Life history, ecology and conservation of riparian cottonwoods in North America. The number and weight of cottonwood seeds. Journal of Biogeography 17:59–73.īessey, D.E. Climatic and hydrologic effects on the regeneration of Populus angustifolia James along the Animas River, Colorado. The model will facilitate analyses of the reproductive ecology of riparian cottonwoods and also permit the prescription of stream stage patterns for cottonwood seedling recruitment along dammed rivers.īaker, W.L. Flood events with recurrences of about 1 in 5 to 1 in 10 years often satisfy the model and provide stream stage patterns with a gradual decline through the recruitment box. The recruitment box model is consistent with dendrochronological interpretations that moderate flood events are naturally required for cottonwood recruitment. The rate of stream stage decline is also critical for seedling survival and should not exceed 2.5 cm per day. fremontii, which grow more rapidly than Tacamahaca species and occur in warmer areas with longer growing seasons (ii) along larger rivers that are characterized by more gradual stage fluctuations and (iii) along streams with finer substrate. Within this range, higher elevation establishment occurs (i) for the Aigeiros cottonwoods, Populus deltoides, and P. The combination of root growth and capillary fringe define the successful recruitment band, which is usually from about 0.6 to 2 m in elevation above the late summer stream stage. A capillary fringe exists above the water table and is often 30 to 40 cm in elevation, but can range from about 5 to 130 cm depending on substrate texture. Along the ‘losing’ streams in semi-arid regions, the riparian water table is an almost horizontal extension from the stream stage.

Cottonwood roots grow about 0.5 to 1 cm per day or 60 to 100 cm in the first year. However, the vast majority of seedlings die, primarily due to drought stress, as root growth is insufficient to maintain contact with the receding zone of moisture.

Germination is rapid, and initial seedling establishment is often prolific. The receding stream exposes moist sites upon which seeds land after transport by wind and water. In western North America, cottonwood seed dispersal generally occurs after annual peak river flows.

This paper describes the ‘recruitment box,’ an integrative model that defines the stream stage patterns that enable successful establishment of riparian cottonwood seedlings.

Cottonwood r lee smith