Amount, distance-dependent and structural effects of forest patches on bees in agricultural landscapes Page: 3
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Rahi mi et a. Agriculture & Food Security (2022) 11:10
We found 100 articles examining the different effects
of forest patches on bees in agricultural landscapes. We
divided these effects into three categories based on the
sampling method: (1) distance-dependent effects: this
group of studies answers the question of what changes in
bee population occur with increasing distance from for-
est patches in the agricultural landscapes. The sampling
method of bees in these studies is based on plots or tran-
sects that examine bees in the farms under study at dif-
ferent distances from forest patches. The first sampling
site is near the forest and the last site is at the farthest
distance from the forest, (2) effects of forest amount:
these studies answer the question of how the amount of
forest cover around the target sites affects the bee popu-
lation. In this type of study, bee populations are examined
in several plots and then their relationship to the forest
amount around the plots is evaluated in different buffers
or scales, and (3) structural effects of forest patches: in
this type of study, plots or transects are placed inside for-
est patches (not on farms). One or more forest patches
are sampled and the relationship of the bee population
within these patches with the structural features of the
patches such as isolation, connectivity, number, area,
shape, and complexity of patches is evaluated. Details of
the studies of each of the mentioned categories are pre-
sented in three separate tables, which contain 36, 32, and
33 articles (93 unique), respectively.
Results
Distance-dependent effects of forest fragments on bees
Table 1 shows the country, the number of forest patches
(NP), their area (ha), the distance of sampling sites or
plots from forest patches (proximity), type of pollinators,
matrix around the patches, and key results of studies that
have examined the distance-dependent effects of forest
patches on bees' populations. This table presents 36 arti-
cles, most of which (22%) have been conducted in Brazil.
Some of these studies have reported the number of for-
est patches and their area in landscapes understudy, but
most of them did not provide details of forest patches, so
we used a dash as a lack of information. The number of
forest fragments reported in these studies varies from 1
to 14 (on average 4 patches). The area of these fragments
varies from 0.3 hectares to 65,000 hectares, with an aver-
age of 3100 hectares.
The proximity column shows the distance between the
plots or sampling sites and forest patches. Some studies
have considered only one distance, but others have exam-
ined several distances. In the proximity column, we have
reported the nearest and farthest distance between the
sites and forest patches. Therefore, in this column, the
first number indicates the distance that the first site was
examined and the second number indicates the farthestdistance. These distances vary from 0 to 30 km of forest
patches, with an average of 1900 m. Approximately 83%
of these studies consider the maximum distance from
forest fragments to be less than 2 km. Some studies have
not presented the details of the understudy species. How-
ever, social bees such as honeybees, bumblebees, and
stingless bees are seen in 54% of these studies. For stud-
ies that have identified a large number of native species,
we used the term "Native bees", which includes all species
except honeybees. The matrix column shows the land
cover around forest patches, of which 27% of the studies
have examined landscapes with a matrix covered by cof-
fee products.
Our data show that 75% of studies emphasized the
positive effects of forest patches on pollinating bees at all
distances. In other words, 75% of studies, regardless of
the number and area of patches, the type of species, and
the landscape matrix, have found that by increasing the
distance from forest patches in agricultural landscapes,
factors such as species richness and abundance, species
diversity, pollen deposition, visitation rate, agricultural
production, pollination success, and pollinator speciali-
zation decrease. However, 15% of total studies found
that with increasing distance from forest fragments, spe-
cies richness and abundance, and /3-diversity increased,
and factors such as parasitism, and mortality rate at the
margins of forest patches increased. Approximately, 9%
of studies have found no relationship between forest
patches and bees. In the case of honeybees, the results of
some studies are inconsistent. For example, some stud-
ies have suggested that honeybee populations decrease
with increasing distance from forest patches [25, 77, 100].
However, Brosi et al. [19] found that at the forest edges,
honeybees made up only 5% of the individuals sampled
whereas away from forests, they increased to 45%. Bravo-
Monroy et al. [14] also showed that in samples far from
the forest, honeybee abundance decreased significantly.
Effects of the forest amount on bees
Table 2 shows the details of studies that have examined
the effects of forest cover around plots or sampling sites
on bees. This table details 33 articles, 27% of which were
conducted in Brazil, which has the highest percentage
compared to other countries. The buffer column shows
the radius (m) around sampling sites. Some studies have
considered only one scale (buffer) while others have con-
sidered multiple scales. In studies performed on multiple
scales, the first number of each row in the buffer column
shows the first scale and the second number shows the
maximum radius studied. The radius around the sample
sites varies from 25 m to 15 km in the studies reviewed
in the present study with an average of 1350 m. Approxi-
mately, 75% of these studies consider the maximumPage 3 of 1 5
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Rahimi, Ehsan; Barghjelveh, Shahindokht & Dong, Pinliang. Amount, distance-dependent and structural effects of forest patches on bees in agricultural landscapes, article, January 21, 2022; (https://digital.library.unt.edu/ark:/67531/metadc1954009/m1/3/: accessed June 22, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Liberal Arts & Social Sciences.