Evidence for rising upper limits of four native new zealand forest trees

Abstract

Since the 1860s New Zealand mean air temperatures have risen about 0.5°C, which might be expected to have led to a rise of about 100 m in altitudinal limits of plants. Four tree species were examined at several South Island localities for evidence of such a rise. Young silver beech plants have established above the upper limit of mature trees, mostly within the last 60 years. However, as beech timberlines are strongly buffered, few of these young plants occur more than 9 m from the forest margin. Above mountain beech timberlines, which lie in drier climates east of the Main Divide, the “advance zone” is usually less than 7 m wide, and does not include the exposed spurs and northerly faces where timberline ascends highest. Above the limit of mature red beech trees, there is a zone in which younger red beech, up to 150 years old, occur through nearly 30 m of altitude. Scanty data for miro suggest a still wider advance zone. The difference between the potential altitudinal rise of upper limits and that which is actually achieved suggests that in the event of rapid and substantial climatic change, species with intrinsically slow rates of spread would be unable to keep pace. Those with narrow environmental ranges could be threatened with extinction unless managed so as to assist dispersal and establishment.To substantiate the prima facie findings of this study, transects have been set up to monitor long term future changes. © 1992 Taylor & Francis Group, LLC.