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

Ari Laurén,Marjo Palviainen,Mika Nieminen,Leena Stenberg,Samuli Launiainen,Hannu Hökkä,Raija Laiho,Iñaki Urzainki,Kersti Leppä

doi:10.3390/f12030293

Ari Laurén, Marjo Palviainen + Show 7 more

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https://doi.org/10.3390/f12030293

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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.

Highlights

Extensive field trials and monitoring studies have outlined connections between drainage, water table (WT) and stand growth [11,12,13], and different drainage norms and recommendations have been proposed for peatland forest management in Fennoscandia, the Baltic countries, Russia, Canada, and the USA [14,15,16,17]
We studied the sensitivity of the model results (i) for such model structures that are difficult to quantify experimentally (zroot, f (e A ), anisotropy), (ii) to identify characteristics that may not be directly available in the forest inventory data, and (iii) to identify drainage options (Ddepth, Swidth ) that can be managed in practical forestry
The model predicted reasonably well the mean WTs in July–August (RMSE 0.15 m, Figure 4a), which is the key period for stand growth

Summary

Introduction

The utilization of managed peatlands has been recently questioned, as they have been recognized as environmental hotspots that contribute to elevated greenhouse gas emissions and nutrient and sediment exports to water courses [4,5,6,7]. The water table (WT) affects both tree stand growth and the adverse environmental effects [2,8]. The effect of drainage on WT depends on complex interactions of rainfall, evapotranspiration, topography, stand characteristics and the hydraulic properties of peat [9,10]. Extensive field trials and monitoring studies have outlined connections between drainage, WT and stand growth [11,12,13], and different drainage norms and recommendations have been proposed for peatland forest management in Fennoscandia, the

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