Spatiotemporal Patterns and Environmental Drivers of Eastern Redcedar (Juniperus virginiana) Abundance along the Missouri River, USA

Abstract

ContextChanges in disturbance regimes, including reductions in flooding and geomorphic dynamism from dam construction and flow regulation, have facilitated invasion by eastern redcedar (Juniperus virginiana L.), an upland tree species, in the understory of floodplain forests along the Missouri National Recreational River (MNRR). ObjectivesOur aim was to determine the spatiotemporal patterns and environmental drivers of redcedar invasion along the MNRR. MethodsWe used the Normalized Difference Vegetation Index (NDVI) calculated from winter Landsat imagery to construct a time series of maps showing spatial changes in redcedar abundance and distribution from 1982-2017 in both riparian and upland habitats along the MNRR. We determined how environmental factors (e.g., soil drainage ability, flood recurrence interval, 1980s LULC, lateral distance to the river, and channel incision) have influenced current (2017) redcedar occurrence and abundance in riparian habitats using Random Forest Models (RFM). ResultsTime-series maps indicated that detectable redcedar cover occurred over less than 5% of the study area before 1985, increased steadily from 1985-2000, and more than tripled from 2000 to 2010. After 2010, redcedar abundance continued to increase in upland areas but declined following the 2011 Missouri River flood in the floodplain. RFMs indicated that river incision, distance to the river, soil drainage, 1984 LULC, and flood recurrence interval were important features influencing redcedar occurrence and abundance in the floodplain. Conclusion Unless preventive measures are implemented, lack of floods and ongoing flow regulation will enable the continued spread of redcedar along the MNRR and other regulated rivers in the eastern Great Plains.

Ecological traits of Saliceae and the species replacing them on the active floodplain

“…Not all woody species that invade floodplains fit neatly into the three ecological groups recognized here. For example, the upland conifer Juniperus virginiana is expanding onto the floodplain of the Missouri River (Illeperuma et al, 2023), while Rhamnus spp. and the native species Zanthoxylum americanum have increased on the Wisconsin River floodplain (Predick & Turner, 2008).…”

“…The spread of these species can be attributed primarily to changes in flow regimes but a contributory factor has probably been the effective dispersal of their fruits by birds. And other, local factors may also have been important—fewer fires in the case of the fire‐intolerant J. virginiana (Illeperuma et al, 2023), and a greatly increased deer population in the case of Rhamnus spp. and Z. Americanum , which are thorny shrubs and not readily browsed (Predick & Turner, 2008).…”