Ecological Niche Modeling of Nuxia capitata and Phyllarthron madagascariensis: Delineating Bioclimatic Envelopes for Sustainable Forest Management in Madagascar

Abstract

Nuxia capitata Baker (Stilbaceae) and Phyllarthron madagascariensis K. Schum. (Bignoniaceae) represent high-value endemic forest resources in Madagascar, traditionally exploited for medicinal applications and timber. However, accelerating anthropogenic pressures and habitat fragmentation severely threaten their wild populations, hampering the transition toward sustainable resource management. This study leverages Maximum Entropy (MaxEnt) ecological niche modeling to delineate their contemporary bioclimatic envelopes, identify primary environmental drivers, and evaluate the conservation efficacy of the national Protected Area network (SAPM). Models were calibrated using primary georeferenced occurrence records and filtered, non-collinear biophysical predictors. The generated algorithms demonstrated exceptional predictive accuracy, yielding training Area Under the Curve (AUC) values of 0.951 for N. capitata and 0.919 for P. madagascariensis. Quantitative spatial assessments indicate that the total suitable geographic range encompasses 76,188.85 km² (13.35% of the national territory) for N. capitata and 127,693.60 km² (22.38%) for P. madagascariensis. Bioclimatic analyses reveal that the distribution of N. capitata is strictly constrained by annual mean temperature (75.6% contribution), showing a high affinity for cool highland ecosystems. Conversely, P. madagascariensis is primarily governed by precipitation seasonality (43.4% contribution), tracing a contiguous latitudinal belt along the eastern humid forest biome. Spatial overlays demonstrate that 31.81% of the N. capitata niche and 36.36% of the P. madagascariensis range intersect protected areas. While the eastern rainforest populations are relatively well-preserved, critical protection gaps exist in the central highlands, particularly within the Analamanga region. Strengthening community-based forest management transfers (VOI) is urgently recommended to secure these fragmented genetic reservoirs and preserve associated indigenous ethnobotanical knowledge.