I agree with your description. But looking at writings from the period that use that exact phrase they go on to detail the abatis I described. I have seen many references to this type. Usually placed between the skirmish line rifle pits and the main line of battle.

"The trees were felled so that the branches reached towards the enemy's line. The ends of branches were sharpened to jagged points, becoming abates themselves, and the leaves, foliage, and underbrush were cleared away. Coniferous trees, such as the common pine found throughout much of north-central Virginia, were ideal for this purpose. The ever-present underbrush was also cut and looped over and the tops twisted."

These types of obstructions were used at the 2nd Battle of Corinth, although they had been placed many weeks earlier (rotted) and had lost their strength and elasticity.

Another idea I had was it maybe a "blow-down" from a storm.

David