Figure 2 : Habitation site and shell midden depth influence on forest canopy height.

From: Intertidal resource use over millennia enhances forest productivity

Figure 2

(a) Forest canopy height (in metres) by distance from the shell midden boundary (red) or distance from random locations (blue) shown with s.d. (red and blue ribbon) of bootstrapped boosted regression tree models, which are an additive regression model where terms are simple trees that are fitted in a forward, stagewise manner52. Mean canopy height across entire study area is shown by a dashed line (15.70 m). All distances are measured within the 30 m ribbon delineated from lidar data. (b) Box plot of difference in canopy height by site type and the depth of shell midden (deep (D)=dark green, medium depth (M)=green, shallow (S)=light green) with forest canopy height at habitation sites significantly greater than all non-habitation sites (P=0.02). Control sites are located along the coast in areas without shell midden where ‘All’ sites include the entire study area shown in yellow in Fig. 1b. Boxes represent first, second and third quartiles with whiskers extending to the highest and lowest value that is within 1.5 × interquartile range (IQR). Significantly higher values are denoted by ‘*’.