DOI: 10.5061/dryad.69p8cz8z0
title: Data from: Local-scale tree and shrub diversity improves pollination services to shea trees in tropical West African parklands

description: Shea (Vitellaria paradoxa) trees bear fruit and seeds of considerable
 economic, nutritional and cultural value in the African Sudano-Sahelian
 zone. In much of West Africa, shea exists within an agroforestry system
 referred to as “Parkland”, where social changes, including migration, have
 resulted in expanding areas of crop cultivation, reductions in both the
 area of fallow land and the duration of fallow periods, and reduced
 diversity of habitats and woody species. Shea benefits strongly from
 pollination by bees and the loss of Parkland biodiversity may reduce the
 availability of pollinators, leading to pollen limitation, and reductions
 in fruit yields. We investigated whether shea trees in Southern Burkina
 Faso experienced pollination limitation, and whether local- and landscape-
 scale diversity was linked to visitation by bees, the degree of limitation
 observed, and the weight of fruit produced. Honey bees (Apis mellifera)
 were observed more frequently in diverse sites, whereas non-Apis species
 were generally widespread but visited trees in greater numbers at diverse
 sites. We found that shea fruit production was significantly limited due
 to lack of pollination and that the degree of pollination limitation was
 greater in sites with lower levels of tree and shrub diversity. Synthesis
 and applications. Sites with greater diversity of tree and shrub species
 had more bee visits and less extreme pollination limitation than less
 diverse sites, indicating that small-scale diversity is associated with
 more efficient pollination services. Consequently, shea yields are likely
 to benefit from retention of a range of different tree and shrub species
 in parklands. We recommend that when fallows are cleared for cultivation,
 such beneficial plants are retained within cultivated fields, and that
 measures to conserve pollinators in the region should target both A.
 mellifera and non-Apis bee species.
description: 2.1
 Study species Shea, or
 <i>Vitellaria paradoxa</i>, is the only member of its genus in
 the family Sapotaceae.  Its range is restricted to the Sudano-Sahelian
 zone of western and central Africa (Fig. 1) and it comprises two
 sub-species: <i>Vitellaria paradoxa ssp. nilotica</i> in the
 east and <i>Vitellaria paradoxa ssp. paradoxa</i> in the
 central and western parts of its range (Naughton et al., 2015).  Shea
 trees bloom during the dry season, between January and April, with peak
 fruiting occurring by the end of July, although anecdotal evidence
 suggests flowering and fruiting periods can vary yearly. Flowers are born
 on inflorescences located at the tips of branches.  The flowers are
 short-lived but buds, receptive flowers and older blooms occur
 simultaneously over a long flowering period (Stout <i>et
 al.</i> 2018).  The flowers are protogynous, with the stigma
 emerging from the bud and becoming receptive before the sepals part to
 reveal the petals and stamens (Hall, Aebischer, Tomlinson, Osei-Amaning,
 & Hindle, 1996).  Although this reduces the likelihood of a flower
 self-pollinating, the presence of flowers at different stages of maturity
 on the same inflorescence indicates that within-inflorescence pollination
 is possible.  The success of pollination by flowers on the same
 inflorescence is not well understood.  Shea produces fruit with sweet pulp
 surrounding a large seed (the shea “nut”), and occasionally more than one
 nut may be produced in a single fruit. 2.2 Site
 selection This study was
 conducted in the Centre-Sud region of Burkina Faso, south of the Kaboré
 Tambi National Park (KTNP) and east of Nazinga Game Ranch (Fig. 1).  All
 data were recorded between February and June 2017. We selected
 ten 1 ha sites (100 m x 100 m) in fields which had been cultivated during
 the previous rainy season. Sites were organised into five pairs located 2
 - 3.5 km apart, and the minimum distance between pairs was 4 km. The
 paired design allowed us to minimise impacts of external factors (e.g.
 distance to a large town or nature reserve).  Within each pair, we
 selected one site with low diversity of woody species and one site with
 higher diversity.  All trees and shrubs, including shea, greater than 3m
 in height were identified and counted in each site, and the mean inverse
 Simpson’s index (1/D) was calculated to represent site diversity. We did
 not include small trees and shrubs (&lt;3 m in height) because local
 knowledge indicated they were unlikely to flower (an observation that
 proved true). Herbaceous species were also excluded from site diversity
 calculations because we worked in ploughed fields that were open to
 grazing animals, with low cover of herbaceous plants (&lt;0.01%
 cover). We mapped and calculated the area of semi-natural habitat within a
 radius of 1 km from the centre of each site in ArcMap 10.4 using satellite
 imagery provided by ESRI world maps and Google Earth (accessed in
 September 2017, photos dated to 2013).  Restricting the radius to 1 km
 avoided an overlap in mapped habitat between sites.  Although the foraging
 range of <i>A. mellifera</i> can greatly exceed this distance,
 studies based on waggle-dances and mark-recapture indicate that African
 honey bee races, including <i>A. mellifera adansonii</i>,
 focus the majority of their foraging within distances of 1km of the hive
 or previous feeding stations (Roubik, 1999; Schneider, 1989).  Diversity
 (1/D) of woody species within our ten sites (site diversity) and area of
 semi-natural habitats then acted as the independent variables (see data
 analysis). We collected
 data regarding pollination services from 10 shea trees within each site
 that met the following criteria: selected trees had a single trunk, were
 greater than 3 metres tall, appeared healthy and had developing flower
 buds. If more than ten trees in a site met the criteria, the ten selected
 trees were distributed as evenly as possible through each site.
 2.3
 Pollination limitation Supplemental
 hand-pollination was carried out over the course of three visits to each
 site during the flowering period.  We selected up to three pairs of
 inflorescences that had a similar number of flowers with receptive stigmas
 on each tree.  The flowers with receptive stigmas on one inflorescence per
 pair were marked for fruit counts later in the season and were left open
 to natural pollination (untreated flowers).  The other inflorescence per
 pair was also marked and left open, but in addition was hand-pollinated
 with pollen from another tree (pollen supplementation). The number of
 trees and inflorescences varied between sites because three comparable
 pairs of inflorescences were not present on every tree (Table 1). In
 total, 2248 flowers were included in the analysis: 1096 untreated flowers
 and 1152 flowers with pollen supplementation by hand.  On average, the
 difference in the number of hand pollinated and control flowers at each
 site was 2.4%. The greatest difference was 8.6%. All results relating to
 flowers and fruit set are from these selected flowers.  2.4 Flower visitors
 We
 surveyed flower visitors during two ten-minute recording episodes per
 tree, one between 6 and 8am and another between 4 and 6pm, when insect
 visitors are most active, on each of three dates during the flowering
 season (January-March 2017) (Stout et al. 2018).   If there were no
 receptive flowers on a tree, no attempt was made to record visitation
 (Table 1).  All bees observed visiting inflorescences during recording
 episodes were caught.  The native honey bee, <i>Apis mellifera
 adansonii </i>Latreille could be identified easily, but other bees
 were placed in 70% alcohol solution and sent for expert
 identification.  2.5 Fruit
 set We counted
 fruit set in early May 2017, when the selected flowers had developed small
 fruits, but before fruits ripened and fell.  Ripe fruits were collected
 and their nuts were weighed in the field in June to August 2017.
 Initially, fruits were hand harvested (n = 35), but proved to be unripe.
 The remaining (n=133) fruits were collected by placing bags around them so
 they could fall naturally as they ripened without being lost. Only the
 ripe fruits collected in bags were included in the analysis of fruit
 weight.