Reforestation mitigates negative impacts of infrastructure by improving habitat connectivity for the Javan leopard

Forest fragmentation, primarily caused by infrastructure expansion and land intensification, is a major threat to biodiversity globally. In Java, the most densely populated island, this fragmentation of remaining forests directly undermines ecological connectivity, which is vital for the persistence of the island's only surviving big cat, the Javan leopard ( Panthera pardus melas ). To evaluate how targeted reforestation may alleviate these impacts, we developed a scenario-based connectivity model using a least-cost framework and two ecological indicators of corridor quality: the ratio of cost-weighted distance to Euclidean distance (CWD:EUC) and the ratio of cost-weighted distance to least-cost path length (CWD:LCP). A baseline scenario that incorporated existing and planned highways and railways was compared with an idealized reforestation scenario simulating the rehabilitation of degraded lands designated as “critical areas”. Across Java, modeled corridors exhibited strong spatial heterogeneity—complex and reticulated in western regions, more linear in central Java, and sparse in the east. Under the reforestation scenario, both connectivity indicators decreased significantly (the mean CWD:EUC ratio decreased by 21%, and the mean CWD:LCP ratio by 24%), reflecting straighter and lower-resistance pathways between core habitats. These results demonstrate that reforestation could potentially improve structural connectivity proxies and may serve as an early indicator of potential functional recovery for wide-ranging carnivores. By linking scenario modeling with quantitative indicators, this study provides a framework for assessing restoration benefits and infrastructure impact in biodiversity-rich yet highly developed tropical landscapes. The findings highlight how strategically located reforestation can partially offset fragmentation, sustain ecological links, and support planning to reconcile development with conservation across Java Island. • We developed an island-wide scenario-based structural connectivity model for the Javan leopard. • We used a least-cost framework to contrast a baseline infrastructure scenario with a reforestation scenario. • We assessed corridor quality based on the ratios of cost-weighted distance to Euclidean distance (CWD:EUC) and to least-cost-path length (CWD:LCP). • The reforestation scenario significantly reduced both ratios, indicating straighter routes and lower mean resistance along optimal paths. • Reforestation can help maintain ecological connectivity in a human-dominated landscape and partially offset the adverse effects of road expansion.