Tree species have different shapes and forest stand dynamics. Light detection and ranging (LiDAR) can measure the three dimensional position of reflective material by sending laser pulses through the canopy. We examined the influence of three forest stand attributes: species, crown closure , and age  on the vertical distribution of aerial LiDAR returns of forested stands. We studied over five thousand regular, even-aged stands in Quebec (Canada) with five dominant species: balsam fir (Abies balsamea (L.) Mill.), paper birch (Betula papyrifera Marsh), black spruce (Picea mariana (Mill.) BSP), white spruce (Picea glauca Moench) and aspen (Populus tremuloides Michx.). We modeled vertical distribution of LiDAR returns against the three attributes using a functional glm and a novel nonparametric graphical test of significance. Results indicate that  aspen stands had the most uniform vertical distribution of LiDAR returns; balsam fir and white birch distributions were similar and centered  around 50\% of the stand height ; black spruce and white spruce distributions were skewed  below 30\% of stand height (p<0.001). An increase in crown closure concentrated the distributions around 50\%  height. Increasing age gradually shifted the distributions higher in the stand until 50-70 years, where it plateaued and slowly declined at 90-120 years. The full model maximal R-squared was 0.47 around 10\% of stand height. Results suggest that the stands vertical distributions of LiDAR returns depend on the three variables studied . This understanding can be used for stand-level species classification and to study the evolution of the forest structure over changing conditions .
 Light detection and ranging (LiDAR) provides information on the vertical structure of forest stands enabling detailed and extensive ecosystem study. The vertical structure is often summarized by scalar features and data-reduction techniques that limit the interpretation of results. Instead, we quantified the influence of three variables, species, crown cover , and age , on the vertical distribution of airborne LiDAR returns from forest stands. We studied 5,428 regular, even-aged stands in Quebec (Canada) with five dominant species: balsam fir (Abies balsamea (L.) Mill.), paper birch (Betula papyrifera Marsh), black spruce (Picea mariana (Mill.) BSP), white spruce (Picea glauca Moench) and aspen (Populus tremuloides Michx.). We modeled the vertical distribution against the three variables using a functional general linear model and a novel nonparametric graphical test of significance. Results indicate that LiDAR returns from aspen stands had the most uniform vertical distribution . Balsam fir and white birch distributions were similar and centered at around 50\% of the stand height , and black spruce and white spruce distributions were skewed to below 30\% of stand height (p<0.001). Increased crown cover concentrated the distributions around 50\% of stand height. Increasing age gradually shifted the distributions higher in the stand for stands younger than 70-years, before plateauing and slowly declining at 90-120 years. Results suggest that the vertical distributions of LiDAR returns depend on the three variables studied .
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Tree species have different shapes and forest stand dynamics.
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can measure the three dimensional position of reflective material by sending laser pulses through the canopy. We examined
provides information on the vertical structure of forest stands enabling detailed and extensive ecosystem study. The vertical structure is often summarized by scalar features and data-reduction techniques that limit the interpretation of results. Instead, we quantified
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forest stand attributes:
variables,
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closure
cover
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,
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aerial LiDAR returns of forested
airborne LiDAR returns from forest
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over five thousand
5,428
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vertical distribution of LiDAR returns
the vertical distribution
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attributes
variables
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glm
general linear model
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LiDAR returns from
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of LiDAR returns; balsam
. Balsam
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at
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;
, and
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to
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An increase in crown closure
Increased crown cover
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of stand
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until 50-70 years, where it plateaued and slowly declined
for stands younger than 70-years, before plateauing and slowly declining
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The full model maximal R-squared was 0.47 around 10\% of stand height.
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stands
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. This understanding can be used for stand-level species classification and to study the evolution of the forest structure over changing conditions