Introduction to the sampling designs of the <scp>N</scp>ational <scp>E</scp>cological <scp>O</scp>bservatory <scp>N</scp>etwork <scp>T</scp>errestrial <scp>O</scp>bservation <scp>S</scp>ystem

Abstract Global change drivers influence ecological processes at multiple scales and manifest across most of Earth as changes in biodiversity, biogeochemical cycles, infectious disease incidence, and ecohydrology. Small‐scale investigations provide compelling evidence of specific effects of global change on local systems, but are of limited use in modeling complex ecological processes at continental‐to‐global scales. Long‐term observations distributed across a diversity of habitat types are needed to improve the ability to forecast ecological change at large spatial and temporal scales. This special issue introduces the Terrestrial Observation System ( TOS ) of the National Ecological Observatory Network ( NEON ), a long‐term, continental‐scale ecological research platform designed to deliver these large‐scale datasets. The TOS measures biodiversity of key biota (soil microbes, insects, plants, small mammals), ecosystem productivity and biogeochemistry, infectious disease dynamics, phenology, and population dynamics. The articles in this special issue describe the scientific rationale for the sampling designs of the TOS , including an overview of protocols, locations, and frequencies of measurements. The science designs are a culmination of design requirements scoped by NEON and the National Science Foundation, best available practices put forth by the scientific community, input from technical working groups, and consideration of logistical and financial constraints by NEON staff. Within each site, measurements have been collocated to the extent possible to optimize linkages among different sampling elements. Integrated analyses of terrestrial observations with sensor‐based, imagery, and remote‐sensing data collected by other NEON subsystems can facilitate scaling of measured parameters to larger spatial and temporal scales. NEON is designed to collect data for 30 years, and make these data freely available on a public data portal ( data.neonscience.org ). Samples and specimens will be archived and available to the scientific community upon request. The open access approach to the Observatory will provide users with the resources necessary to map, understand, and predict the effects of global change drivers on ecological processes at a continental scale.