🧬 biology

Influence of forest structure on butterfly diversity in tropical deciduous forests of Sambalpur district, Odisha, India

This study demonstrates that Reserve Dense Forests in the Sambalpur district of Odisha support the highest butterfly diversity compared to open and plantation forests, highlighting the critical role of vegetation structure and seasonal variation in shaping butterfly communities within tropical deciduous landscapes.

Original authors: BASUDEV BACHA, AYUSMITA NAIK, ANIRBAN MAHATA

Published 2026-10-22

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: BASUDEV BACHA, AYUSMITA NAIK, ANIRBAN MAHATA

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

In the complex web of life, some creatures act as living barometers, rising and falling with the health of their environment. Butterflies are among the most sensitive of these indicators. Because they rely so heavily on specific plants for food and shelter, and because they cannot survive long without the right temperature and humidity, their presence or absence tells a clear story about the condition of a forest. When a forest is healthy, with a mix of tall trees, thick undergrowth, and plenty of flowers, butterflies thrive. When that structure is broken by human activity or climate shifts, the butterfly community changes, often losing its most specialized members. Understanding these shifts is crucial for conservationists, as protecting the butterflies often means protecting the entire ecosystem they inhabit.

A recent study in the tropical deciduous forests of western India sought to understand exactly how the physical shape of a forest influences the variety of butterflies living within it. Researchers focused on the Sambalpur district in the state of Odisha, an area characterized by dry forests that lose their leaves during the hot summer months. They chose to compare three distinct types of forest habitats that exist side by side in this region: an open forest where the canopy is thin and sunlight reaches the ground; a dense forest with a thick, continuous roof of leaves; and a plantation forest, which consists of trees managed by humans. Over the course of a full year, from January to December 2022, the team walked along six specific paths, two in each type of forest, counting every butterfly they saw. They walked these paths once a month, carefully noting the species and the time of day, to build a complete picture of how these insects move and live throughout the changing seasons.

The results revealed a clear preference for complexity. The dense, natural forest, where trees grow close together and the vegetation is layered and varied, supported the richest and most diverse community of butterflies. In this habitat, the researchers recorded the highest number of different species and the most even distribution of individuals among those species. This area was home to 98 different species of butterflies belonging to six distinct families. The most common family found was the Nymphalidae, which included 37 different species, followed by the Lycaenidae with 23 species. In contrast, the open forest and the human-managed forests held fewer species and were dominated by just a few common types that could tolerate more open, disturbed conditions. The study found that the dense forest was not just a place with more butterflies, but a place with a more balanced community, where no single species completely took over.

The physical structure of the forest mattered just as much as the type of forest. The dense forest provided a stable environment with a wide variety of host plants for butterfly caterpillars and nectar sources for adult butterflies. This structural complexity allowed many different species to find their own specific niche, reducing competition and allowing them to coexist. The open forest, which was recorded as having high levels of human interaction and grazing, supported fewer species and was largely inhabited by generalist butterflies that could survive in a range of conditions. The plantation forest, while better than the open forest, still lacked the natural variety needed to support the full range of butterfly life found in the dense, untouched woods. The researchers noted that four of the species they found are legally protected under Indian law, highlighting that these forests are critical refuges for wildlife that is at risk.

Time also played a major role in the story. The number of butterflies and the variety of species changed dramatically depending on the season. The highest diversity and the greatest number of butterflies were observed during the post-monsoon period, the time immediately following the heavy summer rains. During this season, the forest was lush, with abundant flowers and fresh leaves, providing an explosion of food and breeding grounds. The summer months, with their intense heat and dry conditions, saw a sharp decline in both the number and variety of butterflies. The winter and monsoon seasons fell somewhere in between, but the post-monsoon peak was unmistakable. This seasonal rhythm suggests that the health of the butterfly population is tightly linked to the timing of the rains and the subsequent growth of the forest.

The study concludes that the physical structure of a forest is a primary driver of butterfly diversity in this region. Dense, heterogeneous forests act as strongholds for biodiversity, supporting a wide array of species including those that are rare or legally protected. Open and plantation forests, while still supporting some life, cannot match the richness of the natural, undisturbed woods. For conservation efforts in eastern India, this means that preserving the structural complexity of existing dense forests is essential. It is not enough to simply have trees; the arrangement, density, and variety of those trees determine whether a forest can sustain a thriving community of butterflies. By monitoring these insects, forest managers can gain a clear, real-time understanding of how their land is faring, ensuring that the delicate balance of the tropical deciduous forest is maintained for the future.

Technical Summary: Influence of Forest Structure on Butterfly Diversity in Tropical Deciduous Forests of Sambalpur District, Odisha, India

Problem Statement
Tropical dry deciduous forests (TDDFs) constitute a significant portion of India's forest cover but face persistent pressures from anthropogenic activities such as agricultural expansion, mining, and fragmentation. These disturbances alter microclimatic conditions and threaten ecosystem integrity. While butterflies serve as reliable bioindicators of ecosystem health and are sensitive to habitat degradation, comprehensive data on their community assemblages across varying forest habitat types in western Odisha remains limited. Specifically, there is a lack of systematic understanding regarding how butterfly species richness, abundance, and assemblages differ among Reserve Open Forests, Reserve Dense Forests, and Reserve Plantation Forests, and how these communities respond to seasonal variations in the Sambalpur district.

Methodology
The study was conducted in the Sambalpur district of western Odisha, located within the central Mahanadi River basin. Three distinct forest habitat types were selected based on forest cover characteristics and management regimes:

Reserve Open Forest (S1): Characterized by high human interference (HI) and grazing (G).
Reserve Dense Forest (S2): Characterized by least human interference and grazing.
Reserve Plantation Forest (S3): Characterized by moderate human interference and least grazing.

Six transects (two per habitat type), each 500 meters long, were surveyed monthly from January to December 2022. Butterfly abundance was assessed using the Pollard Walk method within a defined sampling window (2.5 m on either side of the transect, 5 m ahead and above). Surveys were conducted between 08:00 and 11:00 h by two observers.

Data analysis involved calculating species richness ( $S$ ) and relative abundance. Diversity was evaluated using Hill numbers: species richness ( $q=0$ ), Shannon diversity ( $q=1$ ), and inverse Simpson diversity ( $q=2$ ). Rarefaction and extrapolation curves were generated using the "iNEXT" package in R to assess sampling completeness. Differences in richness and abundance among sites and seasons (Winter, Summer, Monsoon, Post-monsoon) were analyzed using non-parametric Kruskal–Wallis tests, followed by pairwise Wilcoxon rank-sum tests with Benjamini–Hochberg correction. Effect sizes ( $r$ ) were calculated to quantify the magnitude of differences.

Key Results

Species Inventory: A total of 98 butterfly species belonging to six families were recorded. The family Nymphalidae was dominant (37 species), followed by Lycaenidae (23), Pieridae (14), Hesperiidae (12), Papilionidae (11), and Riodinidae (1). Four species (Pachliopta hector, Papilio clytia, Hypolimnas misippus, and Tanaecia lepidea) are listed under the Wildlife (Protection) Act, 1972.
Habitat Comparison: The Reserve Dense Forest (S2) supported the highest diversity, with the highest Shannon index ( $^1D = 54.75$ $^{1} D = 54.75$ ) and inverse Simpson index ( $^2D = 36.57$ $^{2} D = 36.57$ ). This was followed by the Plantation Forest (S3) and the Open Forest (S1).
- Richness: Significant differences were found among sites ( $p < 0.01$ ). S2 had significantly higher richness than both S1 and S3, while no significant difference existed between S1 and S3.
- Abundance: S2 showed significantly higher abundance than S1 ( $p < 0.05$ ). No significant differences were found between S1 and S3 or S2 and S3.
- Community Composition: Generalist species (e.g., Catopsilia pomona, Euploea core) were common across all sites, while habitat specialists like Tagiades gana and Troides helena were primarily restricted to the dense forest (S2).
Seasonal Variation: Significant seasonal variation was observed for both richness and abundance ( $p < 0.05$ ). The post-monsoon season exhibited the highest species richness (median 65) and abundance (median 435), significantly differing from summer, monsoon, and winter. Summer recorded the lowest richness and abundance.
Sampling Completeness: Rarefaction curves approached asymptotes for all habitats, and sample coverage was high (99.88%–100%), indicating adequate sampling effort.

Key Contributions
This study provides baseline data on butterfly diversity in the western Odisha region, a area previously underrepresented in comprehensive forest habitat studies. It quantifies the specific influence of forest structural complexity (Open vs. Dense vs. Plantation) on butterfly assemblages, demonstrating that structurally complex, undisturbed dense forests support higher diversity and evenness compared to open or plantation forests. Furthermore, the research elucidates the temporal dynamics of these communities, identifying the post-monsoon period as a critical window for peak biodiversity.

Significance and Claims
The authors claim that the findings demonstrate that dense and structurally heterogeneous forest habitats are essential for supporting diverse butterfly communities in tropical deciduous landscapes. The presence of legally protected and habitat-specialist species in the study area underscores its value as a regional refuge. The study emphasizes that maintaining intact dense forest patches and regulating anthropogenic disturbances are critical for conservation. Additionally, the authors assert that integrating butterfly-based monitoring into forest management and landscape-level conservation planning is necessary to safeguard these ecological indicators against ongoing land-use changes and climate variability in eastern India. The paper concludes that the observed diversity patterns are driven by habitat quality, structural complexity, and seasonal resource availability, rather than methodological artifacts.

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