Contrasting radial growth and canopy recruitment patterns in Liriodendrontulipifera and Nyssasylvatica: gap-obligate versus gap-facultative tree species
Radial growth patterns, canopy recruitment characteristics, and disturbance histories were examined in a shade-tolerant species, Nyssasylvatica Marsh., and a shade-intolerant species, Liriodendrontulipifera L., to determine the influence of canopy gaps in species with contrasting life histories. Tree cores of these co-occurring species were taken from three mixed-Quercus forests in northern Virginia. Most N. sylvatica individuals became established prior to 1850 and experienced multiple release and suppression periods coinciding with logging during the late 1800s and early 1900s. Many L. tulipifera became established during the early 1900s following logging, and only a few individuals experienced prolonged suppression periods. Regardless of site, L. tulipifera grew faster than N. sylvatica (average radial growth >1.70 mm/year for L. tulipifera vs. 2 mm (15–37 years for L. tulipifera vs. <5 years for Nsylvatica). Consecutive growth <0.5 mm/year ranged from 43 to 66 years in N. sylvatica vs. 2–11 years in L. tulipifera. Ring width patterns indicate that both species used different strategies following disturbance that enabled them to coexist in these forests. Nyssasylvatica persisted in subcanopy positions for extended periods of time but was capable of responding to release even after 170 years (i.e., gap facultative). In contrast, L. tulipifera appeared to rely on a strategy of rapid height and radial growth for canopy accession following large disturbances (i.e., gap obligate). The results of this study indicate the importance of using dendroecological techniques in the study of forest dynamics and species' growth strategies.