Abstract
Cultivation of cash crops, such as cardamom (Elettaria cardamomum) in the forest understorey is a common practice in many tropical forests. Over time, cultivation may change forest structure and species composition, leading to gradual degradation of biodiversity and ecosystem services. Effective conservation of these forests requires an enhanced understanding of the demographic processes such as soil seed bank that may greatly influence future forest composition. We examined how the soil seed bank structure and composition responds to cardamom cultivation in a high conservation value Sri Lankan montane rain forest. Soil samples from natural forest with abandoned cardamom plantations (CP) and adjacent natural forest (NF) patches without cardamom were collected in dry and wet seasons. Soil samples were spread out in trays in a shade house and germination was recorded weekly for 19 weeks. The density of seeds in the soil seed bank was much higher in CP than NF. While grasses and forbs contributed the highest number and percentage of seeds in soils of both forest types, their densities in the soil seed bank were 9 and 2 times greater in the CP than the NF, respectively. Seeds of the non-native herbs Ageratina riparia and E. cardamomum were 4 and 20 times greater in the soil of CP, respectively. Seeds of light demanding tree species such as Macaranga indica were restricted to soils of CPs. Overstorey tree community of each forest type was poorly represented in their respective soil seed banks. The high density of seeds of pioneer trees and non-native herbs in the soil of CPs, combined with higher light transmission to the ground floor may exacerbate competition for resources with the seedlings of late successional trees of high conservation value. To overcome this barrier and enhance conservation value of the forest, restoration strategies may need to focus on transplanting seedlings of these species into forest with abandoned cardamom plantations.
Highlights
Agro-ecosystems are important elements of many tropical landscapes, as they contribute to local livelihoods and provide environmental services
We examined how the soil seed bank structure and composition responds to cardamom cultivation in a high conservation value Sri Lankan montane rain forest
As in other areas in the tropics where perennial crops have been integrated with forest trees (Bhagwat et al, 2008; Parthasarathy, 1999; Pascarella et al, 2000; Rivera et al, 2000; Rivera & Aide, 1998), in parts of Asia many forests have been cultivated with the high-value spice crop cardamom (Elettaria cardamomum (L.) Maton) (Buckingham, 2004; Kumar et al, 1995; Reyes et al, 2006)
Summary
Agro-ecosystems are important elements of many tropical landscapes, as they contribute to local livelihoods and provide environmental services. Cardamom cultivation and management involves the selective removal of canopy trees and regular maintenance by removal of competing plants in the forest understorey (Anon, 2002; Bandaratillake, 2005; Buckhingham, 2004; Kumar et al, 1995). This system of cultivation may hinder the capacity of forests to regenerate and undermine their conservation value (Ashton et al, 2001). Research on restoration techniques for high conservation value forests affected by repeated cardamom cultivation should be a high priority to conserve biodiversity and ecosystem services they support
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