## Poor Site Calibration Adjustments

The default Acadian calibration is not currently well suited for marginal forest land with severe-extreme growth restrictions (tree bogs, barrens, high elevation, coastal exposed). Neither BGI (biomass growth index) nor provincial/state ecological site classification systems are currently mapped at high enough spatial accuracy to consistently differentiate between marginally productive forest and productive forest sites with high confidence. This noise in spatial information (exact plot locations, biophysical mapping accuracy) made it difficult to develop a separate calibration for these areas. During validation, it was observed that forest ecologically mapped as having very poor productivity consistently grew very poorly if the following conditions also existed: 1) stand was unmanaged (no recent silviculture), 2) stand volume was low (< 125 m3/ha), and 3) stand contained a significant proportion of lowland softwood species associated with poor sites (e.g., black spruce). For most of these poor sites, predicted rates of growth, ingrowth, and survival had to be reduced substantially to match field observations. Site stocking capacity (self-thinning A-line intercept) on these poor sites was also observed to be less than productive forests. In cases where the site was ecologically classed as poor (e.g., organic soils) and there was strong indication from the field survey that the site was not poor (high volume, upland species, silviculture treatments) no changes to calibration were made.

### What landscape conditions should be considered as Poor Sites?

Organic soils, very poorly drained, rocky/barren, and/or high-elevation taiga/alpine.

Other poor site indicators in Nova Scotia include:

· Softwood land capability class of <= 2 from the NS forest inventory should also be considered poor sites.

· Atlantic Coastal, Western Barrens, Taiga, Cape Breton Highland eco-regions/districts.

### How do I turn Poor Site calibration adjustments on?

A ‘PoorSite’ Boolean column should be added to your OSM_StandList table and values should be set to TRUE for plots on poor sites. For sites that have some evidence of trees, but growth and stocking is extremely constrained, consider assuming no appreciable growth or regeneration will occur over the foreseeable future at these locations.

### What happens in OSM when I turn Poor Site on?

If PoorSite = TRUE, OSM will not modify the default calibration unless the following criteria are met at the beginning of the simulation:

· Management = ‘None’

· Gross merchantable volume (GMV) < 125 m3/ha

· Black Spruce basal area > 25%

· Lowland softwood species (white pine, cedar, tamarack, fir, red spruce) basal area > 50%

If conditions above are entirely met, then the calibration will be modified as follows:

If GMV < 50 m3/ha

· Diameter and height increment reduced by 50%

· Tree annual mortality will be doubled

· Ingrowth will be reduced by 95%

· Maximum stocking reduced by 15% if present stocking less than this threshold

Else

· Diameter and height increment reduced by 25%

· Tree annual mortality will be multiplied by 1.5

· Ingrowth will be reduced by 85%

· Maximum stocking reduced by 30% if present stocking less than this threshold

These poor site adjustments are made during the self-thinning stage of the simulation, after model predictions and after any user prediction amendments.

These adjustments were derived from crude trial and error comparisons of predicted to observed stand dynamics. They serve as a temporary calibration solution for areas with severe growth restrictions. As mapping of eco-sites and productivity improves over the next few years, it is likely a more robust and statistically defensible calibration will be developed that will perform well across all forested sites.

Be aware that even when ‘PoorSite’ is set to TRUE, predicted growth and survival rates on barren, poorly drained organic soils, exposed coastal, and/or high elevation alpine sites were usually over predicted by OSM. Over prediction of growth, survival, and stocking was most notable in Nova Scotia for Atlantic Coastal, Western Barrens, Taiga, and Highland eco-regions/districts. For many of these sites, stocking, regeneration, and growth have been severely limited over the past 50 years. Areas previously mature balsam fir in the NS Cape Breton highlands in the 1960-1970s showed consistent stand-breakup in the 1970s (likely caused by spruce budworm) and many of these sites have failed to recover; possibly due to severe herbaceous competition, moose browse, and harsh climate. These regeneration constrained sites are not necessarily considered poor and can sometimes be upland sites dominated by balsam fir. OSM will currently over predict stand re-establishment and development in for these conditions.