LTSP Study: Effects of Organic Matter Removal on Nitrogen and Carbon Leaching Fluxes in Douglas-Fir PlantationMarcella Menegale1, Robert Harrison1, A.B. Adams1, Scott Holub2 and Nathan Meehan2

(1)School of Environmental and Forest Sciences, University of Washington, Seattle, WA (2)Weyerhaeuser Co., Springfield, OR

IntroductionSoil carbon and nitrogen are important tools to understand the variability in soil fertility and growth of trees, reflecting in cycling and uptake of nutrients for timber production along the years. The increasing interest in energy production from woody biomass may possibly affect the uptake of these nutrients in soil due to the removal of great quantities of branches and foliage during the timber harvesting when compared to the conventional harvest process, bole-only harvest – it can lead to a decrease in organic matter content in soil and, consequently, to a lack of nutrients for the upcoming years.

ObjectiveThe purpose of this study is to look at the fate of the influence of organic matter removal during timber harvest: how does the presence/absence of harvest debris (such as chips, branches) in the area influence the accumulation of nutrients in the soil and, consequently, the final productivity of Douglas-fir plantation.

Methods• Site location: Mackenzie River

watershed - Eugene, OR - Calapooya Tree Farm, owned by Weyerhaeuser Company.

• Initial stand composed by Douglas-fir. The latest harvest in the site occurred in April/May 2013.

• The total area has 20 plots, with 1 acre in each plot.

• Three types of harvest were conducted in the different plots: bole-only harvest, total-tree harvest and total-tree harvest plus forest floor removal. Also, soil compaction or not.

• Treatments compared:• A – Bole-only harvest, non-

compacted soil• B – Total-tree harvest, non-

compacted soil• C – Bole-only harvest,

compacted soil• D – Total-tree harvest,

compacted soil• E – Total-tree harvest plus forest

floor removal

• Lysimeters installation: 4 lysimeters per plot - 2 lysimeters at 20-cm depth and 2 lysimeters at 100-cm depth. Totally, there will be installed 80 lysimeters.

• Analysis: • Vegetation and Forest Floor : C

and N• Soil Samples:

• C and N• Macronutrients and

micronutrients• pH

• Soil Solution Samples: Alkalinity Dissolved Inorganic Carbon

(DIC) Dissolved Organic Carbon

(DOC) and Dissolved Organic Nitrogen (DON)

Macronutrients and micronutrients

Figure 5. Mackenzie River plot layout (2012).

Figure 1. Bole-only harvest treatment

Figure 3. Total-tree harvest plus forest floor removal treatment

Figure 2. Total-tree harvest treatment

Figure 4. 100-cm depth lysimeter