Socioecological implications of modifying rotatio

Authors: JeanMichel Roberge Hjalmar Laudon Christer Björkman Thomas Ranius Camilla Sandström Adam Felton Anna Sténs Annika Nordin Anders Granström Fredrik Widemo Johan Bergh Johan Sonesson Jan Stenlid Tomas Lundmark

Publish Date: 2016/01/07

Volume: 45, Issue: 2, Pages: 109-123

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Abstract

The rotation length is a key component of evenaged forest management systems Using Fennoscandian forestry as a case we review the socioecological implications of modifying rotation lengths relative to current practice by evaluating effects on a range of ecosystem services and on biodiversity conservation The effects of shortening rotations on provisioning services are expected to be mostly negative to neutral eg production of wood bilberries reindeer forage while those of extending rotations would be more varied Shortening rotations may help limit damage by some of today’s major damaging agents eg root rot cambiumfeeding insects but may also increase other damage types eg regeneration pests and impede climate mitigation Supporting water soil nutrients and cultural aesthetics cultural heritage ecosystem services would generally be affected negatively by shortened rotations and positively by extended rotations as would most biodiversity indicators Several effect modifiers such as changes to thinning regimes could alter these patternsA major proportion of the world’s managed forests are subjected to evenaged management systems where stands are harvested through clearcutting The stands are subsequently regenerated naturally or artificially and allowed to grow with or without thinning until final felling A key parameter describing evenaged forest management systems is rotation length ie the time elapsed between two final fellings The choice of a rotation length is an integral part of any forest management regime Curtis 1997 It is dictated by the goals of forest management and biophysical factors In many evenaged systems the main management goal is the production of woodbased commodities such as saw timber pulpwood or woody biomass In this context the optimal rotation is mostly dictated by economic drivers in interaction with factors influencing wood volume growth such as tree species and site productivity However in many parts of the world forest management needs to consider an increasing range of forest values beyond traditional wood products such as recreation biodiversity conservation and climate change mitigationConsidering the increasing variety of demands put on forests and the need to adapt forestry to changing conditions eg climate economy rotation lengths are unlikely to remain constant in the future Over recent decades rotation lengths have been shortened in the coniferous forests of the northwestern USA Curtis 1997 New Zealand’s radiata pine Pinus radiata plantations from 40–50 years in the 1970s to 25–30 years in the 1990s Brockerhoff et al 2008 and the beech Fagus sylvatica forests of Central Europe Lange et al 2014 to mention a few examples In addition to these observed trends various stakeholders in the forest sector increasingly argue for modifying forest rotation lengths in the future For example the largest forest owner association in southern Sweden recently recommended to shorten rotations by 10–15 years in Norway spruce Picea abiesdominated forest where typical rotations are ~60–80 years to decrease the risk of storm and root rot damage Södra Skog 2012 In some countries a minimum allowable felling age is specified in the legislation In Sweden for instance this minimum age varies from 45 to 100 years depending on site productivity and geographic location Fries et al 2015 However to ensure wood supply in spite of increasing protection of older forest with high conservation value the Swedish state forest company has lately expressed a desire to be allowed to harvest some types of forest stands earlier than currently permitted by law Fries et al 2015 Moreover to improve logistics and conditions for the forest industry the Finnish government recently abolished regulations imposing a minimum felling age Fries et al 2015 In parallel policy tools have also been developed to provide incentives for longer rotations eg the temporary ‘conservation contracts’ in Fennoscandia Mönkkönen et al 2009 as well as ‘ageing forest islands’ in continental Europe Lassauce et al 2013 and North America Jetté et al 2013 used to promote biodiversity conservation Considering these recent trends it is crucial to understand how modified rotation lengths may influence the variety of values attributed to forestsMost past studies about rotation lengths have focused on economic aspects of wood production very few have addressed the effects on several forestbased values simultaneously see however Weslien et al 2009 Zanchi et al 2014 The present paper aims to review the socioecological implications of modifying rotation lengths by evaluating potential effects on a wide range of ecosystem services and on biodiversity conservation both concepts sensu MEA 2005 We use boreal Fennoscandian forestry as a case providing a common platform for these analyses Fennoscandia is characterized by a long history of forest management the majority of productive forest land having been actively managed for wood production for at least a century This region is particularly suited as a case because of 1 the dominance of evenaged management systems since the 1950s and 2 a long tradition of research addressing economic ecological and social aspects of forest managementWe use an interdisciplinary approach to evaluate the potential effects of shortened and extended rotation lengths on provisioning ecosystem services wood production berry and mushroom yields as well as forage for hoofed game and reindeer regulating services control of biotic and abiotic damage to forest resources climate change mitigation supporting services hydrology water quality and soil nutrients cultural services aesthetics and recreation cultural heritage protection and biodiversity conservation The latter is considered a foundation for all ecosystem services MEA 2005 The studied ecosystem services and biodiversity implications capture a breadth of issues that are common to many other forested regions worldwide making our case internationally relevant Building on the Fennoscandian case we then discuss the implications for forest landscape planning and highlight the key knowledge gapsTo evaluate the implications of modified rotation lengths there is a need to define a benchmark for comparison Here we use the economically optimal rotation length for wood production based on a discounting rate of 25  as a benchmark representing current practice in Fennoscandian forestry Simonsen et al 2010 Considering current silvicultural costs and timber pricelists this generally represents rotation lengths in the range 60–120 years in boreal Fennoscandia depending on site productivity and tree species Hereafter we use the adjective “mature” to depict a stand which has reached an age corresponding to the benchmark rotation length for a given site productivity and tree speciesExpected implications of shortened and extended rotation lengths on ecosystem services Symbols indicate expected general changes relative to the benchmark rotation length no change Open image in new window increase Open image in new window or decrease Open image in new window in ecosystem service Bold arrows Open image in new window Open image in new window indicate a stronger effect than plain arrows Effect strength is only comparable within a given row and within one arrow direction Combinations of several symbols depict multiple possible effects depending on the magnitude of rotationlength change or due to uncertainty The symbols are presented in tentative order of estimated commonness or likelihood The expected general changes pertain to the average situation over a complete rotation without modification of the thinning regime and include landscapescale effects wherever relevant The rightmost column presents key effect modifiers 1 potential adaptations of the thinning regime as a response to changed rotation length ‘Thinning’ 2 high levels of tree retention at final felling ‘HighRet’ 3 systematic salvage logging of windthrown trees within stands ‘Salvage’ 4 main tree species forming the stand ‘TreeSp’ and 5 presence of a thick snow cover during winter ‘Snow’ Whenever different from the general patterns we present the expected effects of shortened ‘S’ or extended ‘E’ rotations under each of these specific conditions For thinning ‘S−’ depicts a shortened rotation where the stand is subjected to fewer thinnings or remains unthinned during its growth as an adaptation to the shorter stand growth period and ‘E+’ depicts an extended rotation where the stand is subjected to additional thinnings as an adaptation to the longer stand growth period

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