Introduction
Over the past several decades, calcium (Ca) concentrations have been declining in Muskoka lakes and forests. In 2014, The Muskoka Watershed Council’s Report Card highlighted Ca decline as a new environmental stressor affecting lake health in the area. The damage caused by declining Ca concentration is all around us. In forests, loss of Ca has resulted in slowed growth, seed production, seedling regeneration and dieback of sugar maple that can impact maple syrup production. In lakes, crayfish that have high Ca-demands are disappearing. Last, in offshore waters, a jelly-clad water flea, Holopedium, is replacing its more Ca-rich competitors, and creating the potential to clog water filters for residents drawing their water from lakes.

One possible solution to combatting Ca decline is active local engagement, if Muskokans become “gardeners of the forest”. As gardeners, we can use wood ash – the residue remaining after the combustion of wood – to return Ca to forest soils where it originated. Wood ash contains many elements – both major and minor – that are required for tree growth (e.g., calcium, potassium, nitrogen, phosphorus). Of the elements present, Ca is the most abundant with calcium compounds forming between 15% and 50% of total ash weight, followed by potassium (K), magnesium (Mg), aluminium (Al), iron (Fe) and phosphorus (P). Due to its high Ca content – mainly as calcium carbonate (CaCO3) – wood ash is relatively alkaline and can be used as a garden fertilizer. In addition, wood ash can be used for pest control, to make soap, to melt ice and snow, absorb odours, remove oil stains on driveway or garage, and polish silver.

The use of wood ash as a forest or soil amendment is not unusual. In north-east United States of America, 80% of wood ash produced is used in land application. In Europe (e.g., Sweden, Finland, and United Kingdom), wood ash is often added to forest soils to enhance biomass production. In Canada, wood ash is mainly used for liming and/or fertilizing in Alberta, British Columbia, New Brunswick, Nova Scotia, and Quebec. In Ontario, wood ash is not regularly used as a soil amendment on agricultural or forest soils, and there are currently no guidelines for such uses.