Differential effects of acorn burial and litter cover on Quercus rubra recruitment at the limit of its range in eastern North America

Primary predators or dispersers such as birds and rodents cache acorns of northern red oak (Quercus rubra L.). A proportion of these acorns are not retrieved, and thus, animals may favour oak regeneration by placing acorns in microsites suitable for recruitment. We experimentally investigated the effects of acorn burial and litter cover on red oak recruitment at two sites at the northern limit of the species' range in North America. Laboratory experiments also tested the effects of acorn burial and litter cover on desiccation and germinability and the influence of soil moisture on germination. Burial and litter protected acorns against predation by deer in the field. Germination was promoted by burial both in field and laboratory experiments. Germination was proportional to acorn water content and to soil moisture. Seedling emergence in the field was enhanced by burial but reduced by litter cover. Acorns buried but uncovered by litter had the highest probability of recruiting a seedling. A potential effect of seed predators or dispersers on red oak regeneration and expansion is suggested, as acorn caching by birds and rodents may actually enhance population recruitment, despite high mortality through acorn consumption.