Effects of an experimental drought on the functioning of a cacao agroforestry system, Sulawesi, Indonesia

Abstract

Agroforestry systems may play a critical role in reducing the vulnerability of farmers' livelihood to droughts as tree-based systems provide several mechanisms that can mitigate the impacts from extreme weather events. Here, we use a replicated throughfall reduction experiment to study the drought response of a cacao/Gliricidia stand over a 13-month period. Soil water content was successfully reduced down to a soil depth of at least 2.5 m. Contrary to our expectations we measured only relatively small nonsignificant changes in cacao (À11%) and Gliricidia (À12%) sap flux densities, cacao leaf litterfall ( 1 8%), Gliricidia leaf litterfall (À2%), soil carbon dioxide efflux (À14%), and cacao yield (À10%) during roof closure. However, cacao bean yield in roof plots was substantially lower (À45%) compared with control plots during the main harvest following the period when soil water content was lowest. This indicates that cacao bean yield was more sensitive to drought than other ecosystem functions. We found evidence in this agroforest that there is complementary use of soil water resources through vertical partitioning of water uptake between cacao and Gliricidia. This, in combination with acclimation may have helped cacao trees to cope with the induced drought. Cacao agroforests may thus play an important role as a drought-tolerant land use in those (sub-) tropical regions where the frequency and severity of droughts is projected to increase.

Response of cocoa trees (Theobroma cacao) to a 13-month desiccation period in Sulawesi, Indonesia

“…The use of deuterium as a natural tracer in this stand showed that these species absorbed water from different horizons (Schwendenmann et al 2010) as the dD signature, i.e. the deuterium to H ratio in the water molecules, measured for xylem sap in February 2007 suggested that water uptake by cocoa occurred primarily in the 0-30 cm horizon, whereas Gliricidia obtained most of its water from depths [30 cm.…”

“…While this decline in W r may be partly attributable to tissue dehydration, it may also suggest that cocoa can achieve significant osmotic adjustment within its roots, thereby helping to stabilise plant water status and sustain continued leaf, stem and root growth. Third, the overstorey Gliricidia trees are likely to have reduced water use by cocoa by shading its canopy (Valle et al 1987), while competition for water was presumably limited by the spatial segregation of the root systems (Schwendenmann et al 2010). A further possible explanation for the absence of any reduction in productivity may be that the experiment was not designed to reduce relative humidity in the stands, as happens during natural droughts.…”

Mengintegrasikan Adaptasi ke dalam REDD+: Dampak Potensial dan Rentabilitas Sosial di Setulang, Kabupaten Malinau, Indonesia

“…Sumber: Sastry (1988) Hasil kakao (Theobroma cacao) dipengaruhi oleh kondisi lingkungan selama pembungaan, polinasi, pembentukan buah, dan pengembangan buah serta proses maturasi (Schwendenmann dkk. 2010).…”

Integrating adaptation into REDD+: potential impacts and social return on investment in Setulang, Malinau District, Indonesia

“…Cocoa (Theobroma cacao) yields are influenced by environmental conditions during flowering, pollination, fruit set and fruit development and maturation (Schwendenmann et al 2010). Nonshaded monocultures are significantly more sensitive than cocoa grown in shaded agroforests.…”

“…Farmers in Sulawesi reported yield declines of up to 38% after strong ENSO-related droughts in 1997 and 2002 (Keil et al 2008); drought events can induce yield reductions of up to 50% . On the other hand, increases in rainfall can lead to increases in yield losses due to black pod disease (Phytophthora palmivora) (Schwendenmann et al 2010).…”