Provenance level differentiation in thermal safety margins
The mean thermal safety margin calculated using Tcrit – Tleaf (TSMcrit-leaf) was 9.8 °C and ranged from 4.4 to 14.2 °C across all species and provenances (Figure 4a). We found no evidence of a provenance effect in any of the species (p > 0.05, Figure 4a). However, it should be noted that averages do follow the same general trend as for TSMcrit-mod (Figure 4c).
For thermal safety margins calculated using Tcrit – Tcan (TSMcrit-can), we found weak evidence to support a provenance effect in C. australe (t (10) = −2.22, p = 0.051) and T. microcarpa (t (10) = 2.16, p = 0.056) (Figure 4c). In the case of C. australe , variation between provenances is in the same direction as for TSMcrit-leafand TSMcrit-mod (Figure 4), whilst for T. microcarpa , the TSMcrit-can of the lowland provenance is higher than the upland provenance.
The mean thermal safety margin calculated using Tcrit – Tmod (TSMcrit-mod) was 12.7 °C and ranged from 8.2 to 18.2 °C across all species and provenances (Figure 4c). In C. australe , we found (only) weak evidence for a provenance effect (t (10) = −1.90, p = 0.0861), with TSMcrit-mod of the lowland provenance lower than the upland provenance and averaging 14.2 °C ± 2.76 and 16.6 °C ± 1.40, respectively (Figure 4c). We found no evidence for a provenance effect in TSMcrit-mod for the other three species (p > 0.05; Figure 4c).
No evidence of a provenance effect was observed in thermal safety margins calculated using T50 for any of the species (p > 0.05, Supporting information S9).