Boreal peatland forests: ditch network maintenance effort and water protection in a forest rotation framework

Jenni Miettinen,Jukka Aroviita,Mika Nieminen,Lauri Valsta,Markku Ollikainen,Jarno Turunen,Soili Haikarainen

doi:10.1139/cjfr-2019-0339

Abstract

Ditch network maintenance promotes forest growth in drained peatland forests but increases nutrient and sediment loads, which are detrimental to water quality. Society needs to balance the harvest revenue from improved forest growth against deteriorating water quality. We examine socially optimal even-aged forest management in drained peatlands when harvesting and ditch network maintenance cause nutrient and sediment loading. The means to reduce loading include establishing overland flow fields and abstaining from ditch network maintenance. We characterize this choice analytically in a rotation framework and examine, in a numerical model, the key factors affecting the choice of forest management and water protection measures. We choose a drained peatland forest site located in northeastern Finland in the vicinity of ecologically vulnerable forest headwater streams. On the given drained forest site, we find a set of parameters under which implementing ditch network maintenance is privately but not socially optimal.

Highlights

Pristine peatlands are wet forest sites where high soil water levels are a limiting factor for tree growth
Ditch network maintenance is a common practice for promoting forest growth in drained peatland forests
The trade-off between increased harvest revenues and decreased water quality due to ditch network maintenance has received scarce attention, even though it is generally accepted that peatland forests are a large source of nutrient and sediment loads

Summary

Introduction

Pristine peatlands are wet forest sites where high soil water levels are a limiting factor for tree growth. Sediment load damage nance costs lengthen the optimal rotation age but reduce the ditch network maintenance effort and the size of the overland flow field. A higher unit cost of the overland flow field decreases its size and higher interest rates, nutrient load damage, and sediment load damage decrease the optimal ditch network maintenance effort. We describe the nutrient and sediment loads caused by final felling and ditch network maintenance and their retention by an overland flow field as a water protection measure. The share of sediment load reduction as a function of the size of the overland flow field, m1 (B refers to the overland flow field and C refers to sediment), is as follows: In drained peatlands, both ditch network maintenance and final felling increase the phosphorus load. Note: NPV, net present value. aThe forest growth impact of DNM varies from the basic run by ±5%

Numerical analysis: the private and social optimum

Ditch network maintenance effort in the private optimum

Ditch network maintenance effort and water protection in the social optimum

Findings

Conclusions