The research team, led by James Michael Machallo of the University of Dodoma’s Department of Biology, focused on surface-active insects, the ants, beetles, spiders, and other arthropods that crawl and forage across the soil surface. These creatures are more than ecological wallpaper. They pollinate plants, decompose organic matter, recycle nutrients, and form the base of food webs that support birds, reptiles, and small mammals. Because they respond quickly to changes in habitat structure and microclimate, their diversity and abundance are widely used as indicators of ecological integrity. Yet while insect communities have been well documented in natural forests, wetlands, and intensive monocultures, relatively little is known about how newly established agroforestry systems in semi-arid regions shape these communities, a gap that matters because agroforestry is increasingly pitched as a flagship land-use strategy for the world’s drylands.

To fill that gap, the team sampled insects across four habitats on the university’s 6,000-acre campus, located about eight kilometers east of Dodoma city. Three of the sites had been transformed by human activity: an agroforestry plot at the College of Natural and Mathematical Sciences, where crops such as bananas and vegetables grow alongside exotic trees like Leucaena leucocephala and Gliricidia sepium; an afforested woodland at the College of Education, dominated by planted exotic species including neem and eucalyptus; and a shrubland behind the College of Humanities and Social Sciences, where natural shrubs and grasses persist after the original bush was cleared. The fourth site, near the College of Informatics and Virtual Education, remained an intact semi-arid bushland dominated by native trees, serving as a reference ecosystem.

Sampling took place in March and April 2025, a deliberately chosen window when the vegetation is fully green, most plants are flowering or seeding, and surface-active insect activity peaks just before the dry season sets in. The researchers laid out two 100-meter transects at each site, spaced 500 meters apart, and placed five one-liter pitfall traps along each transect at 20-meter intervals. Each trap was filled with 250 milliliters of water spiked with a few drops of detergent to break the surface tension, and no bait was used, ensuring that every insect caught was there by chance encounter rather than attraction. Over three consecutive days, the team emptied all 40 traps every 24 hours, accumulating 120 samples across roughly 2,880 trapping hours. Specimens were preserved in 70 percent alcohol and identified in the laboratory using standard taxonomic keys, regional guides, and, where necessary, morphospecies designations based on distinct physical traits.

The haul was substantial: 2,889 individual insects representing 53 species from 14 orders. Afforested sites proved the busiest, accounting for 30 percent of all captures, with agroforestry close behind at 28 percent. Shrubland contributed 25.4 percent and bushland just 16.6 percent. But abundance told only part of the story. When the researchers calculated species richness and diversity, the rankings flipped. Shrubland, the remnant habitat of natural shrubs and grasses, supported the highest number of species at 36, along with the highest Shannon diversity index of 1.86 and the highest Simpson index of 0.75. Afforested woodland followed with 34 species, while bushland and agroforestry each hosted only 29. Agroforestry recorded the lowest diversity values of any habitat, and its community was heavily dominated by a single species, the predatory ant Pachycondyla tarsata, which made up 17.44 percent of that site’s assemblage.

Dominance by a handful of tolerant species emerged as a recurring theme in the transformed habitats. Across the whole study area, spiders (Araneae) were the most abundant group at nearly 30 percent of all individuals, followed by Pachycondyla tarsata at 27 percent and ants of the genus Lepisiota at nearly 27 percent. At the other end of the scale, species such as the termite Amitermes, the praying mantis Epioscopomantis chalybea, and crickets of the family Gryllacrididae were recorded only twice each. The researchers suggest that the non-native vegetation and more frequent disturbances typical of agroforestry and afforested plots filter out sensitive species while allowing a few hardy generalists to proliferate, a pattern that shifts communities from balanced diversity toward dominance.

Statistical modeling sharpened the picture. Generalized linear models, with afforested habitat as the reference category, showed that only afforested sites had a significantly positive effect on insect abundance, richness, and both diversity indices. None of the other habitats, including agroforestry, showed a meaningful effect. In other words, the apparent richness of shrubland may reflect local sampling variation rather than a consistent ecological advantage, while the structural complexity of the woodlands, with their leaf litter, shade, and buffered microclimates, appears to provide genuinely stable microhabitats that sustain diverse assemblages. This finding diverges from earlier studies that reported higher insect richness in shrublands and bushlands, a discrepancy the authors attribute to differences in habitat age, successional stage, and the presence of residual natural vegetation.

The community composition analysis delivered perhaps the study’s most technically intriguing result. Non-metric multidimensional scaling, an ordination technique that arranges samples in two-dimensional space based on Bray-Curtis dissimilarities, produced a visually clear separation of the four habitats, with an excellent stress value of 0.068 indicating the ordination reliably captured community differences. Yet a formal PERMANOVA test found that habitat explained 41.8 percent of the variance in composition but was not statistically significant, with an F value of 0.96 and a p value of 0.546. The plot thickened when the team ran PERMDISP, a test of homogeneity of multivariate dispersions. That analysis detected highly significant differences in the spread of samples within each habitat group, with p values below 0.001. The interpretation is subtle but important: the habitats did not differ so much in which species they contained as in how variable their communities were from sample to sample. Within-habitat heterogeneity, not habitat type per se, appears to be the primary driver of community structure in these transformed landscapes.

That conclusion carries real weight for conservation practice. If fine-scale features such as vegetation patchiness, canopy cover, litter depth, and microhabitat diversity matter more than broad habitat categories, then simply designating land as agroforestry or woodland is not enough. The authors argue that conservation strategies in semi-arid landscapes should prioritize maintaining habitat heterogeneity and structural complexity to stabilize insect communities and sustain the ecosystem services they underpin. Afforested woodlands, despite being planted with largely exotic species, emerge as valuable refuges that should be protected and expanded with minimal disturbance. Agroforestry systems, by contrast, need targeted interventions, such as integrating native tree species and reducing disturbance, to shift from abundance-driven dominance toward balanced diversity. The high diversity of remnant shrubland and bushland underscores their role as reservoirs of insect biodiversity that should be conserved outright.

The study is candid about its limitations. Sampling was confined to a single seasonal peak, so temporal dynamics across the year remain invisible. Pitfall traps capture crawling, surface-active taxa but miss flying insects, including many key pollinators. Crucially, environmental variables such as rainfall, temperature, humidity, canopy cover, litter depth, and soil characteristics were not systematically measured, which limits how much of the observed variation can be explained. The age of each transformed ecosystem, a factor known to influence its capacity to support diversity, was also not assessed. Future work, the authors say, should extend sampling across seasons, deploy complementary collection methods to capture a wider range of insect guilds, and integrate detailed vegetation and microclimate data. For now, the message from Dodoma is clear and slightly counterintuitive: in the world’s drylands, planting trees can fill the ground with insects, but only heterogeneous, structurally complex habitats can fill it with many different kinds, and it is the variety, not the volume, that keeps ecosystems resilient.

Subject of Research: Effects of agroforestry and land-use transformation on ground-dwelling insect abundance, richness, and diversity in semi-arid Tanzania

Article Title: Effects of agroforestry practices on insect abundance, richness, and diversity, in transformed ecosystems of the semi-arid area, Dodoma, Tanzania

Article References: Machallo, J. M., Ngongolo, K., & Mmbaga, N. E. (2026). Effects of agroforestry practices on insect abundance, richness, and diversity, in transformed ecosystems of the semi-arid area, Dodoma, Tanzania. Frontiers in Conservation Science, 7, Article 1918561. https://doi.org/10.3389/fcosc.2026.1918561

Image Credits: AI Generated

DOI: 10.3389/fcosc.2026.1918561

Keywords: agroforestry, insect diversity, semi-arid ecosystems, Tanzania, pitfall traps, species richness, habitat heterogeneity, afforestation, community composition, biodiversity conservation, Pachycondyla tarsata, ecosystem services