Examining relationships between canopy characteristics and terrace geomorphology in the Peruvian Amazon

Background/Question/Methods

The vast majority of the Peruvian Amazon is supported by terrace surfaces, which are no longer a part of an active floodplain, often referred to as terra firme. Despite their prevalence, the ecological complexity of these systems has received relatively little focus. The relationship between vegetation characteristics in this heterogeneous system and environmental gradients has been challenging to understand due to the large spatial extent and fine spatial resolutions that are required to assess the nature of this relationship. New airborne remote sensing technologies are providing tools that allow us to address these issues at appropriate scale. In 2013 the Carnegie Airborne Observatory (CAO) mapped over 100 km of lowland humid tropical forest in the southwestern Peruvian Amazon.  The CAO collected digital elevation and canopy structure with its high-resolution dual waveform LiDAR and 214 contiguous 10nm bands of high-fidelity imaging spectroscopy data with its Visible-Shortwave Imaging Spectrometer (VSWIR).  The LiDAR data were used to conduct topographic analysis within the study area. The spectral data, which are related to canopy chemical and structural properties, were used to identify gradients in canopy characteristics across this landscape at high resolutions. 

Results/Conclusions

Using high-resolution, LiDAR derived, digital elevation models, we found that this terrace landscape is dissected by streams that have incised up to thirty five meters into the original terrace surface, creating strong topographic gradients within these geomorphic units.  We found that the spectral characteristics of canopies, which are known to be related to foliar biochemical characteristics, vary with these geomorphic gradients. A principal components rotation of the spectral reflectance data from canopies within this terrace, reveals that, when aggregated at five meter elevation intervals, one third of the first twenty principal components are strongly correlated with the depth of incision into the terrace surface (R²>0.6). This indicates that in tropical forests there are biotic responses to within-terrace variability, despite the fact that terraces are often thought to contain fairly uniform, if diverse, forests. These results indicate that topographic gradients, detectable with high resolution elevation data, are important for understanding insight into the organization of terra firme tropical forest ecosystems.