DOI: 10.5061/dryad.dfn2z356w
title: A decade of diversity and forest structure: Post-logging patterns across life stages in an Afrotropical forest

description: Tropical forests are under threat of increasing pressure from
 income-generating land uses. Selective logging is a compromise that allows
 the use of the land while leaving much of the forest canopy intact across
 a landscape. However, the ecological impacts of selective logging are
 unclear, with evidence of positive, negative, and negligible effects on
 forest structure and diversity. We examined the impact of selective
 logging on the structure and diversity of evergreen tropical forests in
 the Monts de Cristal region, a chain of mid-elevation hills in
 northwestern Gabon. For three size classes (seedling, sapling, and adult)
 of woody plant species, we tested whether forest structure (canopy
 openness, stem density, basal area, and relative liana abundances) and
 diversity were altered in forests that had been logged one year and ten
 years prior, compared to unlogged forest. In general, we found no large
 impact of selective logging treatment on the structure and diversity of
 adult woody plant communities, but the seedling and sapling communities
 were affected. Compared to unlogged forest, one-year post-logging forest
 had greater variation in canopy openness and lower sapling stem density.
 Ten-year post-logging forest had higher seedling and sapling species
 evenness, higher sapling species diversity, and higher relative abundance
 of sapling-sized lianas compared to unlogged forest. Our results show that
 key differences between intact and selectively logged forests persist in
 the understory at least a decade after logging. Overall, these results
 contribute an additional data point in the literature on selective
 logging, specifically representing the impacts of very low impact
 selective logging in Central African forests. Our study highlights the
 value of exploring selective logging impacts at multiple time periods of
 recovery, and makes an important contribution to the knowledge of Central
 African managed forests.
description: To assess the impact of selective logging on forest structure and
 diversity, we established a total of 80 vegetation plots between September
 2018 and October 2019 (Fig. 1C). Each plot was 400
 m<sup>2</sup> in area (20 × 20 m). In order to capture the
 heterogeneous impact that selective logging can have on the forest, we
 randomly located 20 plots within each of three logging treatment areas:
 recently logged forest that had been logged approximately one year prior,
 older logged forest that had been logged ten years prior, and two unlogged
 forest areas. We measured two separate unlogged areas in order to try and
 capture some of the natural spatial variation in these forests. For all
 analyses, we considered the two unlogged areas as a single control
 treatment. We generated random point sampling schemes based on boundaries
 of yearly logging blocks using the <em>sp</em> package
 (Pebesma and Bivand, 2005, Bivand et al., 2013). To
 sample the adult tree community, all free-standing woody stems ≥10 cm DBH
 were tagged, measured, and identified. For species that were difficult to
 identify in the field, we collected vouchers and deposited them at the
 National Herbarium (L’Herbier National du Gabon) which provided
 determinations for as many species as possible. We also tagged and
 measured climbing lianas ≥10 cm DBH following Gerwing et al. (2006),
 though we could not identify many individuals due to the limitations of
 collecting voucher specimens for lianas where leaves can only be found at
 the top of the canopy. To sample juvenile trees, saplings, and shrubs, we
 set up two subplots (10 × 10 m) nested within each plot. Within these
 subplots, we tagged, measured DBH, and identified all free-standing woody
 stems ≥1 cm and &lt;10 cm DBH, and tagged and measured climbing lianas
 as above. For seedlings, we tagged, measured height, and identified all
 free-standing woody species and lianas ≥1 cm and ≤1 m in height in nine 1
 × 1 m<sup>2</sup> subplots at 9 points (at the four corners,
 center, and four middle points of each side) within the main plot. We
 measured canopy openness at each of the 9 seedling subplots per plot,
 using a Spherical Crown Densiometer, Concave Model C (Forestry Suppliers,
 Jackson, MS, USA) (Lemmon, 1956) held level 1 m above the ground. Values
 were averaged to yield one canopy openness value for each adult tree
 plot. 
 To check for differences among treatments in topography, we
 measured elevation at each of the 9 seedling subplots per plot, using a
 Garmin GPSmap 64 s device (GARMIN, Olathe, KS, USA) and used the data to
 calculate slope and mean elevation values for each plot. Values were
 averaged to yield one elevation value for each adult tree plot. Plots had
 similar slope across all treatments (mean = 8 m, range = 1–26 m; Kruskal
 test, p = 0.16; Fig. A1B). Mean elevation was similar in older logged (505
 m) and unlogged (503 m) forests (Dunn’s test, p-adjusted = 0.194), but was
 slightly higher in recently logged forests (531 m) compared to older
 logged and unlogged forests (Dunn’s test, p-adjusted &lt; 0.001 and
 0.0001, respectively; Fig. A1A). However, there was broad overlap in
 elevation values for all three treatments (ranges: older logged, ranges =
 464–585 m in unlogged, 488–561 m in recently logged, and 451–654 m in
 older logged forest). To look at climate differences across sites, we used
 worldclim data (Fick and Hijmans, 2017) to consider differences in mean
 annual temperature and mean annual precipitation across sites (Table A2),
 and found that differences across treatments were small.