Towards lidar-based mapping of tree age at the Forest Tundra Ecotone

Johanna Jensen, Columbia University, jej2141@columbia.edu (Presenter)
Andrew Maguire, University of Idaho, magu7563@vandals.uidaho.edu
Rose Oelkers, Lamont Doherty Earth Observatory, roelkers@ldeo.columbia.edu
Laia Andreu-Hayles, Lamont Doherty Earth Observatory, lah@ldeo.columbia.edu
Natalie Boelman, Lamont-Doherty Earth Observatory, Columbia Univ., nboelman@ldeo.columbia.edu
Rosanne D'Arrigo, Lamont Doherty Earth Observatory, rdd@ldeo.columbia.edu
Kevin Lee Griffin, Columbia University, griff@ldeo.columbia.edu
Carlos Silva, University of Idaho, csilva@uidaho.edu
Jyoti Jennewein, University of Idaho, jjennewein@uidaho.edu
Arjan JH Meddens, University of Idaho, ameddens@uidaho.edu
Micah Russell, University of Idaho, russ5140@vandals.uidaho.edu
Lee A Vierling, University of Idaho, leev@uidaho.edu
Jan Eitel, University of Idaho, jeitel@uidaho.edu

Climate change may cause spatial shifts in the forest-tundra ecotone (FTE). To improve our ability to study these spatial shifts, information on tree demography along the FTE is needed. The objective of this study was to assess the suitability of lidar-derived tree heights as a surrogate for tree age. We calculated individual tree age from 62 tree cores collected at basal height from white spruce (Picea glauca) within the FTE in northern Alaska. Tree height was obtained from terrestrial lidar scans (< 1 cm spatial resolution). The relationship between age and height was examined using a linear regression model. We found a very strong predictive relationship between tree height and age (R² = 0.6951, RMSE = 29.32 years) for trees that ranged between 14 to 230 years old and 0.29 to 15.2 m tall. Regression models were also developed for small (height < 3 m) and large trees (height >= 3 m), however, these models captured less variance in the data (R² = 0.4292, RMSE = 14.05 years and R² = 0.2383, RMSE = 41.15 years, respectively). Although a strong, predictive relationship between age and height is uncommon in light-limited forest environments, we hypothesize that the sparseness of trees within the FTE may explain the strong tree height-age relationships found herein. Using this relationship and tree height extracted from an individual tree detection algorithm (Silva et al., in review), we predicted age for six 2,500 m² plots within white spruce (Picea glauca) stands previously determined to be along the FTE. From these predictions, we generated age distributions to assess population dynamics. Age distributions show substantially fewer trees which are < 40 years old with increasing latitude. Further analysis of 36 additional tree cores recently collected within the FTE near Inuvik, Canada will be performed. Our analysis suggests that lidar-derived tree height could be a reliable proxy for tree age at the FTE, thereby establishing a new technique for scaling tree structure and demographics across larger portions of this sensitive ecotone.

Associated Project(s): 

• Eitel-01
• D'Arrigo-01

Poster Location ID: 69

Session Assigned: Vegetation Dynamics and Distribution