Seed Transfer Zones

Successful restoration of native plant communities depends on proper seed selection. Environmental conditions vary across a species’ range, and plant populations become adapted to their local environment. Individuals with genes favorable to the local environment produce lots of seeds and thus pass their genes on. Those with unfavorable genes produce fewer seeds or none at all. Over time, this results in a plant population with a genetic makeup adapted to those particular environmental conditions. If seed from a particular species is collected from a cool and moist environment and then used for a restoration project in a hot and dry environment, those plants are likely to do poorly if they manage to survive at all.

To address this issue, seed transfer zones (STZs) have been developed to distinguish areas with similar climatic characteristics within which seed can be transferred and still be well-adapted to its surroundings. The idea of a good seed zone is captured in the mantra of the  National Seed Strategy 

The right seed in the right place at the right time.

Since native plant restoration efforts require seed from the same seed transfer zone in order to maximize their chances of success, CPNPP takes seed zones into account when coordinating seed collection efforts to ensure there is available seed from as many zones as possible

The most broadly applicable STZs are Provisional, meaning they are developed without species-specific information. They use geospatial climate data, such as winter minimum temperature and indices of aridity, which are strong factors influencing plant distributions and adaptations across space and time, to derive regions of relative climatic similarity. There are two current types of provisional STZs: Bower et al (2014) and Shryock et al (2018). CPNPP is moving from using  Bower et al (2014)  provisional STZs to  Shryock et al (2018)  provisional STZs, which are likely more climatically accurate in the southwestern US. Switch between the two types of Provisional STZ layers in the interactive map below. Switch between the two types of Provisional STZ layers in the interactive map below.

A species-specific guide of seed source choice combines climatic information with species-distribution models to derive species-specific Climate-based STZs. Because the guidance is more specific, climate STZs can decrease the number of estimated seed sources per species needed across the Colorado Plateau. CPNPP funded USGS development of climate-based STZs for five priority species.

Genetics-based STZs can further improve the accuracy of species-specific STZ guidance. Landscape-scale, geospatially-specific molecular analyses or common garden studies can be used to generate species-specific STZs that are more accurate than climate STZs. CPNPP funded USGS development of genetics-based STZs for five priority species (see 2019 and 2020 reports  here ). Results also confirmed the empirical STZ for Indian ricegrass (see map below). Analyses for four more species are in progress

Empirical STZs are the most accurate STZ guidance; they are derived from empirical data, which can be collected from field-based experiments, with or without accompanying molecular studies. The number of empirical STZs varies per species across an area, but empirical STZs utilizing both molecular and field-based data represent the best scientifically-substantiated guidance for seed choice in reclamation and restoration, when project-specific seed collection is not possible. CPNPP works with partners to gather empirical data to test and refine current climate- and genetics-based priority species STZs.

 WWETAC Threat and Resource Mapping: TRM Seed Zone Data  

 Genetically informed seed transfer zones for Pleuraphis jamesii, Sphaeralcea parvifolia, and Sporobolus cryptandrus across the Colorado Plateau and adjacent regions 

Bower, A.D., J.B. St. Clair, & V. Erickson. 2014. Generalized provisional seed zones for native plants. Ecological Applications 24(5):913-919.  https://doi.org/10.1890/13-0285.1 

Doherty, K.D., B.J. Butterfield, & T.E. Wood. 2017. Matched seed to site by climate similarity: Techniques to prioritize plant materials development and use in restoration. Ecological Applications 27(3): 1010-1023.  https://doi.org/10.1002/eap.1505 

Shryock, D.F., L.A. Defalco, & T.C. Esque. 2018. Spatial decision-support tools to guide restoration and seed-sourcing in the Desert Southwest. Ecosphere 9(10):e02453.  https://doi.org/10.1002/ecs2.2453