Interspecific interactions between olive trees and grapevines in vineyard agroforestry systems in an arid climate region
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In the face of climate change and environmental degradation, conventional viticulture risks the threats of reduced soil fertility, increased heat stress, water scarcity, unseasonal frost, extreme climate events, wind damage, reduced biodiversity, increased erosion, and increased pest and disease pressure. Agroforestry is a sustainable land-use system proven to address many of these conservation and production issues, and yet, agroforestry's applications in viticulture have been severely overlooked. This thesis summarizes the existing body of knowledge surrounding vineyard agroforestry systems in an extensive literature review, and also contributes new research about olive tree and wine grape vineyard agroforestry systems in an arid and irrigated grape growing region in Mendoza, Argentina. The existing body of knowledge surrounding vineyard agroforestry systems shows that the incorporation of trees into vineyards reduces pest and disease pressure, prevents wind damage and erosion, increases stomatal aperture and leaf area, and protects vines against heat and frost damage. Existing research on competition for resources in vineyard agroforestry systems suggests that competition for water may not affect grapevines in a negative way, but that competition for nutrients may affect vines within 4 m of trees, although other studies suggest that trees may actually improve vineyard soil quality. Existing literature also shows that vine yield is reduced within 4 m of trees. Our experiment on a Malbec/olive tree alley cropped vineyard agroforestry system examined the effects of olive trees on grape quality, growth, and production parameters at five different distances from an olive tree hedgerow. Results revealed that proximity of grapevines to the hedgerow was associated with significantly higher quality must, including higher glucose/fructose levels, higher brix levels, higher must density, and higher total acidity. However, within 4 m of the hedgerow, grapevines also experienced significantly lower yield, with yield reductions up to 50 [percent] in vines at 2 m from the hedgerow. Our study also revealed that there were no significant differences in nutrient status between treatments in any pattern that would indicate competition, suggesting that competition for nutrients was not a major competitive factor. The information summarized in this literature review, along with the results of our study, broaden our understanding of vineyard agroforestry systems in different growing contexts and can help determine under which conditions agroforestry should be utilized as an appropriate technology in vineyards. In an arid region with a tree-crop combination of olives and grapevines, the presence of trees was correlated with higher must quality but lower yields. Depending on winemaker goals, the beneficial effects that trees impart on grape must quality parameters, in addition to their whole-farm benefits and ecosystem services, may be determined to outweigh the negative effects that trees have on yield in the rows nearest to trees. Additionally, as many arid grape growing regions anticipate higher temperatures in the coming years due to climate change, utilizing trees in vineyards may be an adaptive strategy for preventing future quality and yield reductions.