Ecosystem functions and services

1 CHAPTER 3 Ecosystem functions and servicesCagan H. SekerciogluIn our increasingly technological society, peoplegive little thought to how dependent they are onthe proper functioning of ecosystems and thecrucial services for humanity thatflow fromthem. Ecosystem services are the conditionsand processes through which natural ecosystems,and the species that make them up, sustain andfulfill human life (Daily 1997); in other words, the set of Ecosystem functions that are useful tohumans (Kremen 2005). Although people havebeen long aware that natural ecosystems helpsupport human societies, the explicit recognitionof Ecosystem services is relatively recent(Ehrlich and Ehrlich 1981a; Mooney and Ehrlich1997).Since the entire planet is a vast network ofintegrated ecosystems, Ecosystem services rangefrom global to microscopic in scale (Table ;Millennium Ecosystem Assessment 2005a).

2 Ecosystems purify the air and water, generateoxygen, and stabilize our climate. Earth wouldnot befit for our survival if it were not for plantsthat have created and maintained a suitable at-mosphere. Organisms decompose and detoxifydetritus, preventing our civilization from beingburied under its own waste. Other species help tocreate the soils on which we grow our food, andrecycle the nutrients essential to agriculture. Myr-iad creatures maintain these soils, play key rolesin recycling nutrients, and by so doing help tomitigate erosion andfloods. Thousands of animalspecies pollinate and fertilize plants, protect themfrom pests, and disperse their seeds. And ofcourse, humans use and trade thousands ofplant, animal and microorganism species forfood, shelter, medicinal, cultural, aesthetic andmany other purposes. Although most peoplemay not know what an Ecosystem is, the properfunctioning of the world s ecosystems is critical tohuman survival, and understanding the basics ofecosystem services is essential.

3 Entire volumeshave been written on Ecosystem services (Nation-al Research Council 2005; Daily 1997), culminat-ing in a formal, in-depth, and global overview byhundreds of scientists: theMillennium EcosystemAssessment(2005a). It is virtually impossible to listall the Ecosystem services let alone the naturalproducts that people directly consume, sothis discussion presents a brief introduction toecosystem function and an overview of criticalecosystem Climate and the Biogeochemical CyclesEcosystem services start at the most fundamentallevel: the creation of the air we breathe and thesupply and distribution of water we photosynthesis by bacteria, algae,plankton, and plants, atmospheric oxygen ismostly generated and maintained by ecosystemsand their constituent species, allowing humansand innumerable other oxygen-dependent organ-isms to survive.

4 Oxygen also enables the atmo-sphere to clean itself via the oxidation ofcompounds such as carbon monoxide (Sodhiet ) and another form of oxygen in theozone layer, protects life from the sun s carcino-genic, ultraviolet (UV) biogeochemical cycles consist of thetransport and transformation of substances inthe environment through life, air, sea, land, andice (Alexanderet ). Through these cycles,the planet s climate, ecosystems, and creatures451 Oxford University Press 2010. All rights reserved. For permissions please email: services , classified according to the Millennium Ecosystem Assessment (2003), and their Ecosystem service providers. Functionalunits refer to the unit of study for assessing functional contributions ( ik) of Ecosystem service providers; spatial scale indicates the scale(s) of operationof the service. Assessment of the potential to apply this conceptual framework to the service is purposefully conservative and is based on the degree towhich the contributions of individual species or communities can currently be quantified (Kremen 2005).

5 ServiceEcosystem service providers/trophic levelFunctional units Spatial scalePotential to applythis conceptualframework forecological studyAesthetic, culturalAll biodiversityPopulations,species,communit ies,ecosystemsLocal globalLowEcosystem goodsDiverse speciesPopulations,species,communities,e cosystemsLocal globalMediumUV protectionBiogeochemical cycles, micro organisms, plantsBiogeochemicalcycles,functionalgro upsGlobalLowPurificationof airMicro organisms, plantsBiogeochemicalcycles,populations,s pecies,functionalgroupsRegional globalMedium (plants)Flood mitigationVegetationCommunities,habitats Local regional MediumDrought mitigationVegetationCommunities,habitats Local regional MediumClimate stabilityVegetationCommunities,habitatsL ocal globalMediumPollinationInsects, birds, mammalsPopulations,species,functionalgro upsLocalHighPest controlInvertebrate parasitoids andpredators and vertebrate predatorsPopulations,species,functionalg roupsLocalHighPurification of water Vegetation, soil micro organisms,aquatic micro organisms, aquaticinvertebratesPopulations,species, functionalgroups,communities,habitatsLoc al regional Medium to high*Detoxification anddecomposition ofwastesLeaf litter and soil invertebrates, soilmicro organisms, aquatic micro organismsPopulations,species,functionalg roups,communities.

6 HabitatsLocal regional MediumSoil generation andsoil fertilityLeaf litter and soil invertebrates, soilmicro organisms, nitrogen fixingplants, plant and animalproduction of waste productsPopulations,species,functionalgr oupsLocalMediumSeed dispersalAnts, birds, mammalsPopulations,species,functionalgro upsLocalHigh* Waste water engineers design microbial communities; in turn, wastewater treatments provide ideal replicated experimentsfor ecological work (Graham and Smith 2004 in Kremen 2005).are tightly linked. Changes in one component canhave drastic effects on another, as exemplified bythe effects of deforestation on climatic change(Phatet ). The hydrologic cycle is onethat most immediately affects our lives and it istreated separately carbon-based life forms, every single organ-ism on our planet is a part of the global carboncycle.

7 This cycle takes place between the four mainreservoirs of carbon: carbon dioxide (CO2)intheatmosphere; organic carbon compounds withinorganisms; dissolved carbon in water bodies; andcarbon compounds inside the earth as part of soil,limestone (calcium carbonate), and buried organicmatter like coal, natural gas, peat, and petroleum(Alexanderet ). Plants play a major role infixing atmospheric CO2through photosynthesisand most terrestrial carbon storage occurs in foresttrees (Falkowskiet ). The global carboncycle has been disturbed by about 13% comparedto the pre-industrial era, as opposed to 100% ormore for nitrogen, phosphorous, and sulfur cycles(Falkowskiet ). Given the dominance ofcarbon in shaping life and in regulating climate,however, this perturbation has already beenenough to lead to significant climate change withworse likely to come in the future [IPCC (Intergov-ernmental Panel on Climate Change) 2007].

8 Because gases like CO2, methane (CH4), andnitrous oxide (N2O) trap the sun s heat, especiallythe long-wave infrared radiation that s emitted bythe warmed planet, the atmosphere creates a nat-ural greenhouse (Houghton 2004). Without thisgreenhouse effect, humans and most other organ-isms would be unable to survive, as the globalmean surface temperature would drop from thecurrent 14 Cto 19 C (IPCC 2007). Ironically,the ever-rising consumption of fossil fuels duringthe industrial age and the resultant increasingemission of greenhouse gases have created theopposite problem, leading to an increase in themagnitude of the greenhouse effect and a conse-quent rise in global temperatures (IPCC 2007).Since 1750, atmospheric CO2concentrationshave increased by 34% (Millennium EcosystemAssessment 2005a) and by the end of this century,average global temperature is projected to rise C (IPCC 2007).

9 Increasing deforestationand warming both exacerbate the problem as for-est ecosystems switch from being major carbonsinks to being carbon sources (Phatet ;IPCC 2007). If fossil fuel consumption and defor-estation continue unabated, global CO2emissionsare expected to be about 2 4 times higher than atpresent by the year 2100 (IPCC 2007). As climateand life have coevolved for billions of years andinteract with each other through various feedbackmechanisms (Schneider and Londer 1984), rapidclimate change would have major consequencesfor the planet s life-support systems. There arenow plans under way for developed nations tofinance the conservation of tropical forests in thedeveloping world so that these forests can contin-ue to provide the Ecosystem service of acting ascarbon sinks (Butler 2008).Changes in ecosystems affect nitrogen, phos-phorus, and sulfur cycles as well (Alexanderet ; Millennium Ecosystem Assessment 2005b;Vitouseket ).

10 Although nitrogen in itsgaseous form (N2) makes up 80% of the atmo-sphere, it is only made available to organismsthrough nitrogenfixation by cyanobacteria inaquatic systems and on land by bacteria andalgae that live in the root nodules of lichens andlegumes (Alexanderet ). Eighty milliontons of nitrogen every year arefixed artificiallyby industry to be used as fertilizer (MillenniumEcosystem Assessment 2005b). However, the ex-cessive use of nitrogen fertilizers can lead to nu-trient overload, eutrophication, and eliminationof oxygen in water bodies. Nitrogen oxides,regularly produced as a result of fossil fuel com-bustion, are potent greenhouse gases thatincrease global warming and also lead to smog,breakdown of the ozone layer, and acid rain(Alexanderet ). Similarly, although sulfuris an essential element in proteins, excessivesulfur emissions from human activities lead tosulfuric acid smog and acid rain that harms peo-ple and ecosystems alike (Alexanderet ).