Drought treatments
We cut trenches beneath the drip line of 24 trees (n=3 per block) on May
20-21, 2013 using methods modified from Devine & Harrington (2008).
Trenches were cut to 33 cm deep using a ditch witch and the interior
walls were lined with 0.15 mm thick polyethylene sheeting to restrict
root growth and water access. Each trench was then backfilled with soil.
We also removed snow within the same drip lines of trenched trees after
every major snowfall during the winter of 2013. As described in Kolbet al . (2019), the study measured tree predawn water potential
and the trenching treatment produced a level of water stress consistent
with moderate drought, similar to previous uses of this method with
ponderosa pine (McCullough & Wagner, 1987). We briefly summarized the
results from Kolb et al . (2019) under Result section below.