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Clarksburg Demonstration Site

Location: Clarksburg, California
Acres: 50
Planted: 2013
Initial Harvest: 2014
Second Harvest: Planned winter 2018
Land Restoration: Planned spring 2018

In spring 2013, a 50-acre tree farm was planted near Clarksburg, CA. The site is located near the Sacramento River and has abundant groundwater available for good poplar growth. The Clarksburg demonstration site receives approximately 21 inches of precipitation per year. The Clarksburg site was established with a planting density of 1,452 stems per acre with rows aligned on 10-foot centers and three feet intervals within each row.

The harvester cutting down poplar trees at the Clarksburg demonstration site and depositing the chips into the truck following it.
The poplars at the Clarksburg demonstration site were first harvested in November 2014.

The Clarksburg site is leased by GreenWood Resources from the Kirtland family for the purposes of the AHB project. The Kirtland’s have farmed in the Sacramento River Delta since 1849 and have identified the field where the poplar is being grown as marginal land. At this site, the clay soil is more saline and the pH is higher than what is considered high production farmland in the Delta. This location is providing important information on the minimal requirements necessary for a productive poplar crop.

The commercial production trials at the Clarksburg site features 13 different hybrid poplar varieties covering the majority of the field, with the remaining land used for research plantings. The commercial trials aim to demonstrate biomass yields, management practices, the cost of production, and harvesting logistics. The research trials include a biomass productivity trial, an alder intercropping trial, and a poplar bioenergy clonal screening trial. You can learn more about the research here.

California Drought

The current drought in California has created unique challenges in managing the Clarksburg site. In 2013, during the site’s first growing season, drought conditions and a mid-July heat wave affected the performance of some poplar varieties. In the site’s second growing season, in summer of 2014, the decision was made to irrigate the trees when soil moisture probes indicated the need for supplemental water.

The trees in Clarksburg responded extremely well to irrigation, with excellent color, vigor, and growth. Over a two-month period in June and July 2014, select monitored varieties grew an average of nearly 1.7 inches per day in height.


The initial harvest of the Clarksburg demonstration site occurred in November 2014 at the conclusion of the second growing season. In total, 254 wet tons of biomass was collected during this harvest. Top performing poplar varieties reached heights of more than 17 feet. The goal of the initial establishment period is for the trees to form a robust root system that will accelerate post coppice growth and biomass production. Future harvests are anticipated to yield more biomass from coppice growth. The Clarksburg site will be harvested again in winter 2018, two growing seasons after the initial coppice harvest.

Coppice growth is vigorous at the Clarksburg demonstration site. By the end of first growing season post-coppice, the poplars averaged over 18 feet in height, which is approximately the same tree height as at the first harvest.

Close up of the base of one of the poplars at Clarksburg that shows the coppice growth.
When poplars are grown for bioenergy they are cut near the ground when they are harvested. This encourages multiple stems of new growth to emerge from the cut stump for subsequent production cycles.