Site Description before Fire (January, 2002 - August, 2020): The mean stand age is 71 years old and the stand age of the oldest 10% of trees is about 108 years old. This site is one of the Metolius core cluster sites with different age and disturbance classes and part of the AmeriFlux network. The overstory is almost exclusively composed of ponderosa pine trees (Pinus ponderosa Doug. Ex P. Laws) with a few scattered incense cedars (Calocedrus decurrens (Torr.) Florin) and has a peak leaf area index (LAI) of 2.1 m2 m-2. Tree height is relatively homogeneous at about 18 m, and the mean tree density is approximately 339 trees ha-1 (Irvine et al., 2008). The understory is sparse with an LAI of 0.2 m2 m-2 and primarily composed of bitterbrush (Purshia tridentata (Push) DC.) and greenleaf manzanita (Arctostaphylos patula Greene). Soils at the site are sandy (69%/24%/7% sand/silt/clay at 0–0.2 m depth and 66%/27%/7% at 0.2–0.5 m depth, and 54%/ 35%/11% at 0.5–1.0 m depth), freely draining with a soil depth of approximately 1.5 m (Irvine et al., 2008; Law et al., 2001b; Schwarz et al., 2004). Green Ridge Fire: On August 20, 2020, the Green Ridge Fire burned through Us-Me2. The fire was ignited by lightning on August 16th, and grew rapidly to the east over the first few days driven by strong, downslope (westerly) afternoon winds. Fire behavior and observed fire effects were highly heterogeneous due to the localized wind pattern carrying the flaming head of the fire forward, and the efforts being made by suppression resources to contain the fire. The site experienced the full range of fire effects, from <1 m high surface fire that charred litter and duff and only consumed shrubs and herbaceous material to full tree (>15 m) crown fire that consumed 100% of needles, small limbs, and surface fuels at high intensity, leaving only ash and bare soil post-fire. Salvage Logging: From late March to late April 2021, salvage logging by the landowner occurred at the site. Almost all trees within the flux footprint were logged except a small area with lower burn severity, where sap flow and automatic soil respiration measurements are continued since the fire.

The research and science objectives of the Metolius Intermediate Pine site are as follows: 1) To quantify how successional stages and management practices in forest ecosystems influence processes controlling net ecosystem exchange of CO2 in varying climatic conditions; 2) Investigate the effects of disturbance processes controlling carbon storage and CO2 and energy exchange with the atmosphere in varying climatic conditions; 3) Measure the effects of disturbance and climate on the CO2 and energy exchange of ponderosa pine forests in the Pacific Northwest; 4) Evaluate the different statistical models for estimating soil surface CO2 efflux from measurements of abiotic factors such as soil temperature and moisture, and nitrogen and carbon in the soil and litter layers; 5) Compare differences in the seasonal patterns of carbon and energy exchange between stands of different ages; 6) Examine the implications of interannual variation of GPP and ecosystem respiration on net ecosystem exchange of CO2 (NEE); 7) Identify patterns in a multiyear record of soil CO2 efflux and ecosystem processes at an AmeriFlux site to generate a parsimonious seasonal model for soil CO2 efflux that has traits of value to the wider research community; 8) Assess the relationship between substrate supply from the canopy and root/rhizosphere respiration. (Anthoni et al. 2002, Schwarz et al. 2004, Irvine et al. 2008)