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Abstract The strength and persistence of the tropical carbon sink hinges on the long‐term responses of woody growth to climatic variations and increasing CO2. However, the sensitivity of tropical woody growth to these environmental changes is poorly understood, leading to large uncertainties in growth predictions. Here, we used tree ring records from a Southeast Asian tropical forest to constrain ED2.2‐hydro, a terrestrial biosphere model with explicit vegetation demography. Specifically, we assessed individual‐level woody growth responses to historical climate variability and increases in atmospheric CO2(Ca). When forced with historical Ca, ED2.2‐hydro reproduced the magnitude of increases in intercellular CO2concentration (a major determinant of photosynthesis) estimated from tree ring carbon isotope records. In contrast, simulated growth trends were considerably larger than those obtained from tree rings, suggesting that woody biomass production efficiency (WBPE = woody biomass production:gross primary productivity) was overestimated by the model. The estimated WBPE decline under increasing Cabased on model‐data discrepancy was comparable to or stronger than (depending on tree species and size) the observed WBPE changes from a multi‐year mature‐forest CO2fertilization experiment. In addition, we found that ED2.2‐hydro generally overestimated climatic sensitivity of woody growth, especially for late‐successional plant functional types. The model‐data discrepancy in growth sensitivity to climate was likely caused by underestimating WBPE in hot and dry years due to commonly used model assumptions on carbon use efficiency and allocation. To our knowledge, this is the first study to constrain model predictions of individual tree‐level growth sensitivity to Caand climate against tropical tree‐ring data. Our results suggest that improving model processes related to WBPE is crucial to obtain better predictions of tropical forest responses to droughts and increasing Ca. More accurate parameterization of WBPE will likely reduce the stimulation of woody growth by Carise predicted by biosphere models.
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Reconstructing groundwater and lake level histories in Northern Wisconsin: isolation of groundwater’s influence on tree rings from climatic and environmental drivers
Abstract Tree rings can reveal long-term environmental dynamics and drivers of tree growth. However, individual ecological drivers of tree growth need to be disentangled from the effects of other co-occurring environmental and climatic conditions in tree rings to examine the histories of stand- to landscape-level ecological processes. Here, we integrate ecohydrological theory of groundwater–tree interactions with dendrochronological approaches and develop a new framework to isolate water-level effects on tree rings from climate induced variability in tree ring growth. Our results indicate that changing depth to groundwater within 1–2.3 m of the land surface exerts a substantial influence on red pine growth and this influence can be quantified and used to reconstruct long-term groundwater and lake level histories from tree ring patterns in Northern Wisconsin. This research suggests a substantial influence of groundwater on tree growth with implications for improving the mechanistic understanding of climate-induced tree mortality and reduce uncertainty in forest productivity models. Further, this is a transferable approach to isolate and reconstruct strong environmental drivers of tree growth that co-occur with other environmental signals.
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- Award ID(s):
- 2025982
- PAR ID:
- 10429012
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- Volume:
- 18
- Issue:
- 7
- ISSN:
- 1748-9326
- Page Range / eLocation ID:
- Article No. 074040
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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