Many studies of plant competition have been directed towards understanding how plants respond to density in monocultures and how the presence of weeds affects yield in crops. In this Botanical Briefing, the development and current understanding of plant competition is reviewed, with particular emphasis being placed on the theory of plant competition and the development and application of mathematical models to crop-weed competition and the dynamics of weeds in crops. By consolidating the results of past research in this manner, it is hoped to offer a context in which researchers can consider the potential directions for future research in competition studies and its application to integrated weed management.

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A central claim of community-based adaptation (CBA) is that it increases resilience. Yet, the concept of resilience is treated inconsistently in CBA, obscuring discussion of the limitations and benefits of resilience thinking and undermining evaluation of resilience outcomes in target communities. This paper examines different participatory assessment activities carried out as part of CBA case studies in Timor-Leste and Solomon Islands. The activities and their outputs were assessed against ten characteristics of resilience previously identified in a systematic review. The findings offer support to the claim that CBA can build resilience in target communities, revealing the inherent strengths of CBA in relation to resilience. However, it is necessary for CBA assessments to simultaneously incorporate activities that consider cultural, political, economic and ecological factors influencing resilience within and between communities. This may demand multiple staff with different skills. The findings also highlight the importance of politics and power in shaping adaptive capacity. In particular, addressing the highly context specific nature of social, cultural and political relations demands an approach that is situated in and responsive to local realities. Overall, our case study suggests that using the ten characteristics as an analytical framework offers support to practitioners looking to develop, implement or evaluate CBA assessment activities. Yet within this, it is critical that a focus on increasing resilience through CBA does not preclude transformation in social relations. Realising the potential to support resilience and transformation requires CBA practitioners to acknowledge the multifaceted nature of resilience, whilst also paying close attention to multiple potential barriers to equitable adaptation.

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Summary 1.Intercropping, the practice of growing two or more crops in close association, is attracting increasing interest in developed countries, primarily due to claims that it can provide increased yields in an environmentally sustainable manner. 2. The land equivalent ratio (LER) is frequently used to attest the claim that intercropping produces a greater total biological productivity per unit area of land than monocropping. However, similar to other indices, the value of the LER is dependent on the relative densities of the two crops and fails to provide an indication of the optimal crop density combination required to produce maximum biological productivity. We used an alternative methodology to predict the optimum density for planting two crops in a mixed stand. 3. Maize and beans were grown both in monoculture and in intercropped stands at a range of densities. Monocrop stands of both maize and bean displayed an asymptotic yield-density relationship. When a second crop was introduced into the stand there was no effect on the yield of maize, but there was a large reduction in the yield of bean. 4. The LER did not demonstrate an unequivocal advantage to intercropping. Less than a third of the LER values, over the range of densities considered, were greater than one, although none was significantly different to unity. The highest values were obtained from those plots sown with a high density of maize.5. An alternative method of analysing the biological productivity of an intercrop system is proposed. This approach requires a combination of (i) an additive experimental design, (ii) the use of a regression model to measure the competitive effect of two species, and (iii) the presentation of the net competitive effect on individual and total yields using a response surface. The reciprocal model was used to dissociate and quantify intra-and interspecific competition, estimate a competitive equivalence coefficient and predict the individual yields of the full complement of density combinations included in the maize and bean experiment. 6. The model explained up to 90% of the variation in the observed yields of maize and bean in an intercrop. An inspection of the response surface for the LER indicated that the minimum density combination required to produce the maximum yield advantage within the density range considered comprised maize being planted at a density of 11 plants m −2 and bean being planted at a density of 39 plants m −2 . Although this combination would provide the maximum biological productivity, it is considered unlikely to provide the maximum gross economic margin. 7. The above methodology may provide a useful tool for managing competition, either between two or more crops in an intercrop, or within a crop-weed interaction.

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