Critical Period Threshold (CPT)

The idea of the “Critical Period” is a key component of integrated weed management. The critical period refers to the portion of a crop’s lifecycle where weeds need to be controlled to avoid yield losses. This concept has been expanded to forest vegetation management with the objective of determining the timing and number of years of vegetation control necessary to optimize stand productivity.

The Critical Period Threshold studies utilizes a complete randomized block design containing eight different VM regimes. The VM regimes are shared across all the CPT study sites and represent different combinations and timings of post-planting herbicide spring release applications during the first five years of stand establishment. Each VM regime is coded by five letters with each of the letters representing one of the first five years after planting. Specifically, the treatments include OOOOO, TOOOO, TTOOO, TTTOO, TTTTO, TTTTT, OOTTT, and OTTTT with an “O” signifying no vegetation control during that growing season while a “T” indicates a treatment year

Combining Weed Control (CW)

Understanding the interactions and synergies between management practices and stock type can have important management implications. The Vegetation Management Research Cooperative (VMRC) installed the Combining Weed Control Study Part I (CW101) in 2009 to evaluate interactions between VM regime and Douglas-fir containerized stock size on seedling growth and survival. The study series was later expanded with the installation of Combining Weed Control Part II (CW201) in 2011 to apply the same concept to bareroot seedlings of varying sizes. Additionally, the VMRC installed two Stock Type study sites to test the effects of containerized Douglas-fir stock size on stand survival and productivity under conditions of operational vegetation control.

Delayed Planting (DP)

The delayed planting study series was established in 2008 to investigate different management options for units harvested during the late spring and summer. Some of the treatments were established during the first year and others delayed for a growing season. The objective of this design was to test whether it is better to treat a recently harvest stand immediately or wait one year to allow the vegetation community to develop before treatment. A secondary objective was to test if including Oust in the fall site preparation treatment had a long-term impact on vegetation cover and/or tree growth.

Reforestation After Fire (RAF)

The objective of this study if to determine the effect of wildfire (Archie Creek Fire, September 9, 2020) on :

• Post-fire vegetation community dynamics, when paired with vegetation management and delayed planted regimes.
• Douglas-fir seedling growth and survival, when paired with vegetation management and delayed planted regimes.
• Soil moisture availability.
• Soil physical and chemical attributes.
• Microclimate conditions.

Alternatives to Herbicides (DNR)

This project is funded by WA-DNR. The main goal of the project is to evaluate the efficacy, costs, and operational feasibility of different herbicide and non-herbicide vegetation management strategies for successful reforestation. The specific objectives are: 1) Compare the effectiveness of alternative treatments of vegetation management on controlling competing vegetation, 2) determine the impact of different vegetation management treatments on the diversity and abundance of competing vegetation, 3) determine the effect of removing glyphosate from the herbicide tank mix, 4) determine the impact of different vegetation management treatments on Douglas-fir seedling height growth, diameter growth, survival, and biomass, 5) determine the impact of different vegetation management treatments on soil moisture availability, and 6) conduct an economic analysis on the costs and benefits of each vegetation management strategy.  

CoSInE (Competition and Site Interactions Experiment)

The main objective is to develop a decision support system with focus on how site conditions and chemical vegetation management treatments interact to effect seedling survival and growth in PNW. The study utilize a 2 x 2 x 2 factorial design, where factor 1 corresponds to fall site preparation, factor 2 corresponds to spring release during growing season 1, and factor 3 corresponds to spring release during growing season 2.

The project aims to better understand the effects of vegetation management treatments on the soil and plant water relations of conifer plantations in the Pacific Northwest by analyzing conifer seedling and competing vegetation interactions during the first two years after planting. The study will include periodic assessments of biomass growth, water use and nutrient content of seedling and competing vegetation. Additional plant water potential and gas exchange will be carried out as well.

GEnESIS (Genetic, Environment and Early Silviculture Interactions Study)

The main objective is to  investigate the influence of GxE, GxS, and GxExS interactions on the performance of 50 genotypes from control pollinated families of Douglas-fir. The environmental treatments will consist of field sites covering a wide range of climatic and soil conditions while the silviculture treatments will consist of different forest vegetation management treatments. The relationship between seedling physiology and field performance of genotypes under different environmental and silvicultural scenarios will also be assessed. The specific objectives of this study are to: i) investigate GxE, GxS, and GxExS interactions for Douglas-fir genotypes, ii) examine interactions between vulnerability to cavitation, field drought stress, and seedling native hydraulic conductivity (degree of cavitation), and iii) evaluate if vulnerability to cavitation is a useful tool for evaluating genotype field performance under different environmental conditions.

Phase 1: Morphological and Physiological assessments of the 50 genotypes in order to select the genotypes to be tested in the field. 

Physiological assessments:

• Stomatal conductance sensitivity to VPD
• Xylem hydraulic conductivity and vulnerability to cavitation 
• Frost hardening 
• Heat tolerance 

Phase 2: Field installations of different genotypes growing under different levels of establishment silviculture in 3-4 sites.

List of Active Study Sites

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