Demographic stimulation of the obligate understorey herb, Panax quinquefolius L., in response to natural forest canopy disturbances. (19th December 2016)

• Record Type: Journal Article
• Authors: Chandler, Jennifer L.; McGraw, James B.
• Editors: Jacquemyn, Hans
• Is Part Of: Journal of ecology. Volume 105:Number 3(2017:May)
• Page Start: 736
• Page End: 749
• Publication Date: 2016-12-19
• Subjects: canopy gap -- climate change -- defoliation -- forest disturbance -- ice storm -- lightning -- Panax quinquefolius L. -- plant population and community dynamics -- stochastic population growth -- transient population dynamics; Plant ecology -- Periodicals; 577.05
• DOI: 10.1111/1365-2745.12695
• Languages: English
• ISSNs: 0022-0477

Abstract

Summary: Natural and anthropogenic forest canopy disturbances significantly alter forest dynamics and lead to multi‐dimensional shifts in the forest understorey. An understorey plant's ability to exploit alterations to the light environment caused by canopy disturbance leads to changes in population dynamics. The purpose of this work was to determine if population growth of a species adapted to low light increases in response to additional light inputs caused by canopy disturbance, or alternatively, declines due to long‐term selection under low light conditions. To address this question, we quantified the demographic response of an understorey herb to three contrasting forest canopy disturbances (ice storms, tent caterpillar defoliation and lightning strikes) that encompass a broad range of disturbance severity. We used a model shade‐adapted understorey species, Panax quinquefolius, to parameterize stage‐based matrix models. Asymptotic growth rates, stochastic growth rates and simulations of transient dynamics were used to quantify the population‐level response to canopy disturbance. Life table response experiments were used to partition the underlying controls over differences in population growth rates. Population growth rates at all three disturbed sites increased in the transition period immediately after the canopy disturbance relative to the transition period prior to disturbance. Stochastic population models revealed that growth rates increased significantly in simulations that included disturbance matrices relative to those simulations that excluded disturbance. Additionally, transient models indicated that population size ( n ) was larger for all three populations when the respective disturbance matrix was included in the model. Synthesis . Obligate shade species are most likely to be pre‐adapted to take advantage of canopy gaps and light influx to a degree, and this pre‐adaptation may be due to long‐term selection under dynamic old growth forest canopies. We propose a model whereby population performance is represented by a parabolic curve where performance is maximized under intermediate levels of canopy disturbance. This study provides new evidence to aid our understanding of the population‐level response of understorey herbs to disturbances whose frequency and intensity are predicted to increase as global climates continue to shift. Abstract : Obligate shade species are most likely to be pre‐adapted to take advantage of canopy gaps and light influx to a degree, and this pre‐adaptation may be due to long‐term selection under dynamic old growth forest canopies. We propose a model whereby population performance is represented by a parabolic curve where performance is maximized under intermediate levels of canopy disturbance. This study provides new evidence to aid our understanding of the population‐level response of understorey herbs to disturbances whose frequency and intensity are predicted to increase as global climates continue to shift.