Intertidal resource use over millennia enhances forest productivity

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 redcedar (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.

Moving beyond the human–nature dichotomy through biocultural approaches: including ecological well-being in resilience indicators

“…By just focusing on the outcomes, one risks missing critical elements that contributed to those outcomes. For example, in the Pacific Northwest of North America, in what is now British Columbia, Canada, humans over thousands of years enriched the terrestrial ecosystems (Trant et al 2016). First Nations resource use, as evidenced by shell middens in nearshore habitation sites, elevated the soil nutrient composition (especially calcium and phosphorous, which are limiting in these forests otherwise), which led to better growing conditions for the forest as a whole.…”

“…Through intentional burying of shells from the intertidal zone and use of fire in and near habitation sites, First Nations altered soil chemistry and nutrient availability. In particular, Trant et al (2016) were able to show the effect of nutrient enrichment on the growth and productivity of the western redcedar (Thuja plicata), a culturally and economically important species. Outcomes-based indicators would focus on the growth and productivity of the cedar and perhaps fail to capture the long-term process of soil nutrient enrichment through the creation of the shell middensthe generations of care that led to their healthy state.…”

Indigenous peoples’ habitation history drives present‐day forest biodiversity in British Columbia's coastal temperate rainforest

“…Forests in this region have been shaped by an extensive anthropogenic fire history (Hoffman, Gavin, Lertzman, Smith, & Starzomski, ; Hoffman, Gavin, & Starzomski, ; Hoffman, Lertzman, & Starzomski, ) and despite the habitation sites being abandoned for over 125 years, the productivity of modern forests growing on habitation sites shows the enhanced productivity (Trant et al., ). Little is known, however, about how these long‐term human modifications have influenced understory vegetation.…”

Ecological legacies of anthropogenic burning in a British Columbia coastal temperate rain forest

“…The combination of sea‐level stability, a mild climate and abundant terrestrial and marine resources supported continuous settlement in the region for at least the last 13,000 years (McLaren et al., ). The study area includes numerous former indigenous habitation sites with an accumulation of shell‐midden deposits and nearshore features including clam gardens, fish traps and culturally modified trees (CMTs) (McLaren et al., ; Trant et al., ). There are no ethnographic accounts of anthropogenic burning in the study area, but elders in the nearby community of Waglisla (Bella Bella) describe older generations repeatedly burning hillslopes and interior mountain sites to increase the abundance of blueberries ( Vaccinium spp.)…”

“…In these forests, fuel moisture levels rarely drop to the point of ignition and a thick layer of fog often blankets the coastline even in the summer months (Daniels & Gray, ). Despite the seemingly unsuitable conditions for fire, recent research suggests that short‐term summer drought does occur (Hoffman, Gavin, & Starzomski, ) and that fire has been an important component of some forests in this region for millennia, with associated impacts on the abundance, diversity and availability of plant resources (Trant et al., ).…”