open defense of PhD thesis by Madhura Niphadkar, PhD student, ATREE
@ATREE auditorium at 11.00 am on 18th January 2017
Invasive alien species are non-native species that have been intentionally or unintentionally introduced into new regions, and have established thriving populations in these new habitats. The establishment and spread of invasive alien species in landscapes and waterscapes across the world is universally accepted as a potentially dangerous threat to persistence of healthy ecosystems. The threat is real not only because of impacts that the invasive species have on native species in their vicinity, but also because of the complete transformations of ecosystems that they may bring about due to their effects on the structure and functioning of biotic communities. Although invasion is detected and reported in literature, long term observational studies on ecosystems where invasion has occurred are hard to come by. It is becoming increasingly important to monitor ecosystems at landscape level with the available advanced tools such as remote sensing (RS), complemented by detailed field data to understand where and why invasive plant species establish and prosper, so as to deploy resources in the appropriate locations for their management.
Starting from a review of literature on what issues are currently faced by remote sensing technology as applied to invasion, I summarize how RS has been used for mapping invasive alien plants in varied habitats, for a diversity of life-forms. I also highlight how certain traits in invasive plants can be mapped more easily than others by RS, and identify traits? that need attention. Subsequently, taking the case of one particular species, Lantana camara, in a study site - Biligiri Rangaswamy Temple Tiger Reserve (BRT TR)- for which long term data are available, I try to identify the dominant habitat where its occurrence may be detectable in the given landscape, and the scale at which this can be done, using only presence data. Next, I consider various environmental factors within the landscape that are conducive to variation in structural formations of Lantana, which may allow for a ground-up characterization of the landscape in which it occurs. I then test the capability of two different RS techniques to map this understorey shrub in the mixed tropical forests of the study site, using field information and RS tools that emphasize the structural and spectral manifestations of the occurrence of the shrub along with the landscape context. This mapping exercise is the first of its kind to map an invasive understorey shrub in the tropical tiered mixed forests of the Western Ghats using very high resolution remotely sensed data and a hierarchical object-oriented approach. Thus, using first a bottom-up approach from ground information and existing vegetation type maps, and later a top-down approach using RS data, this thesis builds upon long-term observational studies of the growth and proliferation of Lantana camara in the BRT TR landscape, highlighting the possibilities of landscape scale monitoring for management purposes.