DOI: 10.5061/dryad.mkkwh710r
title: Proximity to forest mediates trade-offs between yields and biodiversity of birds in oil palm smallholdings

description: There is much debate about how best to mitigate the effects of
 agricultural expansion on biodiversity, especially in the tropics. Recent
 studies have emphasised that proximity to natural habitats can enhance
 farmland biodiversity, yet few studies have examined whether or not such
 proximity mediates local trade-offs between yields and biodiversity, and
 hence alters conclusions about the ecological benefits of alternative
 farming strategies. Here we examine yield-biodiversity trade-offs,
 focusing on birds in oil palm smallholdings at different distances from
 remaining areas of forest, including a large forest reserve, in Ghana. We
 found significantly fewer birds on higher-yielding than lower-yielding
 farms, in terms of both species richness and abundance. For forest
 specialist birds (likely to be highly vulnerable to conversion of land to
 agriculture) we also found a greater trade-off (i.e. lower richness and
 abundance for a given yield) at farms further from forest, to the extent
 that increasing distance to the nearest forest from 1 to 10 km had a
 similar effect as a 3- to 5-fold increase in fruit yield brought about by
 increased intensification. Our study highlights the importance of
 accounting for the effects of natural forest in the landscape when
 considering agricultural policies for biodiversity protection, underlining
 the importance of a landscape-scale approach to conservation.
description: The dataset was collected during 2017 on 31 oil palm
 smallholdings and nearby primary forest in the Central region of
 Ghana. Birds were sampled at each of 92 sampling
 stations (80 in oil palm; 12 in forest) from 5:30 to 8:30 and 15:00-18:00
 GMT during fine weather, with each station surveyed twice (morning and
 evening) on different days in July 2017. Two observers walked to the
 middle of the station on each occasion, waited one minute for birds to
 return to normal activity then recorded the identity of all birds seen or
 heard within 30 m during a period of 15 mins, excluding African
 palm-swifts <i>Cypsiurus parvus</i>, which were often detected
 above the canopy. Unfamiliar vocalizations were recorded using a Tascam
 DR-05V2 handheld stereo recorder (Tascam, Montebello, USA) and
 subsequently compared with the Xeno-Canto online bird call database
 (http://xeno-canto.org/) for confirmation of identity (not to determine
 abundance which was always done in the field). Non-crop
 vegetation structure was assessed by recording the following data at all
 80 sampling stations in oil palm: number of large trees (diameter at
 breast height [dbh] &gt;25cm), small trees (dbh10-25cm) and saplings
 (dbh&lt; 10cm) within 30m in each of four quadrants centered at the
 station; dbh and distance to the two nearest large trees, small trees and
 saplings in each quadrant  (up to eight large trees, eight small trees and
 eight saplings per station); estimated vegetation cover (%) at ground
 level and height of non-woody vegetation. All measurements were made to
 the nearest 1 cm with a tape measure. Ground cover, to the nearest 5%, was
 recorded as the mean of at least two independent estimates; these varied
 among recorders by no more than 10%. These data were then used to
 calculate the density of large trees, small trees and saplings at each
 station. Oil palm fruit yield data were obtained for
 each study farm from 1<sup>st</sup> May to
 30<sup>th</sup> September 2017. A field assistant was
 appointed in each of the two focal smallholder communities and was
 responsible for liaising with the selected smallholders on a daily basis
 and measuring and recording the number of fresh fruit bunches (FFBs)
 obtained whenever harvesting took place, together with the combined weight
 of FFBs and loose fruit. All weight measurements were obtained using a 200
 kg Silverline 251087 heavy-duty spring hanging scale (Silverline Tools
 Ltd, Yeovil, UK). We then used log<sub>10</sub> of the sum of
 the combined weights over a five-month period, multiplied by 12/5 to give
 an annual equivalent and divided by the area (ha) of the oil palm crop on
 each farm, as our standardized measure of FFB yield
 ha<sup>-1</sup> at each farm (palms were planted at a uniform
 density of ~150 stems ha<sup>-1</sup>).
description: These datasets contain all the information needed to use them,
 including an information sheet in each file that explains each column of
 data.