We investigated the changes in stand structure, species composition, and soil characteristics of jack pine (Pinus banksiana Lamb.) disjunct stands on the southern shore of Lake Michigan in North America. Our NMS (Non-metric Multidimensional Scaling) ordination revealed a chronosequence of the succession from jack pine stand to black oak (Quercus velutina Lam.) woodland. A majority of jack pine seedlings appeared to be recruited near wet pannes (shallow intradunal ponds with standing water) where the water table was relatively high, expanded in dry pannes, and followed by invasions of black oak and other upland tree species on dune ridges. Expansion of canopy cover, along with dominance of black oak, have likely led to a major reduction in herbaceous cover and a shift in the composition of the understory species. Species richness and diversity have increased. However, much of the increase was attributed to species that were not native to the Lake Michigan sand dunes. Soil pH and nitrogen concentration changed significantly from the younger wet panne to the older dune ridge plots, but other measures of soil fertility did not differ among the plots. The reduction in soil pH in the older plots was likely due to the neutralization of calcareous soil by carbonic acid leached from accreted sands and organic acids produced by litter decomposition. Nitrogen accumulation in the soil is expected to continue beyond the equilibrium values predicted from mature oak woodland soil. Jack pine seedlings have been documented to be tolerant of xeric conditions. However, we found that seedling survival was over five times higher in moist soil near the wet pannes. In this respect, failure in formation of new pannes may reduce the size of the region's jack pine population in the foreseeable future.
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