Patterns and causes of temporal variation in tree seed production

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Masting behavior (defined as the spatially synchronous and temporally episodic production of seed crops) in tree species is of tremendous importance in ecology (e.g. dramatic trophic effects for deer and rodents; eruptions of granivorous bird populations; pollen flux in anemophilous species; etc). It is also quite important in forestry-the unpredictable nature of masting events has favored the more expensive but more reliable regeneration option of planting. As of now the only consensual statements one might make are that a mast year is of regional extant with inter-annual pollen and ovule production closely linked, most species within a region are not synchronized with one another, and weather undoubtedly plays a major role (generating resources and/or cues for bud differentiation). The proposed study has a number of objectives including a global examination of the dependence on masting on latitude, altitude, longitude, and life history traits such as aerial seedbanks and obligate bird dispersal of some Pine species. I will extend my on-going data set from 6 to 11 years, measuring ovulate cones per basal area of Picea glauca (white spruce) and the very close-related P. engelmannii (Engelmann spruce) in the same 68 stands from Colorado to the Arctic Ocean (Inuvik), and from interior Alaska to Newfoundland; and then I will use these data to test models of reproduction that are resource-based, cue-based, or a combination of resource and cue. Further, I will compare the effect of resources vs weather cues in governing annual reproductive output in a series of experiments in young white spruce stands in western Alberta, central Manitoba, and northwest Quebec by inducing water stress during normal years, irrigation during very dry years, removal of immature female cones during mast years, and installation of artificial clusters of cones to imitate the shading of real cones during mast years. Finally, I will relate cones per basal area and area burned in four spatially independent regions of the boreal forest to ascertain if big fire years are typically followed by mast crops.