| Popis: |
Changes in the environmental limitations upon tree-ring growth have been documented during the instrumental periods, but it is more difficult to examine whether environmental change altered dendroclimatological responses over the longer timescales applicable to paleoclimate reconstructions. We present a method to evaluate changes in the relationship between temperature and tree-ring growth over the last five centuries that leverages nonlinear growth relationships between individuals trees within a stand as suggested by Liebig's Law of the Minimum. Furthermore, using this method, we show that regional tree growth was more sensitive to temperature during colder climates over the last five centuries at global and regional scales. These results provide strong confirmation that climate variations alter dendrochronological sensitivity to temperature over the last five centuries. Change in sensitivity is small, however, with an average stand-level increase in sensitivity of 2.7% per °C warming. Our results thus also demonstrate that dendroclimatological reconstructions are generally stable over at least the last five centuries. It may also be possible to use the nonlinear inter-relationships among tree growth within a stand as an independent proxy of low-frequency fluctuations in climate. |
