Intertidal resource use over millennia enhances forest productivity, Trant 2016

Abstract: Human occupation is usually associated with degraded landscapes but 13,000 years of repeated occupation by British Columbia’s coastal First Nations has had the opposite effect, enhancing temperate rainforest productivity. This is particularly the case over the last 6,000 years when intensified intertidal shellfish usage resulted in the accumulation of substantial shell middens. We show that soils at habitation sites are higher in calcium and phosphorous. Both of these are limiting factors in coastal temperate rainforests. Western red cedar (Thuja plicata) trees growing on the middens were found to be taller, have higher wood calcium, greater radial growth and exhibit less top die-back. Coastal British Columbia is the first known example of long-term intertidal resource use enhancing forest productivity and we expect this pattern to occur at archaeological sites along coastlines globally [Trant 2016: 1].

Although focused on forests and not farmland, this study shows that, as in the Amazon, where indigenous people created SOM-rich terra preta soil (akin to biochar-enhanced soil), human populations can increase soil quality and ecosystem productivity beyond what the potential would have been absent human activity.

This is an interesting point with respect to global potential for soil carbon sequestration. Scientists often refer to an equilibrium point, up to which soils can regain carbon previously lost through exploitive human activity. Equilibrium is generally seen as being the point at which new SOC levels are equivalent to or somewhat less than what they were prior to human exploitation of the soil, and never greater than the original amount. While Trant et al. [2016] have found evidence of calcium and phosphorus (not carbon) enrichment due to human activity, their findings raise questions about the extent to which intentionally building soils through all the methods we know to maximize carbon storage could increase various soils’ presumed equilibrium points.