• Frost dates;
  • Trend discontinuities;
  • Frost impacts;
  • Regional trend analysis;
  • North-east USA


Uncertainty in projections of future climate, along with a need for policy makers and management to respond to change in climate, highlight the importance of the detection of trends in climatological time series. Selected indicators of regional climate status and change may well be related to indicators of ecological condition. Climate factors are known to stress ecosystems. With the identification and description of trends in biologically important climate descriptors this knowledge could be used to provide scenarios of biological changes. One aspect of climate which stresses forest ecosystems is described by the annual date of the last hard spring-freeze (minimum temperature ⩽ −2·2°C). Averaged for New England, there was a significant linear trend indicating an earlier initiation of frost-free conditions (negative slope) for the period 1961–1990.

Significant time trends were detected locally at stations throughout much of the New England regions as well. Temporal discontinuities in trend, spatial relationships, and urban influence were considered. The presence of trends in time does not appear to be related to geographical location. The direction of trend (positive or negative) exhibits some geographical coherency, which may be related to climatological variables such as percentage of possible sunshine and cloud cover.