Givnish, Thomas , Farquhar, Graham .
Determinants of maximum tree height in Eucalyptus along a steep climatic gradient in Victoria, Australia.
We present a conceptual model linking biomass allocation, hydraulic limitation, and vertical stratification of environmental conditions to patterns in vertical tree growth and tree height. Maximum tree height should increase with relative moisture supply and both should drive variation in apparent stomatal limitation. Carbon isotope discrimination (Δ) should not vary with maximum tree height across a moisture gradient when only hydraulic limitation or biomass allocation limit height, but increase with moisture supply when both hydraulic limitation and biomass allocation limit maximum tree height. We quantified tree height and Δ along a gradient in annual precipitation from 300 to 1600 mm from mallee to temperate rainforest in southeastern Australia; Eucalyptus on this gradient span almost the entire range of tree heights found in angiosperms worldwide, ranging from 4 to 90 m. Maximum tree height showed a strong, essentially proportional relationship to the ratio of precipitation to evaporation. Δ increased with ln P/E, suggesting that both hydraulic limitation and biomass allocation determine maximum tree height. SLA, % leaf N, estimated photosynthetic rate per unit leaf mass increased with tree height and P/E, as did soil silt content, [P], and [NO3]. Surprisingly, trunk diameter increased linearly with tree height in Eucalyptus. We propose that coordinated shifts in several plant traits should result in different species having an advantage in vertical growth rate at different points along this moisture gradient, and in maximum tree height increasing with relative moisture supply, photosynthetic rate, nutrient supply, and xylem diameter.
1 - University Of Wisconsin, Department Of Botany, Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
2 - Australian National University, Research School of Biology, Canberra, ACT, Australia
maximum tree height
Presentation Type: Oral Paper:Papers for Topics
Candidate for Awards:None