The implications of American chestnut reintroduction on landscape dynamics and carbon storage

Abstract

Abstract. In the eastern United States, American chestnut (Castanea dentata) was historically a major component of forest communities, but was functionally extirpated in the early 20th century by an introduced pathogen, chestnut blight (Cryphonectria parasitica). Because chestnut is fast-growing, long-lived, and resistant to decay, restoration of American chestnut using blight-resistant stock could have the potential to increase carbon sequestration or storage in forested landscapes. However, carbon dynamics are also affected by interspecific competition, succession, natural disturbance, and forest management activities, and it is unknown how chestnut restoration might interact with these other processes. We used the PnETSuccession extension of the LANDIS-II forest landscape model to study the implications of chestnut restoration on forest composition and carbon storage in the context of other disturbances, including timber harvest and insect pest outbreaks. Our results imply that it could take a millennium or more for chestnut to fully occupy landscapes without aggressive restoration efforts. When successful, chestnut restoration activities displaced other species approximately in proportion to their abundance on the landscape, rather than replacing a single species or genus (e.g., Quercus). Insect pests increased the rate of chestnut colonization by reducing the abundance of competitors, and also had a dominant effect on carbon dynamics. Although chestnut is fast-growing, moderately shade-tolerant, and decomposes very slowly, our results suggest that it can only modestly increase the carbon storage potential of eastern forests. However, our results also demonstrate that compositional changes in forest communities can have noticeable effects on biomass accumulation, even with the large uncertainties introduced by invasive pests.

How disturbance, competition, and dispersal interact to prevent tree range boundaries from keeping pace with climate change

“…Although it uses parameters that can be estimated from the literature, modest calibration of some parameters is required, which introduces uncertainty. We used parameter settings that were successfully calibrated and used for studies in Wisconsin (Gustafson et al., ) and Maryland (Gustafson et al., ), and validated for this study using eddy‐flux data from New England (Duveneck et al., ). The climate projections for the study used a single emission scenario coupled with a single Global Circulation Model.…”

More than the sum of its parts: how disturbance interactions shape forest dynamics under climate change

“…Spatial extent of individual outbreaks is specified by user‐defined parameters, while the patterns of damage within these spatial extents are based on host density at a site and the previous year's defoliation, dictated by statistical relationships parameterized by multi‐year remotely sensed outbreaks (Gustafson et al. ). Insect‐host impacts are species‐specific and, unlike BDA, are defined by cumulative defoliation functions which determine both growth reduction and mortality (Foster ).…”

Forecasting for intended consequences

“…And what are the consequences for ecosystem structure and functioning (Jacobs, Dalgleish, & Nelson, 2013)? To address these considerations, Gustafson et al (2017Gustafson et al ( , 2018 simulated the reintroduction of blight-resistant chestnut using a suite of increasingly aggressive restoration approaches and forecasted its long-term effects on forest composition and carbon storage in Maryland, USA. They found that restoration would need to be extensive and committed to succeed within a reasonable time frame (50-100 years).…”