The site is located on land designated as a Research Natural Area (RNA). The site is very open, with even-aged stands of old-growth trees, young trees and mixed aged stands. The eddy-flux tower footprint was classified as ~ 48% mixed aged, ~27% pure old growth and ~25% young aged stands. The data in this workbook describes the mixed aged component. A separate workbook describes the pure old growth component. Law et al (2001) Global Change Biology 7, 755-777; Law et al (2001) Agricultural and Forest Meteorology 110, 27-43; Anthoni et al (2002) Agricultural and Forest Meteorology 111, 203-222; Irvine & Law (2002) Global Change biology 8,1183-1194, Irivne et al (2004) Tree Physiology 24,753-763.

The research and science objectives of the Metolius Old 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) Investigate how soil water deficit influences the process driving NEE in two seasonally water-limited ponderosa pine stands of contrasting ages; 5) 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; 6) Examine how CO2 exchange rates differ in response to environmental factors between young and old-growth ecosystems; 7) Compare differences in the seasonal patterns of carbon and energy exchange between stands of different ages; 8) Determine the factors limiting soil microbial activity in undisturbed old growth and regenerating ponderosa pine stands under the semi-arid climate of central Oregon. (Law et al. (1999a), Anthoni et al. (2002), Irvine et al. (2002), Kelliher et al. (2004)). In 2023 and 2024 The tower was rebuilt and flux measurements resumed. In addition to extending the data record for the above objectives, the site was restarted to provide a continuing record of mature ponderosa pine fluxes proximate to the footprint of US-Me2 before the 2020 Greenridge fire.