Can a managed forest be healthier than a non-managed one?
I suspect you will see arguments both ways based on the definition of healthier. If healthy is natural, then no, one cannot manage a forest to be healhier than a natural forest. A natural forest has occasional fires, droughts, wind storms, pests, etc. As your inclusion on a limited basis implies, I believe the timeframe matters. Managed forests, like preventing forest fires, appears good until the US gets a few years of drought and has huge forest fires because the natural clearing of flammable debris from smaller fires was prevented. Harvesting a forest and planting faster-growing single variety trees is good for harvesting more wood, until a blight or pest wipes out the single specie. Diverse (natural) forests have better resistance to natural occurrences. Life is interesting. As some have noted, life exists everywhere on earth (e.g., hydrogen sulfide vents on the ocean floor, at the top of Mt. Everest) except in a test tube. After scientists created some complex amino acids in a test tube in 50s or 60s, with predictions of creating life in a test tube in years, it has yet to happen over 50 years later.