What does vine density have to do with wine quality?

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Dear Dr. Vinny,
What does vine density have to do with wine quality?
—Keith, Emeryville, Calif.
Dear Keith,
There are a lot of opinions about vine density out there, including a trending notion that densely planted vineyards produce grapes that make high quality wines. The thinking is that when vines are planted close together, they have to compete with each other for nutrients and water in the soil, which makes their root systems expand farther, ultimately delivering more complex elements of the terroir to the grapes.
It’s a popular thought, but vine spacing is just one of many factors in the vineyard that can potentially affect grape quality. And tight vine spacing can be tricky, requiring more labor, attention, irrigation lines and canopy management.
There are land considerations, too. Can the soil support the vines? Is it rich enough in nutrients? Is there enough water? Simple economics suggests that winegrowers are incentivized to plant as many vines as they can per acre so they can make as much wine as possible, but to make great wine, they need to find the magic combination of grapes, clones, rootstock, soils and spacing that will give the best quality.
—Dr. Vinny