A friend asked me to summarize what's meant by this term. Since winelovers are a lot more familiar with oxidation, I could simply say that to chemists, reduction is its opposite. Reductive strength is just a synonym for anti-oxidative power.
But this didn't register much. So I said that when you buy roses at the florist, if you're five years old you buy the most open, beautiful ones, but if you are older and wiser, you buy them when they've just begun to open or even totally closed, if you want them to last the longest. You weigh the joy of the initial presentation against the shelf life.
Same with wine. Wines with staying power tend to be a bit closed in youth. White Burgundies, unlike their California Chardonnay cousins, take around four years to start showing well. We are only just releasing the 2003 vintage of my Chablis-style Faux Chablis for this reason, and I assure you that it is not stale goods.
In addition to being closed, reduction often produces stinky aromas like rotten egg (hydrogen sulfide, not to be confused with sulfites) and deisel or onion (ethyl mercaptan). This stinkiness, if not too strong, will disappear with a year in the bottle if not too strong, and as I explain in The Good Side of Stinky, is really a mark of quality and integrity.
Staying power is enhanced by living soil practices (which also give minerality) proper ripeness (not too much), and cellar practices such as yeast lees stirring. Since they don't pass oxygen, screwcaps will also tend to exacerbate reductive characteristics more than cork ageing.