Southern Swamp Ash

Ash Stratocasters have a bright top end and good bass response with a slight dip in the midrange. This provides for excellent note definition and clarity. Great for getting a tight, in your face, Dino tone. Ash Stratocasters will usually cut through the mix a little better than the other common Strat body wood. Also, they tend to work very we'll for three pickup / humbucker or dual rails in the brige position models as the body wood doesn't rob or de-emphasize the humbuckers or dual rails of their available high end. Excellent for a lead player in a two guitar player band format. Ash Strats excel in sustain.

From Guitar Player Magazine Online

Ash. Best known as the wood of classic ’50s Fender guitars, ash is most desirable in the form of swamp ash—wood taken from the lower portions of southern-grown wetland trees that have root systems growing below water level. Good swamp ash is both light and resonant, and generally carries a broad grain that looks great under a translucent finish. The swamp-ash sound is twangy, airy, and sweet. It offers firm lows, pleasant highs, a slightly scooped midrange, and good sustain. Ash from the upper portions of the tree has also been used, as has harder northern ash. Both tend to be denser and heavier, and have a brighter, harder sound that might be more useful when cutting, distorted tones are desired. Ash is traditionally used for single-wood, slab-bodied guitars, but has sometimes been employed by more contemporary designers in multi-wood (or laminated) bodies—most commonly with a carved-maple top, or as the top of a semi-hollow or chambered guitar with a back made from a different wood.

From John Suhr 

Swamp Ash – Popular in the 50's for electric guitars, this wood is alive and lightweight. Swamp ash just wants to vibrate. Bright and sweet at the same time with excellent grain patterns, all transparent finishes look great on Swamp Ash. One-piece Maple neck is a natural for Ash. Pau Ferro fingerboards also work well. Rosewood fingerboard on Ash body will give too much sizzle for many players. We would only build such combination if you are positive that this is what you want.

From Warmoth

Ash (Fraxinus americana).
Swamp Ash is a prized wood for many reasons. It is a fairly light weight wood which makes it easily distinguishable from Hard Ash. A Strat® body will normally weigh under 5 lbs. Many of the 50's Fenders were made of Swamp Ash. The grain is open and the color is creamy. This wood is a very nice choice for clear finishes. Swamp Ash is our second most popular wood. It is a very musical wood offering a very nice balance of brightness and warmth with a lot of "pop".

From USA Custom Guitars

SWAMP ASH - Has a tight bottom end (which we all like), scooped mids and a bright top end. It has a very quick attack when striking the strings - which is great for some players and bad for others. It has very open grain, which makes it a pain in the backside to finish. It is a very resonant wood, so it sounds phenomenal played clean. Great for Funk, Surf Music, Blues with a bite, Country twang, vintage Rock, and clean smooth Jazz.

From the Frank Falbo DRG Tonewoods article

Swamp Ash

Not to be confused with Northern "Hard Ash" Swamp Ash has huge, open pores with hard and soft layers within each ring of the tree. So you basically have a very rigid skeleton with open and softer pores throughout. It is very resonant across the whole frequency spectrum. It has clear bell-like highs, pronounced mids, and strong lows. It has some random combing away of mid frequencies, which will vary the sound per guitar more than Alder or Basswood. Two Ash bodies are more likely to sound more different from one another, whereas Basswood and Alder are more consistent. A heavier piece, or a piece from higher up on the tree will be more dead and lifeless. More dull sounding, because the wood is harder and more uniformly dense. So the sweetness of the soft open pores is gone, and left is the compressed sound of a rigid, non-responsive wood, without all the brightness and sustain of a harder wood or the openness of a softer wood.

Note the Fender Artist series guitar models using Ash for the body wood

Mark Knopfler Strat
Buddy Guy Strat, (non Polka Dot model).