There and back again: genetic trials enable the transfer of Douglas-fir distribution models across continents

Figure 1. Role of seed origin in buffering the effects of climate change on potential distribution. Potential distribution of two provenances, Darrington originating from cascade region of Washington in North America and Adams lake originating from interior British Columbia. Under climate change the potential distribution of the cascade provenance is wider compared to the interior provenance providing evidence to the role of seed origin in buffering the effects of climate change on trees species distribution.

By Silvio Schueler

Climate change is likely to result in novel conditions with no analogy to current climate. Therefore, the application of species distribution models (SDMs) based on the correlation between observed species' occurrence and their environment is questionable and calls for a better understanding of the traits that determine species occurrence. Here, we compared two intraspecific functional trait-based SDMs with traditional occurrence-based SDMs, all developed from European data, and analyzed their transferability to the native range of Douglas-fir in North America. The trait based SDMs include the genetic variation in functional traits such as dominant height and basal area as a response to climate of planting location and seed origin. The occurrence based SDM is based on correlation between current occurrence of Douglas-fir and its climate.

Both models performed well within their calibration range in Europe, but model transfer to its native range in North America was superior in case of the URF-SDMs (Fig. 2). The high transferability of the URF-SDMs is a testimony of their applicability under novel climatic conditions highlighting the role of intraspecific trait variation for adaptation planning in climate change. 

The trait based intraspecific SDMs we developed are capable of modeling the distribution of potential seed sources under any climate and therefore circumvents a major criticism of traditional occurrence based SDMs (i.e lack of functional traits and intraspecific variation). Here we can see how choice of planting material or seed origin can buffer the effects of climate change (Fig. 1).

Figure 2. Transferring SDMs calibrated in Europe to North America (A) The observed distribution of Douglas-fir in 71,182 inventory plots in North America. The predicted distributions with: (B) Functional trait- based SDM; (C) Occurrence-based SDM. Black represent areas predicted by the models to have climate suitable for Douglas-fir whereas gray area represents climatically unsuitable areas. See how the occurrence-based SDMs calibrated in Europe missed to predict the entire interior distribution of Douglas-fir when transferred to North America.

Keywords: Species distribution models, genetic variation, trans-continental transfer of SDM

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