Four North Dakota reclaimed mined sites 1 to 4 years old were studied for patterns of species colonization, biochemical interaction among species, competitive phenomena, and management applications. Kochia scoparia, a colonizer, was the dominant species for the first 2 years, but was completely eliminated by the fourth year; the planted agropyron grasses concomitantly increased during the 4-year period. Competition experiments between kochia and agropyron revealed that kochia initially acted as a "nurse" crop for agropyron establishment, but later in the first season began to shade excessively, reducing agropyron tillering. Studies on the plant population biology of kochia showed that it conformed well to several established laws governing yield versus density relationships. Field and growth chamber experiments revealed that decaying kochia leaves and roots were toxic to kochia growth and were partially responsible for the rapid demise of the species. Chemical analysis of the soils and plant tissues indicated nutritional imbalances may be responsible for the autotoxicity. Another bioassay experiment implicated allelochemics to be important in several other colonizing species. Mowing the first year colonizing species just prior to seed set provided to be effective in reducing weed populations and improving planted agropyron populations in the second year.