Strand plant communities of the Indian sub-continent

Strand plant-communities, other than the mangroves, composed of psammophytes, halophytes have been described along with bioclimatic, edaphic factors for the seven coastal biogeographic sub-divisions of the sub-continent

Frost maintains forests and grasslands as alternate states in a montane tropical forest–grassland mosaic; but alien tree invasion and warming can disrupt this balance

1. Forest–grassland mosaics, with abrupt boundaries between the two vegetation types, occur across the globe. Fire and herbivory are widely considered primary drivers that maintain these mosaics by limiting tree establishment in grasslands, while edaphic factors and frosts are generally considered to be secondary factors that reinforce these effects. However, the relative importance of these drivers likely varies across systems. In particular, although frost is known to occur in many montane tropical mosaics, experimental evidence for its role as a driving factor is limited. 2. We used replicated in situ transplant and warming experiments to examine the role of microclimate (frost and freezing temperatures) and soil in influencing germination and seedling survival of both native forest trees and alien invasive Acacia trees in grasslands of a tropical montane forest–grassland mosaic in the Western Ghats of southern India. 3. Seed germination of both native and alien tree species was higher in grasslands regardless of soil type, indicating that germination was not the limiting stage to tree establishment. However, irrespective of soil type, native seedlings in grasslands incurred high mortality following winter frosts and freezing temperatures relative to native seedlings in adjoining forests where freezing temperatures did not occur. Seedling survival through the tropical winter was thus a primary limitation to native tree establishment in grasslands. In contrast, alien Acacia seedlings in grasslands incurred much lower levels of winter mortality. Experimental night‐time warming in grasslands significantly enhanced over‐winter survival of all tree seedlings, but increases were much greater for alien Acacia than for native tree seedlings. 4. Synthesis. Our results provide evidence for a primary role for frost and freezing temperatures in limiting tree establishment in grasslands of this tropical montane forest–grassland mosaic. Future increases in temperature are likely to release trees from this limitation and favour tree expansion into grasslands, with rates of expansion of non‐native Acacia likely to be much greater than that of native trees. We suggest that studies of frost limitation to plant establishment are needed across a range of tropical ecosystems to re‐evaluate the general importance of frost as a driver of vegetation transitions in the tropics

On the mediterranean climatic regime of West Pakistan

Taking mediterranean climate as one having mild winter, rainfall during the cool seasons of the year and summer drought, the stations of West Pakistan subject to this climate are listed. Degrees of mediterraneity are recognized on the basis of intensity of estival dryness (summer rainfall as percentage of the total). Three categories are recognised and mapped out: pure mediterranean (e. g. Nokkundi: no summer rain), moderate mediterraneity (<40% summer rains on an average, e. g. Quetta, Kalat), attenuated mediterraneity (>40% rainfall in hot season) marking a transition towards tropical or bixeric climates (e. g. Fort Sandeman, Dera Ismail Khan). Whereas the stations of tropical regime have the highest coefficient of variation of rainfall and number of rainy days during cool seasons and the least during summer, contrary is the case for the stations having moderate degree of mediterraneity. For those of attenuated character, the position is more or less intermediate but leaning towards tropical regime. In tropical and bixeric climates, it is the summer rainfall (and number of rainy days during summer) expressed as percentage of the annual total that occupies the dominant position; in the moderate mediterranean regime, winter has the most prominent position followed by spring-autumn and then by summer. Further attenuation in the degree of mediterraneity is marked by corresponding increase in summer rainfall

Probable impact of deforestation on hydrological processes

The various ways in which the forest cover may influence the atmospheric and soil processes controlling the hydrological cycle are examined. Case studies of extensive deforestation affecting the rainfall pattern are reviewed

Tropical dry deciduous forests of Peninsular India

The paper deals with structure, composition, floristic elements, bio-climatic conditions and palaeoecology of the dry deciduous forests. On the basis of dominance, these forests are divided into the teak, sal and miscellaneous types and the latter into Anogeissus latifolia-Terminalia, Hardwickia binata and Anogeissus pendula sub-types. Teak forest is the richest in the number of species followed by sal; A. pendula is the poorest type. Undergrowth contains the largest number of species, followed by upper canopy, understorey and liana in all the types exept in A. latifolia-Terminalia where upper canopy takes the first place. Of the 14 floristic elements, Indian and Indo-Malaysian dominate all the strata but Sudano-Rajasthanian has certain importance in A. pendula forest. Fossil record from the Deccan Intertrappean series indicates marshy and coastal conditions which go in favour of Upper Cretaceous age. Fossils of evergreen and moist deciduous formations from this series and from W. Rajasthan Kutch suggest a wetter climate during Upper Cretaceous-Mid Tertiary for which probable causes are outlined. Trends of progression of the dry teak forest has been discussed in relation to bio-climatic factors

Variability and the concept of a probable climatic year in bioclimatology with reference to the Indian sub-continent

The degree of stability of 31 stations of the sub-continent is analysed by consideration of four bioclimatic factors: number of rainy days, dry months, precipitation and its seasonal incidence (regime). Cases of exceptional deviations from the average values are pointed out. Taking coefficient of variation of the mean value above 32% as high variability for the first three factors, and less than 85% years in one of the four types of regimes (tropical, mediterranean, bixeric, irregular) as criterion of high variability in regime, the stations are graded according to the number of factors in which they show high variability. No correlation could be found between precipitation amount and variability though in case of rainy days and dry months an inverse relation has been noted with coefficient of variation, barring few exceptions. High annual variability might be contributed by all the seasons or the main agricultural season may be less affected. Stations are classified as presenting low, moderate, high variations in summer, winter, spring-autumn precipitation. In general, higher the variability, lesser the seasonal precipitation. A probable year is defined as one corresponding in precipitation, rainy days and dry months to the figures of mean value, plus or minus standard deviation. Percentage number of years corresponding to the pattern of probable year is noted. The percentage varies considerably for some stations when the regime of the most common type(s) is introduced as the fourth factor in the concept of probable year. No correlation exists between the percentage number of years agreeing with the probable year and the number of factors presenting high variability

A diagram for depicting the interyearly variability in bioclimatic factors

In cases of unstable climates like that of Peshawar (West Pakistan) which exhibit variations in rainfall amount, length of distribution and season of occurrence from year to year, averages have little meaning in bioclimatic studies. Range and coefficient of variation are indicated as well as average and median values of annual precipitation, the number of rainy days in the year, the length of the dry season in months and the xerothermic index, in order to give an idea of the magnitude of variability. A diagram to illustrate the variability in the bioclimatic elements has been designed

A phytoclimatic approach to the problem of mediterraneity in the Indo-Pakistan sub-continent

In the N. W. part of the sub-continent winter-spring rains coupled with low temperature and dry, hot summer create mediterranean conditions. Variants may be recognised in relation to aridity, temperature of the coldest month and intensity of summer dryness based on the contribution of average summer rainfall and rainy days to the annual total, percentage frequency of estival rainfall and rainy days, percentage number of years showing mediterranean regime. The degrees of mediterraneity (pure, moderate, attenuated) recognised according to the above criteria are supported by phytogeographic evidence. Dry evergreen sclerophyllous forests, with one ore more of the typical mediterranean species like Olea cuspidata, Pistacia khinjuk, P. mutica, Quercus baloot, Punica granatum, Cedrus deodara occur under moderate degree of mediterraneity. Some of these and few others of mediterranean stock persist under attenuated degree though the forest physiognomy is not well developed. The floristic elements viz. mediterranean, tropical, arid zone and general, show close correlations with the degrees of mediterraneity, aridity and temperature regimes

Is the Sind-Rajasthan desert the result of a recent climatic change?

The author reviews the problem whether the Sind-Rajasthan desert of the Indo-Pakistan sub-continent is of recent origin and which factors are responsible for its creation: climatic change, shifting of rivers, floods, or yet social causes such as wars and man's abuse of his environment resulting in ecological imbalance