Age and growth of cottonwood trees along the Missouri River, North Dakota

The relict plains cottonwood (Populus deltoides subsp. monilifera) forest along the Missouri River between Lakes Sakakawea and Oahe includes trees as large as two meters in diameter. We cored 24 of these trees to determine their age and suitability for flow reconstruction. Because most of the trees were rotten in the center, we developed a method to estimate the date of the center ring that accounts for the increase in ring width toward the center. Estimated center ring dates were as early as 1806. Cottonwood growth at a dry site was correlated with April–August flow prior to construction of Lake Sakakawea (1929–1953; r = 0.50, P = 0.011) and to Palmer Drought Severity Index following construction (1954–2014; r = 0.38, P = 0.003). We conclude that cottonwood rings can be used to improve reconstructions of Missouri River flows before the beginning of stream-gage records.