Species richness in agroecosystems can be important to sustain production, reduce the impact of climate change, conserve biodiversity and preserve ecosystem services. A major practical reason small farmers and agroecologists have for supporting mixtures of two or more crops - as opposed to the corresponding set of monocrops – is that absolute yield and land use efficiency can be higher in multicrops. Unfortunately, this is not always the case. Furthermore, these two benefits (namely, DY>0 and RYT>1) are frequently confused and do not necessarily go hand in hand. The tradeoff between them has ecological explanations and also practical consequences. Both indexes are sensitive to environmental change. Multicrops in some parts of the tropics are subject to strong spatial and temporal variation in average soil moisture and to a historical reduction in this resource due to climate change. It is not clear if and when DY>0 and/or RYT>1will persist in the face of reduced soil moisture, and how the relation between these benefits might change. In this paper we develop a relatively simple framework for analyzing these questions in specific cases.
Results/Conclusions
We propose a relative multicrop resistance index (RMR) that captures all possible scenarios of absolute and relative multicrop overyield resistance. We establish the RMR threshold values for the most relevant scenarios. We dissect the ecological components of RMR (defined as the relative change in DY components) to keep track of changes in the relation between DY and RYT and to better understand the ecological causes of different overyield resistance scenarios. For this purpose, we extend the analysis of DY components developed by Loreau and Hector (2001) and Fox (2005) to the case of a soil moisture gradient. We also provide simple graphical tools and suggested applying simple but robust statistical procedures to these compound variables (based on bootstrap methods) to compare RMR - and its component - among different multicrops, plant parts and/or multicropped species. This framework proved useful and consistent when analyzing data from a 128 microplot greenhouse experiment with small annual crops, arranged as seven-species multicrops and their corresponding monocrops, under two contrasting watering regimes.