320 THE JOUKNAL OF INDIAN BOTANY.
the Allahabad thorn scrub is not truly xerophilous. According to Brandis the area ought to be able to support a "really successful forest". In adjacent hilly regions, especially to the south, where there is a much smaller amount of land suitable for cultivation, and the population consequently is much less, a successful forest occurs (Fig. 16). It appears as if forests and density of population may be definitely correlated with each other in India.
We must assume then that if the human factors were lessened or eliminated, the area would more or less rapidly pass into the complete thorn scrub stage, or even into a true thorn forest. In the protection of the grasses, shrubs, and trees of this forest,' a more mesophyfcic type of forest would develop. Some of the thorn scrub trees, as Zizpyhus jujuba, Acacia arabica, and Alangium lamarckii, would develop to much larger dimensions (Fig. 15). Butea frondosa would become abundant. Such a forest is pioneer to the climatic climax in the mountainous region to the south. Other trees, as Dalbergia sissoo Eoxb, and Holoptelea integrifolia Planch, at present exclusively culti- vated would quite readily become self-perpetuating components of such a forest. Finally, there would be the slower influx of truly climax trees from neighboring forested areas.
The development of such a forest might result in some increase of rainfall, making conditions still more favorable for the development of a high forest. Brandis records (2) an instance of slight increase of rainfall following thorough-going protection of a large forest tract in Central India. Certainly a dense intermediate forest, with its accompanying herbaceous and shrubby floor vegetation, would greatly conserve rainfall by preventing rapid run-off of the monsoon rains, and by increasing the relative humidity during the hot season.
Climatic climax monsoon deciduous forest stage. Probably the dominant constituents of the ultimate climatic climax forest would be immigrants from neighboring forested areas to the north and south. We should expect to find Terminalia tomentosa Bedd, and Tectona grandis L., dominant. Almost certainly species of Sterculia, Bombax malabaricum DC, Anogeissus latifolia Wall, Stephegyne parvifolia Korth., Buchanania latifolia Eoxb., Eugenia jambolana Lamk., and other fine trees, and Dendrocalamus strictus Nees would invade the area from the forests both to the north and to the south. Acacia catchu Willd., and even Shorea robusta Gaertn, might finally be represented. With such immigrants, and in the protection of their shade, a new herbaceous and shrubby vegetation, at present unknown in the area, would spring up. Perhaps several species now found only in favored places in protected planted groves would become compon- ents of this undergrowth.
