Environmental niche and demographic modeling of American chestnut near its southwestern range limit

The inadvertent introduction and rapid spread of chestnut blight (caused by Cryphonectria parasitica (Murr.) Barr) in the early 20th century resulted in the demise of American chestnut (Castanea dentata (Marsh.) Borkh.; Fagaceae) as a major component of forest canopies and had negative impacts on eastern forest communities. Research efforts over the last century have documented the persistence of occasional trees and root crown/stump sprouts throughout much of the historic range of the species providing the basis for ongoing breeding of blight-resistant stock and restoration efforts. Unfortunately, it remains unclear how much of the historic range remains climatically suitable for remnant trees that may harbor unique genetic variation for successful reintroduction efforts. Here we investigate whether the southwestern portion of the historical range remains environmentally suitable for undiscovered remnant populations of C. dentata using environmental niche modeling. We also use stage-structured matrix projection models to investigate the potential demographic future of C. dentata in W Tennessee, N Mississippi, SW Kentucky, and NW Alabama based upon observations of American chestnut in these areas over the last several decades. We found that suitable habitat associated with higher elevations and areas of high forest canopy cover occurs throughout much of southwestern portion of the historical range and that populations of American chestnut in these areas are predicted to drastically decline over the next ~100-200 years without conservation interventions to mitigate the negative consequences of chestnut blight.

The politics of genetic technoscience for conservation: The case of blight-resistant American chestnut

Innovations in genetics and genomics have been heavily critiqued as technologies that have widely supported the privatization and commodification of natural resources. However, emerging applications of these tools to ecological restoration challenge narratives that cast genetic technoscience as inevitably enrolled in the enactment and extension of neoliberal capitalism. In this paper, we draw on Langdon Winner’s theory of technological politics to suggest that the context in which genetic technologies are developed and deployed matters for their political outcomes. We describe how genetic approaches to the restoration of functionally extinct American chestnut trees—by non-profit organizations, for the restoration of a wild, heritage forest species, and with unconventional intellectual property protections—are challenging precedents in the political economy of plant biotechnology. Through participant observation, interviews with scientists, and historical analysis, we employ the theoretical lens provided by Karl Polanyi’s double movement to describe how the anticipations and agency of the developers of blight-resistant American chestnut trees, combined with chestnut biology and the context of restoration, have thus far resisted key forms of the genetic privatization and commodification of chestnut germplasm. Still, the politics of blight-resistant American chestnut remain incomplete and undetermined; we thus call upon scholars to use the uneven and socially constructed character of both technologies and neoliberalism to help shape this and other applications of genetic technoscience for conservation.

Bumble bee (Bombus impatiens) survival, pollen usage, and reproduction are not affected by oxalate oxidase at realistic concentrations in American chestnut (Castanea dentata) pollen

Transgenic American chestnut trees expressing a wheat gene for oxalate oxidase (OxO) can tolerate chestnut blight, but as with any new restoration material, they should be carefully evaluated before being released into the environment. Native pollinators such as bumble bees are of particular interest: Bombus impatiens use pollen for both a source of nutrition and a hive building material. Bees are regular visitors to American chestnut flowers and likely contribute to their pollination, so depending on transgene expression in chestnut pollen, they could be exposed to this novel source of OxO during potential restoration efforts. To evaluate the potential risk to bees from OxO exposure, queenless microcolonies of bumble bees were supplied with American chestnut pollen containing one of two concentrations of OxO, or a no-OxO control. Bees in microcolonies exposed to a conservatively estimated field-realistic concentration of OxO in pollen performed similarly to no-OxO controls; there were no significant differences in survival, bee size, pollen use, hive construction activity, or reproduction. A ten-fold increase in OxO concentration resulted in noticeable but non-significant decreases in some measures of pollen usage and reproduction compared to the no-OxO control. These effects are similar to what is often seen when naturally produced secondary metabolites are supplied to bees at unrealistically high concentrations. Along with the presence of OxO in many other environmental sources, these data collectively suggest that oxalate oxidase at field-realistic concentrations in American chestnut pollen is unlikely to present substantial risk to bumble bees.