# Assisted Migration Field Tests in Canada and Mexico: Lessons, Limitations, and Challenges
## 3 Field Tests Examined
### Canada. Picea glaucac \(\times\) engelmannii Hybrid Complex (Interior Spruce)  
Materials and Climate Data  
As _Picea glauc_ (Moench) [PERSON], _Picea engelmannii_ Parry ex Engelm., and their hybrids (known locally as interior spruce, but herein referred to as _Picea glauc \(\times\) engelmannii_) are among the most ecologically and economically important species in BC and throughout Canada [55], a large, long-term field provenance trial of _Picea glauc \(\times\) engelmannii_ was established by the BC government in 2005. The trial consisted of 128 natural stand populations and orchard seedlots from Canada and USA planted at each of 17 sites in BC, Yukon, and Alberta. Details regarding the populations, test sites and experimental design can be found in [PERSON] et al. [56] (Figure 2).  
Height and survival were assessed at the end of the 10 th field season. At each site, a productivity index (PI10) was obtained for each of the 97 natural stand populations by multiplying population mean height by population survival proportion. Values of mean coldest month temperature (MCMT) for the 1961-1990 period (hereafter referred to by its center year, 1975) were obtained for each provenance and test site from ClimateBC or ClimateNA ([[http://climatebc.ca/](http://climatebc.ca/)]([http://climatebc.ca/](http://climatebc.ca/))) version 6.22 [57]. Mean coldest month temperature was selected because it is frequently identified as being among the most important of climate variables in accounting for population differentiation in _Picea glauc \(\times\) engelmannii_[51] and other North American temperate confer species [58; 59].  
A universal transfer function (UTF), which predicts the productivity of any population at any location, was developed following methods of [PERSON] et al. (2008; Appendix A). Individual transfer functions were first fitted to each site by relating population PI10 to  
Figure 2: Seed source and test site locations used in the _Picea glauc \(\times\) engelmannii_ provenance trial. The High Level test site is located in northwest Alberta.  
population MCMT_tx (MCMT of the test site minus MCMT of the seed source) using a Cauchy function. Linear and quadratic relationships were then developed between the fitted coefficients and test site MCMT. Fitting of peaked transfer functions at the warmest and coldest sites was facilitated by the imputation of a single warm and cold anchor point population using an approach similar to that of [PERSON] et al. (2016). Likewise, fitting of the scale parameter was enabled by the imputation of a single warm ghost test site using an approach similar to that of [PERSON], [PERSON], [PERSON] (2017). For details of the imputation procedures see the Appendix A.  
The impact of assisted migration was assessed in two ways. First, the climate of the vertex of each individual transfer function (i.e., the climate of the population expected to have the greatest productivity) was determined at each site. Second, fitted equations for the three Cauchy function parameters were substituted back into the transfer function, and response functions were estimated for a \"local\" population from MCMT = \(-18\)\({}^{\circ}\)C, and a \"migrated\" population from MCMT = \(-15\)\({}^{\circ}\)C, representing climates of northern and central BC, respectively. As response functions illustrate population productivity across a range of climates, responses of alternative seed sources over time can be compared to assess their relative merit over time when planted in a common climate.