The influence of dispersed trees on microclimatic conditions, gas exchange and productivity of maize (Zea mays L.) in a Grevillea robusta-based agroforestry system in semi-arid Kenya was examined to test the hypothesis that the benefits of shade seen in savannah ecosystems may be outweighed by competition for below-ground resources. Meristem temperature, cumulative thermal time, intercepted radiation, spatial distribution of shade and gas exchange were determined for maize grown as sole crops, in an agroforestry system, or under shade nets providing 25 or 50% reductions in incident radiation to discriminate between effects of shade and below-ground competition. The major benefit of shade was to reduce exposure to the supra-optimal temperatures experienced in many tropical regions, and which are predicted to become increasingly common by climate change models. However, although trees decreased photosynthetic photon flux density (PPFD) incident on understorey maize by ca. 30%, the yield reduction was much greater than in the 25% shade net treatment in four seasons providing contrasting rainfall. Maize yield was unaffected by 50% artificial shade in the driest season (168 mm) but decreased with increasing shade when rainfall was high (628 mm). Shade reduced meristem temperature and delayed flowering by 5-24 days depending on treatment and seasonal rainfall. Thermal time to flowering in the agroforestry system doubled from 600 to 1200 C day as rainfall decreased. Photosynthetic and transpiration rates for understorey maize were similar to the 25 and 50% shade treatments when rainfall was high, but were ca. 10% of those for unshaded sole maize in dry seasons. PPFD-saturated photosynthetic rate was initially similar in all treatments but fell sharply in the agroforestry system as the season progressed. Radiation conversion coefficients did not differ between unshaded sole and understorey maize. The results suggest that the ameliorative influence of tree shade was greater in low rainfall seasons, as in savannah systems, but that potential benefits were outweighed by below-ground competition. This may be managed by root-pruning trees.
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O CIFOR-ICRAF publica mais de 750 publicações todos os anos sobre agrossilvicultura, florestas e mudanças climáticas, restauração de paisagens, direitos, política florestal e muito mais – em vários idiomas..
CIFOR-ICRAF alcança impacto baseado na ciência. Conduzimos pesquisas inovadoras, fortalecemos a capacidade dos parceiros e nos engajamos ativamente no diálogo com todas as partes interessadas, trazendo os insights mais recentes sobre florestas, árvores, paisagens e pessoas para a tomada de decisões globais.
CIFOR-ICRAF aborda desafios e oportunidades locais ao mesmo tempo em que oferece soluções para problemas globais para florestas, paisagens, pessoas e o planeta.
Fornecemos evidências e soluções acionáveis para transformer a forma como a terra é usada e como os alimentos são produzidos: conservando e restaurando ecossistemas, respondendo ao clima global, desnutrição, biodiversidade e crises de desertificação. Em suma, melhorar a vida das pessoas.
CIFOR–ICRAF achieves science-driven impact. We conduct innovative research, strengthen partners’ capacity and actively engage in dialogue with all stakeholders, bringing the latest insights on forests, trees, landscapes and people to global decision making.
CIFOR–ICRAF publishes over 750 publications every year on agroforestry, forests and climate change, landscape restoration, rights, forest policy and much more – in multiple languages.
CIFOR–ICRAF addresses local challenges and opportunities while providing solutions to global problems for forests, landscapes, people and the planet.
We deliver actionable evidence and solutions to transform how land is used and how food is produced: conserving and restoring ecosystems, responding to the global climate, malnutrition, biodiversity and desertification crises. In short, improving people’s lives.
