"Windows of opportunity" for recruitment in long-lived clonal plants: experimental studies of seedling establishment in Vaccinium shrubs

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Abstract
Two experiments were performed to analyse seedling recruitment in Vaccinium myrtillus, Vaccinium vitis-idaea, Vaccinium uliginosum, and Vaccinium oxycoccos. The purpose was to examine the probability of recruitment at "windows of opportunity," i.e., spatially or temporally unpredictable conditions in which seedling recruitment is possible within stands of established conspecific adults. Seedling emergence in all four investigated species depended on a combination of seed and microsite (disturbance) availability. In V. myrtillus, which was studied in more detail than the other species, emergence and survivorship were similar on non wood substrate and on decaying wood, but seedling growth was favored on the latter substrate. An experiment along an environmental gradient with all four species showed that recruitment required approximately similar conditions even though the adults of the species exhibited a clear zonation along the gradient. For all species except V. oxycoccos, recruitment was confined to only a part of the adults' range. Vaccinium species are generally good seed dispersers and have a high fecundity but usually lack developed seed banks. This behavior is interpreted as a response to occurring windows of opportunity for recruitment, i.e., small disturbances with high moisture and organic soil content. Recruitment at windows of opportunity is suggested as one distinct pattern of recruitment among clonal plants, along with previously suggested repeated and initial seedling recruitment patterns, and some implications of this distinction are briefly discussed. Keywords: clonal plants, genets, life histories, population dynamics, seedling establishment, Vaccinium.