Using small-format, stereo photogrammetry to characterize changes in the three-dimensional crown architecture of loblolly pine (Pinus taeda L.)

The objectives of this research were two fold: (1) to develop new tools and techniques that could be used to nondestructively obtain detailed, three-dimensional information about crown architecture; and (2) to use these new techniques to examine changes in the three-dimensional crown architecture (i.e., quantity of foliage and its distribution) of loblolly pine in East Texas one year following treatments with nitrogen, phosphorus and nitrogen plus phosphorus fertilizer. The new tools and techniques were based upon stereophotogrammetric techniques using small-format (35-mm), non-metric cameras. New procedures were developed to alleviate the error inherent in these cameras. First, the Analytical Grid-Line Method (AGLM) was developed to inexpensively and accurately determine radial lens distortions (one of the largest sources of error) in 35-mm cameras using easily constructed calibration targets. Second, an addition of a glass reticle to the bodies of 35-mm cameras was shown to eliminate the limitations of these cameras due to lack of fiducials and film flatness (the main limiting feature of 35-mm cameras). Third, the two improved cameras were used in a "shop-built" stereo mounting unit and stereophotogrammetric techniques were developed to provide real-world, three-dimensional coordinates for crown elements.; The CASP method (Crown Architecture from Stereo Photographs) was used to test hypotheses concerning effects of fertilization on crown architecture. Differences in the vertical as well as the horizontal distribution of total foliage cluster length between fertilized and control subplots were statistically tested for five separate stands distributed throughout East Texas. In addition, vertical and horizontal crown profiles were constructed and examined. Results indicated that there is a mixed response to fertilization in loblolly pine crowns. Some stands supported the hypothesis that open crown structure of loblolly pine would show an increase in foliage amounts in the mid- and lower-crown positions when fertilized, while other stands did not. The predominant factor that possibly explains the different responses is the variation in the degree of canopy closure between the stands. That is, stands with complete canopy closure typically showed increases in foliage towards the main stem while those with sparse canopy closure promoted foliage along the crown's periphery and increased crown diameter.