Title page for ETD etd-10172000-15110052

Type of Document Master's Thesis
Author Battaglia, Michael Anthony
Author's Email Address mbattagl@vt.edu
URN etd-10172000-15110052
Title The Influence of Overstory Structure on Understory Light Availability in a Longleaf Pine (Pinus palustris Mill.) Forest
Degree Master of Science
Department Forestry
Advisory Committee
Advisor Name Title
Mou, Paul P. Committee Chair
Jones, Robert H. Committee Member
Mitchell, Robert J. Committee Member
  • longleaf pine
  • light measurements
  • heterogeneity of light
  • canopy structure
  • hemispherical photography
Date of Defense 2000-09-15
Availability unrestricted
Understory light environments are inherently heterogeneous and therefore difficult to characterize. Numerous methods to measure understory light have been assessed in closed-canopied forests; however, the reliability of these methods has not been addressed for open-canopied forests. Therefore, the first objective of this study, presented in Chapter 3, was to test the accuracy and precision of various light measurement techniques at different time scales and sky conditions. The methods assessed performed differently depending on the sky condition and time of year when the sample was taken. To estimate annual photosynthetic photon flux density transmittance (annual %PPFD), the use of a 10-minute average of PPFD measured on an overcast day (%PPFDovercast) was effective, but accuracy decreased with decreasing solar altitude (ie season change). Hemispherical photographs used to estimate weighted canopy openness and gap fraction were effective methods, but gap light index (GLI) also derived from hemispherical photographs performed better. Accuracy of daily %PPFD estimates using %PPFDovercast, weighted canopy openness, and gap fraction were strongly affected by solar altitude and sky condition. Gap light index was very effective in estimating daily %PPFD for all sky conditions and time periods. The second objective of this study, presented in Chapter 4, was to characterize the relationship between canopy structure and spatial distribution of light by using three replicates of one uncut treatment and three harvest treatments: single tree, small gap (0.1 ha), and large gap (0.2 ha). Each harvest retained similar residual basal area but with different spatial patterns of the residuals, ranging from uniformly dispersed (single tree) to different degrees of aggregation (small and large gap). Average stand level light availability increased 12-22% when the same residual basal area of trees was distributed in clusters versus a uniform distribution. The variation of light availability increased as stands became more aggregated and larger amounts of the variation was explained by the spatial pattern of the canopy structure. Spatial autocorrelation range was twice as large in the small gap harvest then the other harvest treatments. It is suggested that seedling growth response to these differences in spatial patterns of light may differ between the different harvests.
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  chap1&2.pdf 172.44 Kb 00:00:47 00:00:24 00:00:21 00:00:10 < 00:00:01
  chap3.pdf 481.06 Kb 00:02:13 00:01:08 00:01:00 00:00:30 00:00:02
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