ecological restoration and global climate change

Download Ecological Restoration and Global Climate Change

Post on 15-Jul-2016

219 views

Category:

Documents

3 download

Embed Size (px)

TRANSCRIPT

  • Ecological Restoration and Global Climate Change

    James A. Harris,1,5 Richard J. Hobbs,2 Eric Higgs,3 and James Aronson4

    Abstract

    There is an increasing consensus that global climatechange occurs and that potential changes in climate arelikely to have important regional consequences for biotaand ecosystems. Ecological restoration, including (re)-afforestation and rehabilitation of degraded land, isincluded in the array of potential human responses to cli-mate change. However, the implications of climate changefor the broader practice of ecological restoration must beconsidered. In particular, the usefulness of historical eco-

    system conditions as targets and references must be setagainst the likelihood that restoring these historic eco-systems is unlikely to be easy, or even possible, in thechanged biophysical conditions of the future. We suggestthat more consideration and debate needs to be directedat the implications of climate change for restorationpractice.

    Key words: climate change, ecosystem change, ecosystemfunction, historical ecosystem, restoration goals.

    Introduction

    In this paper, we examine the likely implications of global cli-mate change for ecological restoration. Ecological restora-tion, particularly in terms of (re)afforestation and restorationof degraded agricultural land, is often seen as one of theimportant responses to climate change because such activitieshelp influence the planets carbon budget in a positive way(e.g., Watson et al. 2000; Munasinghe & Swart 2005). How-ever, climate change also has the potential to significantlyinfluence the practice and outcomes of ecological restorationcarried out for other purposes because of the changed bio-physical settings that will be prevalent in the future.The practice of ecological restoration, and the science

    of restoration ecology, has developed rapidly over the pastfew decades to the extent that a cohesive body of theory isbeginning to emerge that is linked to increasingly sophisti-cated restoration practices (e.g., Higgs 2003; van Andel &Aronson 2006; Falk et al. 2006). However, we need to en-sure that the theory, and the practice, fit with the realitiesof our brave new world, also known as our planet inperil, where rapidly changing environmental and socio-economic conditions seem to be spinning entirely out ofcontrol, or at least out of all historical ranges of variability.Set against this is a tendency in much restoration prac-

    tice, and indeed in much of the theoretical discussion onrestoration, to respect historical conditions either as thebasis for explicit objectives or to reset ecological processesto defined predisturbance conditions (e.g., White & Walker

    1997; Swetnam et al. 1999; Egan & Howell 2001). Here wediscuss the potential impacts of climate change on ourability to achieve such a goal and then suggest possibleways forward in framing meaningful and realistic restora-tion objectives for the future.

    Climate Change Impacts

    It is increasingly likely that the next century will be char-acterized by shifts in global weather patterns and climateregimes, according to current climate predictions (Watsonet al. 2001; McCarthy et al. 2001; Munasinghe & Swart2005). The predictions, although containing wide latitudesof potential outcome, are all pointing the same way:

    d Changes in weather patternsd Increases in mean temperaturesd Changes in patterns of precipitationd Increasing incidence of extreme climatic eventsd Increasing sea level

    These changes are likely to be sudden (in some casesover periods of

  • to incorporate serious consideration of expected futureenvironments into restoration planning and practice.Even without the predicted changes in climate over 50

    years, the direct impacts of increasing CO2 concentrationsin the atmosphere would themselves have importantimplications for restoration practices. For instance,detailed studies of African savanna dynamics by Bond &Midgley (2000) and Bond et al. (2003) indicate that thebalance between herbaceous and woody components ofsavannas is strongly linked to atmospheric CO2 concentra-tions. This suggests that historical treegrass proportionsare unlikely to be replicated under current or future ele-vated CO2 levels; hence, the restoration of savanna eco-systems to a previous state may not be possible in thefuture with reasonable effort. Concurrently, Bellamy et al.(2005) have demonstrated severe and rapid loss of carbonfrom soils in the United Kingdom attributed to climatechange. This situation is likely to be ubiquitous in extra-tropical regions globally.Although future climate change scenarios vary in inten-

    sity of impact (Watson et al. 2001), they share some com-mon features, such as change in mean annual temperaturesand changes in patterns of precipitation. In the southernUnited Kingdom, for example, the lowest impact scenarioshave annual changes of 12.5C and between 10 and 20%less precipitation, characterized by warmer, wetter wintersand warmer, drier summers by 2080 (UKCIP 2005).Recent work to map changes in biophysical regime in theU.S.A. found that half of the area would have shifts inmoisture, temperature, and soil conditions unable to sus-tain historic ecosystems in those areas, that is, thoselikely to be present pre-settlement (Saxon et al. 2005).More substantial change is anticipated for high northernlatitudes, and evidence of significant change is alreadybeing detected (ACIA 2004). Within the next 100 years,and much sooner in some regions, prescribing restorationsusing purely historical references will prove increasinglychallenging at best and at worst lead to failure.Ecological restoration programs have a timescale of

    at least this long, particularly when considering woodedecosystems and reestablishment of complex food chains. Forexample, there is much focus on conservation of ancientwoodlands in the United Kingdom, ancient woodlandbeing defined as land believed to have been continuouslywooded since at least 1600 AD (Spencer and Kirby 1992).This leads to the question how appropriate are historicalecosystem types when faced with rapidly changing bio-physical conditions? Is it appropriate to consider a tem-perate woodland restoration endpoint in an area likely tobe flooded by rising sea level? Why establish wetland inan area likely to become semiarid?As much as rapid climate change makes for difficult

    scientific and technical issues, there are vexing moralquestions, too, that make our thinking and action evenmore complicated. Threatened species and ecosystemswill be increasingly hard to predict, and their recoverymore difficult, sometimes practically impossible, to achieve.

    Whatever means develop for restoring rapidly shiftingecosystems, the translocation of species is a likely tech-nique. This bears the burden of breaking our relations withparticular places and upsetting long-duration place-specificevolutionary processes. There is the hazard of becomingmore comfortable with serving as active agents in ecosys-tems to the extent where historical fidelity is almostentirely abandoned. It is one matter to watch change happenin ecosystems and wonder how and how much to inter-vene, and quite another to become a determining agent inthat change. How smart can we be, and how much hubrisis there in presuming that we can understand and predictecological change? Finally, and this is by no means anexhaustive list of moral concerns, there are consequencesfor the vitality of restoration as a practice in a broaderpublic giving up critical support for ecological integritywhen ecosystems are changing rapidly. Why, after all, sup-port the finely honed techniques and ambitions of restora-tion when mere ecological productivity appears adequate?

    Static Conservation and Restoration Objectives

    The predicted climate change scenarios will thus be partic-ularly challenging in the context of national legislativeframeworks designed to protect habitat types and impor-tant species. In the United Kingdom, for example, the des-ignation of Sites of Special Scientific Interest for wildlifeprotection is made on the basis of the presence of partic-ular named species being present on those sites (Depart-ment for Environment, Food and Rural Affairs 2003).Similarly, in Canada, recent legislation to protect speciesat risk focuses primary attention on species instead ofecosystems at risk, which binds recovery and restorationefforts to targets that may become increasingly difficult andexpensive to reach. As the biophysical envelope changesgeographically, these sites will no longer support many ofthe species used in the notification and designation pro-cess, which must then bring their special status into ques-tion. How then are these species to be protected? Activeecological restoration of appropriate sites in new locationswould appear to be one answer.Conservation schemes tying assemblages to one place

    may actually lead to ossification of those ecosystemsineffect making them more fragile and less resilient by notproviding space for the elements of the total gene pool onthe fringes of the bell-curve niche space for occasionalregeneration, and thereby reducing or eliminating the abil-ity of the species and ecosystem to adapt to changes in bio-physical regime. In a constant environment, for example, oneforced by conservative conservation practices, an opti-mum phenotype is selected for, and extremes selectedagainst. Individuals that vary from this mean are elimi-nated, reducing the potential for adaptation to a rapidlyshifting biophysical regime, as may occur under certain cli-mate change scenarios (Rice & Emery 2003).This could be visualized by considering the two primary

    physical constraints to vegetation assemblage composition,

    Ecological Restoration and Global Climate Change

    JUNE 2006 Restoration Ecology 171

  • st

Recommended

View more >