Abstract
Productivity of coffee plantations is threatened by both climate change and decreasing revenues of coffee growers. Using shade trees might protect against temperature variability, erosion and excessive radiation but there may be trade-offs in productivity and quality. While impacts of shade trees on arabica (Coffea arabica) have been reviewed, a global synthesis on robusta (Coffea canephora) coffee is lacking. We assessed how shade affects robusta growth and productivity, and what are the interactions and trade-offs. We conducted a systematic literature search in Web of Science and CAB s on 16 December 2019. Thirty papers fulfilled our inclusion criteria of being experimental studies on the impact of overstory trees with approximately half being from Brazil or India. Shade improved robusta tree growth and yield with some contrasting effects on physicochemical and biochemical properties. Shade (> 30%) was associated with reduced beverage quality. Significant interactions between shade and location, rainfall level and robusta clone were found. Among the clones tested, 06V, C153, LB1, GG229 and JM2 showed a higher productivity and growth (from + 17 to + 280%) under moderate shade (41–65%). This is the first meta-analysis of the effects of shade on robusta coffee. By synthesizing data from different studies, we highlight for the first time that the effect of shade on robusta coffee depends on tree age. Shade had positive impacts on older robusta trees (mean of 16 years), while the impact of shade on younger trees was either insignificant or negative. We highlight the importance of both clone type and tree ages. Research gaps included a lack of knowledge on the effects of shade with respect to coffee and shade tree age as well as interactive effects. More in-depth studies are needed to understand the mechanisms of how shade trees affect robusta coffee.
Highlights
Remaining publications were screened using the full text according to the following exclusion criteria: interview/questionnaire as the main process of data acquisition, no obvious relation with shade, observational units not based on robusta coffee plants or environment, paper not available after extensive acquisition attempt, paper unclear, intercropping of coffee plants only with ground-level crops
As shade is known to reduce biennial fluctuation of yield (Damatta 2004) and as yield has generally been measured among several years, this should not constitute a bias. In this meta-analysis, based on 30 peer-reviewed studies, we found that shade trees positively impacted growth, yield, physiological, photosynthetic, ecological and microclimatic variables of robusta coffee plants
Clones 06V, C153, LB1, GG229 and JM2 showed a higher productivity and growth under significant amount of shade (41–65%). These clones can be recommended for shade systems and farmers are likely to be interested in integrating shade trees with these clones as shade increases robusta coffee yield
Summary
More than 9 billion kilogrammes of coffee are consumed annually worldwide (International Coffee Organization 2016). Plants and Pathogens Group, Research Institute Land Nature and Environment, HEPIA, HES-SO University of Applied Sciences and Arts Western Switzerland, Jussy, Geneva, Switzerland. National Institute of Agronomical Research (INIAP) - Central Experimental Station of Amazonia, km 3 Vía Sacha - San Carlos, Cantón Joya de los Sachas, Province of Orellana, Ecuador. The consumption of coffee is steadily increasing with an average annual growth rate of 1.3%, since the coffee production year 2012–2013 (International Coffee Organization 2016). Large-scale intensive coffee production led to an increase in productivity per hectare resulting in reduction of shade trees inside the coffee agroecosystem, higher inputs costs (machinery, equipment, materials) and higher breakeven point (Rodriguez and Vasquez 2008)
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