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Cross-scale interactions affect tree growth and intrinsic water use efficiency and highlight the importance of spatial context in managing forests under global change
Citation:
Ruzicka, K., K. Puettmann, AND J. Renee Brooks. Cross-scale interactions affect tree growth and intrinsic water use efficiency and highlight the importance of spatial context in managing forests under global change. Journal of Ecology. John Wiley & Sons, Inc., Hoboken, NJ, 105(5):1425-1436, (2017).
Impact/Purpose:
Global climate change, especially as reflected in increased drought events, is projected to affect ecosystems and valuable services at multiple scales and processes. A main challenge in planning for global change is to identify the scales over which ecosystem processes will be impacted, and how they interact with management actions at more local scales. We investigated the potential of cross-scale interactions to affect the outcome of density reduction in a large-scale silvicultural experiment. The results of this study demonstrated management prescriptions, such as density reductions to increase resistance and resilience of trees to drought, need to consider cross-scale interactions, as specific magnitude and mechanisms of growth responses can only be predicted when multiple scales are taken into account. Inference made on studies using single stands or averaging across regions cannot be simply extrapolated to global scales, other regions of the world, or easily downscaled to local management options without the context of multiple interacting scales. This paper contributes to ACE 4.02/CIVA-2.
Description:
1. We investigated the potential of cross-scale interactions to affect the outcome of density reduction in a large-scale silvicultural experiment. 2. We measured tree growth and intrinsic water-use efficiency (iWUE) based on stable carbon isotopes (13C) to investigate the impacts of thinning across a range of progressively finer spatial scales: site, stand, hillslope position, and neighborhood position. In particular, we focused on the influence of thinning beyond the boundaries of thinned stands to include impacts on downslope and neighboring stands across sites varying in soil moisture. 3. Trees at the wet site responded to thinning with increased growth when compared with trees at the dry site. Additionally, trees in thinned stands at the dry site responded with increased iWUE while trees in thinned stands at the wet site showed no difference in iWUE compared to unthinned stands. 4. We hypothesized that water is not the primary limiting factor for growth at our sites, but that thinning released other resources, such as growing space or nutrients to drive the growth response. At progressively finer spatial scales we found that the responses of trees was not driven by hillslope location (i.e., downslope of thinning) but to changes in local neighborhood tree density. 5. The results of this study demonstrated that water can be viewed as an “agent” that allows us to investigate cross-scale interactions as it links coarse to finer spatial scales and vice versa. Consequently, management prescriptions, such as density reductions to increase resistance and resilience of trees to drought, need to consider cross-scale interactions, as specific magnitude and mechanisms of growth responses can only be predicted when multiple scales are taken into account.
