**4. Discussion**

#### **4.1 Practical applications**

The null hypothesis that placing founders at differing distances from the edge of a restoration preserve will have no effect on subsequent population growth or genetic diversity was falsified according to results involving the first series trials with the basic dispersal conditions only (Figures 1 through 3). These results confirm that populations can manifest different degrees of population growth and genetic edge effects (Rogstad & Pelikan, 2011) depending on the distance of founders from preserve borders. In terms of population development, increases in growth rates were correlated with increasing distances of founder placement from a border up to a point: with the "basic" gene dispersal distances, planting founders 300 grid points (1500 m) into the preserve is as good as planting them 500 grid points (2500 m) into a 5 km x 5 km or larger preserve. Increasing founder placement up to 300 grid points increasingly allows founders a greater number of viable grid points to establish their offspring thereby reducing mortality levels. As for genetic diversity, the greatest loss of alleles occurred when founders were placed less than 100 grid units from the border (trial a, Figure 2). However, even at the corner, losses were not considerably greater than placing the founders 100 grid points into the preserve (corner trial a retained 90.4% while trial b retained 93.9% of the founding alleles). A preserve manager not interested in maximizing population growth but who only wants to maximize genetic diversity retention could thus plant the founders 100 grid points (500 m) into a 5 km x 5 km or larger preserve. Beyond that, planting further into the preserve does not significantly increase the number of founding alleles conserved. Differences in losses of

Fig. 6. Changes in F values in populations after 100 bouts of mating (the same populations shown in Figures 4 and 5). Trial conditions differed with regard to both founder inset distance and offspring and pollen dispersal distances as indicated (see summaries for A through F to the right of the graph). Connected data points show F values under one set

The null hypothesis that placing founders at differing distances from the edge of a restoration preserve will have no effect on subsequent population growth or genetic diversity was falsified according to results involving the first series trials with the basic dispersal conditions only (Figures 1 through 3). These results confirm that populations can manifest different degrees of population growth and genetic edge effects (Rogstad & Pelikan, 2011) depending on the distance of founders from preserve borders. In terms of population development, increases in growth rates were correlated with increasing distances of founder placement from a border up to a point: with the "basic" gene dispersal distances, planting founders 300 grid points (1500 m) into the preserve is as good as planting them 500 grid points (2500 m) into a 5 km x 5 km or larger preserve. Increasing founder placement up to 300 grid points increasingly allows founders a greater number of viable grid points to establish their offspring thereby reducing mortality levels. As for genetic diversity, the greatest loss of alleles occurred when founders were placed less than 100 grid units from the border (trial a, Figure 2). However, even at the corner, losses were not considerably greater than placing the founders 100 grid points into the preserve (corner trial a retained 90.4% while trial b retained 93.9% of the founding alleles). A preserve manager not interested in maximizing population growth but who only wants to maximize genetic diversity retention could thus plant the founders 100 grid points (500 m) into a 5 km x 5 km or larger preserve. Beyond that, planting further into the preserve does not significantly increase the number of founding alleles conserved. Differences in losses of

of trial dispersal conditions when founders were placed at diagonally increasing

distances from the preserve corner (x-axis). See text for more details.

**4. Discussion** 

**4.1 Practical applications** 

genetic diversity as indicated by changes in observed heterozygosity or F values were not pronounced at age 100 among these trials, and thus are not of major concern to a restoration manager through the initial establishment period modeled.

The second series of trials in which offspring and pollen movement distances were varied in populations with founders placed at increasing distances from the border (Figures 4 through 6) demonstrate that population and genetic edge effects are further affected by variations in gene dispersal distances. Compared to the basic conditions used in Figures 1 through 3, population growth was increasingly reduced (Figure 4) when pollen dispersal was more restricted and offspring dispersal was more distant (trial E), when offspring dispersal was less distant but pollen dispersal matched the basic conditions (trial B), when pollen dispersal was more distant and offspring dispersal less distant (trial F), and when offspring dispersal was most restricted but pollen dispersal matched the basic conditions (trial C). Only when offspring establishment was more distant but pollen dispersal matched the basic conditions (trial D) did population growth exceed that exhibited when the basic dispersal condition applied (trial A). These results suggest that in restoration projects with conditions similar to those simulated here, large gains in population growth might be promoted by ensuring that more offspring establish at greater distances than are occurring naturally.

Differences in founding allele retention among this second series of trials were also evident (Figure 5), with the greatest retention in alleles being under the basic and offspring more distant dispersal conditions (trials A and D respectively). For trial conditions A, B, C, and F, there was a sharp increase in allele retention by moving founders from the corner inwards 100 m, after which further gains were not as pronounced to various degrees for different trial conditions at increasing distances. Under trial conditions E and D, placing founders at 300 grid points would be preferable since significant gains in allele retention were not had beyond that distance. Across all of these trials, the greatest difference in allele retention was 9.6% (between trial E founders at the corner and trial D founders inset by 400 grid points). Inbreeding and subdivision appear to attain the highest values under the basic dispersal conditions with founders inset into the preserve (Figure 6), although none of the values are yet approaching pronounced levels. Causes driving the minor differences seen in F values among trials are not always readily interpretable (e.g., note trials E versus F versus C).

Overall, the relationships among trial conditions, inset distance, population growth, genetic diversity retention, and inbreeding/subdivision can be complex and are not necessarily intuitive. Given this complexity, NEWGARDEN modeling can be used to suggest restoration management strategies. As noted earlier, restoration programs and management need to be as cost-efficient as possible. By understanding interactions between life-history characteristics of *C. dentata* and inset distance for founder establishment, program managers can estimate the best methods to minimize such costs. For example, results of this study suggest that planting and stewarding a limited number of founders (thousands at one location are not needed) at least 1500 m into a preserve and promoting successful offspring establishment beyond that which is occurring naturally, rather than expending that effort promoting establishment within the developing stand, is less costly and potentially more successful in terms of ease of population establishment and growth, maintenance, as well as retention of genetic diversity and avoidance of inbreeding and subdivision compared to other options. Managers may have to make cost-benefit decisions such as which is more important: saving funds by planting near a border, maintaining genetic diversity at the sacrifice of maximizing population growth, or planting further into a preserve at greater expense. The results here stress the need for accurate knowledge of realized gene dispersal attributes (and of other life history attributes) in any modeling-derived restoration management planning. Lacking such information, restoration managers should preferably take the most conservative approach to restoration using as accurate estimations of life history characteristics as possible, in this case, planting the founders at least 1500 m from a border.
