Fuelwood return rates and distance walked with repeated harvesting of fuelwood on the forelands of the Cape south coast

Description

Foraging and availability of fuelwoods are likely to have impacted the fitness of hunter gatherers and may have influenced their mobility patterns. We investigated the resilience to repeated foraging of fuelwood by people indigenous to the study area on the coastal forelands of the Cape south coast of South Africa. We assessed fuelwood depletion patterns through repeated fuelwood foraging by human agents in six different vegetation types, namely Floodplain Woodland, Renosterveld, Subtropical Thicket, Strandveld, Sand Fynbos, and Limestone Fynbos. The latter two vegetation types were sampled in both unburnt and recently burnt (within three years of our sampling) states, which enabled investigation of fuelwood foraging rates in eight different habitat types. We calculated fuelwood return rates and the distance walked during consecutive harvesting bouts. Neither fuelwood return rates nor the distance walked during foraging declined/increased significantly in any of the eight habitats over 12 person hours of foraging from a central point. Return rates differed significantly among the habitat types, with return rates being the lowest in Renosterveld and Subtropical Thicket and highest in Floodplain Woodland. Foragers generally chose to walk in a different direction each time they started from the central point and they preferred pre-existing trails. Distance walked was highest in Subtropical thicket and lowest in burnt Fynbos where foragers were able to access with relative ease the burnt skeletons of Proteaceae overstorey shrubs. Our results indicate that, fuelwood on the Cape south coast shows little evidence of depletion after intense harvesting.

Steps to reproduce

Experimental fuelwood foraging was conducted in eight different habitat types, including six vegetation types in an unburnt state and two vegetation types that burnt within three years of our sampling. In each habitat type, two sites were sampled, the first of which in March 2021 and the second in January–February of 2022. We defined a foraging bout (or ‘bout’) as a 30-min period during which a human forager searched for and harvested fuelwood in a particular patch (site). Note that by this definition, patch size was not fixed but depended on the density, accessibility and apparency of the dry fuelwood in that patch. Thus, patch size was determined by the humans’ foraging strategy, away from a central point that was demarcated in each site. Foragers also had to return the harvested wood to this central point where the wood was weighed and recorded. At each site, sampling was undertaken on a single day with four foragers concurrently conducting six consecutive half-hour bouts with a resting period of approximately 30 minutes between consecutive bouts. The mass of wood harvested per forager per half-hour bout constituted the unit of replication (n = 384, i.e. 8 habitat types x 2 sites x 4 foragers x 6 consecutive bouts). This measure, hereafter referred to as the fuelwood ‘return rate’, was the primary response variable of interest, converted to be expressed as kilograms of wood harvested per forager per hour. Ad hoc behavioural observations of harvester activities were also recorded. To track spatial patterns of foraging, we randomly assigned GPS devices to two of the four foragers undertaking foraging bouts which enabled measurements of the distance walked per foraging bout. This would have produced 192 records (8 habitat types x 2 sites x 2 agents x 6 consecutive bouts) but there were 29 cases of device failure. Our dataset thus comprised 163 records of distance walked per bout. This measure comprised the second response variable of interest, also converted to be expressed as distance (m) walked per forager per hour of foraging.

Institutions

• Nelson Mandela University Faculty of Science

  Port Elizabeth

Categories

Funders

• Nelson Mandela University

  Eastern Cape, South Africa
• African Centre for Coastal Palaeoscience

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