Peter Marshall

Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.


Research Classification

Research Interests

Plants and Forests
Forest measurements
Forest stand dynamics

Relevant Degree Programs


Graduate Student Supervision

Master's Student Supervision (2010 - 2020)
Validation of the Jack pine version of CroBas-PipeQual (2012)

The objective of this study was to validate the performance of the jack pine (Pinus banksiana L.) version of the growth simulator CroBas-PipeQual. A data-based approach and a simulation approach were applied. For the data-based validation, Ontario permanent sample plots (PSPs) were used as input to the CroBas-PipeQual simulator to obtain predicted values for growth of dbh, height, basal area per ha, changes in crown height and number of trees per ha. The corresponding growth (change) in these variables was compared with the measured growth (change) on the PSPs. For the simulation studies, I assessed the impact of different initial stand densities, different initial heights, and different values of the model parameters on the output variables and compared the simulated response to biological expectations. CroBas-PipeQual simulator generally underestimated growth/change of all variables at the stand and single tree level using both default and adjusted values of alpha-r. Running the simulator with the adjusted values of alpha-r did not show marked improvements in the simulator´s performance. The simulator generally produced logical results based on the simulations conducted. In denser stands, trees had a smaller average dbh at a given age, and basal area growth and change in number of trees were higher. Initial density had almost no influence on height and crown height growth. The number of stems per ha remained essentially the same on sites with different productivities, indicating that there may be problems with estimating mortality in the simulator. Varying the initial heights had almost no impact on the number of stems per ha, dbh growth and basal area growth. Overall, the simulator performed reasonably. However, it requires further testing. More testing with suitable data will allow assessing the simulator´s applicability to other site types and geographical locations. Another area that needs attention is modelling mortality. Recalibrating some of the equation parameters internal to the jack pine version of CrosBas-PipeQual is recommended, followed by further testing. Finally, the accuracy of predictions of variables not evaluated in this study (e.g., branch sizes, numbers, and locations) should be assessed before these components of the simulator are used operationally.

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Regeneration in thinned and unthinned uneven-aged interior Douglas-fir stands (2011)

The specific objectives of this study were to: (i) assess the impact of overstory conditions and disturbance history of interior Douglas-fir dominated stands on the quantity and quality of regeneration present; and (ii) document the impact of mountain pine beetle (Dendroctonus ponderosae Hopkins) on the regeneration in these types of stands. Overstory tree data from permanent sample plots and regeneration data from newly installed permanent subplots on each of the overstory plots were collected and compiled by plot, block, and treatment on a pre-commercial thinning experiment installation. This installation is located in drybelt Douglas-fir stands on the Knife Creek Block of the UBC Alex Fraser Research Forest in the vicinity of Williams Lake, BC. Several methods of assessing regeneration quantity (number of germinants and seedlings) and quality (three-year height growth) were used: mixed models, zero-inflated general linear models, and Classification and Regression Tree.Regeneration quantity and quality differed across the study site. Block B had relatively few seedlings and all were Douglas-fir; the other two blocks (C and D) had more regeneration comprised of several species. The control plots on all blocks had low amounts of Douglas-fir regeneration. Seedlings in the control plots had the lowest predicted three-year height growth, while the best height growth was found in the 5 m clumped spacing. Plot (larger scale) variables were less important than other variable types for determining the number of seedlings in a subplot. Having less than 35% ground coverage of crown litter (dead needles, small twigs, etc.) on a subplot was the best indicator of the presence of germinants. The best variables to predict the presence of seedlings were grass and herb ground coverage of more than 15% and less than 25% ground coverage by crown litter. The number of germinants did not vary significantly among treatments, although fewer were found on the control plots.Plots were compared to determine the effect of lodgepole pine mortality on the quantities of seedlings or germinants present. There was only weak evidence that seedling quality (as reflected by three-year height growth) was better on plots that had higher levels of recent mortality.

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Membership Status

Member of G+PS
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