Variation in Responses of Late-Seral Herbs to Disturbance and Environmental Stress

Abstract

Clonal herbs that attain maximum development in late-seral forest are often assumed to have similar responses to disturbance and to be functionally equivalent. However, little is known about the demographic or physiological responses of these plants to disturbance or to the altered conditions of the post-disturbance environment. Following harvest of a mature coniferous forest, we compared abundance, demographic changes, and physiological acclimation of three clonal herbs (Asarum caudatum, Clintonia uniflora, and Pyrola picta) that differ in belowground morphology and leaf longevity. We measured ramet density, leaf area, and demographic variables (survival, clonal growth, flowering, and seedling establishment) before and for two years after harvest, and in adjacent undisturbed forest. Acclimation to increased solar radiation was assessed two years after harvest by measuring leaf mass per unit area (LMA) and chlorophyll a:b ratios of leaves produced in the current year. Although initial declines in abundance were similar, demographic responses indicate that patterns of recovery varied greatly among species. Two years after logging, ramet survival and clonal growth (production of new ramets) of Clintonia were greater in the harvest area than in the forest. Asarum had lower survival in the harvest area, but greater clonal growth, and Pyrola showed no difference in either survival or growth between environments. Only Asarum produced seedlings, although their survival was low in the harvest area. All species had higher LMA in the harvest area, but only Clintonia (with annual leaves) had a higher chlorophyll a:b ratio, suggesting the greatest potential for acclimation to increased light. Our results demonstrate that forest herbs with greater rhizome plasticity and shorter leaf duration have greater potential to acclimate after disturbance than those with rigid architectures and persistent leaves. Thus, species with comparable successional roles can vary substantially in their demographic and physiological responses to disturbance, with potential consequences for long-term recovery.

Long‐term vegetation responses to reintroduction and repeated use of fire in mixed‐conifer forests of the Sierra Nevada

“…This may not be surprising for highly diverse groups such as perennial forbs with species that exhibit diverse regenerative strategies and responses to burning (McLean 1969, Halpern 1989, Schimmel and Granstrom 1996, Knapp et al 2007). Many are tolerant of fire; however, others that are adapted to shade or deep accumulations of litter (e.g., Pyrola picta, Chimaphila menziesii; Harvey et al 1980, North et al 2005) may be more sensitive to burning (e.g., Halpern 1989) or to the higher levels of light or moisture stress (e.g., Nelson et al 2007) that characterize the larger openings created by higher severity fire. That pre-treatment cover was a significant predictor in most models of response suggests that at least the dominant perennials are tolerant of higher severity fire and post-treatment variability is shaped by the factors that contribute to initial variation in abundance (stand structure, microclimate, and soils; North et al 2005).…”

Effects of thinning intensity on understory vegetation inChamaecyparis obtusastands in South Korea

“…Especially, seedlings of broadleaf tree species can appear and grow as understory vegetation in a thinned plantation of coniferous species, and can also promote ecological succession (Son et al 2004;Kang et al 2014). In other studies, the influence of forest management, especially thinning, on understory vegetation has been evaluated by using short-term approaches (Nelson et al 2007;Peterson and Anderson 2009), chronosequence approaches (Puettmann and Berger 2006), retrospective studies (Bailey et al 1998;Lindh and Muir 2004), and the Density Management Study (DMS) (Cissel et al 2006;Peterson and Anderson 2009).…”

Multi‐scale spatial controls of understory vegetation in Douglas‐fir–western hemlock forests of western Oregon, USA

“…v www.esajournals.org proportionally more resources towards height growth (Givnish 1982, Tappeiner et al 1991, Tappeiner and Zasada 1993, Givnish 1995, Lezberg et al 1999, Nelson et al 2007). Hence, the establishment of early-seral species at low overstory densities may depend in part on the cover of late-seral species, and the extent to which disturbance reduces the cover of late-seral species.…”

“…Unexplained variability within and among sites may be related to a variety of factors not included in our model including differences in age, soil properties and disturbance history. For example, variability in slash treatment among sites at the time of stand initiation and/or in association with the experimental treatments, and associated spatial patterns of slash and ground disturbance, may have effects on understory plant communities that persist through the stem exclusion phase of stand development (e.g., Halpern 1989, Nelson et al 2007, Halpern and Lutz 2013, Harrington et al 2013. The fact that models explained less of the variability and spatial autocorrelation in lateseral cover than early-seral cover is consistent with differences in traits between the two groups.…”

“…Early-seral species are characterized by high rates of colonization, fast growth rates, short lifespans, tall stature and an intolerance of stressful, low-resource conditions (e.g., shade, drought ;Halpern 1989). In contrast, late-seral species are generally short in stature with long pre-reproductive periods, clonal reproduction, short-distance dispersal, slow rates of growth and tolerate low resource conditions in the understory (Givnish 1982, Lezberg et al 1999, Nelson et al 2007). Thus, early-seral species may be more responsive to variation in resources and disturbance, and more competitive in highresource environments than late-seral species, which may persist, or thrive, in low-resource conditions.…”