Em. Nel et al., DIGITAL AND VISUAL ANALYSIS OF THEMATIC MAPPER IMAGERY FOR DIFFERENTIATING OLD-GROWTH FROM YOUNGER SPRUCE-FIR STANDS, Remote sensing of environment, 48(3), 1994, pp. 291-301
The process of old growth conservation would be greatly facilitated if
remote sensing could be used to locate America's few remaining old gr
owth forests. The use of multispectral remote sensing in the identific
ation of old growth has been largely confined to efforts in the Pacifi
c Northwest. The purpose of this study was to determine which image pr
ocessing techniques best discriminate between old growth and younger s
pruce-fir stands in the southern Rocky Mountains. Various image proces
sing techniques were applied to TM imagery of the Marvine Lakes valley
in the Colorado White River National Forest. The study focused on two
major structural differences between the forest types. 1) multistorie
d (old growth) vs. single-storied (young growth) canopies and 2) highe
r frequency of standing dead in old growth. Field measurements of phot
osynthetically active radiation confirmed the hypothesis that old grow
th canopies contain more gaps than the young post-fire stands. Texture
analysis, color-ratio techniques, and vegetation indices successfully
identified old growth. Evaluation of the success of old growth identi
fication within a geographic information system suggested that digital
per-pixel classification was inferior to visual interpretation. Spati
al and spectral methods must be used in combination if structurally va
riable old growth forests are to be detected.