PS 21-44
A quantitative approach for collocating NEON’s sensor-based ecological measurements and in-situ field sampling and observations
The National Ecological Observatory Network (NEON) is a continental-scale research platform currently in development to assess the causes of ecological change across a projected 30-year timeframe. A suite of standardized sensor-based measurements (Terrestrial Instrument System (TIS) measurements) and in-situ field sampling and observations (Terrestrial Observation System (TOS) activities) will be conducted across 20 ecoclimatic domains (60 terrestrial sites) in the U.S.
NEON’s TIS measurements and TOS activities are designed to observe the temporal and spatial dynamics of key drivers and ecological processes and responses to change within each of the 60 terrestrial research sites. To establish valid relationships between these drivers and site-specific responses, two contradicting requirements must be fulfilled: (i) both types of observations shall be representative of the same ecosystem, and (ii) they shall not significantly influence one another.
We outline the theoretical background and algorithmic process for determining areas of mutual representativeness and exclusion around TIS measurements and develop a procedure which quantitatively optimizes this trade-off through: (i) quantifying the source area distributions of TIS measurements, (ii) determining the ratio of user-defined impact threshold to effective impact area for different TOS activities, and (iii) determining the range of feasible distances between TIS locations and TOS activities.
Results/Conclusions
For a given TOS activity, the upwind distance from the TIS location required to stay below the same impact threshold differs among sites. These differences arise from site-specific environmental properties and corresponding differences in the TIS setups. As an example, we present results for three NEON sites (Disney, Harvard, Sterling). For below- and above-ground biomass sampling, as well as insect traps the minimum distances vary among sites in the range of 30 m–70 m, 35 m–105 m, and 180 m–245 m, respectively. Analogously, the maximum distance for mutual representativeness (90% cumulative flux footprint) varies between 290 m–610 m.
This approach provides an evidence-based and repeatable method for combining sensor-based measurements and field sampling and observations at predefined levels of disturbance and spatial representativeness. This approach provides an evidence-based and repeatable method for combining sensor-based measurements and field sampling and observations at predefined levels of disturbance and spatial representativeness. Such a framework is an essential prerequisite to warrant establishing reliable relationships between ecosystem drivers and responses that are captured by different observation methods. Ultimately, the ability to improve our understanding of continental-scale ecology depends on the comparability of these relationships among research sites.