Live crown tops of Japanese cedar (Cryptomeria japonica) approach one another in height at urban forest sites

Since the 1980s, we have found Japanese cedar, Cryptomeria japonica (L. f.) D. Don, trees with crown tops affected by dieback in isolated urban forests on the low altitude plain. To clarify future growth of C. japonica in these forests, we investigated their growth, decline levels and water status. The live crown-top heights from the ground (LCTHs) per diameter at breast height (dbh) were lower in forests with C. japonica top dieback than in forests with no top dieback. Furthermore, in a forest with C. japonica top dieback, the LCTHs were similar between trees although dbh and decline levels were different. Moreover, water status near the top of the live foliage was very similar although decline levels were different, suggesting that in urban forests, where C. japonica top dieback is observed, the LCTH is subject of restriction. A sudden increase in temperatures since the 1980s may be restricting the LCTHs of C. japonica in urban forests. We conclude that LCTHs of C. japonica in urban forests are becoming lower and more equal in each forest. If temperature continues to increase, height restriction will become more severe and LCTHs of C. japonica in urban forests will become even lower.