Seed Collection Zones Research Articles

Table Mountain Pine (Pinus pungens): Genetic Diversity and Conservation of an Imperiled Conifer

Abstract Table Mountain pine (Pinus pungens Lamb.) is an imperiled tree species endemic to the southern and central Appalachian Mountains. Generally reliant on fire for regeneration, its fragmented but widespread distribution has declined in recent decades. We quantified the genetic diversity of 26 populations across the range of the species using data from seven highly polymorphic simple sequence repeat (SSR) loci. The species was relatively inbred whereas differentiation among populations was relatively low. Differentiation was significantly but weakly associated with geographic distance among populations. We detected minor genetic differences between northern and southern seed collection zones established based on climate similarity. We conducted a series of simulations using SSR data from 498 seedlings, grown from seed collected from five natural stands of Table Mountain pine, to assess the genetic consequences of different strategies for deploying collected seed in ex situ conservation plantings. Results indicated that reducing the number of families in a planting would not substantially affect the conservation of common alleles but would affect the representation of rare alleles and overall allelic richness. These findings add to our limited knowledge of genetic variation across the distribution of this rare conifer and offer some guidance for its effective genetic conservation.

Recruitment varies among milkweed seed sources for habitat specialist but not generalist

If sufficient seedling establishment can be achieved, seed‐based restoration provides an affordable, active restoration approach that can be implemented quickly at scale. However, establishment has served as a major restoration bottleneck, highlighting the need for improved understanding of seed germination niche and interactions with site conditions. Germination niche breadth (NB) is expected to increase with gene flow, resulting in broader environmental tolerance range, reduced sensitivity to site conditions, and less variation among seed sources. To investigate how germination NB relates to inter‐ and intraspecific variation in establishment from seed, we compared field recruitment for two milkweeds (Asclepias), the larval host plant of the monarch butterfly and thus a high priority group for habitat creation. Consistent with species‐level NB derived from laboratory trials, there was strong evidence that early life stages of the habitat specialist (Asclepias incarnata) varied among seed collection regions (separated by 423–572 km) but no evidence that the generalist (A. syriaca) varied among seed sources collected across an approximately 750‐km transect. Regeneration trends demonstrate that A. incarnata is significantly more sensitive to seed source and therefore requires more restricted seed zones. However, climate change may necessitate that we separate seed collection zones from seed application zones, upending the traditional framework of seed transfer zones. Until taxon‐specific studies have identified the scale of adaptive, phenotypic variance, restoration practitioners should continue to adjust the scale of seed collection zones for milkweeds and other taxa based on species traits known to influence gene flow, such as abundance and habitat specificity.

New Seed-Collection Zones for the Eastern United States: The Eastern Seed Zone Forum

AbstractAbstractReforestation and restoration efforts have traditionally relied on “local” seed sources as planting stock. The term “local” has different meanings in different locales, since no single set of seed-collection zones has yet been widely adopted across the eastern United States. Given concerns about mitigating the effects of climate change, forest managers are increasingly seeking to move seed sources in a process called assisted migration, which would be facilitated if a common set of seed-collection zones were available. We developed a map of 245 seed-collection zones for 37 states by combining two ecologically important layers: plant hardiness zones and ecoregions. These new seed-collection zones should be used by seed collectors and nurseries to describe the origin of seed for plants and trees in the eastern United States. Common garden studies remain the gold standard for determining how far to move seed from any particular seed-collection zone. For species that have not been field-tested, seed movement that is limited either within a seed-collection zone or between adjacent seed-collection zones is a reasonable general guideline.

Delineation of seed collection zones based on environmental and genetic characteristics for Quercus suber L. in Sardinia, Italy

Abstract: The assessment of seed zones or regions of provenance (RoP) to preserve local adaptation of tree species is an effective tool for the correct management of forest reproductive materials. The RoP for a species or sub-species is the area or group of areas subject to sufficiently uniform ecological conditions in which stands or seed sources show similar phenotypic or genetic characters, taking into account altitudinal boundaries where appropriate. However, the delineation of RoPs is commonly based on estimates of intrinsic environmental homogeneity, mainly climate and/or soil characteristics. The integration of genetic data into RoP maps is an important strategy to obtain a sound tool for managing forest reproductive materials. A study on Quercus suber (cork oak) in Sardinia (Italy) was carried out with the aim of determining ecological regions of provenance, investigating the genetic diversity among populations at the regional scale and identifying possible areas of interest for valorising the available germplasm. Identification of these areas was performed by Reserve Selection Analysis, which allows to identify priority areas by assessing the minimum number of sites required to include all the genetic diversity estimated by genetic analysis. Four spatial clusters were obtained based on environmental data: the northern and northern-eastern parts of the island were included in the Northern RoP; the second RoP covered the western part; and the third RoP enclosed the south-eastern region. The last group was distributed on the central part of the island (Central RoP) and includes the higher elevations. The sampled populations showed a low differentiation among populations and low diversity. According to the Reserve Selection Analysis, four conservation priority areas were identified. These indications can be useful at the local level because these sites can be proposed as stands for seed collection for future plantations.

Genetic delineation of local provenance defines seed collection zones along a climate gradient.

Efforts to re-establish native plant species should consider intraspecific variation if we are to restore genetic diversity and evolutionary potential. Data describing spatial genetic structure and the scale of adaptive differentiation are needed for restoration seed sourcing. Genetically defined provenance zones provide species-specific guidelines for the distance within which seed transfer likely maintains levels of genetic diversity and conserves locally adapted traits. While a growing number of studies incorporate genetic marker data in delineation of local provenance, they often fail to distinguish the impacts of neutral and non-neutral variation. We analysed population genetic structure for 134 amplified fragment length polymorphism (AFLP) markers in Stylidium hispidum (Stylidiaceae) along a north-south transect of the species' range with the goal to estimate the distance at which significant genetic differences occur among source and recipient populations in restoration. In addition, we tested AFLP markers for signatures of selection, and examined the relationship of neutral and putatively selected markers with climate variables. Estimates of population genetic structure revealed significant levels of differentiation (ΦPT = 0.23) and suggested a global provenance distance of 45 km for pairwise comparisons of 16 populations. Of the 134 markers, 13 exhibited evidence of diversifying selection (ΦPT = 0.52). Using data for precipitation and thermal gradients, we compared genetic, geographic and environmental distance for subsets of neutral and selected markers. Strong isolation by distance was detected in all cases, but positive correlations with climate variables were present only for markers with signatures of selection. We address findings in light of defining local provenance in ecological restoration.

An ecological genetic delineation of local seed‐source provenance for ecological restoration

An increasingly important practical application of the analysis of spatial genetic structure within plant species is to help define the extent of local provenance seed collection zones that minimize negative impacts in ecological restoration programs. Here, we derive seed sourcing guidelines from a novel range-wide assessment of spatial genetic structure of 24 populations of Banksia menziesii (Proteaceae), a widely distributed Western Australian tree of significance in local ecological restoration programs. An analysis of molecular variance (AMOVA) of 100 amplified fragment length polymorphism (AFLP) markers revealed significant genetic differentiation among populations (ΦPT = 0.18). Pairwise population genetic dissimilarity was correlated with geographic distance, but not environmental distance derived from 15 climate variables, suggesting overall neutrality of these markers with regard to these climate variables. Nevertheless, Bayesian outlier analysis identified four markers potentially under selection, although these were not correlated with the climate variables. We calculated a global R-statistic using analysis of similarities (ANOSIM) to test the statistical significance of population differentiation and to infer a threshold seed collection zone distance of ∼60 km (all markers) and 100 km (outlier markers) when genetic distance was regressed against geographic distance. Population pairs separated by >60 km were, on average, twice as likely to be significantly genetically differentiated than population pairs separated by <60 km, suggesting that habitat-matched sites within a 30-km radius around a restoration site genetically defines a local provenance seed collection zone for B. menziesii. Our approach is a novel probability-based practical solution for the delineation of a local seed collection zone to minimize negative genetic impacts in ecological restoration.

Sample Size Effects on Estimates of Population Genetic Structure: Implications for Ecological Restoration

AbstractThe field of ecological restoration is growing rapidly, and the sourcing of suitable seed is a major issue. Information on the population genetic structure of a species can provide valuable information to aid in defining seed collection zones. For a practical contribution from genetics, a rapid approach to delineating seed collection zones using genetic markers (amplified fragment length polymorphisms [AFLPs]) has been developed. Here, we test the effects of sampling regime on the efficacy of this method. Genetic data were collected for an outcrossing seeder,Daviesia divaricatassp.divaricata, an important species in urban bushland restoration in Perth, Western Australia. The effect of sample size and number of AFLP markers on estimates of genetic variation and population structure was examined in relation to implications for sourcing material for restoration. Three different sample sizes were used (n= 8, 15, and 30) from six urban bushland remnants. High levels of genetic diversity were observed inD. divaricata(87.4% polymorphic markers), with significant population differentiation detected among sampled populations (ΘB= 0.1386,p&lt; 0.001). Although sample size does not appear to affect the spatial pattern in principle co‐ordinates analysis (PCA) plots, the number of polymorphic loci increased with sample size and estimates of population subdivision (FSTand ΘB) and associated confidence intervals decreased with increasing sample size. We recommend using a minimum of 30 plants for sourcing seed for restoration projects.

Genetic Variation in Three Native Plant Species across the State of Minnesota

Restoration of native plant communities requires adapted germplasm; thus, information is needed to guide native seed collection and production. Analysis of genetic variation has potential to provide insight into diversity and relatedness of natural populations. Our objectives were to examine genetic diversity of native species in Minnesota to discover if variation is related to biomes or distance, and possibly to develop seed collection zones. Our study included prairie cordgrass (Spartina pectinata), purple prairie clover (Dalea purpurea), and spotted joe‐pye weed (Eupatorium maculatum). Using amplified fragment length polymorphisms, we analyzed 100 samples from eight populations for prairie cordgrass, 152 samples from nine populations for purple prairie clover, and 127 samples from 10 populations for spotted joe‐pye weed. We found moderate to high levels of genetic diversity within each species. Small populations were not necessarily lower in diversity than larger ones. Analysis of molecular variance results indicate clear population differentiation. However, rather than displaying geographic or ecological associations, the variation had discontinuous patterns. Therefore, we were not able to develop unambiguous recommendations for seed collection. We discuss the applicability of molecular markers in detecting adaptive potential.

Rapid genetic identification of local provenance seed collection zones for ecological restoration and biodiversity conservation

The ecological restoration of native plant communities requires the collection of large amounts of seed. Use of non-local provenance seed can have detrimental consequences for the success of restoration if there is a home-site advantage, and for nature conservation through the erosion of natural patterns of population genetic structuring and/or genetic swamping (and extirpation) of locally significant genotypes. As part of an ongoing project to genetically delineate local provenance seed collection zones for species within a large urban bushland remnant of high conservation value, we assessed population genetic differentiation in two widespread coastal leguminous species, Acacia rostellifera and A. cochlearis (Fabaceae), commonly used in restoration programmes in SW Australia. Using amplified fragment length polymorphism (AFLP), we found very high levels of genetic differentiation among populations, with an analysis of molecular variance (AMOVA) showing more than 50% of the total genetic variance to be partitioned among populations ( Φ ST = 0.58 and 0.51 for A. rostellifera and A. cochlearis , respectively), and marked non-overlap of almost all potential seed source populations from the local population in ordinations. Our results suggest extremely restricted natural dispersal among populations, possibly due to a combination of low seed set, seed dispersal by ants, clonality, a linear distribution of naturally fragmented populations and possibly low outcrossing rates. We suggest a narrow seed collection zone should be applied to these species for the conservation of genetic diversity and natural patterns of population genetic structure, and we highlight the value and importance of provenance evaluation to ecological restoration.

METHODOLOGICAL INSIGHTS: Rapid genetic delineation of provenance for plant community restoration

Summary Best practice in native plant community restoration and/or revegetation recognizes the importance of using material of local provenance. At the practical level, various guidelines exist but these have limitations. The challenge is to deliver accurate provenance information rapidly to the restoration industry. We demonstrate a novel approach to the rapid delineation of genetic provenance by utilizing minimal sampling, the power and efficiency of the AFLP DNA fingerprinting technique and a multivariate spatial autocorrelation analysis for four species with high priority for minesite revegetation in south‐west Western Australia. A significantly positive genetic correlation was found between individuals in the smallest distance class for three species. Correlograms then stabilized, with no significant genetic correlation between individuals at any other distance class. A local genetic provenance distance was here defined as the distance where the correlogram goes from significant to non‐significant, which was approximately 26 km, 20 km and 20 km for these three species. In contrast, for the fourth species, no significant genetic correlation was seen at any distance class, suggesting a very broad genetic provenance (up to 100 km), although the possibility of significant structure below the smallest distance class used here (20 km) cannot be dismissed. Whilst spatial autocorrelation has identified significant spatial genetic structure for 3 of 4 species assessed, a robust delineation of provenance distance, or patch size, is problematic because it is dependent on properties of sampling and analysis such as the scale of sampling and the choice of distance class size, especially when sample sizes are small. Synthesis and applications. The determination of seed collection zones for revegetation projects is a complex problem. We demonstrate a new approach for the rapid delivery of genetic provenance delineation for native plant community restoration, and provide recommendations for seed collection zones for each of four species. This approach can be applied to other species and other areas. We discuss the limitations of the approach, and conclude that further research is required to assess an appropriate minimal sampling strategy that leads to a more robust delineation of provenance distance. We also note that revegetation programmes provide an opportunity to experimentally assess the biological significance of the local provenance as defined, through an assessment of the relative performance of plants sourced from within and beyond defined provenances.

Geographic Variation of China Fir (Cunninghamia lanceolata (Lamb.) Hook) in Taiwan: Analysis of Provenance Division by Ecotype and by Province

China fir shows significant geographic variation because it grows in a great diversity of ecological environments; it is subject to geographic and reproduction isolation; and it has been cultivated selectively and separately by many local farmers. In order to match provenances and planting sites for greater genetic gain, seed collection zones are to be delineated. Forest geneticists in mainland China have separated China-fir provenances into 9 ecotypes. Using growth and isozyme data obtained from 2 test plantations (Liukuei and Lienhuachih) we tested the effectiveness of such ecotype delineation. We found that the grouping of China-fir provenances into 9 ecotypes was most effective for the analysis of early growth at the Liukuei plantation. It was only moderately effective for analysis of later growth at the Lienhuachih plantation. The grouping of provenances was not useful for isozyme frequency or heterozygosity analysis. The different degrees of effectiveness may be possible because the construction of such ecotype classifications in China were based solely on early growth data; no isozyme data were used. Grouping provenances by ecotypes was superior to grouping by political provincial origins for early growth. On the other hand, provincial grouping seemed to be better than ecotype grouping for later growth. When the 2 best ecotypes or 2 best provinces were selected, provincial selection seemed to be able to yield a higher genetic gain than ecotype selection. However, the selection results and their rankings seemed to be more consistent in the ecotype division than in the provincial division.

Gene flow, spatial patterns and seed-collection zones

Models of gene flow, selection and demography were employed to determine the minimum limits and amplitudes of seed-collection and seed-transfer zones in forest trees, using loblolly pine ( Pinus taeda L.) and white spruce ( Picea glauca (Moench.) Voss.) as examples. Seed-collection zones were defined in terms of spatial patterns for polygenic (growth) characters. Fora given character, the boundaries of a seed-collection zone were found to be determined by interactions among gene flow, selection strength and genetic variation for that character at a specific age. For example, the width of a seed-collection zone for 5-year-old trees of loblolly pine was found to be larger if it was based on diameter rather than height growth. Conversely, the width of these zones differed between 5- and 15-year-old trees for either diameter or height growth. A similar trend was evident for white spruce. The average minimum width of seed-collection zones for loblolly pine and white spruce varied from 324 to 400 m. These results are consistent with many reports on gene flow, selection and differentiation in natural populations of forest trees. Seed-transfer zones should be based on the amount of genetic variation in the adaptive traits of each population representing a seed-collection zone. The adaptive amplitudes of populations from various seed-collection zones on a large geographical scale must be determined on the basis of the homeostatic properties specific to each population.

Preliminary study on the germination of Toona sinensis (A. Juss.) roem. seed from eleven Chinese provenances

A preliminary germination study was carried out on seed of eleven provenances of Chinese mahogany [ Toona sinensis (A. Juss.) Roem.]. The species is native to China and characterized by high density and dark colored wood, which is used mainly in furniture making. Seeds of the eleven provenances were tested on a thermoplate gradient germinator at temperatures of 15°C, 18°C, 22°C, 25°C, and 28°C. The three upper temperatures (22°C, 25°C, and 28°C) provided the fastest and highest germination among the eleven provenances, and on the average 25°C was considered as optimum temperature for the species. Based on mean time to germination, germination values, root length and hypocotyl length, it was possible to delineate the eleven provenances into three geographic groups. Additional studies using more evenly distributed samples from the whole range of the species are expected to further define seed collection zones for this important species in China.

Effect of test environment on expression of clines and on delimitation of seed zones in Douglas-fir

Clinal models of population structure in an indigenous tree species can be used to delineate seedcollection zones and breeding zones, and to devise transfer rules. Models may be developed by growing populations in test environments; however, a clinal description may be a function of test environments as well as of population genotypes. This possibility was studied by growing seedlings from 40 populations of northwestern U.S. Douglas-fir (Pseudotsuga menziesii var. 'menziesii' [Mirb.] Franco) in eight nursery-bed treatments which contrasted air and soil temperatures and nutrition. Growth traits measured were stem diameter, top height, and dry weight; phenological traits were bud-burst and bud-set dates, extension period, and extension period midpoint. Population samples interacted significantly with soil temperature for growth traits, and with soil and air temperatures combined for phenological traits. Interactions were at least partly explained by complex clinal associations of seedling performance with elevation, with latitude, and with distance from the ocean of the populations sampled. Both the complexity and the gradient of the clinal pattern depended on the trait and on the specific test environment.The clinal patterns of greatest complexity were expressed in warm air and soil treatments. Dry top-weights of population samples were associated with latitudes for samples grown in warm soils, but this relationship was not apparent in cool soils. A discrepancy in bud-burst dates between extreme coastal and more inland populations was greatest in warm soil-warm air treatments and was negligible in cool soil-cool air treatments. Populations X temperature interactions were attributed to the differential response of population samples to spring temperature and photoperiod. It is proposed that first attempts at devising a model can be based on nursery or growthchamber tests, and that test environments should stress contrasting photo- and temperature-regimes.The estimate of clinal structure in Douglas-fir suggests that there is more risk within northwestern U.S. in moving provenances east-west than north-south, that this risk increases with elevation of provenances, and that north-south transfers are more critical near the coast than inland.