Temporal dynamics of soil moisture in a northern temperate mixed successional forest after a prescribed intermediate disturbance

TitleTemporal dynamics of soil moisture in a northern temperate mixed successional forest after a prescribed intermediate disturbance
Publication TypeJournal Article
Year of Publication2013
AuthorsHe L, Ivanov VY, Bohrer G, Thomsen JE, Vogel CS, Moghaddam M
JournalAgricultural and Forest Meteorology
Pagination22 - 33
Date Published10/2013

Forested ecosystems may experience intermediate disturbances that involve changes of crown-scale canopy characteristics. When such changes occur, soil moisture under disturbed canopy may become either drier or wetter, depending on the interplay between small-scale hydrological processes, tree-scale vegetation function, and meteorological forcing. Understanding the contributing factors that impact small-scale soil water dynamics is vital for predicting long-term and larger-scale changes of forest hydrology following disturbances, succession, and management processes. In this study, we initiated half-hourly,three-meter deep measurements of soil moisture at four plots in a northern temperate mixed forest near the University of Michigan Biological Station. Two of the plots (one aspen- and the other oak dominated) are located near the AmeriFlux tower; this forest area represents an undisturbed control site. Two other plots are located near the Forest Accelerated Succession Experiment (FASET) flux tower. An intermediate disturbance was prescribed in this area through stem girdling of all canopy-dominant, early successional aspen and birch trees to simulate the anticipated large-scale succession process in the Upper Great Lakes area. The data collected at the four plots provide observational evidence of changes in hydrological dynamics that were induced by species-specific crown-scale disturbances of the canopy structure. Data analysis reveals that the soil water storage under the girdled aspen was persistently higher, as compared to the undisturbed plots over the observational period of 2009–2011. The study argues that the larger water storage resulted from increased net precipitation and reduced transpiration during growing seasons following the girdling operation. These processes “out competed” the presumably enhanced interception and transpiration by understory plants as well as increased soil evaporation. Additionally, surface soil layer at the disturbed plot exhibited highest temporal variability among all monitored plots. The moisture profiles at the four plots were different, with the disturbed plot exhibiting relatively wetter shallow soil layers. Furthermore, water loss at the disturbed plot was concentrated in shallower soil layers, signifying a shift of uptake and/or change of dominant processes.