Helicopter Liming to Help Restore Acidified Forest Soil Productivity

Decades of acid deposition across northeastern North America has caused excess leaching of soil base cations (Ca²⁺, Mg²⁺, K⁺) and increases in bioavailable aluminum (Al³⁺) that, in combination, have resulted in widespread decreases in potential forest productivity. Despite major reductions in SO₂ and NO_x emissions since the 1990s, forest soils across the region have shown few signs of recovery from acid deposition impacts and it could take decades or centuries for natural recovery to occur. As a result, affected forests are stressed, less productive, and more prone to climate change-induced damage. Helicopter liming of upland forests may be an effective way to jump-start the soil recovery process. Here we report on early results (one-year) from a helicopter liming trial in Nova Scotia, Canada where 10 tonnes/ha of dolomitic limestone was applied to approximately 8 ha of mature red spruce (Picea rubens) and mature tolerant hardwood (Acer spp. and Betula spp.) forest. Data are presented on (i) the effectiveness of helicopter liming in forests; (ii) the initial chemical response of forest floor organic and mineral soil horizons; and (iii) the initial chemical response of red spruce foliage, maple foliage, and ground vegetation. Preliminary results showed that despite non-uniform lime distribution, there were significant increases (P < 0.05) in Ca²⁺, Mg²⁺, pH, and base saturation (BS), and significant decreases in total acidity in forest floor organic horizons in both the mature red spruce and tolerant hardwood stands; however, there were no significant changes in Al³⁺. The initial chemical response in sugar maple and red spruce foliage showed significant increases in the Ca/Al molar ratio .  The initial response in ground vegetation (Schreber’s moss; Pleurozium schreberi and wood fern; Dryopteris intermedia) showed significant increases in Ca²⁺ and decreases in K⁺ for both species; however, Schreber’s moss also showed significant increases in Mg²⁺ and Al³⁺ while wood fern did not. These early chemical results are promising and further support the use of helicopter liming as an effective tool to combat lingering effects from acid deposition in acidified forests.