Patterns of annual seed production by northern hemisphere trees: A global perspective

We tested whether annual seed production (masting or mast fruiting) in Nort hern Hemisphere trees is an evolved strategy or a consequence of resource t racking by comparing masting patterns with those of annual rainfall and mea n summer temperatures, two environmental variables likely to correlate with available resources. There were generally significant negative autocorrela tions between the seed crop in year x and year x + 1 (year x + 2 in species of Quercus requiring 2 yr to mature acorns), as expected if resources are depleted in mast years in part by switching resources from growth to reprod uction. Spatial autocorrelation in annual seed production generally decline d with distance but was statistically significant over large geographic are as. Variability in annual seed production was relatively high and inversely correlated with latitude and generally not bimodally distributed. Patterns of spatial autocorrelation in annual rainfall and summer temperatures are generally similar to those exhibited by annual seed production, and relativ e variability in annual rainfall is also inversely correlated with latitude . However, these environmental variables exhibit distinctly different patte rns of temporal autocorrelation, are much less variable, and are more norma lly distributed than annual seed production. Combined with the inverse rela tionship between growth and reproduction previously documented, these resul ts support the hypothesis that variability in annual seed production is an evolved strategy and that annual seed production is more or less normally d istributed rather than an all-or-none phenomenon.