The Andrews Forest Dynamics Plots are a network of 7 large stem-mapped forest research plots across a 900 m vertical gradient in elevation in the western Cascade Mountains of Oregon in the Pacific Northwest region of the United States. These forests have some of the tallest trees and largest above-ground biomass of any in the world. The Andrews Forest Dynamics Plots network includes one 12-ha plot at ~900 m elevation and six satellite plots (each 3-ha) that span a range of environmental types and elevations (450 m to 1,350 m elevation). All 7 of these large forest plots are matched with long-term forest and climate datasets (each plot is expanded from a central 1-ha core plot that has been surveyed since the 1970s). As of 2022, we have completed mapping the 12-ha plot and 2 of the 3-ha plots, with approximately half of the area of the other four 3-ha plots mapped. We anticipate mapping of all plots will be completed in summer 2023. The 12-ha plot was first censused in 2019-2021, and the other 2 completed 3-ha plots were mapped in 2019. In addition, we have collected auxiliary data within these plots to create high-resolution maps of biotic and abiotic factors in these plots including microclimate, soil chemistry, microtopography, and fungal microbiome. Thus, the resulting data will integrate well with ongoing NSF-funded LTER (Long Term Ecological Research) studies.
The Andrews Forest Dynamics Plots represent a shift in tree species dominance along the elevation gradient. At lower elevations, plots are dominated by Douglas-fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), and western redcedar (Thuja plicata), with big-leaf maple (Acer macrophyllum), Pacific yew (Taxus brevifolia), and a number of understory hardwood species also present. At mid elevations, Pacific silver fir (Abies amabilis) starts to become prevalent, and higher elevation plots transition to being dominated by true firs (including Abies amabilis and Abies procera). These shifts in tree-species dominance reflect shifts in dominance across the Pacific Northwest region, making the network of Andrews Forest Dynamics Plots a potential microcosm for forest dynamics in the region. These plots will make an excellent comparison with several other mixed conifer/deciduous and temperate plots in North America and Asia at similar latitudes, as well as other elevation gradients in forest plots. The geography, size, and range of ecological conditions included in the Andrews Forest Dynamics Plots were selected to include large amounts of continuous, expansive, and varied natural forest landscape that will yield opportunities for the study of forest dynamics and demography while leveraging a large amount of existing science infrastructure across the broader Andrews LTER site (e.g., long-term meteorological stations, pre-existing smaller long-term forest plots, nearby forest management experiments, replicated gauged watersheds) that will enable the integrated study of ecosystem processes (e.g., biogeochemistry, hydrology, carbon dynamics) and forest dynamics. The shifts in dominant tree species across the elevation gradient may also have implications for ecosystem function and dynamics.