This repository includes 12 Hz three-axis acceleration data from an accelerometer mounted to the bole of an Abies lasiocarpa (subalpine fir) next to the C-1 Ameriflux tower at Niwot Ridge LTER, Colorado, USA. The data were recorded from November 2014 through August 2020. More information on the installation can be found in Raleigh et al. (in review, Water Resources Research). The data are stored in netCDF files, chunked based on the collection date when the data were downloaded from the accelerometer. File metadata: Filename GCDC_L01_Raw_Data_Niwot_TreeXX_collection_YYYYMMDD.nc where XX = tree number (01 = spruce, 02 = fir) YYYYMMDD = year (YYYY), month (MM), and day (DD) of data collection Each netCDF includes four variables: 1. serial_date = time increment (fractional days), as defined by Matlab: "A serial date number represents the whole and fractional number of days from a fixed, preset date (January 0, 0000) in the proleptic ISO calendar." The serial dates are in mountain standard time (MST) with no adjustments for daylight savings. 2. Ax = acceleration in the vertical direction (counts) 3. Ay = acceleration in the east-west direction (counts) 4. Az = acceleration in the north-south direction (counts) To convert the "counts" unit to gravitational units (g), divide Ax, Ay, and Az each by 2048, as explained in the manufacturer's user manual.