Abstract
Leaf Area Index (LAI) is an important input variable for forest ecosystem modeling as it is a factor in predicting productivity and biomass, two key aspects of forest health. Current in situ methods of determining LAI are sometimes destructive and generally very time consuming. Other LAI derivation methods, mainly satellite-based in nature, do not provide sufficient spatial resolution or the precision required by forest managers for tactical planning. This paper focuses on estimating LAI from: (i) height and density metrics derived from Light Detection and Ranging (LiDAR); (ii) spectral vegetation indices (SVIs), in particular the Normalized Difference Vegetation Index (NDVI); and (iii) a combination of these methods. For the Hearst Forest of Northern Ontario, in situ measurements of LAI were derived from digital hemispherical photographs (DHPs) while remote sensing variables were derived from low density LiDAR (i.e., 1 m−2) and high spatial resolution WorldView-2 data (2 m). Multiple Linear Regression (MLR) models were generated using these variables. Results from these analyses demonstrate: (i) moderate explanatory power (i.e., R2 = 0.53) for LiDAR height and density metrics that have proven to be related to canopy structure; (ii) no relationship when using SVIs; and (iii) no significant improvement of LiDAR models when combining them with SVI variables. The results suggest that LiDAR models in boreal forest environments provide satisfactory estimations of LAI, even with narrow ranges of LAI for model calibration. Models derived from low point density LiDAR in a mixedwood boreal environment seem to offer a reliable method of estimating LAI at high spatial resolution for decision makers in the forestry community. This method can be easily incorporated into simultaneous modeling efforts for forest inventory variables using LiDAR.
Highlights
The Boreal Forest of Canada covers over 300 million hectares, stretching more than 1,000 km from the Atlantic to Pacific coasts [1]
The results suggest that Light Detection and Ranging (LiDAR) models in boreal forest environments provide satisfactory estimations of Leaf Area Index (LAI), even with narrow ranges of LAI for model calibration
Models derived from low point density LiDAR in a mixedwood boreal environment seem to offer a reliable method of estimating LAI at high spatial resolution for decision makers in the forestry community
Summary
The Boreal Forest of Canada covers over 300 million hectares, stretching more than 1,000 km from the Atlantic to Pacific coasts [1]. Ontario alone is covered by more than 71 million hectares of forest, resulting in almost two-thirds of the land base being forested, over half of which is in the Boreal region [2]. In order to monitor vegetation health and sustainability at strategic (i.e., future planning) and tactical (i.e., short term) scales it is important to properly select vegetation metrics that are robust and easy to measure. Net primary productivity (NPP), the rate at which an ecosystem accumulates biomass, is a good long term gauge of ecosystem health due to its reliance on a combination of basic ecosystem drivers: water, nutrient availability and sunlight [4]. Tracking NPP over time can provide managers with a relative estimate of forest health and long-term growth
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