Local adaptation to serpentine soils in Pinus ponderosa

Local adaptation to serpentine soils is studied using both transplant experiments and molecular genetic techniques. In long-lived species, such as pines, it is unclear how soon after germination local adaptation becomes detectable. Here I present results of a 36-year reciprocal transplant experiment using Pinus ponderosa, along with allozyme analyses from the same trees. Using a repeated measures analysis of variance, there is evidence for adaptation to serpentine soils; however, significant differences between source soil types do not become apparent until 20 years after the start of the experiment. Analysis of allozyme data showed no evidence for differentiation between the serpentine and non-serpentine populations. Comparing the performance of families over the course of the experiment found that there was little correlation between performance after 1 or 4 years of growth in the Weld and performance after 36 years. This suggests that short-term transplant experiments may not provide definitive evidence for adaptation to serpentine soils. A literature survey of all transplant studies using pine species growing on and off of serpentine soils found that studies that lasted fewer than 2 years showed no evidence for adaptation. However, in the two experiments ( this one included) that lasted more than 2 years, both showed evidence for adaptation to serpentine soils. More long-term experiments are required to validate these results. Local adaptation to serpentine soils is studied using both transplant experiments and molecular genetic techniques. In long-lived species, such as pines, it is unclear how soon after germination local adaptation becomes detectable. Here I present results of a 36-year reciprocal transplant experiment using Pinus ponderosa, along with allozyme analyses from the same trees. Using a repeated measures analysis of variance, there is evidence for adaptation to serpentine soils; however, significant differences between source soil types do not become apparent until 20 years after the start of the experiment. Analysis of allozyme data showed no evidence for differentiation between the serpentine and non-serpentine populations. Comparing the performance of families over the course of the experiment found that there was little correlation between performance after 1 or 4 years of growth in the field and performance after 36 years. This suggests that short-term transplant experiments may not provide definitive evidence for adaptation to serpentine soils. A literature survey of all transplant studies using pine species growing on and off of serpentine soils found that studies that lasted fewer than 2 years showed no evidence for adaptation. However, in the two experiments (this one included) that lasted more than 2 years, both showed evidence for adaptation to serpentine soils. More long-term experiments are required to validate these results.