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This leaf trait database contains measurements made across multiple years and sampling campaigns. Generally, the methods were kept the same, but some differences are noted here. All sampling campaigns occurred during the growing season (July – early September), with the exception of sampling campaign TF_2018 and TF_2023, where samples were collected monthly throughout the growing season (May to December or June to August, respectively) to track leaf trait developments from leaf-out through senescence (broadleaf) or dormancy (needleleaf). Foliage samples were collected either by shotgun sampling, pole pruning, or pruning from a mobile canopy lift. The height of each sample was measured using a TruPulse 360R laser range finder. During campaigns TF_2022 and CAP_2022, the height of the tree was also recorded. The diameter at breast height (DBH) of sampled trees was measured for most trees.

Immediately upon collection, samples were placed in plastic bags with a moist paper towel and stored in a cooler to prevent desiccation prior to sample processing. Samples were always processed within 48 hours of collection. The number of leaves sampled from each tree differed across campaigns; for broadleaf species, 10-50 leaves were measured, and for needleleaf species, 20-200 needles were measured (See Number_Leaves_Sampled column for specifics). During TF_2018, needles were separated by current and previous year growth for trait measurements; all other campaigns combined needleleaf growth years.

Broadleaf petioles were removed and measured for length. In later campaigns (all campaigns following TF_2020), petioles were also weighed for total wet mass. Both broadleaf and needleleaf leaves were weighed for a total wet mass and scanned for area measurements using either a flatbed scanner (all campaigns) or a portal leaf area scanner (LI-3000C) (BEF_2017, TF_2018, TF_2020). Leaves scanned using the flatbed scanner were post processed for leaf shape traits (area, length, width) using ImageJ (https://imagej.net/).

Once scanned, the samples were oven dried at 60 °C for a minimum of 48 hours. The leaves and petioles were then reweighed for a total dry mass. Leaf mass per area (LMA) was calculated for each sample based on the bulk dry mass and leaf area. Both leaf and petiole water content were calculated as the difference between the bulk wet mass and bulk dry mass divided by the bulk wet mass. Petioles were then discarded, and the leaves were ground into a homogenized powder using a Wiley Mill for chemical and isotopic analysis (%N, %C, C:N, δ15N, δ13C) via flash combustion on an Elementar Pyrocube elemental analyzer coupled to a Geovision isotope mass spectrometer.

For campaign TF_2018, a subsample of leaf tissues was collected for chlorophyll analysis. For broadleaf species, three 28 mm-2 discs were punched from the leaf while three intact needles were selected for the needle-leaf samples. The chlorophyll samples were placed in 2 mL microcentrifuge tubes and frozen in the field on dry ice before being transported to the lab where they were stored at -20 °C in the dark until processing. Chlorophyll was extracted from the leaves using 1.5 mL of 95% ethanol for four hours at 65 °C. After the incubation period, tubes were vortexed for 30 seconds and centrifuged for 3 minutes. Chlorophyll A and chlorophyll B concentrations were determined colorimetrically based on absorbance at 652 and 665 nm using a Versamax microplate spectrophotometer. Concentrations were corrected to a 1 cm pathlength according to Ritchie et al (2006) and then were scaled to leaf area and dry mass based on a sample leaf mass per area basis.