Site Description

The Niwot Ridge Ameriflux study site is located in a subalpine forest ecosystem just below the Continental Divide near Nederland, Colorado (40 degrees 1'58'' N; 105 degrees 32'47'' W). The site is located at 3050 m elevation above sea level, within 600 m of the NOAA C1 long-term monitoring station, approximately 8 km east of the Continental Divide and 50 km northwest of downtown Denver. The surrounding subalpine forest was established from natural regrowth after extensive logging from 1900-1910. The forest surrounding the tower is composed of subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii) and lodgepole pine (Pinus contorta). The understory is relatively sparse, containing tree seedlings from all three species and patches of Vaccinium myrtillus (25% average coverage). The forest slopes gently (6-7%) and uniformly, decreasing from west to east. Subalpine forest extends to 2 km west of the tower, where it forms a Krumholz, treeline ecotone that ultimately blends into alpine tundra. Winds at the site tend to originate from the west (downslope winds that carry air that has passed over remote areas of Utah, Idaho and Nevada). Annual precipitation for the site averages 800 mm and the mean annual temperature is 1.5 C. Major features of the site are as follows:

maximum leaf area index averages 4.2 m2 (projected needle area)/m2 (ground area)

woody fraction averages 0.3 m2 (projected wood area)/m2 (ground area)

canopy height averages 11.4 m

canopy gap fraction averages 17%

canopy displacement height averages 7.6 m

canopy roughness index averages 1.79 m

mean tree densities in the 1 km2 east of the tower are subalpine fir (10 trees/100m2), Engelmann spruce (7 trees/100 m2), lodgepole pine (27 trees/100m2).

mean tree densities in the 1 km2 west of the tower are subalpine fir (16 trees/100 m2), Engelmann spruce (10 trees/100 m2) and lodgepole pine (9 trees/100 m2).

bole biomass averages 16.0 kg m2

branch biomass averages 4.4 kg m2

needle biomass averages 4.0 kg m2

bole nitrogen averages 31.4 g N m2 (on a mass basis, 0.22% of dry bole mass)

branch nitrogen averages 28.9 g N m2 (on a mass basis, 0.66% of dry branch mass)

needle nitrogen averages 39.9 g N m2 (on a mass basis, 0.99% of dry needle mass)



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