Fig. 2: Trend attribution (TA) includes direct and indirect pathways for terms in Eq. (1).
From: Continent-wide tree fecundity driven by indirect climate effects
a Trends in climate variables (since 1990) include minimum T in spring, mean summer T, and moisture deficit (D = cumulative monthly PET-P). The brown contour separates positive and negative trends. Shaded contours are green (decreasing) to brown (increasing). b Indirect effects have two elements. An arrow from b to F includes a growth effect (dG/dt) and a climate-growth interaction (C × dG/dt). An arrow from b to c depends on the uncertain relationship between tree diameter G and fecundity F shown in panel (b). If fecundity continues to increase with tree size (solid line in b), then accelerated growth (orange arrows are dG/dt) moves trees into more productive size classes, but not if fecundity eventually declines (dashed line). c Average diameter of trees (restricted to trees >20 cm) is high in the West, meaning that the effects of tree growth depend on [if] fecundity continues to increase or declines with size in panel (b). The effect of size on fecundity (arrow from c to F) comes through an interaction with climate (G × dC/dt in Eq. (1)).
