Question 2: Does each forest ecosystem have a unique
three-dimensional structural signature?
Forest structure is influenced by many factors including the arrangement
of individual trees, differences in species morphology, the availability
of light, moisture, and soil nutrients, disturbance regimes, and forest
management practices (Franklin et al., 2002; Onaindia et al., 2004;
Vanwalleghem and Meentemeyer, 2009; Von Arx et al., 2013). These factors
interact uniquely with climate variables at local scales to organize
forests within different biomes and regions in North America (Hakkenberg
and Goetz, 2021). We find that many of the forest ecosystems across
North America vary significantly in structure, but it is difficult to
say that they are all unique based on any one metric. Based on canopy
height, any given forest ecosystem was significantly different from 4 of
the other 12 forest ecosystems on average, indicating a gradient of
differences. Previous studies have shown similar structural differences
in North American forests using different methods, such as grouping
forests using the Environmental Protection Agency’s level 1 and 3
ecoregion boundaries (Rishmawi et al., 2021). However, these ecoregions
are delineated using geology, landforms, soils, vegetation, climate,
land use, and many other factors known to influence natural vegetation.
Thus, any differences in structure between ecoregions could be
influenced by the abiotic factors that were used to delineate that area
in the first place. Since our results are based solely on the dominant
tree species to delineate forest ecosystems, any significant differences
in structure are more likely attributed to the forest arrangement
itself, illustrating that many forest ecosystems are structurally
different depending on how structure is measured.