**Founder Placement and Gene Dispersal Affect Population Growth and Genetic Diversity in Restoration Plantings of American Chestnut**

Yamini Kashimshetty1, Melanie Simkins2, Stephan Pelikan3 and Steven H. Rogstad1 *1Department of Biological Sciences 2Department of Environmental Studies 3Department of Mathematical Sciences University of Cincinnati, OH USA* 

#### **1. Introduction**

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Variation of Wild *Panax ginseng* C.A. Meyer (Araliaceae) by AFLP Markers. *Chin. Med.*, Vol.5, No.21, (June 2010), ISSN1749-8546 (Electronic), Available from The American chestnut, *Castanea dentata* [Marsh.] Borkh (Fagaceae), was an abundant canopy tree inhabiting the mixed mesophytic forests of eastern North America. The species was struck by a fungal pathogen (*Cryphonectria parasitica* [Murrill] Barr*)* introduced from East Asia in the late 1800's on imported Asian chestnut material with the consequence that billions of trees have been destroyed (Barakat *et al.,* 2009; Pierson *et al.,* 2007; Elliot & Swank 2008; Jacobs 2007; Stilwell *et al.,*2003; Paillet, 2002; Huang *et al.,* 1998; Russel, 1987). The near elimination of this once important species has had widespread effects on the ecological functioning of eastern North American forests, and has also had a severe impact on economic forest extraction practices (e.g., strong workable lumber; chestnuts as food and forage). *Castanea dentata* has escaped complete elimination from its native range by persisting as occasional sprouts from the root collar of trees damaged by the blight; these sprouts rarely reach full sexual maturity (Jacobs, 2007; Stilwell *et al.,*2003; Paillet, 2002). Efforts are underway to restore this former keystone species and prevent extinction, reestablishing its ecological and economic roles in its natural habitat. Breeding of blight-resistant strains is being attempted (e.g., by the American Chestnut Foundation, TACF) through a series of initial hybridizations between *C. dentata* and the Chinese chestnut *(C. mollisima* Blume), followed by a series of backcrosses with the American chestnut always selecting for blight-resistance, to develop strains that are predominantly American chestnut in genotypic constitution but which retain Chinese blightresistance genes. For example, some of the most recent blight-resistant strains ready for reintroduction are calculated to be genetically 94% American chestnut and 6% Chinese chestnut (Jacbos, 2007; Diskin *et al.,* 2006).

The conservation of endangered plant species often involves restoring these species back to their natural habitats and/or *ex situ* rescue plantings (Merritt & Dixon, 2011), and the American chestnut is no exception. Considerable resources are being expended in generating blight-resistant strains of *C. dentata*, thus necessitating optimization of restoration programs which are usually labor-intensive and expensive. Costs of such restoration efforts include propagule generation and collection, storage, treatment, site preparation, planting, protecting, provisioning, travelling to and from the introduction site, monitoring, and future manipulations of individuals (Rogstad & Pelikan, 2011).

One approach to optimizing restoration of the American chestnut is to use computer programs to model the population growth and genetic effects of restoring plant populations in different ways. While restoration programs have been widely undertaken for a number of plant species, we lack the tools to analyze how factors like founder number and geometry of placement within a restoration habitat interact with varying founder or species life history characteristics, and whether these factors impact resultant population growth rates and preservation of genetic diversity. While ecological edge effects have been documented as being evident at the borders and edges of restoration preserves due to altered microenvironments in terms of wind-speeds, light availability and organismal composition among other factors (Primack, 2010), less is known about whether placement of founders at varying distances from the preserve edge impacts the population dynamics and genetic diversity measures of establishing populations. Further, can differing founder placement patterns interact with other life-history characteristics such as pollen and offspring dispersal distances to bring about different population growth rates and genetic diversity levels? Exploring these potential demographic and genetic edge effects in the field with *C. dentata* would not be feasible due to the costs associated with carrying out such experiments on a wide-scale to ensure statistical reliability of data, especially since blight-resistant individuals are expensive and time-consuming to produce, and thus must be used judiciously. In this case modeling virtual populations through computer simulations represents a more tractable alternative to field experiments, potentially providing valuable insight for restoration managers on how best to re-introduce the American chestnut into preserves.

In this study, the computer program NEWGARDEN (Rogstad & Pelikan, 2011) was used to model blight-resistant American chestnut population restoration in a virtual preserve to explore the population growth and genetic effects of placing founders at different distances from preserve borders under differing patterns of gene dispersal. Our null hypothesis is: Varying American chestnut founder placement at various diagonal distances from the preserve border, while altering offspring and pollen dispersal distances, will have no effect on population growth rates or retention of founding genetic diversity. We used comparative trials to examine the degree to which some patterns of introduction might be preferable over others.
