Seedlings of winged elm (Ulmus data Michx.), bur oak (Quercus macrocarpa Michx.), black walnut (Juglans nigra L.), eastern redcedar (Juniperus virginiana L.), and loblolly pine (Pinus taeda L.) were treated in nutrient solution with ring-labeled 14C-tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or 14C-hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione]. Four hours later, 14C was detected in all sections of winged elm treated with 14C-tebuthiuron and 14C-hexazinone. Root absorption of the tebuthiuron label by the other species occurred in the order: loblolly pine > bur oak > black walnut = eastern redcedar. The sequence of 14C-hexazinone absorption was: loblolly pine > black walnut ≥ bur oak = eastern redcedar. Foliar accumulation of the tebuthiuron label occurred in the order: bur oak > loblolly pine > eastern redcedar = black walnut, whereas the sequence with hexazinone was loblolly pine > bur oak > black walnut = eastern redcedar. The presence of the three metabolites of hexazinone in loblolly pine suggests that it may be resistant to hexazinone as a result of its ability to degrade hexazinone rather than its ability to limit uptake.

A record of estimated annual (prior August to current July) precipitation derived from a regional bur oak (Quercus macrocarpa Michx.) tree-ring chronology indicates that southern Manitoba's hydroclimate has been relatively stable over the last 200 yr. Although this stability was interrupted briefly by pronounced wet intervals in the late A.D. 1820s and 1850s, hydroclimatic conditions since permanent Euro-Canadian settlement were much less variable and persistent than those prior to A.D. 1790. The reconstruction indicates that the Red River basin experienced extremely dry conditions between A.D. 1670 and 1775, with below-normal precipitation occurring approximately 2 years out of 3. Annual precipitation was estimated at more than two standard deviations below the mean during A.D. 1477, 1485, 1556, 1595, 1612, 1644, 1661, 1743, 1900, and 1980. Comparisons with limnological records from North Dakota and Minnesota suggest that multidecadal fluctuations in regional hydroclimate have been remarkably coherent across the northeastern Great Plains during the last 600 yr. However, individual dry years in the Red River basin were usually associated with larger scale drought across much of the North American interior.