protected boolean updateLodOffCount(final LodCalculator lodCalculator) {

        if (lodCalculator.isLodOff()) {
            // we want to calculate the base lod at least once
            if (lodOffCount == 1) {
                return true;
            } else {
                lodOffCount++;
            }
        } else {
            lodOffCount = 0;
        }

        return false;
    }
Call this when you remove the terrain or this control from the scene.
It will clear up any threads it had.
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainLodControl.java