This has been eating at me for a few years now. I believe I read this in one of the 'best sci-fi of the year' aggregations.
The plot centers around an old warrior living in peace in a small town. He was once part of a unit or army that had been fighting a war for hundreds or thousands of years. I don't think the town people know about the war or even that these two species exist (because they hide/camouflage maybe).
At some point, the warrior realizes that the enemy has found him and will be attacking soon. He then starts performing some sort of ritual meant to individually call his old friends from the unit, but each ritual reveals that they have died.
Eventually his enemies arrive on the planet (after numerous signs) and he has to fight alone and knows he will probably die. I believe the fighting was primarily fencing/sword fighting. Also, the warrior is some sort of plant species and he grows bark as a shield.