A response to: Limitations within "The Limits to Tree Height".

Here we respond to the communication in American Journal of Botany (96: 542-544 in this issue) by Netting, who proposes several ways in which our paper "The Limits to Tree Height" (Nature 428: 851-854) may have erred in estimating the biophysical limits to height growth in Sequoia sempervirens. We first explain that because embolism repair requires long time periods and is generally incomplete, xylem vulnerability characteristics offer a sound basis for estimating performance limits in woody plants. We reaffirm our earlier use of vertical gradients of foliar carbon isotope composition with new data for S. sempervirens. We support these arguments with reference to studies in other tree species. We take exception with Netting's view that the turgor pressure-cell expansion relationship for Zea mays is applicable to S. sempervirens. Finally, we second Netting's call for more work on carbon allocation vis a vis height growth limits.