A possible role of NDVI time series from Landsat Mission to characterize lemurs habitats degradation in Madagascar

Abstract

Deforestation is one of the main drivers of environmental degradation around the world. Slash-and-burn is a common practice, performed in tropical forests to create new agricultural lands for local communities. In Madagascar, this practice affects many natural areas that host lemur habitats. Reforestation within nature reserves including fast-growing native species is desirable, for example in this area using native bamboo with the aim of restoring the habitat increased plantation success. In this context, the extensive detection of forest disturbances can effectively support restoration actions, providing an overall framework to address priorities and maximizing ecological benefits. In this work and with respect to a study area located around the Maromizaha New Protected Area (Madagascar), an analysis was conducted based on a time series of NDVI maps from Landsat missions (GSD = 30 m). The period between 1991 and 2022 was investigated to detect the location and moment of forest disturbances with the additional aim of quantifying the level of damage and of the recovery process at every disturbed location. It is worth noting that the Maromizaha New Protected Area currently hosts 12 species of endangered lemurs, highlighting its pivotal role as a critical conservation and restoration priority due to the ecological significance of preserving habitat integrity to sustain these threatened species. Detection was operated at pixel level by analyzing the local temporal profile of Normalized Difference Vegetation Index - NDVI (yearly step). Time of the eventual detected disturbance was found within the profile looking for the first derivative minimum. Significance of NDVI change was evaluated testing the Chebyshev condition and the following parameters mapped: i) year of disturbance; ii) significance of NDVI change; iii) level of damage; (iv) year of vegetation recovery; (v) rate of recovery. Accordingly, the level of the damage and the rate of recovery were used to estimate resistance and resilience indices of lemurs' habitat (inherently forested areas). Finally, temporal trends of both forest loss and recovery were analyzed to investigate potential impacts onto local lemur populations and, more in general, to the entire Reserve.