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- Title
Unthinned slow-growing ponderosa pine ( Pinus ponderosa) trees contain muted isotopic signals in tree rings as compared to thinned trees.
- Authors
Sohn, Julia; Brooks, J.; Bauhus, Jürgen; Kohler, Martin; Kolb, Thomas; McDowell, Nathan
- Abstract
Key message: The muted wood isotopic signal in slow-growing trees of unthinned stands indicates lower responsiveness to changing environmental conditions compared to fast-growing trees in thinned stands. Abstract: To examine the physiological processes associated with higher growth rates after thinning, we analyzed the oxygen isotopic values in wood (δO) of 12 ponderosa pine ( Pinus ponderosa) trees from control, moderately, and heavily thinned stands and compared them with wood-based estimates of carbon isotope discrimination (∆C), basal area increment (BAI), and gas exchange. We found that (heavy) thinning led to shifts and increased inter-annual variability of both stable carbon and oxygen isotope ratios relative to the control throughout the first post-thinning decade. Results of a sensitivity analysis suggested that both an increase in stomatal conductance ( g) and differences in source water among treatments are equally probable causes of the δO shift in heavily thinned stands. We modeled inter-annual changes in δO of trees from all treatments using environmental and physiological data and found that the significant increase in δO inter-annual variance was related to greater δO responsiveness to changing environmental conditions for trees in thinned stands when compared to control stands. Based on model results, the more muted climatic response of wood isotopes in slow-growing control trees is likely to be the consequence of reduced carbon sink strength causing a higher degree of mixing of previously stored and fresh assimilates when compared to faster-growing trees in thinned stands. Alternatively, the muted response of δO to climatic variation of trees in the control stand may result from little variation in the control stand in physiological processes (photosynthesis, transpiration) that are known to affect δO.
- Subjects
PONDEROSA pine; TREE-rings; TREE growth; PLANT growth; TREE physiology
- Publication
Trees: Structure & Function, 2014, Vol 28, Issue 4, p1035
- ISSN
0931-1890
- Publication type
Article
- DOI
10.1007/s00468-014-1016-z