Estimates of landscape composition from terrestrial oblique photographs suggest homogenization of Rocky Mountain landscapes over the last century

Abstract

While orthogonal (i.e., aerial or satellite) imagery has become the more conventional source of land cover data because it can yield spatially accurate land cover maps, terrestrial oblique photographs present a valuable, relatively untapped source of raw optical data for studies of land cover change. We present a case study contrasting how these two types of imagery sample landscape composition and using repeat oblique photographs to evaluate long‐term land cover change in a remote region of the Canadian Rocky Mountains. We classified 46 historical oblique photographs and their corresponding modern repeats using the same discrete land cover classes employed in a Landsat‐based map of the same area. We compared landscape‐level composition estimates from both sources and regressed the land cover proportions from Landsat against the modern oblique images, hypothesizing a linear relationship for most classes. We found that the two sources sampled the landscape in broadly similar ways, with near‐concordance for dominant land cover classes, yet that oblique photographs more frequently detected narrow landscape features and estimated higher proportions of rock compared to satellite imagery, possibly due to the higher spatial resolution of the oblique photographs, and to their angle of incidence against steep slopes. We then evaluated land cover change from corresponding historical and repeat photographs and found that the landscape has homogenized over the past century via increased coniferous forest cover. Our work shows that terrestrial oblique photographs can be used to estimate landscape composition, particularly in mountain environments. This is helpful for analyzing past landscape conditions in historical photographs, monitoring decadal‐span landscape change and assessing habitat to model biodiversity through time.

Forest closure and encroachment at the grassland interface: a century‐scale analysis using oblique repeat photography

“…To make the most effective use of historical oblique imagery, we advise the following: (1) limit the areas to be classified within the image to where vegetation categories can be clearly identified (i.e., restrict the viewshed); (2) rather than sequentially georeferencing and then classifying images to cover the landscape, determine the best image to use to classify specific locations (proximity and angle of view); (3) classify the images at a finer resolution to enable more detailed measurements to be taken of the vegetation; (4) develop supervised classification methods unique to oblique imagery to enable analysis of larger collections of imagery (Fortin et al. ).…”

“…, Watt‐Gremm , Kubian , Fortin et al. ), their real potential to evaluate large spatial scale ecological change throughout the Alberta Rocky Mountain region has remained largely untapped.…”

Automatic Detection of Spatiotemporal Urban Expansion Patterns by Fusing OSM and Landsat Data in Kathmandu

“…We tallied the built-up area changes on the map with changes on historic and recent photos of the same location. On each photo pair, we inserted a grid to easily inspect built-up area proportions [63,64].…”

A century of high elevation ecosystem change in the Canadian Rocky Mountains

“…In most instances, oral and traditional knowledge around treeline change is incomplete or restricted to areas of local interest, lacking broad spatial coverage 17 . Repeat photography, while often lacking species-specific information, can provide large spatial and temporal coverage and has been used successfully to document treeline and northern landscape change [18][19][20][21] .…”