Drainage and Stand Growth Response in Peatland Forests—Description, Testing, and Application of Mechanistic Peatland Simulator SUSI

Abstract

Drainage is an essential prerequisite in peatland forest management, which generally, but not always, increases stand growth. Growth response depends on weather conditions, stand and site characteristics, management and biogeochemical processes. We constructed a SUSI-simulator (SUoSImulaattori, in Finnish), which describes hydrology, stand growth and nutrient availability under different management, site types and weather conditions. In the model development and sensitivity analysis, we used water table (WT) and stand growth data from 11 Scots pine stands. The simulator was validated against a larger dataset collected from boreal drained peatlands in Finland. In validation, SUSI was shown to predict WT and stand growth well. Stand growth was mainly limited by inadequate potassium supply, and in Sphagnum peats by low oxygen availability. Model application was demonstrated for ditch network maintenance (DNM) by comparing stand growth with shallow (−0.3 m) and deep ditches (−0.9 m): The growth responses varied between 0.5 and 3.5 m3 ha−1 in five years, which is comparable to experimental results. SUSI can promote sustainable peatland management and help in avoiding unnecessary drainage operations and associated environmental effects, such as increased carbon emissions, peat subsidence, and nutrient leaching. The source code is publicly available, and the modular structure allows model extension to cost–benefit analyses and nutrient export to water courses.

Controls of Organic Carbon and Nutrient Export from Unmanaged and Managed Boreal Forested Catchments

“…Likewise, it has been discovered that TN and TP concentrations are much higher among drained peat-dominated catchments in comparison with unmanaged (undrained) peatlands [21]. We suppose that the effect of drainage on N and P concentrations is related to increased nutrient mineralization and aerobic decomposition of the organic surface layers [64]. Moreover, the results of the present study are consistent with Nieminen et al [21,85] in suggesting that peatland drainage is at least in part responsible for the increased TN and TP export from boreal forests.…”

“…Drainage is linked to hydrological conditions in the catchment and thus affect leaching [63], resulting in higher leaching of TOC. In less intensively drained areas TOC is not leached readily because organic matter decomposition is slowed down by higher water table [64]. While in more intensively drained areas water flow path and water residence time are shorter [65] thus increasing leaching, in less drained sites these are longer, allowing more efficient retention [66] and biodegradation of TOC during the transport [52].…”

Defining guidelines for ditch depth in drained Scots pine dominated peatland forests

“…The hydrological model of SUSI simulator has also been successfully applied in two recent studies, which provide further confidence on WTD predictions (Leppä et al 2020b;Laurén et al 2021).…”

“…We applied the hydrological modules of SUSI simulator described in detail in Laurén et al (2021) to model how WTD responses to drainage parameters, peat characteristics, stand volume, and climatic conditions in peatland forests. The model simulates daily WTD variation across a crosssection of a forested drainage strip (Fig.…”

“…The goal of this study is to provide new guidelines for the planning and implementation of DNM in drained peatland forests which incorporate ditching parameters, the quality and thickness of the peat profile, stand water use, and climatic conditions. To accomplish this, we use a process-based hydrological model SUSI (Laurén et al 2021) to determine the minimum ditch depth (later referred as the effective ditch depth) necessary to keep the late summer WTD below a threshold value determined based on previous literature. The study focuses on Scots pine (Pinus sylvestris L.) dominated stands, which are the most common targets of DNM in Finland.…”