LIDAR remote sensing for secondary Tropical Dry Forest identification

Abstract

This study evaluates the use of waveform LIDAR data for the characterization of secondary forests stages in a Tropical Dry Forest (TDF) area of Guanacaste, Costa Rica. A secondary forest succession is defined here as regrowth of woody vegetation following a complete or heavy forest clearance for pasture, agriculture, or other human activity. We first compare the known spatial distribution of three main TDF successional stages (Early, Intermediate and Late successional stages) as constrained by published field observations of tree height with that obtained from a three-class classification of the LIDAR data. In doing so we explicitly assess the possibility of using LIDAR data to map the distribution of the three main TDFs stages. We demonstrates that changes in the forest vertical structure (such as height) associated with principal successional stages (Early, Intermediate and Late) of TDF secondary growth can be effectively identified from LIDAR data. The successional sequence observed is related to changes in the vertical distribution of woody components that occur when forest patches evolve from an Early Stage which is dominated by sparse trees and grass, to initial stages of intermediate secondary succession characterized by small canopies and a high density of understory regeneration, and then to more complex and developed stages of intermediate and late stage secondary succession which share some attributes of Old growth forests. We then focus on the Intermediate successional Stage since it is of highest interest to policy makers dealing with programs implementing payments for environmental services. We show that an analysis of the LIDAR data can identify successional three subclasses within the Intermediate Stage providing further insights in the development of secondary forest growth. A validation of the three new forest classes is provided using field observations showing a mean tree height and standard deviation of 6.16±0.87, 7.82±0.31 and 8.62±1.22. m.