Figure 4. Relationship between climate effects on willow shoot
growth, and lagged climate. Tests are the same as those shown in Fig.
2b, except that analyses are run separately for each of the experimental
treatments. Abbreviations are as described in the legend to Fig. 3 and
in Table 1.
The effects of climate on shoot growth were also similar across
treatments, generally with a positive relationship between climate
effects and growing degree days (Fig. 4). Recall that negative climate
effects suggest that warming will have a negative impact on shoot
growth, whereas positive effects suggest that warming leads to increases
in shoot growth – our results therefore suggest that at low
temperatures, warming will have an overall negative effect on growth,
whereas at higher temperatures, warming will have an overall positive
effect. Interestingly, treatments that included vertebrate herbivores
and no rejuvenation (P , RP ) tended to experience more
positive effects of climate, such that the effect was consistent over a
range of previous year thermal conditions. In contrast, rejuvenation
treatments tended to suppress the positive relationship between climate
and climate effects, such that there was a fixed, negative effect of
climate regardless of growing degree days. However, for the treatment
that included both vertebrate herbivores and rejuvenation, the positive
relationship returned, and the overall pattern was similar to that for
shoot growth in conditions without browsers (N ).