The effects of human disturbances The effects of human disturbances on the productivity of ecosystemson the productivity of ecosystems

Lisa Orman Lisa Orman February 28, February 28, EEES 4760 EEES 4760

Energy flowEnergy flow

Light converted by plantsLight converted by plants Into organic matterInto organic matter Transferred into other organismsTransferred into other organisms Nutrients (N, P) cycle between living and Nutrients (N, P) cycle between living and

non living parts of ecosystemnon living parts of ecosystem These nutrients flow between many These nutrients flow between many

different levels, from cells to ecosystemsdifferent levels, from cells to ecosystems

Healthy ecosystemsHealthy ecosystems

Healthy ecosystems are able to sustain Healthy ecosystems are able to sustain functionality and servicesfunctionality and services

Healthy ecosystems retain soil, water, Healthy ecosystems retain soil, water, nutrients and organic matternutrients and organic matter

Landscapes are composed of two or more Landscapes are composed of two or more land units positioned so they are linked by land units positioned so they are linked by processesprocesses

The connection between landscape The connection between landscape heterogeneity and disturbance heterogeneity and disturbance

dynamics is one of the most dynamics is one of the most important challenges facing important challenges facing

ecologists todayecologists today

Turner et al, 2001Turner et al, 2001

DisturbancesDisturbances

DisturbancesDisturbances

Produce a series of successional stages Produce a series of successional stages that maintain structure and functionthat maintain structure and function

The degree of impact is important in the The degree of impact is important in the flow of energy flow of energy

Minor disturbances can occur at regular Minor disturbances can occur at regular intervalsintervals

Large disturbances can completely Large disturbances can completely change the nutrient flowchange the nutrient flow

The ecosystem process is The ecosystem process is ultimately determined by the ultimately determined by the

interaction between the biological interaction between the biological community and environmental community and environmental

factorsfactors

Zhang, 2007Zhang, 2007

Ways to study ecosystem functionWays to study ecosystem function

Sapling densitySapling density Leaf areaLeaf area Aboveground net primary productionAboveground net primary production Aboveground biomassAboveground biomass Carbon cycleCarbon cycle Percent of ground coverPercent of ground cover Net primary productionNet primary production

Amount of solar energy converted to chemical energyAmount of solar energy converted to chemical energy

Net ecosystem productivityNet ecosystem productivity Balance of gross primary production minus ecosystem respirationBalance of gross primary production minus ecosystem respiration

NPPNPP

Primary source of food for heterotrophic Primary source of food for heterotrophic organismsorganisms

Influenced byInfluenced by Regional prevailing climateRegional prevailing climate Variation in fractional vegetation coverVariation in fractional vegetation cover Degree to which an ecosystem is altered relative to Degree to which an ecosystem is altered relative to

nearby non urban areas, fertilization, irrigation, and nearby non urban areas, fertilization, irrigation, and invasive speciesinvasive species

Seasonal patterns of photosynthetic activity in line Seasonal patterns of photosynthetic activity in line with urban heat island hypothesis with urban heat island hypothesis

Imhoff et al, 2004Imhoff et al, 2004

Carbon storage and budgetsCarbon storage and budgets

Net ecosystem carbon balance represents Net ecosystem carbon balance represents the net flux of C entering or leaving an the net flux of C entering or leaving an ecosystemecosystem

Typically after a disturbance, NECB will be Typically after a disturbance, NECB will be negative due to decomposition negative due to decomposition

Over time, growth rate become greater Over time, growth rate become greater than decomposition ratesthan decomposition rates

Case studiesCase studies

Urban sprawlUrban sprawl DrylandsDrylands ForestsForests Spatial resolutionSpatial resolution

Urban sprawlUrban sprawl

Urban sprawlUrban sprawl

One third to one half of the planet’s One third to one half of the planet’s surface has been transformed by humans surface has been transformed by humans (Imhoff et al, 2004)(Imhoff et al, 2004)

In 1992, urban landscape increased by In 1992, urban landscape increased by 25% in the U.S. (Golubiewski, 2006)25% in the U.S. (Golubiewski, 2006)

Typically urban sprawl takes over highly Typically urban sprawl takes over highly productive lands--lands with high NPPproductive lands--lands with high NPP

Urban sprawlUrban sprawl

Replaces native vegetation with suburban Replaces native vegetation with suburban turfgrass, shrubs, and the occasional treeturfgrass, shrubs, and the occasional tree

Requires irrigation and fertilizationRequires irrigation and fertilization Non-native species are often bred to out-Non-native species are often bred to out-

compete native speciescompete native species Urbanization accounts for a loss of 4.15 x 10^-2 Urbanization accounts for a loss of 4.15 x 10^-2

Pg of photosynthetically fixed carbonPg of photosynthetically fixed carbon Global NPP decrease of 5% (Imhoff et al, 2004)Global NPP decrease of 5% (Imhoff et al, 2004)

DrylandsDrylands

DrylandsDrylands

40% of the land surface of the globe is 40% of the land surface of the globe is drylandsdrylands

In Australia, they cover 5 million sq kmIn Australia, they cover 5 million sq km Used for rangelands for domestic livestockUsed for rangelands for domestic livestock

WheatbeltWheatbelt

180,000 sq km180,000 sq km 90% cleared90% cleared Fragmented Fragmented

landscapelandscape Remaining vegetation Remaining vegetation

plays an important plays an important goal in the goal in the conservation of the conservation of the regionregion

Chequamegon National ForestChequamegon National Forest

Chequamegon National Forest Chequamegon National Forest (CNF)(CNF)

Management dominated by timber Management dominated by timber production and silvicultural techniquesproduction and silvicultural techniques

AGB used to study productivity, C cycles, AGB used to study productivity, C cycles, nutrient allocation, and fuel accumulationnutrient allocation, and fuel accumulation

Remote sensing failed to estimate Remote sensing failed to estimate biomass levels at landscape levelbiomass levels at landscape level

Field observations are necessary to Field observations are necessary to understand landscape levelsunderstand landscape levels

Pacific NorthwestPacific Northwest

Pacific NorthwestPacific Northwest

Accumulation of biomass in PNW coniferous Accumulation of biomass in PNW coniferous forests among highest in the worldforests among highest in the world

Logging of the PNW creates a large C source Logging of the PNW creates a large C source (burning and decomposition) and C sink (long-(burning and decomposition) and C sink (long-lived forest products)lived forest products)

Estimates of NPP and NEP greatly affected by Estimates of NPP and NEP greatly affected by satellite resolutionsatellite resolution

As land use becomes more intensive and As land use becomes more intensive and extensive, scale dependent errors may become extensive, scale dependent errors may become potentially largepotentially large

In conclusionIn conclusion

The function of an ecosystem can be The function of an ecosystem can be measured by the biomass and production measured by the biomass and production of the ecosystemof the ecosystem

The health of an ecosystem is not always The health of an ecosystem is not always so straight forwardso straight forward

Landscape ecology needs continuous Landscape ecology needs continuous studies to learn how patterns and their studies to learn how patterns and their dynamics influence ecological processes dynamics influence ecological processes (Turner, 2001)(Turner, 2001)