Plantation-Driven Watershed Degradation and Intergenerational Erosion of Traditional Ecological Knowledge in the Chittagong Hill Tracts, Bangladesh: A Multi-Ethnic Comparative Study

Abstract

The Chittagong Hill Tracts (CHT) of Bangladesh harbors at least 13 indigenous communities whoselivelihoods, cultural identities, and ecological knowledge systems are intimately embedded in a forestedhill landscape now undergoing rapid transformation. This study investigates a theoretically proposed butempirically untested causal chain: that plantation expansion reduces spring water availability, which inturn severs the ecological contexts of traditional ecological knowledge (TEK) transmission, drivingmeasurable intergenerational knowledge loss. Drawing on a mixed-methods design comprising multitemporal Landsat LULC analysis (1993-2023), a structured household survey (n=600) using an adaptedTEK Transmission Index (TEK-TI), and qualitative life-history interviews (n=60) across five ethniccommunities (Chakma, Marma, Tripura, Mro, and Khasi) in all three CHT districts, the study tests thisstructural mechanism using piecewise structural equation modelling (piecewiseSEM) with bootstrapmediation analysis. Results reveal that dense forest cover declined by 6.23% and settlement/plantationarea increased by 10.34% between 1993 and 2023, with rubber monoculture a primary driver. SpringWater Availability Index (SWAI) scores declined significantly across all communities, with communitiesin high-plantation-exposure zones reporting 47% lower SWAI than low-exposure communities. Theintergenerational TEK-TI gap, the difference in mean ecological knowledge scores between elders (55+)and youth (18-29), averaged 28.4 points (on a 0-100 scale) across all communities, with the Mrocommunity exhibiting the highest gap (34.7) and the Khasi the lowest (21.3). Piecewise SEM confirmsthat watershed degradation fully mediates the effect of plantation expansion on TEK erosion (indirectpath coefficient: β = −0.41, 95% CI [−0.56, −0.27], p < 0.001), with the direct effect rendered nonsignificant once SWAI is controlled. Multi-group invariance testing reveals significant ethnic moderation,with land tenure security and cultural transmission institution strength moderating the plantationwatershed-TEK pathway. These findings provide the first empirical quantification of hydrologicallymediated TEK erosion, with direct implications for CHT forest governance, indigenous land rights policy,and the integration of biocultural diversity conservation into the Bangladesh Delta Plan 2100.