Meta-analysis increases the amount of information that can be extracted from field trials across a range of sites and broad conclusions can be drawn (e.g., Johnson and Curtis 2001). Meta-analysis can be used with categorical variables in ANOVAs to test for specific differences between treatments, and with continuous variables to examine gradients that would explain biomass harvesting treatment responses and help define response thresholds. Results can be used (within the limits of the data available) to test hypotheses and increase scientific knowledge, which provides a foundation for the development of guidelines and standards.

Building on previous meta-analysis within the LTSP network (Fleming et al., 2006), we are now embarking on a program to apply meta-analysis to intensive harvesting (i.e., biomass removal) trials across broader geographic areas, stand and site conditions. In particular, we are interested in examining the effects of harvest intensity on crop tree growth, soil and overall site productivity in relation to species identity and functional group, ecosystem type, climate, and both inherent soil properties (e.g., texture, moisture regime, surficial and bedrock geology) and those potentially affected by harvest removals (e.g., major nutrients, base cations, and acidity). The work is proceeding sequentially by creating (i) a database of potential field trials and associated metadata, (ii) a bibliography of literature that contains results for each field trial, (iii) a table cataloguing what published data is available for each trial, and finally (iv) a data set for use in the meta-analysis. The literature usually only reports site-level mean values, and un-published plot-level data is also being used to increase the power of the meta-analysis. Each of the first three steps lead to discrete outputs whose use extends beyond the meta-analysis; the final data set may also be useful for other analyses.

An invitation is being extended to the scientific community to ensure that their published data has not been overlooked, and potential collaborators willing to contribute plot-level data are currently being sought.

References

Fleming, R.L. et al. 2006. Effects of organic matter removal, soil compaction, and vegetation control on 5-year seedling performance: a regional comparison of Long-Term Soil Productivity sites. Canadian Journal of Forest Research 36: 529-550.

Johnson, D.W., and P.S. Curtis. 2001. Effects of forest management on soil C and N storage: meta analysis. Forest Ecology and Management 140: 227-238.