Action: Retain or plant native trees and shrubs amongst crops (agroforestry)
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- Seven studies evaluated the effects of retaining or planting native trees and shrubs amongst crops on bat populations. Two studies were in South America, four were in Mexico, and one was in Tanzania.
COMMUNITY RESPONSE (7 STUDIES)
- Community composition (1 study): One replicated, site comparison study in Tanzania7 found different compositions of bat species in coffee plantations with different amounts and types of shade cover.
- Richness/diversity (7 studies): Four of six replicated, site comparison studies in Colombia, Mexico and Costa Rica found a similar number of bat species in shaded and unshaded coffee plantations, and in coffee plantations with different amounts and types of shade cover. The two other studies found more bat species and higher bat diversity in coffee, cacao and banana plantations with varied shade cover, than in plantations with a single shade species or no shade. One replicated, site comparison study in Tanzania found more bat species in shaded coffee plantations than in traditional mixed agroforestry systems with natural forest vegetation.
POPULATION RESPONSE (5 STUDIES)
- Abundance (5 studies): Two replicated, site comparison studies in Mexico captured more bats in coffee plantations with varied shade cover than in plantations with a single shade species. One replicated, site comparison study in Mexico found higher activity (relative abundance) of forest bat species in plantations with a varied shade cover than in plantations with a single shade species, but the opposite was true for open habitat bat species. One replicated, site comparison study in Costa Rica found no difference in the number of bats captured between cacao and banana shade plantations and unshaded monocultures. One replicated, site comparison study in Tanzania found greater bat occurrence in shaded coffee plantations than in traditional mixed agroforestry systems with natural forest vegetation.
USAGE (0 STUDIES)
This intervention involves growing crops under shade trees that are either native tree species that are remnants from cleared vegetation, or other crop trees (often referred to as ‘agroforestry’). This approach provides a more complex habitat than conventional monoculture farming and can support higher levels of biodiversity.
Supporting evidence from individual studies
A replicated, site comparison study in 1999–2000 of 18 sites in coffee plantations and forest fragments in the Central Andes, Colombia (Numa et al 2005) found that there was no significant difference in bat species richness in shaded and unshaded coffee plantations. Bat species richness overall was similar in shaded coffee (14 species) and unshaded coffee plantations (12 species). In landscapes dominated by shaded coffee, there was no significant difference in bat species richness between shaded (9.4 species) or unshaded coffee plantations (9.8 species) and native forest fragments (9.9 species). However, in landscapes dominated by unshaded coffee plantations, bat species richness was higher in native forest fragments (14.6 species) than in shaded (9.4 species) or unshaded coffee plantations (7.9 species). Six sites of each habitat type were surveyed (shaded coffee, unshaded coffee, and native forest fragments). Shaded coffee plantations had native shade trees. Unshaded plantations were coffee monocultures with no trees or containing just isolated trees. Bats were sampled with 50–80 m of mist nets for three consecutive nights/site between October 1999 and February 2000.
A site comparison study in 2004–2005 in five agroforestry plantations and one montane rainforest in southeastern Chiapas, Mexico (Estrada et al 2006) found that coffee agroforestry plantations with different amounts and types of shade cover had a similar number of bat species. The number of bat species captured (23–26) did not differ significantly between five coffee agroforestry plantations with different amounts and types of shade cover. However, the number of bat species captured across all sites was found to be positively correlated with the number of vegetation layers, and the height and cover of trees (data reported as statistical model results). More bat species were recorded in native rainforest (37 species) than in any of the five coffee agroforestry plantations. One native rainforest site was sampled, and five coffee agroforestry plantations with different heights (6–25 m), layers (2–3 strata), types (native rainforest trees, shimbillo Inga spp. or banana Musa spp.) and amounts (40–90%) of shade cover. Management intensity (pruning, weeding, and use of chemicals) also varied between sites. At each of six sites, bats were captured with six mist nets placed along a 150 m transect for six hours from sunset on two nights. Surveys were repeated every 50 days from March 2004 to June 2005.
A replicated, site comparison study in 2002–2003 in 28 agroforestry plantations and seven tropical lowland forest sites in Talamanca, Costa Rica (Harvey & González Villalobos 2007) found that banana and cacao agroforestry plantations had higher bat diversity and more bat species than unshaded plantain monocultures, but the total number of bats captured did not differ. Bat diversity (reported as diversity indices) and the number of bat species was significantly higher in banana (14 bat species) and cacao (15 bat species) agroforestry plantations than in unshaded plantain monocultures (10 bat species). A similar number of bats were captured in banana (76 bats) and cacao (89 bats) agroforestry plantations and in unshaded plantain monocultures (83 bats). Banana and cacao agroforestry plantations had similar or higher bat diversity, number of bat species and bat captures as native forest (13 bat species, 47 bats captured). Banana and cacao agroforestry plantations were grown organically with a shade canopy of native trees or planted fruit and timber trees. Plantain monocultures were grown without shade and with the use of chemicals such as insecticides. Thirty-five sites were sampled including seven replicates each of native forest, plantain monoculture and banana agroforestry, and 14 replicates of cacao agroforestry. At each of 35 sites, bats were captured with four mist nets for five hours on one night in May–November 2002/2003 and one night in February–November 2003.
A replicated, site comparison study in 2006–2007 of 44 sites in coffee agroforestry plantations and native rainforest fragments in Chiapas, Mexico (Williams-Guillén & Perfecto 2010) found that traditional agroforestry plantations had a similar number of leaf-nosed Phyllostomidae bat species to more intensively managed agroforestry plantations, but species composition differed and more bats were captured in traditional plantations. A similar number of bat species but significantly more bats were captured in traditional agroforestry plantations (24 species, average 2.5 bats/mist net/hour) than in plantations with moderate (22 species, 1.6 bats/mist net/hour) or high intensity management (22 species, 1.4 bats/mist net/hour). A similar number of bat species were also captured in native forest (24 bat species). The proportion of bat species in all feeding groups decreased as management intensity increased, except for large fruit-eating bat species which increased in proportion (from 30% in native forest and traditional plantations to 48% in high intensity plantations). Bats were sampled in traditional agroforestry coffee plantations (coffee and other plants grown under original forest trees, 12 sites), moderate intensity coffee plantations (coffee grown under a variety of fruit and timber trees, 11 sites), high intensity coffee plantations (coffee grown under shimbillo Inga spp. trees, 10 sites) and native forest fragments (11 sites). At each of 44 sites, bats were captured with mist nets for 8–10 hours during one night between November 2006 and August 2007.
A replicated, site comparison study in 2006–2007 of 44 sites in coffee agroforestry plantations and tropical rainforest in Chiapas, Mexico (Williams-Guillén & Perfecto 2011) found that traditional agroforestry plantations had a similar number of insect-eating bat species to more intensively managed agroforestry plantations, but species composition differed. The number of insect-eating bat species did not differ significantly between traditional agroforestry plantations (18 species) and plantations with moderate (23 bat species) or high intensity management (21 bat species). Activity of forest bat species was significantly lower in high intensity plantations (average 6 bat passes/night) than moderate intensity (14 bat passes/night) or traditional plantations (21 bat passes/night). The opposite was true for open habitat bat species (high intensity plantations: average 3 bat passes/night; low intensity and traditional plantations: 1 bat pass/night). Native forest had a similar number of bat species (19) to all three types of plantations. Bats were sampled in traditional agroforestry coffee plantations (coffee and other plants grown under original forest trees, 12 sites), moderate intensity coffee plantations (coffee grown under a variety of fruit and timber trees, 11 sites), high intensity coffee plantations (coffee grown under shimbillo Inga spp. trees, 10 sites) and native forest fragments (11 sites). At each of 44 sites, sampling was carried out with mist nets and bat detectors for 8–10 hours during one night between November 2006 and August 2007.
A replicated, site comparison study in 2008–2009 of nine farms in Veracruz, Mexico (Castro-Luna & Galindo-González 2012) found that coffee plantations with a mix of shade species had significantly more bats and bat species captured within them than coffee plantations with few shade species and little understorey or pastures. More fruit and nectar-eating bats and bat species were captured in coffee plantations with a mix of shade species (378 bats, 20 bat species) than in coffee plantations with few shade species and little understorey (64 bats, 10 bat species) or pastures (26 bats, 8 bat species). Three coffee plantations had a varied shade layer including fruit trees and native tree species. Three coffee plantations were shaded only by mainly shimbillo Inga spp. trees with few understorey species. Three pastures were cattle-grazed with introduced grass species and isolated trees. Nine farms (three of each type) were surveyed eight times across three different seasons between April 2008 and September 2009. Bats were captured using 10 mist nets/site placed end to end at ground level for four hours from sunset.
A replicated, site comparison study in 2010–2011 in 19 plantation, forest and grassland sites on the southern slopes of Mount Kilimanjaro, Tanzania (Helbig-Bonitz et al 2015) found that shaded coffee plantations had greater overall bat occurrence and species richness than traditional agroforestry systems, grasslands or natural forests, and species composition also differed. Overall bat occurrence was significantly greater in shaded coffee plantations (average 49 occurrences) than traditional agroforestry systems (34 occurrences), grasslands (29 occurrences) or natural forests (15 occurrences). Species richness was higher in shaded coffee plantations (10 different types of bat echolocation call) than traditional agroforestry systems (8 types of bat call), grasslands (7 types of bat call) or natural forests (6 types of bat call). Species composition also differed between habitat types (data reported as statistical model results). Surveys were conducted in 4–5 plots (0.5 ha) within each of four habitat types: shaded coffee plantations (coffee plants with native or non-native tree species), traditional agroforestry systems (mixed agricultural plants with natural forest vegetation and large shade trees), grasslands (frequently cut to feed livestock) and natural forests. Four points/plot were surveyed from sunset for 4 x 5 minute intervals. Each plot was surveyed on one night in December–March 2010/2011 and June–September 2011.
- Numa C., Verdú J.R. & Sánchez-Palomino P. (2005) Phyllostomid bat diversity in a variegated coffee landscape. Biological Conservation, 122, 151-158
- Estrada C.G., Damon A., Hernández C.S., Pinto L.S. & Núñez G.I. (2006) Bat diversity in montane rainforest and shaded coffee under different management regimes in southeastern Chiapas, Mexico. Biological Conservation, 132, 351-361
- Harvey C. & González Villalobos J.A. (2007) Agroforestry systems conserve species-rich but modified assemblages of tropical birds and bats. Biodiversity and Conservation, 16, 2257-2292
- Williams-Guillén K. & Perfecto I. (2010) Effects of agricultural intensification on the assemblage of leaf-nosed bats (Phyllostomidae) in a coffee landscape in Chiapas, Mexico. Biotropica, 42, 605-613
- Williams-Guillén K. & Perfecto I. (2011) Ensemble composition and activity levels of insectivorous bats in response to management intensification in coffee agroforestry systems. PLoS ONE, 6, e16502
- Castro-Luna A.A. & Galindo-González J. (2012) Enriching agroecosystems with fruit-producing tree species favors the abundance and richness of frugivorous and nectarivorous bats in Veracruz, Mexico. Mammalian Biology, 77, 32-40
- Helbig-Bonitz M., Ferger S.W., Bohning-Gaese K., Tschapka M., Howell K. & Kalko E.K.V. (2015) Bats are not birds - different responses to human land-use on a tropical mountain. Biotropica, 47, 497-508