Abstract
A prerequisite for sustainable peatland forestry is sufficiently low water table (WT) level for profitable tree production. This requires better understanding on controls and feedbacks between tree stand and its evapotranspiration, drainage network condition, climate, and WT levels. This study explores the role of spatial tree stand distribution in the spatiotemporal distribution of WT levels and site water balance. A numerical experiment was conducted by a three-dimensional (3-D) hydrological model (FLUSH) applied to a 0.5 ha peatland forest assuming (1) spatially uniform interception and transpiration, (2) interception and transpiration scaled with spatial distributions of tree crown and root biomass, and (3) the combination of spatially scaled interception and uniform transpiration. Site water balance and WT levels were simulated for two meteorologically contrasting years. Spatial variations in transpiration were found to control WT levels even in a forest with relatively low stand stem volume (<100 m3/ha). Forest management scenarios demonstrated how stand thinning and reduced drainage efficiency raised WT levels and increased the area and duration of excessively wet conditions having potentially negative economic (reduced tree growth) and environmental (e.g., methane emissions, phosphorus mobilization) consequences. In practice, silvicultural treatment manipulating spatial stand structure should be optimized to avoid emergence of wet spots.
Highlights
Large-scale drainage of peatlands and paludified forests during the 1930s–1980s has remarkably increased forest growth in Finland [1] and elsewhere in the boreal region (e.g., [2,3])
The effects of spatial stand distribution on hydrological processes and water table (WT) of a drained peatland forest were demonstrated in this study via numerical experiments using a distributed hydrological model
Comparison between the stand description scenarios revealed that the role of stand heterogeneity is significant in the spatial variability of WT level during a dry summer, and the variability is more sensitive to transpiration than that of rainfall interception
Summary
Large-scale drainage of peatlands and paludified forests during the 1930s–1980s has remarkably increased forest growth in Finland [1] and elsewhere in the boreal region (e.g., [2,3]). In Finland, peatlands contribute to the total forest growth by about 25% [4], and drainage efficiency continues to be the key factor in the management of peatland forests [5,6]. Water balance in drained peatlands is driven by meteorological conditions and controlled by (1) drainage efficiency, (2) peat type (hydraulic conductivity and water retention properties) and peat layer thickness, (3) underlying mineral soil type, (4) stand and ground vegetation properties, and (5) site topography. Hydrological effects of peatland forest drainage have been extensively studied with experimental approaches during the past decades. Forests 2018, 9, 645 the role of vegetation in particular, as controls of water table (WT) levels and their spatial and temporal variability, is still poorly understood.
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