Ecosystem processes and heterogeneity

Landscape Ecology

Today

   Global NPP Lake position Moose impacts

Questions/Comments

Ecosystem processes

 What do we mean? ◦ Energy ◦ Matter   Carbon Nutrients

Spatial Heterogeneity in ecosystem process

 What can cause ecosystem processes to vary spatially? ◦ Temperature ◦ Moisture ◦ Topography

 What factors affect NPP? ◦ Climate ◦    Temperature Light Precipitation Nutrients

 Where is global marine NPP highest?  Why?

 Where is global terrestrial NPP highest?  Why?

Paradox…

    How do the factors that drive NPP differ between marine and terrestrial ecosystems? the basic processes of plant photosynthesis are the same for terrestrial and marine/aquatic plants the key factors must be the physical and chemical properties of the environments in which plant growth occurs, or the carbon allocation and life history dynamics of the plants themselves.

Marine NPP

  “Marine NPP was a major driver of the preindustrial cultures and economies of civilizations in the higher latitudes, and is still a major driver of the global fishing industry” Driven by: ◦ Nutrients – upwelling ◦ Geology

Terrestrial NPP

  “The most remarkable feature of the terrestrial NPP distribution is that it is the opposite of the pattern of marine NPP” Driven by: ◦ ◦ Climate?

Why not nutrients?

Nutrients in Tropics

   Are the tropics a good place for agriculture? The basic processes of soil weathering have several inevitable consequences that result in a decline in soil fertility, and thus in the resources available to support plant growth and NPP over time as soils age. All of these processes occur most rapidly in the tropics.

Global Nutrient Content

 “Why should marine productivity be positively correlated with the availability of mineral nutrients in the oceans and the adjacent continents, while the productivity of the plants growing in the soil on those continents is inversely correlated with nutrient availability?”

Conclusions

    In fact, the highest short-term rates of NPP (eNPP) apparently occur in temperate and boreal forests.

These patterns of forest productivity are consistent with the global distribution of soil fertility as well as the productivity of certain types of crops and the standardized economic value of agricultural production

Why is might our current paradigm about NPP wrong?

 Hard to measure NPP  Satellites measure green leaves, not necessarily carbon that goes into wood.

Landscape Position and Lakes

 ◦ ◦ ◦ What factors influence the ecosystem functions of a lake?

◦ Geology Size/Depth Climate Terrestrial inputs  ◦ ◦ What about the spatial arrangement of lakes can influence functions? ◦ Geology Climate Hydrologic connectivity

What type of ecosystem properties could be influenced?

How to test?

 Observational study..

Conclusion

 ◦ ◦ ◦ Many factors change with position ◦ Ionic composition Biota Size Primary Production

Species and ecosystem function

 How do species influence ecosystem function?

Effects of Moose Browsing on Vegetation and Litter of the Boreal Forest, Isle Royale,Michigan – McInnis et al. Spatial patterns in the moose-forest-soil ecosystem on Isle Royale, Michigan USA – J. Pastor et al.

Background

   Landscape heterogeneity affects population dynamics and movement. Animals can alter ecosystem function due to their behavior. ◦ Ecosystem engineer? Large herbivores could have large impacts: ◦ Large home ranges. ◦ Eat a lot.  But only what is tasty.

Background cont.

  With selective feeding, herbivores can affect species composition, nutrient cycling, etc. ◦ Obvious on a local scale. Can herbivores alter ecosystem function at the scale of their home range, or of a valley?

Effects of Moose Browsing on Vegetation and Litter of the Boreal Forest, Isle Royale,Michigan   Observations: ◦ Herbivores change the structure, biomass, production, and species composition of vegetation in heavily browsed or grazed areas Questions:  Results:

Effects of Moose Browsing on Vegetation and Litter of the Boreal Forest, Isle Royale,Michigan    Observations: Questions: ◦ What are the effects of browsing upon the biomass and production of trees, shrubs, and herbs? ◦ Does browsing alter species composition of the vegetation? ◦ Do changes in species composition affect the quality and quantity of litterfall in browsed areas? Results:

 What are the effects of browsing upon the biomass and production of trees, shrubs, and herbs?

 Does browsing alter species composition of the vegetation?

Effects of Moose Browsing on Vegetation and Litter of the Boreal Forest, Isle Royale,Michigan    Observations: Questions: ◦ What are the effects of browsing upon the biomass and production of trees, shrubs, and herbs? ◦ Does browsing alter species composition of the vegetation? ◦ Do changes in species composition affect the quality and quantity of litterfall in browsed areas? Results: ◦ Higher biomass, alters species composition, …

Spatial patterns in the moose-forest-soil ecosystem on Isle Royale, Michigan USA – J. Pastor et al.  Observations:  Hypotheses:  Results:

Spatial patterns in the moose-forest-soil ecosystem on Isle Royale, Michigan USA – J. Pastor et al.    Observations: ◦ Moose preferentially forage on aspen and avoid conifers.

Hypotheses: ◦ If moose browsing causes a shift in dominance from hardwoods to conifers across adjacent areas, we should expect corresponding changes in soil nutrient availability over the landscape. Results:

What was the study about?

 Examine the large-scale landscape distribution of moose browsing intensity in relation to plant community composition and size structure, as well as soil nitrogen availability.

◦ Do moose control plant community composition and soil nitrogen at large scales?

What did they measure?

   Available browse.

Annual consumption by moose.

Soil nitrogen availability.

They tested three models

   Random Short-range autocorrelation Higher order of regularly arranged patterns

What would these models look like?

   Random ◦ No autocorrelation – constant variance Short-range autocorrelation ◦ Low-variance at short distances Higher order of regularly arranged patterns ◦ Low-variance at short distance and low variances at large distances as well.

Spatial patterns in the moose-forest-soil ecosystem on Isle Royale, Michigan USA – J. Pastor et al.    Observations: ◦ Moose preferentially forage on aspen and avoid conifers.

Hypotheses: ◦ If moose browsing causes a shift in dominance from hardwoods to conifers across adjacent areas, we should expect corresponding changes in soil nutrient availability over the landscape. Results:

  

What did Pastor conclude?

Tested hypothesis… ◦ Moose causing patterns. ◦ ◦ Alternative hypotheses? Slope Aspect ◦ ◦ Fire Bedrock ◦ Geology ◦ Beavers No differences in nitrogen availability or consumption due to slope or aspect.

◦ Spatial patterns not caused by topographic relief.

◦ Nor other factors.

What did Pastor conclude?

 Conclusion: ◦ Patterns are a result of dynamic interactions between moose foraging and plant communities.

◦ Uncommonly strong impact for a large mammal. ◦ This patterns has occurred in less than 50 generations.