The demographics and regeneration dynamic of hickory in second-growth temperate forest

Abstract

Hickory (Carya spp.) is an economically and ecologically important genus to the eastern deciduous forest of North America. Yet, much of our knowledge about the genus comes from observational and anecdotal studies that examine the genus as a whole, or from research that examines only one species, in only one part of its range. Here, we use data sets from three different spatial scales to determine the demographics and regeneration patterns of the four most abundant hickory species in the Northeastern United States. These species were the shagbark (C. ovata), pignut (C. glabra), mockernut (C. tomentosa), and bitternut (C. cordiformis) hickories. We examine trends in hickory demographics, age class and structure at the regional scale (New England and New York), the landscape scale (a 3000 ha forest in northwestern Connecticut) and at the stand scale (0.25–5 ha). Our analysis at all three scales show that individual hickory species are site specific with clumped distribution patterns associated with climate and geology at regional scales; and with soil moisture and fertility at landscape scales. Although hickory represents a fairly small percent of the total basal area (2.5%) across a forest landscape, upland oak-hickory stands can have a much higher basal area of hickory (49%), especially in the larger height and diameter classes. Additionally, dendrochronological results show that hickory trees in mature, second growth forests originated or were released over a half-century long period of stand development; but patterns in seedling recruitment in the understory is continuous and builds up as advance regeneration over decades, with some surviving in a suppressed state for over forty years. This contrasts with oak where recruitment of regeneration is strongly pulsed in association with mast years.