Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092211

    Growth and release of understory trees in partially-cut pine stands
Project lead: Astrup, Rasmus (Bulkley Valley Centre for Natural Resources Research and Management)
Contributing Authors: Lefrancois, Marie-Lou; Hall, Erin C.; Coates, K. David
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Clearcutting followed by planting has been the dominant stand-scale management practice in the sub-boreal forests of British Columbia. In the past 15 years, retention of 5-15% of canopy trees has become common, but growth projections are still based on open-grown planted seedlings. Simultaneously, the mountain pine beetle (MPB) epidemic has created vast areas of complex multi-storied stands and extensive areas of MPB damaged forest will remain unsalvaged. Future timber-supply in these stands will depend on some combination of future natural regeneration, under planting, and the release of surviving understory and sub-canopy trees. We have very limited data on the performance of underplanted trees under different levels of canopy retention because of the past dominance of clearcutting. We also lack direct data on the release potential of understory trees after mountain pine beetle attacks. To develop appropriate silvicultural systems for unsalvaged MPB stands and complex stands in general, we require a good understanding of the growth and release capabilities of understory trees.

Interest and experimentation with complex stand management in sub-boreal forests was common after WW2 until the advent of widespread clearcutting in the mid- to late- 1960s. We propose to use an old experiment [Experimental Plot 591 (EP 591)], established by Dave Armit in 1962-1963, to investigate current issues in complex stand management. EP 591 was established to study natural, seeded and planted spruce performance in partially-cut lodgepole pine stands with overstory pine densities varying from approximately 400 to 1500 stems/ha. The experiment was established with 10 different treatments consisting of: (1) fall and spring planting of spruce, (2) spruce seeding on scarified and unscarified sites, and (3) no seeding on scarified and unscarified sites on a total of 15 study sites. Today, 10 of the original 15 sites still exist, but within the past two years most of the overstory lodgepole pine have been attacked and killed by MPB.

Today, EP 591 represents a unique research opportunity for answering pressing questions. The BC Forest Service measured the experiment in 1963, 1965, 1967, 1993, and 2003 providing a legacy of data on survival and growth of understory spruce under varying levels of overstory pine densities. The data have not been complied, analyzed, or published. We see four major research opportunities to address current complex stand management questions: (1) Compilation and analyze of the existing data to characterize how planted and seeded understory spruce develop in partially-cut stands, (2) use the existing understory spruce trees (with a known history) to study future survival and release under variable levels of MPB killed overstory, (3) opportunistically select other understory tree species present in the experiment for monitoring of future survival and release, and (4) monitor ingress of natural regeneration after the MPB attack.

The main objectives of this proposal are to: (1) compile and analyze the existing data from EP 591 to characterize the effect of overstory structures on development of planted, seeded, and naturally regenerated spruce and (2) re-measure EP 591 to access how understory trees (spruce, subalpine fir and aspen) release after MPB attack of vaying overstory densities.

We propose an analysis of the existing data and a refocusing of the experiment to examine understory responses to overstory mortality. In the first year of this project, we propose to: (1) compile the existing five experimental re-measurements into a single database, (2) analyze the initial 40 years (1962 - 2003) of experimental data, (3) re-measure the experiment, and (4) establish a set of new permanent experimental sub-plots to monitor ingress of natural regeneration and release of non-spruce species (subalpine fir and trembling aspen). In the second year, we will prepare a journal paper based on the analysis of the 40 years of experimental data. In the third and final year, we propose to re-measure the original plots, re-measure the sub-plots established in the initial year, and analyze the data with regard to understory release. With the measurements from 2003 and the proposed measurements in 2007 and 2009, we will have growth rates from just prior to the MPB attack until 6 years after the attack. This period should be sufficient to observe and quantify the release potential of the understory trees.

The 40-year results, from before to the MPB attack, can be used as guidelines for development and growth of underplanted and naturally regenerated spruce in partially cut stands. We believe that results from a 40-year experiment are unique in the SBS and would be very valuable given the current interest in silvicultural regimes such as variable retention, partial cutting, and underplanting.

The investigation of understory release and ingress of natural regeneration after MPB attack is crucial for predicting the future growth trajectories of MPB stands. Consequently, this study can aid in making strategic decisions related to silvicultural and timber-supply issues in MPB damaged stands and landscapes.
Related projects:  FSP_Y081211FSP_Y103211

Executive summary (61Kb)

Updated August 16, 2010 

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