The impacts of land mosaics and human activity on ecosystem productivity

1. The impacts of land mosaics and human activity on ecosystem productivity Jeanette Eckert

2. Reasons for concern • Urban development is taking place on the most fertile land (Imhoff) • Quantity does not necessarily = quality • Potential photosynthetic productivity of the planet has been reduced by 5% due to increase in agricultural land conversion over the last couple of decades (DeFries) • Relates to above: replacing agricultural land with less productive land will decrease overall NPP • Anthropogenic activity influences C pools more than the biophysical environment in urban green spaces (Golbiewski) • Shows simple human activities such as lawn maintenance can have impact

3. How do land mosaics affect productivity? • The overall mosaic of a landscape can affect ecosystem processes and productivity • Mosaics are created and impacted naturally: • Naturally occurring wildfires • Storms • Erosion/geological processes

4. …or through human activity • Deforestation • Human-started fires • Wetland conversion • Conversion to agricultural • Urbanization

5. Mosaics affect ecosystem processes by… • Being fragmented • Productivity decreases in edge areas • Proximity of patches • Ecosystem interactions • Physical barriers and features • Topography, water features

9. Total reduction or gain in annual NPP (Imhoff)

10. Why study productivity in relation to landscapes? • Approximately ½ of the carbon released into the atmosphere from the burning of fossil fuels (a purely anthropogenic activity) is unaccounted for in global C models. (Amthor 1995) • Where is it going? • Oceans and/or terrestrial ecosystems

11. How do you measure production? • Most common way is to quantitatively measure NPP or NEP • Gross Primary Production, GPP, is the total amount of CO2 that is fixed by the plant in photosynthesis. • Respiration, R,is the amount of CO2 that is lost from an organism or system from metabolic activity. • Net Primary Production, NPP,is the net amount of primary production after the costs of plant respiration are included. Therefore, NPP = GPP - R • Net Ecosystem Production, NEP,is the net amount of primary production after the costs of respiration by plants, heterotrophs, and decomposers are all included. Therefore,  NEP = GPP – (Rp + Rh +Rd) • A measure of NEP is of great interest when determining the CO2 balance between various ecosystems, or the entire earth, and the atmosphere.

12. Another common way is to measure aboveground biomass (AGB) • Useful in studying productivity and C cycles • A good relationship exists between AGB and NPP in forests before stands reach old age • Easiest way to study productivity of large plants and trees

13. Scale comes into play… • When looking at a global issue, such as a global C cycle, it is most helpful to collect measurement at a large scale, but: • Observational data difficult to collect at large scale • Remote sensing is extremely helpful, but must be calibrated

14. D.Turner et al. • NPP, NEP, AGB vary with age • Scale of human disturbance is often less than 1km; thus, resolution down to 30m is necessary • Scale should be significantly smaller than the scale of relevant heterogeneity

15. It becomes necessary to compile integrated databases • D. Zheng et al.: • Combined field measurements with vegetation indices from Landsat • Used regression analysis to produce AGB map for Chequamegon National Forest • Common regression models can be used to accurately predict measurements at tree, plot, and stand levels, but must be linked to vegetation indices to be accurate at landscape level • Results were comparable to previous measurements in the area • Studies such as this are necessary to compile useful data for future studies

17. Large-scale endeavors:Mapping NPP of China’s forests

18. Est. NPP from measured data

19. Est. NPP from remote sensing data

20. statewide: California

23. Conclusions • Humans have an overall negative effect on NPP • We continue to spread outward from cities, consuming agricultural land • This can’t be replaced with less fertile land • Should we be concerned for food supply?

24. Remote imaging is fairly accurate when calibrated properly • Patterns in China and US similar: decreased NPP in urban areas • Lesson from California study: exotic and invasive species make significant portion of species richness measurements, and warmer daily temperatures have positive impact for exotics and negative impact on native plants