Architecture of relict charcoal hearths in northwestern Connecticut, USA

Abstract

Relict charcoal hearths are round or elliptical earthen platforms up to 11 m in diameter and a widespread feature of historical industry that supplied charcoal used in the production of iron in furnaces or smelters. The iron industry dominated Litchfield County, Connecticut, and surrounding areas in the northeast United States throughout the 19th century, peaking in ∼1850. The large number of charcoal hearths in this region is a relic of >150 years of widespread iron production.In this study, we describe the architecture and soil stratigraphy of 26 charcoal hearths in LitchfieldCounty. This contribution aims to (1) compare soils that comprise the charcoal hearths with "natural" adjacent soils, (2) measure the thickness of topsoil developed upon the hearths, and (3) characterize the stratigraphy associated with these features. Results indicate that the black topsoils overlying the charcoal hearths contain residual charcoal and are on average 2.6 times thicker than adjacent Cambisols. Charcoal hearths display two or more black, charcoal-rich strata separated by layers of reddish-brown soil low in charcoal content indicating multiple episodes of use. We also find that many charcoal hearths have been stabilized with boulders on the downslope side during construction and repeated use. Overall, the results presented here provide significant information regarding the construction, use, and associated impacts of earthen platforms for charcoal production in the northeast United States, with further relevance to other areas where historical charcoal production occurred. K E Y W O R D Santhropogenic, anthropogenic soils, geomorphology, forest use, past land use, Terra Preta Geoarchaeology 2017; 32: 502-510

Soils on Historic Charcoal Hearths: Terminology and Chemical Properties

“…2a and 2^BAu in Fig. 3b) can be interpreted as being a result of the preparation of a new platform for a second usage of the charcoal hearth site (Raab et al, 2017). In situ formation of this wedge-like layer by pedogenic processes can be excluded; we found no indications for podsolization or lessivage-like eluvial or illuvial features.…”

“…Concentrations of nitrogen and carbon significantly differ between the approximately 150-yr-old charcoal hearths (Raab et al, 2017) and the surrounding undisturbed soils, but sulfur concentrations do not vary between the sites (Fig. 4).…”

“…In situ formation of this wedge-like layer by pedogenic processes can be excluded; we found no indications for podsolization or lessivage-like eluvial or illuvial features. According to the interpretation from Raab et al (2017), the colliers raked substrate from upslope along the old platform to build a new and stable platform with noninflammable substrate on top. An erosive origin of the substrate by slopewash from upslope was discussed by Stolz and Grunert (2010) and Hildebrandt et al (2007), but, because historic instructions from Germany for charcoal production on hillslopes (von Berg, 1860) explicitly prescribe the preparation of a former charcoal hearth for further reuse by applying a cover of fresh substrate, we favor a purposeful application.…”

“…The large number of charcoal hearths in this region is due to historic iron production, with the founding of the first furnace in 1762, peaking around 1850, and extending to the late 19th Century (Gordon, 2001;Raab et al, 2017). To support this industry, forests in Litchfield County were divided into blocks ranging from 50 to several hundred acres in size and dedicated for charcoal production; some blocks were cut successively up to five times.…”

“…Due to the abundance and wide distribution of charcoal hearths, their occurrence in different ecosystems, the range of ages, and the persistence of PyOM, charcoal hearth sites have the potential for enriching ongoing discussions about the longer-term influence of biochar in soils. The architecture, usage, and geoarchaeological background of relict charcoal hearths in Connecticut recently have been described by Raab et al (2017). In this study we focus on the soil properties of the sites.…”