Reference to Nutrient Budgeting in the SGEM (Final ed., July, 2021)
Nutrient sustainability is fundamental to long-term site productivity. Forest harvesting can harm nutrient sustainability if biomass removal rates do not consider site-specific nutrient budgets. Over the last several years, the Nova Scotia Department of Lands and Forestry has been working to test and update a forest nutrient budget model (NBM-NS) that allows nutrient sustainability to be integrated into forest management planning (Keys et al., 2016). This ongoing work includes a provincial sampling program to acquire current soil and tree tissue chemistry data for model calibration. Enough progress has been made that NBM-NS can now be used to inform harvest planning by estimating sustainable mean annual increment (SusMAI) values for various combinations of FEC vegetation and soil types across Nova Scotia. In addition, these estimated SusMAI values consider historic and ongoing acid rain impacts on base cation nutrient (calcium, magnesium, potassium) contents. Having such detailed data enables greater attention to be given to the promotion of forest soil health.
To ensure that silvicultural prescriptions are in keeping with nutrient sustainability estimates, harvest mean annual increment (HarMAI) values (total merchantable harvest volume/age of harvest material) will be calculated and compared to SusMAI tables. If HarMAI is greater than SusMAI for a given vegetation type (VT) and soil type (ST) combination, the proposed prescription will be adjusted until HarMAI is less than or equal to SusMAI, in order to ensure nutrient sustainability.
Retention levels must be reviewed at each harvest entry to ensure that the proposed harvest is sustainable from a nutrient perspective using the Nutrient Budget Model. If they are not sustainable, harvest plans must be revised.
p. 166 (Glossary)
NSNBM: Nova Scotia’s Nutrient Budget Model
Sustainable Mean Annual Increment (SusMAI): The sustainable amount of merchantable volume a site can sustain per hectare each year based on soil site productivity constraints based on the Nova Scotia Nutrient Budget Model (NSNBM).
Comments on the penultimate Draft by David P
“…. The revised SGEM includes a procedure for assessing sustainability of nutrient supply as a factor in harvest planning. However the guide is vague in regard to what happens when the calculations show that a proposed harvest is not compatible with maintaining nutrient supply: “If HarMAI is greater than SusMAI for a given vegetation type (VT) and soil type (ST) combination, then harvest plan adjustments will be made.” What are the adjustments? These must be specified.
“But more serious in my view is that the objective, as I understand it, is to maintain the current nutrient status. There is no provision to allow the nutrient status to improve on soils which are severely calcium depleted because of acid rain combined with the inherently poor soils that dominate on much of our landscape; previous harvesting has also contributed.”