on the southern aspects and 1,066 m. on the northern. The other chief trees found in these forests are sain, bakli, jhingan, haldu, kanju, sandhan, rohini and amaltas. The bakli is utilised for preparing charcoal. The wood of the sandhan is used for making agricultural implements. The khair trees are also met with in these forests.Grass abounds in sal forests, wherever sufficient light reaches the ground. In most sal forests, sal comprises 80 to 90 percent of the dominant tree species and tends to form a dense treecanopy, The sal forests had originally contained a much higher percentage of miscellaneous species.
These forests ordinarily extend on the southern aspects from 1,000 m. to 2,150 m. and on the northern aspects from 900 m. to 2,000 m. throughout the district, growing best in the valleys of the Bhillangana and its tributaries, the Alaknanda and the Mandakini. Chir is found On almost all geological formations though, On certain southern slopes with a limestone subsoil, it is unable to exist on account or the dryness of the soil coupled with relatively high temperatures. Nevertheless, Chir forests can establish themselves on dry southern aspects where owing to xerophytic conditions and the prevalence of fires, few other trees or shrub species survive. In all chir forests, the pine is the dominant tree species present though, on the northern aspects where, there is more moisture in the soil and fires are less destructive, scattered trees of there species also occur. Chir forests are seldom very dense. The ground is covered with grass, sometimes dense, whatever the aspect of density or overhead canopy, and there is also a discontinuous undergrowth 0f shrubs, often so widely scattered that even from a short distance their presence is scarcely noticeable. The open nature of these forests, the absence of other tree species and the poverty of the undergrowth are attributable to fires which have in the past swept annually throughout their length and breadth, to the xerophytic conditions under which they grow and to the fact that the chir is often located near tracts under cultivation which leads to its heavy lopping and felling. Towards its lower limit, chir gets mixed up with trees of miscellaneous species and, less frequently, with sal forests. Towards its upper limits and in moist and shady ravines, it gradually gives place to banj. The chir is tapped for resin and its wood is used for building purposes. The seed also yields oil and, when baked, it becomes edible. The dry leaves are- utilised for manuring.
These forests occur in the northern part of the district in tehsil Pratapnagar, in a area of Ghansali and Dhanolti , associated with blue pine and cypress between the altitudes of 1,520 m, and 2,150 m. above sea level. The forests are open and the trees do not attain great height. The timber of deodar is the most highly prized of all the conifers for house. building, granaries, boat-building and railway sleepers.
Fir and Spruce Forests-
These forests occur in the northern part of the district between the altitudes of 2,150 m. and 3,050 m. Wherever silver fir occurs, it is the dominant species excepting when it occurs mixed with spruce even where, it is equally important. Parts of such forests are covered with kharsu or moru.
The three principal oaks are banj, moru and kharsu, each occupying more or less a distinct altitudipal zone in the district.Banj forests are ordinarily found between the heights of 1,800 m., and 2,150 m., above sea-level but they also occupy moist ravines running down into the chir zone where they reach levels as low as 1,050 m. A notable feature of the banj is its capacity to establish itself on the most unfavorable southern aspects. Those on the northern aspects are comparatively more dense. On southern aspects, the ground is almost invariably clothed with dense grass, while on northern aspects the incidence of grass is much less. The banj has a large number of shrubs associated with it.
Moru forests are found at between 1,980 m. and 2,750 m. above sea-level and occupy an intermediate zone between banj and kharsu, which form extensive forests on the southern aspects, where the moru occurs sporadically. It attains its maximum development at elevations between 2,125 m. and 2,450 m. on moist soils and especially where the subsoil is limestone. On account of the density of growth and prevailing moist conditions, fires only penetrate into such forests rarely. Some other species compete with morn for dominance, the commonest being the deodar and the kharu.
The kharsu forests occupy very extensive tracts at heights between 2,350 m. and 3,500 m. in the northern part of tehsil Pratapnagar (except in the north-east) and in the north-eastern part of tehsil Devaprayag. It is found equally on the northern and southern aspects and has few successful competitors, excepting silver fir and moru. The fir, however, occurs only on a small fraction of the area occupied by kharsu. Moru can complete with success only on northern aspects. As its lower limit, kharsu often passes into banj forests though, on some northern aspects, it frequently gives place to moru, spruce or silver fir. At its upper limit, it passes into forests of birch and silver though, on southern slopes, it more frequently passes directly into pastureland without any gradual transition. Typical khasru forests are dense, the most common associate being burans ,which is almost as aboundant in the kharsu forests as it is in the banj forests. Shrubs occur in great variety, the commonest being timla.
These are found in the north eastern part of the district in tehsil Pratapnagar and Devaprayag between heights of 3,500 m. and 5,000 m. above sea-level. The land in these parts is covered with snow from October to May but, from June to September, varieties of grasses, herbs, shrubs and flowers grow in the area in abundance. The area provides beautiful and extensive pasture lands for the cattle. On the northern aspects, the birch is also met with and its stems give the famous Bhurjpatra or Bhoj-paper on which books were written before the advent of paper.