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 ).