Long-term demography and matrix modeling reveal mechanisms of chestnut oak (Quercus montana) population persistence through sprouting and decline

The regeneration class within populations of some canopy tree species can persist within a forest understory for decades, existing as a single dominant stem or replacing dominant stems via sprouting. Trees with the ability to sprout, including oaks, can use multiple strategies to persist in the understory, including long-term persistence and "shrinking" in size as a result of the ability to produce sprouts. This study is the first to examine the long-term effects of sprouting in a population of oaks (Quercus) across all life history stages. We established a 15-year study of the fine-scale demographics in a stand of chestnut oaks (Quercus montana) on the Cumberland Plateau, which enabled us to examine the role of sexual reproduction and sprouting on population persistence. Using a size-class distribution matrix model parameterized from the long-term demography, we project the population 50 years into the future, identifying size classes that represent population bottlenecks. We compare size-class distribution patterns to two other chestnut oak populations in the region. We find that midstory individuals are "shrinking" through stem replacement or dying over time, and it is very rare for an individual to increase in size class. Sprouting (both existence of sprouts and number of sprouts) was associated with the death of a genetic individual. Our matrix model indicated a slow decline of the population over the next 50 years, a pattern reflected in the regional patterns of chestnut oaks. We suggest that the chestnut oaks studied may represent a "remnant population" which slowly declines until either local extinction or the existence of favorable environmental conditions.