Abstract

Authors

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Dataset Citation

Verity Salmon, Colleen Iversen, Peter Thornton, Stan Wullschleger. 2022. NGEE Arctic Plant Traits: Shrub Transects, Kougarok Road Mile Marker 64, Seward Peninsula, Alaska, 2016-2017. Next Generation Ecosystem Experiments Arctic Data Collection, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, USA. Dataset accessed on [INSERT_DATE] at https://doi.org/10.5440/1346197.

Dates

2016-07-25 - 2017-07-28

Geographic Location

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Methodology

We surveyed shrubs using the point center quarter (PCQ) method at Kougarok in July 2016 and at Kougarok, Council, and Teller in July 2017. At each sample point on the transect, a GPS coordinates was recorded. In 2016 a handheld Garmin eTrek 10 handheld GPS was used and in 2017 a Garmin Montana 680t and the Avenza map app on an iphone were used to record coordinates. At each sample point, the nearest tall shrub was identified in each cardinal quadrant (NE, SE, SW, NW). The distance to each of these shrubs was recorded as was the species. Shrub height was defined as the vertical distance from the tallest portion of the shrub to the ground was measured using a meter stick or avalanche probes cm markers. Stem basal diameter was measured with an electronic caliper. For many individuals (genets) there are multiple stems emerging at ground level (ramets). We measured and recorded the diameter of each ramet on an individual as near to the ground surface as possible. Total basal area for each genet was calculated by summing the basal areas for each ramet after basal diameters for each ramet have been converted to basal area. Sampling points were placed 20m apart but on transect “C_TALLSHRUB” at Kougarok the sampling points were 50m apart. For each transect there were target shrub species of measured and this determined the survey type listed. “Mixed Tall Shrub” surveys targeted shrub species known to grow to grow over 1.5m high under ideal conditions. At our sites this included Alnus viridis (ALNFRU), Betula glandulosa (BETGLA), Salix alaxensis (SALALA), Salix glauca (SALGLA), Salix lanata (SALLAN), Salix pulchra (SALPUL), and Salix richarsonii (SALRIC), and an unknown Salix (unknown 1). Note that though these species are known to grow over 1.5m high, not all the individual shrubs surveyed were over 1.5m high. The shrubs were chosen based on their species having the potential to grow into a tall shrub, not based on them being tall. “Alder” surveys targeted only the species Alnus fruticosa (ALNFRU). Betula nana surveys only targeted Betula nana (BETNAN) which is a dwarf shrub does not usually grow over 1m. We calculated a moving average for density (shrubs per m2) as well as shrub basal area (cm2 stem per m2 ground). To do this, the mean distance to nearest shrub was calculated for each sample point (based on the four quarters observed at each sample point). According to Cottam & Curtis, (1956) the mean density along a PCQ transect equals 1/((mean distance)^2). Each transect was sorted by distance from the beginning of the transect and a moving average density was calculated for segments of the greater transect that each span three sample points. Basal area (cm2 stem per m2 ground) was calculated by multiplying the moving average density (shrub per m2) by the average basal area per shrub (cm2 per shrub) at a given sample point. It should be noted that currently our density calculations along the transects assume that every observation for which no shrub was present in a quarter was the result of a shrub being present at the 20m limit of range. This assumption seemed sound for Kougarok, the area sampled in the 2016 surveys. The 20m distance was assigned is to avoid removing the "not present" observations for sample points that had quadrats with and without shrubs. Removing absent shrubs from these mixed sample points would result in an overestimate of shrub density. In 2016, when a no shrubs were present in any of the four quarters of a sample point, zero was used for the average shrub height, basal total, and basal area. Warde & Petranka (1981) provides more information on correction factors for missing observations that could be calculated in lieu of this assumption. In 2017, we were aware of the dangers of absent shrubs in the dataset and measured the distance to the nearest shrub no matter how far we had to search (occasionally >100m). Relevant allometries for Salix, Betula, and Alnus shrubs in arctic and boreal systems can also be found in Berner et al. (2015).

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