Table 2.
Summary of predicted relationships, variables tested, apparent mechanisms, and the study results.
| predicted pattern | response variable | mechanism | prediction supported? |
|---|---|---|---|
| inter-annual flowering variability lower than seed variabilitya | total pollen | flower production is relatively constant across years, and it is the flower to fruit transition that generates variation among years in fruit crops | yes |
| seed production not related to flowering intensitya | site-level average acorn production | as above | yes |
| flowering synchrony related to air temperature and rainfall during flowering | pollen season duration | homogeneous conditions during warm and dry pollen seasons enhance flowering synchrony among trees | yes |
| seed production related to flowering synchrony (veto 1) | site-level average acorn production | higher flowering synchrony among trees enhances pollination efficiency | yes |
| seed production related to spring water deficit (veto 2) | site-level average acorn production | high water stress induces acorn abscission | yes |
| accumulated rainfall from January until June enhances seed production | site-level average acorn production | high summed precipitation increases N mineralization and enhances trees photosynthetic capacity allowing higher crop productionb | yes |
| previous year's veto interacts with the current year's veto in driving seed production | site-level average acorn production | passive resource storage: environmental veto prevents resource spending, increasing the resource pool for next year's reproductive allocation | yes |
| environmental veto drives among-site synchrony in seed production | CV of seed production among sites | low water stress allows seed production, decreasing the among-site variation in reproductive output | yes: water stress |
| environmental veto drives within-site synchrony in seed production | CV of seed production among trees, within sites | low water stress and short pollen seasons allow seed production decreasing the among-tree variation in reproductive output | yes: water stress and phenological synchrony |
aWe predicted that oaks will show fruit maturation masting, i.e. seed production will be not related to flower production, but rather will be determined by flower to fruit transition driven by phenological synchrony and drought. Therefore, variability of flower production is expected to be lower than variability of seed production (see also [19]).