DOI: 10.5061/dryad.j6q573n9s
title: Data from: Limited biomass recovery from gold mining in Amazonian forests

description: Gold mining has rapidly increased across the Amazon Basin in recent years,
 especially in the Guiana shield, where it is responsible for &gt;90%
 of total deforestation. However, the ability of forests to recover from
 gold mining activities remains largely unquantified.  Forest
 inventory plots were installed on recently abandoned mines in two major
 mining regions in Guyana, and re-censused 18 months later, to provide the
 first ground-based quantification of gold mining impacts on Amazon forest
 biomass recovery.  We found that woody biomass recovery rates on
 abandoned mining pits and tailing ponds are amongst the lowest ever
 recorded for tropical forests, with close to no woody biomass
 recovery after 3-4 years.  On the overburden sites (i.e. areas
 not mined but where excavated soil is deposited), however, aboveground
 biomass recovery rates (0.4 - 3.5 Mg ha-1 yr-1) were within the
 range of those recorded in other secondary forests across the Neotropics
 following abandonment of pastures and agricultural lands.  Our
 results suggest that forest recovery is more strongly limited by severe
 mining-induced depletion of soil nutrients, especially nitrogen, than by
 mercury contamination, due to slowing of growth in nutrient-stripped
 soils.  We estimate that the slow recovery rates in mining pits
 and ponds currently reduce carbon sequestration across Amazonian secondary
 forests by ~21,000 t C yr-1, compared to the carbon that would have
 accumulated following more traditional land uses such as agriculture or
 pasture.  Synthesis and applications. To achieve large-scale
 restoration targets, Guyana and other Amazonian countries will be
 challenged to remediate previously mined lands. The recovery process is
 highly dependent on nitrogen availability rather than mercury
 contamination, affecting woody biomass regrowth. The significant recovery
 in overburden zones indicates that one potential active remediation
 strategy to promote biomass recovery may be to back-fill mining pits and
 ponds with excavated soil. 
description: Plots were installed in two central gold mining areas in Guyana,
 namely Mahdia (5°16'0.01"N 59°08'60.00"W) and Puruni
 (6°00'0.00"N 59°11'60.00"W), from January to March,
 2016, and re-censused approximately 18 months (June to August, 2017)
 later. Both sites are currently mined by artisanal and small-scale miners.
 At each study site, measurement plots were established on previously mined
 vegetation patches, ranging in age from 0.6 to 3 years since abandonment
 of mining activity at the time of establishment. Nine
 0.25 ha (50 m x 50 m) plots and a control old-growth forest plot (100 m x
 100 m) were established at each location. However, approximately half of
 all plots (five in Mahdia and four in Puruni) were re-mined before the
 2017 re-census and thus were excluded in this study. Each plot was
 positioned to include all three mining zones, i.e. the mining pit, the
 mine tailings and the overburden. Within each plot and within each mining
 zone, three nested subplots of 3m x 3m and 1m x 1m were established. All
 trees &gt;2 cm DBH (diameter at reference height of 1.3m) were
 measured and tagged with a unique number in the larger 0.25 ha plot and
 identified to species level where possible. All tree saplings 25-200 cm
 tall and all tree seedlings 5-25 cm tall were identified and counted in
 the 3m x 3m and 1m x 1m subplots respectively. Nested subplots were also
 established in the 1-ha control plot, where all trees &gt;10 cm DBH
 were measured and recorded and standard RAINFOR protocols applied to map,
 measure and identify trees (Phillips, Baker, Feldpausch, &
 Brienen, 2015). Tree species in all plots were identified by a local
 botanist. Heights of larger trees were measured using a
 laser rangefinder, whereas a tape measure was used to measure the height
 of saplings and seedlings. In the re-census in 2017, the diameter of all
 individuals still standing from the first census was re-measured, along
 with all new recruits &gt;2 cm DBH in each 0.25 ha plot and &gt;25
 cm and &gt;5 cm tall in our nested 3m x 3m and 1m x 1m subplots
 respectively. Trees not present in the second census but present in the
 first census were assumed to have died. Vouchers were only collected for
 non-woody species which were unknown and logged at the Centre for
 Biodiversity, University of Guyana.
description: This dataset contains plot data for abandoned gold mining sites
 in Guyana (Mahdia and Puruni) along with respective coordinates,
 description of header titles and vegetation to bareland cover
 ratio. Highlighted plots were sites which were not re-mined in 2017
 (Census II) and therefore used in the analysis of the paper. Data for
 control plots at both Mahdia and Puruni were deposited within the
 ForestPlots.net/RAINFOR network (https://www.forestplots.net).