National forest inventories (NFI) are founded upon statistical sampling designs that make unbiased, representative estimates of important forest attributes (e.g., area, volume, number of trees). In the US, the Forest Inventory and Analysis Program measures forestland conditions at great extent and with relatively high spatial resolution (sampling intensity of 1 plot per ~6,000 acres). This now includes the collection of increment cores in the forest plots of the Interior West (IW-FIA), enhancing the baseline plot data with species-specific, annually resolved ring-width increment. IW-FIA has used increment cores in ways that are consistent with traditional forestry practices (estimating vigor, age, site index), but these data can also support other important research questions. We describe the opportunities that arise from the existence of a network of increment cores collected in a NFI sampling design by detailing results that address three research questions. We also characterize the challenges of using these data by focusing on where different research goals can complement one another.
Results/Conclusions
The key opportunity of using tree-ring data collected from a representative NFI is that inferences characterize the underlying population. Trees sampled from NFI plots can thus be considered representative of important ecological processes such as competition and mortality. For example, integrating increment cores with tree- and plot-level data to estimate above-ground biomass increment allows us to simultaneously assess the influence of climate and other drivers. Second, an assessment of Douglas-fir in the Interior West indicated that the putative age-related growth decline disappeared when tested using tree-ring data collected from the IW-FIA. Finally, targeted sampling of tree-ring data for the purposes of dendroclimatic reconstruction overestimates forest response to climate warming by as much as 50%, and higher elevation forests appear much less vulnerable to drought-caused decline. While the “ordinary” challenges of collection, preparation, measurement, crossdating, and data storage are familiar to dendrochronologists, a larger challenge is reconciling sampling protocols within and among multiple NFIs to assemble even larger networks. Ultimately, NFIs document baseline population change, and their associated tree-ring data offer the opportunity to characterize annual-scale population changes in the face of extreme events at national, continental, and even global scales.