Document: PAU-3-29-19

Growth in high light vs. survival in low light as a key tradeoff that determines shade tolerance: A test in a mesic forest in southeast Texas.

LIN, J.* ¹, P.A.HARCOMBE ¹, R.W.HALL ² and M.R.FULTON ³

Rice University, Houston, TX, U.S.A. ¹
Auburn University at Montgomery, Montgomery, AL, U.S.A. ²
Bemidji State University, Bemedji, MN, U.S.A. ³

Abstract:
For seven species in a mature mesic forest in southeast Texas, we estimated species-specific parameters representing radial growth in high light and sensitivity of growth to low light for tree saplings of different species. We also used survival analysis to characterize survival-growth relationships using a demographic dataset collected over 15 years. Shade-intolerant species had higher asymptotic growth rates and lower sensitivity of growth to increasing light than tolerant species. They had lower growth at low light than did the shade-tolerant species. They also had a higher mortality risk at zero growth (low light) and stronger sensitivity of mortality to increasing growth (and light) than shade-tolerant species. Inspection of species positions on graphs of low-light performance (either survival or growth) vs high-light radial growth rate suggests that the tradeoff of low-light growth vs. high-light growth is more evident than the tradeoff of low-light survival vs high-light growth among the important species in this forest, in contrast to results from northern forests. One possible explanation is that the southern forest is brighter than northern forests, so all species may be able to maintain a positive carbon budget. Therefore, in at least some circumstances, survival may not be as important in determining future success in tree saplings as growth.

Keywords: Shade tolerance; sapling; mortality risk; growth; mesic forest

This abstract is being presented at: 3:30 PM in session:
Oral Session #10: Light Relations in Plants.