Monitoring Tropical Forest Degradation in Betampona Nature Reserve, Madagascar Using Multisource Remote Sensing Data Fusion

This paper demonstrates how animal and plant species diversity in the Betampona Nature Reserve (BNR), Madagascar has become threatened through forest degradation and the introduction of invasive species over the last two decades. First, land-use changes and agricultural activities were analyzed using Landsat and IKONOS-2 data from 1990 to 2010. Then, a decision tree algorithm was developed to map under canopy invasive plant species using high resolution optical stereo imaging, land-use classification, and characterizing plant growth using Interferometric Synthetic Aperture Radar (InSAR) and polarimetric InSAR observations from Phased Array type L-band Synthetic Aperture Radar (PALSAR). Next, causal association between land use, climate change, and spatial and temporal dynamics of invasive plant species distribution was explored using satellite derived and in situ climate variables, changes in drought regimes, and tropical cyclones. Results showed that the region experienced intense land-use changes characterized by significant increase in agricultural lands at the cost of primary forest and other land-cover types. Encroachment by habitat-altering invasive plants from 2005 to 2012 within the reserve was obvious, and were probably attributable to illegal logging, erosion of the reserve boundary from anthropogenic activities and cyclone damage as well as shifts in drought regimes. The spatial extent of guava (Psidium cattleianum) has increased from 5.6% of the reserve in 2005 to 7.9% in 2012, a 55-ha increase over less than 7 years. Madagascar cardamom (Aframomum angustifolium) has increased by 1.7% and Molucca raspberry (Rubus moluccanus) by 2.3%, respectively.