Pruning and thinning

State of the art

There are multiple discrepancies in the literature on cocoa pruning. A mid-century study trial on Ghanaian cocoa showed that even though pruned cocoa trees were initially higher yielding, yields were lower in the following years. Some authors found discretionary pruning to have a positive effect on yields while others estimated a non-significant negative effect (Balasimha, 2009). The positive effects of pruning, however, can lower costs of chemical fertilizer and pesticides. Sanitation pruning, for example, reduces the contagion of frosty pod rot disease (Bieng, et al. 2017) and black pod rot if done along with other disease management methods (Ndoumbe-Nkeng, et al. 2004). Cocoa leaves are highly sensitive to winds; therefore, shade tree pruning should be reduced during the Harmattan in West Africa, for example (Schroth, et al. 2016). Excessive pruning should be avoided as it can significantly reduce carbon stocks (Schroth, et al. 2016).

TYPES OF PRUNING

Sanitary pruning:

Removal of diseased or pest affected pods and branches. In some cases (e.g. CSSV in West Africa) the complete tree has to be cut down/

Reduce production losses due to disease + Less pesticide required

Shade tree pruning:

Cutting of branches of shade trees. Pruning frequency depends on re-growth rate and cocoa life-cycle stage. Determines rain throughfall, sunlight reaching cocoa trees, plot temperatures, evapotranspiration, etc.

Microclimate management + Increase yields after seedling stage + Remains used as biomass increase soil nutrient richness

Formative pruning:

Cutting of cocoa branches for improved plant structure.

Increase cocoa yields and resource efficiency

Outlook

It is hard to separate the effects of pruning on a plantation, intensification efforts are often coupled with other measures such as increased fertilizer use, replanting and tree removal (Schroth, et al. 2016). Pruning methods should vary according to the species present in the plot and the level of self-shading of the cocoa plant. While much is known about legume trees there is a lack of research on native tree pruning (Tscharntke, et al. 2011). More research is needed into pruning regimens of different shade tree species and more training of farmers is required as they often lack management and pruning experience to manage the cocoa farm microclimate (Clough, et al. 2009).

Importance in terms of CSA

Productivity: The yield effects of pruning are unclear, however, reductions in pest and disease incidence may be conducive to higher yields. Adequate microclimate management through pruning in agroforestry systems may also be helpful in balancing the yield and shade cover trade-off.

Adaptation: Pruning increases the adaptation capacity of farmers, especially when they can make use of weather forecasts to improve the timing of pruning. After prolonged and intensive rainfall, pruning increases aeration of the farm and reduces humidity levels that may be favourable for the spread of fungal diseases. As the variability in the climate increases farmers will become increasingly reliant on short-term adaptation practices like pruning.

Mitigation: Excessive pruning may lead to the release of significant levels of carbon stocks. Nonetheless, pruning may also improve plant structure and growth, leading to greater carbon stocks. Pruning remains increase soil organic matter and reduce the dependency of farmers on fertilizers, thereby somewhat reducing GHG emissions.

Complexity and link to other practices

Pruning is related to several CSC practices, and success in the implementation of these practices partially depends on adequate pruning regimes. The remains of regular pruning can be left as biomass on the soil to increase its nutrient richness (Jacobi, et al. 2015). Pruning reduces pest and disease incidence, (Akrofi-Atitianti, et al. 2018). In cocoa agroforestry systems, legume shade trees (Gliricidia and Erythrina) are recommended since they have the capacity to re-grow quickly and provide large amounts of nitrogen to the soil, this requires frequent pruning.

Key studies

– Balasimha, D., 2009. Effect of spacing and pruning regimes on photosynthetic characteristics and yield of cocoa in mixed cropping with arecanut. Journal of Plantation Crops, 37(1), pp.9-14.

– Niether, W., Armengot, L., Andres, C., Schneider, M. and Gerold, G., 2018. Shade trees and tree pruning alter throughfall and microclimate in cocoa (Theobroma cacao L.) production systems. Annals of Forest Science, 75(2), p.38.

– Tscharntke, T., Clough, Y., Bhagwat, S.A., Buchori, D., Faust, H., Hertel, D., Hölscher, D., Juhrbandt, J., Kessler, M., Perfecto, I. and Scherber, C., 2011. Multifunctional shade‐tree management in tropical agroforestry landscapes–a review. Journal of Applied Ecology, 48(3), pp.619-629.

Study cases

Case study 1: Bolivia

Shade trees and tree pruning alter throughfall and microclimate in cocoa (Theobroma cacao L.) production systems – Niether, et al. 2018

Background

The structure of the canopy in shaded cocoa agriculture, including tree species and density, determine the microclimate and throughfall. This structure can be modulated and adapted through the practice of regular pruning. The authors review results from a trial in Bolivia in the period 2013-2015. The evaluation was carried out in three different cocoa production systems: monoculture, agroforestry, and successional agroforestry.

Relation to CSA

CSC encourages the adoption of agroforestry systems and the practice of regular pruning to increase plant productivity. Climate change is likely to increase the incidence of climate extremes. Full-sun intensification provides no protection against increased climate variability. Agroforestry systems in combination with pruning allow farmers to regulate microclimate conditions. Agroforestry systems have higher soil moisture than full-sun plots. Heavy pruning reduces the temperature regulating capacity of the canopy, but it increases throughfall. Pruning timing is crucial, throughfall should be encouraged in dry periods without compromising the temperature buffering capability of the canopy cover.

Case study 2: Indonesia

The effect of pruning on photosynthetic rate of cacao trees in a novel cropping system – Susanti, et al. 2017

Background

A lack of literature on the effect of pruning, trellis, and branch number on yields and photosynthesis motivated this field experiment in the Mars Cocoa Research Station in Sulawesi, Indonesia. The trial took place over a three-year period in one monoclonal setting and one setting with two clones under seven different pruning treatments (combinations of trellis application ad branch numbers). Measurements of photosynthesis and stomatal conductance were taken. Pruning was carried out four times a year, six weeks after leaf flushing.

Relation to CSA

Pruning aids in balancing the trade-off between shade cover and yields. It regulates canopy light interception and microclimate. A CSA cocoa plot is characterized by an agroforestry production system to increase climate change resiliency and regular pruning to increase soil biomass and yields through increased sunlight. The main objective of the study is related to the productivity pillar of CSC: pruning leads to increases in the photosynthetic rate of cocoa and consequently higher yields. Although the authors do not refer to adaptation benefits from pruning, they find differences in transpiration rates between different canopy heights, which may be useful for regulating on-farm humidity levels. Results support CSA advice on frequent pruning in terms of increasing productivity. Trellis shade systems, which may be more labor intensive, did not have a significant effect on photosynthetic rates and neither did the number of branches of the cocoa plant.

Case study 3: India

Effect of spacing and pruning regimes on photosynthetic characteristics and yield of cocoa in mixed cropping– Balasimha, 2009

Background

Results from this study are based on a trial conducted in a research station in Vittal, India, by the Central Plantation Crops Research Institute. Cocoa is a minor crop in India and is typically intercropped with arecanut and coconut. In this experiment, cocoa was intercropped with arecanut. Previous research by the same author suggested that there is a significant interaction between pruning regimes and tree spacing. Two spacing treatments were applied (2.7m x 2.7m and 2.7m x 5.4) under three different canopy sizes. Arecanut was planted four years before cocoa and cocoa pruning started four years after planting. Results were recorded for 10 years, which is an unusually long period for cocoa productivity studies.

Relation to CSA

The effects of pruning on cocoa productivity are directly related to canopy cover and light interception. Pruning also has significant effects on temperature, humidity, and vapor pressure deficits. CSA training manuals recommend pruning as a method of increasing yields in agroforestry systems and adapting to short-term climatic changes. The results of this study relate to pruning for improving adaptation and productivity outcomes. CSC also recommends cocoa tree spacing of 3mx3m, close to the 2.7mx2.7m under study by Balasimha (2009). Cocoa pod yield increased progressively with time and was affected by the interaction between cocoa tree spacing and canopy cover. The pruning regime that left the largest canopy cover (16-20 cubic meters) and spacing between cocoa trees was shown to be the highest yielding. This apparently refutes the notion that the greater the canopy cover the lower the yields, suggesting a more nuanced relationship between these two variables. The author also finds a significant interaction effect between cocoa tree spacing and the pruning regime.