ESTABLISHMENT OF A RARE RIPARIAN TREE, ALNUS MARITIMA
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Alnus maritima is a rare, riparian tree species showing no recruitment from seeds. We conducted studies to identify factors potentially limiting establishment. First, we surveyed current known populations to determine population size and developed niche models to determine possible locations for re-establishment. Second, we studied the effect of field stratification to evaluate if low winter temperatures decrease seed viability or otherwise alter seed dormancy. Third, because A. maritima is an early successional species that requires high light environments, we investigated seedling establishment after burning or clipping vegetation at study sites. Lastly, we compared how presence or absence of the native root microbiome associated with A. maritima nodules influenced survival, growth, and establishment of seedlings. The most likely suitable habitat was identified in the southern portion of Oklahoma with isolated hotspots, with the majority of locations occurring along the current known populations. There were no differences in mean total seed germination between stratified seeds and non-stratified seeds, but longer periods of stratification promoted earlier seed germination, indicating a non-deep physiological dormancy. Neither burning nor clipping influenced seedling growth or survival initially. However, seedling survival decreased in burned plots due to the release of an aggressively growing competitor. Surprisingly, seedlings inoculated with the native microbiome had reduced survival compared to uninoculated individuals, and uninoculated individuals showed a decline in survivorship after natural inoculation in the field, suggesting that the microbiological “mutualists” may be a physiological stress on seedlings during establishment. These results indicate that seedling survival is limiting establishment of this species.
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