Evergreen and Deciduous Trees in the Western Ghats Blur the Leaf Economics Spectrum

For decades, ecologists have leaned on one of the most influential frameworks in plant science to predict how trees make a living: the leaf economics spectrum. The idea is elegant. On one end of the spectrum sit the fast-living species, whose leaves are cheap to build, rich in nitrogen, thin, and short-lived, capturing carbon in quick bursts before being shed. On the other end sit the slow-living species, whose leaves are expensive, tough, dense, and long-lived, conserving hard-won nutrients over months or years. If the framework holds in its simplest form, a tree’s leaf habit—whether it keeps its leaves year-round as an evergreen or drops them seasonally as a deciduous species—should map cleanly onto one end or the other. A new study from the seasonally wet forests of India’s central Western Ghats suggests that, in these environments at least, the tidy correspondence between leaf habit and leaf strategy largely breaks down.

The research, published in BMC Plant Biology by Mahim Bhat of the Manipal Centre for Natural Sciences and colleagues, examined 93 co-occurring woody species in a seasonally wet evergreen forest of the central Western Ghats, a mountain chain along India’s western coast that ranks among the world’s most important biodiversity hotspots. Of the species sampled, 67 were evergreen and 26 were deciduous. The team measured seven key leaf functional traits that together capture the core axes of the leaf economics spectrum: leaf area, specific leaf area, leaf thickness, leaf dry matter content, leaf tissue density, mass-based leaf nitrogen content, and the carbon-to-nitrogen ratio. These traits are the standard currency of comparative plant ecology, chosen because each one reflects a measurable trade-off between acquiring resources quickly and conserving them over time.

Specific leaf area, for instance, is the light-capturing surface a leaf presents per unit of dry mass; high values typically signal the fast, acquisitive end of the spectrum, while low values indicate investment in durable tissue. Leaf dry matter content and leaf tissue density quantify how much structural material a leaf packs into its volume, which relates to toughness, defense, and lifespan. Leaf nitrogen content tracks the photosynthetic machinery, since the enzymes that fix carbon are nitrogen-hungry, and the carbon-to-nitrogen ratio offers a complementary window into how much of the leaf’s budget is devoted to structure rather than metabolism. Leaf area, meanwhile, shapes water and energy balance. If evergreen and deciduous species truly occupy distinct economic strategies, these traits should differ systematically and consistently between the two groups.

That is not what the data showed. When the researchers compared each trait individually between evergreen and deciduous species, the differences failed to survive statistical scrutiny. None of the seven traits remained significant after the authors applied the Holm correction, a procedure that guards against the false positives that inevitably arise when many comparisons are made at once. In other words, any apparent differences in specific leaf area, nitrogen content, or the other measures between the two phenological groups were within the range expected by chance once the multiplicity of tests was properly accounted for. For a framework as widely assumed as the leaf economics spectrum, the absence of trait separation between leaf habits is a striking result.

The multivariate picture told the same story. Using principal coordinates analysis, a technique that projects the full suite of traits into a common space so that species can be visualized as points, the researchers found that evergreen and deciduous species overlapped substantially, with roughly 45.86 percent of the multivariate trait space shared between the two groups. Rather than forming two discrete clusters, the species formed a continuum in which deciduous trees frequently sat amid evergreens and vice versa. A formal test of the multivariate trait composition, PERMANOVA, did detect a statistically significant difference between the groups overall, and a companion test, PERMDISP, indicated that the difference was accompanied by differences in dispersion, with deciduous species showing greater spread in trait space than their evergreen counterparts.

That combination of results is worth unpacking, because it illustrates a subtlety that often gets lost in headline summaries of ecological statistics. A significant PERMANOVA can arise either from a genuine shift in the location of a group within trait space or simply from one group being more dispersed than the other. The PERMDISP result suggests that at least part of the signal the researchers detected reflects the wider, more variable trait repertoire of the deciduous species rather than a clean separation of the two groups into distinct economic zones. Deciduous species in this forest appear to be anything but a uniform guild of fast-investing, nitrogen-rich leaf builders; instead, they scatter across a broad swath of the same functional space that evergreens occupy.

The team also examined the functional trait space of each group using three complementary indices. Functional richness captures the total volume of trait space a group fills, functional dispersion measures how spread out species are around the group’s center, and functional divergence quantifies how strongly species cluster near the edges of that space rather than the middle. Functional divergence did not differ between evergreens and deciduous species. Functional dispersion, consistent with the PERMDISP finding, was greater among deciduous species. The raw estimates of functional space extent were larger for evergreens, but the authors were careful to test whether that impression survived a fair comparison. Because the evergreen sample contained more than twice as many species as the deciduous sample, raw estimates of occupied trait space could simply reflect sample size, since larger samples tend to fill more of the available space by chance alone.

When the researchers adjusted for sample size, the apparent advantage of evergreens evaporated. The larger raw evergreen estimates of functional space extent, they concluded, should not be interpreted as evidence that evergreens intrinsically occupy a broader range of functional strategies. This kind of methodological caution matters well beyond the Western Ghats. Functional diversity indices are sensitive to sampling effort, and comparisons between groups of unequal size can easily generate spurious conclusions about which group is functionally more diverse. By explicitly correcting for the imbalance, the study models a standard of rigor that comparative trait ecology increasingly demands.

What explains the overlap? The authors point to the distinctive environment of a seasonally wet tropical forest. Unlike savannas or dry forests, where drought is severe and prolonged enough to impose a strong, shared filter on leaf design, seasonally wet forests experience moisture stress that is real but buffered. Soils may retain water through much of the dry season, humidity remains comparatively high, and the dry period, while predictable, is not extreme enough to force every deciduous species into the same water-conserving leaf architecture. Under such conditions, both evergreen and deciduous species can achieve viable combinations of traits, and the phenological difference—when leaves are produced and shed—becomes a matter of timing rather than of fundamentally different leaf construction. Leaf habit, in other words, may be a poor proxy for leaf economics wherever the environmental filter is moderate rather than harsh.

The implications ripple outward. Global vegetation models and Earth system simulations often assign plant functional types on the basis of phenology, treating evergreen and deciduous categories as ecologically meaningful units with distinct trait values. If leaf habit does not reliably predict leaf economics in seasonally wet forests, those models may be mischaracterizing carbon and nutrient cycling in exactly the kinds of ecosystems—monsoon-driven tropical forests—that cover large and climatically important regions of the planet. The study also adds to a growing body of work suggesting that the leaf economics spectrum, while robust at global scales, expresses itself differently in local communities, where evolutionary history, soil conditions, and disturbance regimes can scramble the expected correlations. For the Western Ghats, a hotspot under pressure from fragmentation and climate change, the message is that conserving functional diversity requires looking at the full spread of leaf strategies within the forest, not simply counting evergreen and deciduous species as if they were two interchangeable boxes. The trees of these wet Indian forests, it turns out, refuse to read the textbook.

Subject of Research: Leaf economic trait overlap between evergreen and deciduous woody plants in a seasonally wet tropical forest

Article Title: Overlapping leaf economic strategies of evergreen and deciduous woody plants in a seasonally wet tropical forest of the western ghats

Article References: Bhat, M., Rajendiran, G., Bhat, V. S., Raghavendra, S., Pujari, A., Vastrad, N., Kumara, H. N., & Pandi, V. (2026). Overlapping leaf economic strategies of evergreen and deciduous woody plants in a seasonally wet tropical forest of the western ghats. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10107-6

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10107-6

Keywords: leaf economics spectrum, leaf functional traits, Western Ghats, tropical forest ecology, evergreen, deciduous, leaf phenology, specific leaf area, functional trait space, plant ecology, BMC Plant Biology, India