Nutrient Balance as a Tool for Maintaining Yield and Mitigating Environmental Impacts of Acacia Plantation in Drained Tropical Peatland—Description of Plantation Simulator

Ari Laurén,Marjo Palviainen,Hannu Hökkä,Iñaki Urzainki,Susan Page,Chris Evans

doi:10.3390/f12030312

Abstract

Responsible management of Acacia plantations requires an improved understanding of trade-offs between maintaining stand production whilst reducing environmental impacts. Intensive drainage and the resulting low water tables (WT) increase carbon emissions, peat subsidence, fire risk and nutrient export to water courses, whilst increasing nutrient availability for plant uptake from peat mineralization. In the plantations, hydrology, stand growth, carbon and nutrient balance, and peat subsidence are connected forming a complex dynamic system, which can be thoroughly understood by dynamic process models. We developed the Plantation Simulator to describe the effect of drainage, silviculture, fertilization, and weed control on the above-mentioned processes and to find production schemes that are environmentally and economically viable. The model successfully predicted measured peat subsidence, which was used as a proxy for stand total mass balance. Computed nutrient balances indicated that the main growth-limiting factor was phosphorus (P) supply, and the P balance was affected by site index, mortality rate and WT. In a scenario assessment, where WT was raised from −0.80 m to −0.40 m the subsidence rate decreased from 4.4 to 3.3 cm yr−1, and carbon loss from 17 to 9 Mg ha−1 yr−1. P balance shifted from marginally positive to negative suggesting that additional P fertilization is needed to maintain stand productivity as a trade-off for reducing C emissions.

Highlights

Peatlands extend from the polar regions to the humid tropics, and may hold over1000 Pg of carbon (C) [1,2], more than the total pool of C in the atmosphere
The good match between the measured and modelled subsidence provides a plausible basis for the nutrient balance calculation, because the nutrient dynamics in deep-peat sites depend on the same biogeochemical processes as the mass balance dynamics reflected by the subsidence
Rates of nutrient consumption are high in tropical short rotation tree plantations, and there is a risk that this could lead to the long-term depletion of soil nutrient resources [24]

Summary

Introduction

Peatlands extend from the polar regions to the humid tropics, and may hold over1000 Pg of carbon (C) [1,2], more than the total pool of C in the atmosphere. The cultivation of peatlands, which requires intensive water management and control of plant nutrition, may turn peatlands into a C source [4,5,6,7,8] and cause other environmental problems, such as peat subsidence [5,9], increased nutrient export to water courses [10], and increased fire risk [11]. In Southeast Asia, ombrogenous peatlands cover approximately 25 Mha [12]. Half of this area is under some form of agricultural use—either for large-scale plantations of oil palm or Acacia for pulp and paper production, or for smallholder farming [13]. Mitigating C losses and associated peat subsidence in these landscapes is of increasing importance in the context of global climate change agenda and regional land use planning [14]

Methods

Results

Conclusion