State Factor Model of Soil and Ecosystem Formation Idea that soils form predictably in response to environmental factors attributable to Dokuchaev in ~ 1880 Hans Jenny (1920’s to 1930’s) transformed conceptual model to a more quantitative theory following tenets of physical chemistry

State Factor Model Concepts Earth surface a continuum of objects –Soils and ecosystems are human constructs Continuum broken into systems for study –Size is arbitrary –System has the following properties Open to surroundings Can exchange matter and energy Properties at any time depend on surroundings Sytem properties depend on –1. Initial state of system –2. External conditions –3. Age of system

State Factor Equation Soil = f (initial conditions, external conditions, time) or, based on field observation

Key Concepts of State Factor Theory Factors are independent of system –System is small relative to surroundings Factors may be independent of each other –Climate not always independent of time for example –If a variable is independent, sites can be selected along a gradient of the variable (a soil sequence) Since state factor assemblage defines a soil or ecosystem, a change in variables defines a new system –Leads to recognition that there are essentially an infinite number of soils

Definitions of State Factors 1. Climate (cl) regional climate climate inside ecosystem is a dependent variable (on all state factors in addition to climate0 2. Biota (  ) Potential biota gene flux that enters an ecosystem over time t Actual (existing) biota reflects  dependent on other state factors. 3. Topography configuration of land at t=0 slope, curvature, aspect, depth to water, etc. 4. Parent Material initial state at t=0 (t=0 can be pre-existing soil) 5. Time elapsed time during present state factor configuration 6. Humans Culture is a human variable that dictates land use, etc.

Using State Factor Approach to Study Soils Hold all factors ‘constant’ except one of interest to develop univariant observational gradients called “sequences” –Climosequences –Biosequences –Toposequences –Lithosequences –Chronosequences –Anthroposequences How to hold factors ‘constant’ Change or incrase in a factor value Soil Property Select sites all with same value of a factor Select sites where state factor is ‘ineffective” dS/dx=0

Using State Factor Approach to Study Soils Hold all factors ‘constant’ except one of interest to develop univariant observational gradients called “sequences” –Climosequences –Biosequences –Toposequences –Lithosequences –Chronosequences –Anthroposequences How to hold factors ‘constant’ Change or incrase in a factor value Soil Property Select sites all with same value of a factor Select sites where state factor is ‘ineffective” dS/dx=0

Attributes of State Factor Model Non-mechanistic/black box approach to examining soils –Tells us relations between soils and variables –Tells us what happens, not why Fundamental approach to designing field studies to examine soil formation –A basic approach to experimental design (control of variables) Widely used in present ecosystems/geological/pedological research –- Some examples of sequences…..

Climosequences West slope of Sierra Nevada as an analogue for how soil C responds to climate change PM = granitic Topo = similar slope, aspect Biotic = constant Age/residence time= similar Climate= varies with elevation

Chronosequences Hawaiian Island Chain PM = basalt/tephra Climate= constant Topo= same (level flows) Biota=constant Time= variable (10 2 to >4 Ma)