Investigating African forest elephant impacts on forest structure and carbon balance using multiscale lidar techniques

Jenna M Keany and Patrick Burns, School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, AZ, Christopher E. Doughty and Andrew Abraham, School of Informatics, Computing, & Cyber Systems, Northern Arizona University, Flagstaff, AZ, Patrick Jantz, School of Informatics, Computing and Cyber Systems, Northern Arizona University, Flagstaff, AZ, Scott J Goetz, School of Informatics, Computing, and Cybersystems, Northern Arizona University, Flagstaff, AZ, Fiona Maisels, Stirling University

Background/Question/Methods
African forest elephants (Loxodonta africana cyclotis) face severe threats from poaching and habitat loss, with estimated population losses between 62-81% in central African since the early 2000’s. Forest elephants are known to transport nutrients across gradients, disperse seeds, and inflict damage to the understory through browsing. It is estimated that changes in vegetation structure from elephant disturbance significantly affect carbon stocks in the Afrotropics, however these findings have not been validated with structural data. This study aimed to quantify the role forest elephants play as ecosystem engineers and their impact on habitat heterogeneity using terrestrial, airborne, and spaceborne lidar (light detection and ranging). Utilizing elephant dung count data, bio-logged tracking data, and four types of lidar for forest composition and structure, urgent questions regarding how elephants impact canopy structure were addressed. Specifically, how do forest elephants impact forest structure? At what lidar resolution can this be detected (cm, 1 m, 18 m, 25 m)? And can lidar be used to identity elephant transitory trails? Not only will these findings address important questions related to ecological function, but they will expand our understanding of forest elephant’s influence on canopy structure.
Results/Conclusions
African forest elephant impact was identified in preliminary results of NASA’s Land, Vegetation, and Ice Sensor airborne lidar (LVIS) returns across high and low elephant areas of Lope National Park, Gabon. Plant area index was averaged across thousands of LVIS waveforms and constrained for distance to road, slope, and canopy cover. Taking the difference in the mean waveforms for high and low elephant areas of the park resulted in a difference in the low to mid canopy (5-20 m), indicating a potential elephant signal of an open understory. Further analysis will include a generalized additive model with variables such as distance to river and human influence, to account for external influences on structure. If elephants impact tropical forests by clearing out the understory and allowing larger trees which store more carbon to succeed, this information could be used by REDD+ to provide additional carbon credits to countries investing in elephant protection. This project would not only assist in conservation efforts of the threatened African forest elephant, but would also improve our understanding of their unique role in the ecosystem.