Responses to climate change

4.3.2.1. Phenotypic change following replanting

By the end of the period of directional selection, predictive provenancing emerged as the seed sourcing strategy which enabled the greatest total change in the mean climatic phenotype of the planted population (Figure 4.6). The populations established under local provenancing achieved less change in climate phenotype and the other two strategies which involved some non-local genotypes (composite, admixture), were intermediate. Unassisted natural regeneration, which was measured as the mean phenotypic change recorded in all patches in which no felling and replanting took place (i.e., a ‘do-nothing’ approach),

achieved the least change to the climate phenotype. This is presumably due to the absence of a pulse of mortality followed by a major recruitment event involving recent selection on planted trees (Kramer et al., 2008; Kuparinen et al., 2010). For this reason, even when locally sourced genotypes are planted, which are the offspring of the felled local parents, a

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greater shift in the distribution of phenotypes towards the new climatic optimum is achieved than when the population regenerates without intervention.

Figure 4.6. Change in the mean climate phenotype during the period of simulation, when parameter settings are

held at default values under the fixed and selective juvenile mortality sub-models. The dashed black line represents the mean value for the changing climatic optimum. Regeneration refers to phenotypic change occurring in patches which have not undergone felling and replacement. Error bars represent 95% confidence intervals. The positions of the points and error bars are artificially offset to avoid overlap.

Differences in the rate of adaptation between years 100 and 200 (i.e. once the climate had stabilised) were calculated by analyses of covariance (interaction terms in Table 4.3). Under selective early mortality, the rate of adaptive change is slowest when predictive

provenancing is applied, but there are no differences between any of the other strategies. When the early mortality rate is fixed, the rate of adaptation (i.e. amount of change per time step) is greatest under local provenancing and natural regeneration and is slower when any strategy involving non-local genotypes is used.

91 Table 4.3. Analysis of covariance table for rates of phenotypic change between years 100 and 200. Local

provenancing is the reference and therefore the parameter estimate for Local provenancing is 0. Only the interaction terms are considered informative.

Establishment model = Fixed

Estimate Standard error t value p value

(Intercept) -1.43e-02 1.72e-03 -8.316 5.32e-07 ***

Year 5.32e-04 1.12e-05 47.563 2.00e-16 ***

Composite 4.39e-02 2.44e-03 18.027 1.41e-11 ***

Predictive 1.04e-01 2.44e-03 42.659 2.00e-16 ***

Admixture 2.96e-02 2.44e-03 12.148 3.65e-09 ***

Regeneration -3.99e-03 2.44e-03 -1.637 0.12253

Year: Composite -1.17e-04 1.58e-05 -7.399 2.22e-06 *** Year: Predictive -2.74e-04 1.58e-05 -17.296 2.56e-11 *** Year: Admixture -5.93e-05 1.58e-05 -3.753 0.00192 **

Year: Regeneration -2.64e-05 1.58e-05 -1.67 0.1157

Establishment model = Selective

Estimate Standard error t value p value

(Intercept) -2.09e-02 2.74e-03 -7.642 1.51e-06 ***

Year 5.95e-04 1.78e-05 33.432 1.68e-15 ***

Composite 1.75e-02 3.88e-03 4.521 0.000406 ***

Predictive 4.98e-02 3.88e-03 12.842 1.70e-09 ***

Admixture 6.49e-03 3.88e-03 1.676 0.114535

Regeneration 1.65e-04 3.88e-03 0.043 0.966525

Year: Composite -4.58e-05 2.52e-05 -1.823 0.088308 .

Year: Predictive -1.33e-04 2.52e-05 -5.281 9.24e-05 ***

Year: Admixture -1.30e-05 2.52e-05 -0.518 0.611677

Year: Regeneration -2.40e-05 2.52e-05 -0.953 0.355477

There is an initial spike in mean population climatic phenotype under predictive and composite provenancing at year 5 (Figure 4.6). This represents the initial step change in mean phenotype of the planting patch compared to that of the felled patch at the end of equilibration. Under both selective and fixed mortality models, a rapid decline occurs by year 25. Under the selective mortality model, this is due to both heavy losses during the five initial years of hard selection on planted trees and, to a lesser extent, subsequent density dependent selection on recruits towards the contemporary optimum.

Under the fixed mortality model, any change in the mean phenotype during the first five years is caused by random genetic drift. This is then followed by natural selection acting upon recruits after the end of the juvenile sensitivity period, causing the mean phenotype of the population to migrate rapidly towards the current optimum. Rapid adaptation can take place at an early stage in the simulation years because, following juvenile mortality, there are

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many gaps on the forest floor and thus many opportunities for recruitment, in which the best fitted individuals in any year become established. Once these gaps have been filled, a process which takes place rapidly; there are fewer annual opportunities for selection to act upon recruits, thereby slowing the rate of ongoing adaptation (Kuparinen et al., 2010). The reduction in the extent of change which occurs under composite and predictive provenancing in the first 25 years occurs because the climate is changing gradually. The planted genotypes were initially ‘overfitted’, i.e. they are adapted to conditions correctly predicted for one hundred years hence but not to the conditions prevailing at the time. Counter-gradient selection causes the population to adapt to a contemporary optimum (when the solid lines intersect the dashed lines on Figure 4.6). However, by this time, the rate of change experienced during the first 25 years can no longer be achieved. Ongoing adaptation is not as fast as it had been initially because there are fewer opportunities for recruitment because the population size approaches carrying capacity and is therefore limited to regeneration following mortality which occurs at a rate of 1/150.

4.3.2.2. Population size following replanting

The initial phenotypic change achieved in the planting patch is concurrent with high levels of juvenile mortality occurring during the phase of hard selection on planted trees. Juvenile mortality was highest when the planted trees are not adapted to contemporary conditions (Figure 4.7) and thus, local origin genotypes have the highest survival rates. The lowest and most variable survival rates were observed when predictive provenancing was applied.

93 Figure 4.7. Size of the planted patch in year 5 following implementation of juvenile mortality functions. In this case,

adaptation is to climate only. Habitat is not considered selectively important.