O objetivo deste trabalho foi avaliar o efeito das árvores de pau-branco (Cordia oncocalyx) sobre parâmetros fisiológicos, altura e biomassa do milho, em diferentes distâncias das árvores, em sistema agrossilvipastoril. Utilizou-se o delineamento experimental de blocos ao acaso, com quatro tratamentos (distâncias do caule das árvores de 1, 2, 3 e 4 m), além do controle (plantas do cultivo tradicional), e cinco repetições. Cada parcela consistiu de uma árvore de pau-branco, ao centro, e linhas de milho plantadas nas quatro distâncias avaliadas do caule. As medidas fisiológicas e a produção de matéria seca foram registradas aos 30, 60 e 90 dias após o semeio do milho. As plantas sob a copa do pau-branco, a 1 e 2 m do caule, tiveram suas trocas gasosas, altura e produção de matéria seca afetadas pelas árvores. As plantas cultivadas a 3 m do caule tiveram desempenho semelhante ao observado no cultivo tradicional, e as cultivadas a 4 m apresentaram maior fotossíntese, condutância estomática, transpiração, altura e produção de matéria seca. As plantas de milho sob a copa são afetadas negativamente pelo sombreamento das árvores, enquanto as plantas fora da copa podem se beneficiar da presença das árvores no sistema.

The objective of this work was to evaluate the effect of "pau-branco" (Cordia oncocalyx) trees on physiological parameters, height, and biomass of maize at different distances from the trees in an agrosilvipastoral system. The experimental design was a randomized complete block with four treatments (distances from trees of 1, 2, 3, and 4 m), besides a control (plants cultivated in the traditional system), and five replicates. The plots consisted of one "pau-branco" tree at the center, and maize rows planted at the four evaluated distances from the tree stem. Physiological measurements and dry matter production were recorded at 30, 60, and 90 days after the sowing of maize. The plants under the canopy of "pau-branco" - at 1 and 2 m from the stem - had their gas exchange, height, and dry matter production affected by the trees. The plants 3 m away from the stem had similar performance to those in the traditional system, and the plants at 4 m of distance had higher photosynthesis, stomatal conductance, transpiration, height, and dry mass production. Maize plants under the canopy are negatively affected by tree shading, whereas plants outside the canopy can be favored by the presence of trees in the system.

Physiological differences in the Cordia oncocalyx tree growing at different densities in two distinct areas were investigated. An agrosilvopastoral system (AGP) and a secondary forest (SF) were studied. Under both types of land-use, C. oncocalyx presented a relative frequency of approximately 50%, and absolute densities of 670 and 80 individuals per hectare, respectively. Net photosynthesis (A), stomatal conductance (g s), and transpiration (E) were measured, and the SPAD index was recorded in sun leaves from the canopy and shade leaves from the lower canopy, in both the wet and dry seasons. We quantified the dry biomass of leaves and fruit on a per-tree basis at the end of the wet season. Net photosynthesis was higher in shaded leaves in the AGP in the wet season, reaching an average of 4.8 μmol m-2 s-1 against 3.2 μmol m-2 s-1 under SF. As trees began to shed their leaves at the beginning of the dry season and more radiation reached the shaded leaves, there was an increase in SF for A, depending on the intensity of light reaching the leaves. In the sun leaves, gas exchange was similar for the land-use systems during the wet season, but stronger in AGP than under SF during the dry season. This happened when the leaves in AGP retained more relative water content during a period of low gravimetric levels of the soil water. The lower tree density in AGP promoted a higher SPAD index and dry biomass in both the sun and shaded leaves, and allowed greater A, E and g s rates in the sun leaves at the beginning of the dry period.