Transcript Lisa Orman
The effects of human disturbances on the productivity of ecosystems Lisa Orman February 28, EEES 4760 Energy flow Light converted by plants Into organic matter Transferred into other organisms Nutrients (N, P) cycle between living and non living parts of ecosystem These nutrients flow between many different levels, from cells to ecosystems Healthy ecosystems Healthy ecosystems are able to sustain functionality and services Healthy ecosystems retain soil, water, nutrients and organic matter Landscapes are composed of two or more land units positioned so they are linked by processes The connection between landscape heterogeneity and disturbance dynamics is one of the most important challenges facing ecologists today Turner et al, 2001 Disturbances Disturbances Produce a series of successional stages that maintain structure and function The degree of impact is important in the flow of energy Minor disturbances can occur at regular intervals Large disturbances can completely change the nutrient flow The ecosystem process is ultimately determined by the interaction between the biological community and environmental factors Zhang, 2007 Ways to study ecosystem function Sapling density Leaf area Aboveground net primary production Aboveground biomass Carbon cycle Percent of ground cover Net primary production Amount of solar energy converted to chemical energy Net ecosystem productivity Balance of gross primary production minus ecosystem respiration NPP Primary source of food for heterotrophic organisms Influenced by Regional prevailing climate Variation in fractional vegetation cover Degree to which an ecosystem is altered relative to nearby non urban areas, fertilization, irrigation, and invasive species Seasonal patterns of photosynthetic activity in line with urban heat island hypothesis Imhoff et al, 2004 Carbon storage and budgets Net ecosystem carbon balance represents the net flux of C entering or leaving an ecosystem Typically after a disturbance, NECB will be negative due to decomposition Over time, growth rate become greater than decomposition rates Case studies Urban sprawl Drylands Forests Spatial resolution Urban sprawl Urban sprawl One third to one half of the planet’s surface has been transformed by humans (Imhoff et al, 2004) In 1992, urban landscape increased by 25% in the U.S. (Golubiewski, 2006) Typically urban sprawl takes over highly productive lands--lands with high NPP Urban sprawl Replaces native vegetation with suburban turfgrass, shrubs, and the occasional tree Requires irrigation and fertilization Non-native species are often bred to outcompete native species Urbanization accounts for a loss of 4.15 x 10^-2 Pg of photosynthetically fixed carbon Global NPP decrease of 5% (Imhoff et al, 2004) Drylands Drylands 40% of the land surface of the globe is drylands In Australia, they cover 5 million sq km Used for rangelands for domestic livestock Wheatbelt 180,000 sq km 90% cleared Fragmented landscape Remaining vegetation plays an important goal in the conservation of the region Chequamegon National Forest Chequamegon National Forest (CNF) Management dominated by timber production and silvicultural techniques AGB used to study productivity, C cycles, nutrient allocation, and fuel accumulation Remote sensing failed to estimate biomass levels at landscape level Field observations are necessary to understand landscape levels Pacific Northwest Pacific Northwest Accumulation of biomass in PNW coniferous forests among highest in the world Logging of the PNW creates a large C source (burning and decomposition) and C sink (longlived forest products) Estimates of NPP and NEP greatly affected by satellite resolution As land use becomes more intensive and extensive, scale dependent errors may become potentially large In conclusion The function of an ecosystem can be measured by the biomass and production of the ecosystem The health of an ecosystem is not always so straight forward Landscape ecology needs continuous studies to learn how patterns and their dynamics influence ecological processes (Turner, 2001)