Three decades of annual forest monitoring reveal a troubling story: from the outside, the dry tropical forests of central India look intact, with mature trees still towering over the land, yet beneath the canopy a hidden demographic decline is unfolding. A study covering eight monitoring plots in the states of Madhya Pradesh and Chhattisgarh analysed the regeneration dynamics of 101 tree species between the years 1991 and 2021, comparing the size structure of the stands at these two points in time. The layer of young regrowth — grassy seedlings and slender saplings — tells a very different story from the outward appearance of the old forest.
The main ecological shift is occurring between functional groups of tree species. Light-demanding pioneer species, which are the first to colonise open areas and bright forest gaps, maintain or even improve their regeneration rates. By contrast, shade-tolerant and late-successional species — the trees that define the character of a mature forest — are gradually losing ground in the younger generation. The flow of their seeds, sprouts and seedlings is thinning year by year, creating a hidden deficit of young individuals that is revealed only through detailed analysis of size structure. Under a changing monsoon climate, characterised by increasingly sharp fluctuations in rainfall and temperature extremes, the trees that form the backbone of the mature forest are proving unable to reliably replace themselves.
At the same time, attempts to predict the fate of individual species solely from their functional traits — light demand, shade tolerance or fruit dispersal type — showed low predictive accuracy. Statistical models explained only a small share of the observed variation in species trajectories, which confirms a fundamental principle: knowledge of a species' ecological traits sets only the general direction of a trend but does not determine its outcome. Local conditions — the nature of seed dispersal by animals and wind, soil properties, competition and interactions between species, as well as the microclimate beneath the forest canopy — have a key and often decisive influence on the survival and growth of young plants.
Using the metric of change in the slope of the size distribution allows forestry and conservation services, without costly long-term measurements of individual trees, to identify species that have entered a critical situation. This method makes it possible to apply targeted conservation and restoration measures in good time: carry out enrichment plantings of rare species, regulate the intensity of thinning of the upper canopy, and protect young regrowth from fire and livestock grazing. Data from three decades of intensive monitoring confirm that the forests of central India have already actively begun to change their species composition and structure.
