Plants & Carbon
In the plant community structure and dynamics module, it is possible to specify the growth of several vegetation components over time, including volume of hardwood and softwood, standing dead trees, down woody material, shrubs, herbaceous vegetation, litter, and a synthetic index of horizontal and vertical structure of forest stands. It is also possible to modify the annual growth of hardwood, softwood, herbaceous vegetation and agricultural crops according to annual variation in precipitation patterns. Annual crop production can be further modified by arthropod outbreaks. The rate at which exotic or invasive plants spread from anthropogenic developments to native plant communities may also be specified. To permit the modelling of biotic carbon in the land base, additional inputs may be specified, including initial soil carbon density, decomposition rates, and the identification of footprints that remove vegetation during their construction or are to be included in carbon pool dynamics analyses.
Table inputs
1. Hardwood growth
For each forest type, enter the average volume (m3/ha) of hardwood by seral stage in stands that originated after forest harvesting or natural disturbance.
2. Softwood growth
For each forest type, enter the average volume (m3/ha) of softwood by seral stage in stands that originated after forest harvesting or natural disturbance.
3. Snag growth
For each forest type, enter the average weight (tonne/ha) of standing dead trees by seral stage in stands that originated after forest harvesting or natural disturbance.
4. Shrub growth
For each forest type, enter the average weight (tonne/ha) of shrubs by seral stage in stands that originated after forest harvesting or natural disturbance.
5. Herbaceous growth
For each forest type, enter the average weight (tonne/ha) of herbaceous material by seral stage in stands that originated after forest harvesting or natural disturbance.
6. Down wood growth
For each forest type, enter the average weight (tonne/ha) of down wood by seral stage in stands that originated after forest harvesting or natural disturbance.
7. Litter metrics
- For each forest type, enter the average weight (tonne/ha) of litter by seral stage in stands that originated after forest harvesting or natural disturbance.
- For each non-forest cover type, enter the average weight (tonne/ha) of litter.
- Enter the average proportion (0 - 1) of carbon in litter that is released by fire.
- Enter the average decomposition rate of phytomass to litter in each landscape type.
8. Forest structure trajectory
For each forest type, enter an index value (0 - 1) indicating the relative amount of forest structure by seral stage in stands that originated after forest harvesting or natural disturbance.
9. Various phytomass & carbon conversions
- Enter the proportion (0 - 1) of aboveground volume that is not included in the hardwood and softwood growth curves (Tables 1 and 2).
- Enter the amount of belowground biomass as a proportion (0 - 1) of aboveground biomass.
- Enter the weight (tonne / m3) of a tree.
- Enter the proportion (0 - 1) of phytomass that is carbon.
- Enter the correction ratio of carbon to CO2
10. Tracking strategies for litter
Enter the strategy by which lfh and soil carbon is tracked in different landscape types as follows:
1 Use a flux approach for a given landscape type. This strategy, generally used for fen and bog complexes, requires an estimate of the proportion of above ground vegetation (trees, snags, down wood, herbaceous, litter) phytomass that is lost each year to the litter pool.
2 LFH and soil carbon levels are permitted to vary among seral stages of rangeland cover types.
3 LFH and soil carbon levels are permitted to vary among seral stages of forest types.
4 Maintain a constant carbon density in each landscape type that does not change over time or after natural or anthropogenic disturbance. The average weight of litter in each landscape type is specified in Table 7.
12. Deletion coefficients for soil carbon in fast and slow pools
- Enter the slow pool soil carbon deletion coefficient for intact areas for each landscape type.
- Enter the slow pool soil carbon deletion coefficient for buffers on each land use footprint type.
- Enter the slow pool soil carbon deletion coefficient for soil beneath each land use footprint type.
- Enter the fast pool soil carbon deletion coefficient for intact areas for each landscape type.
- Enter the fast pool soil carbon deletion coefficient for buffers on each land use footprint type.
- Enter the fast pool soil carbon deletion coefficient for soil beneath each land use footprint type.
13. Which footprints create a buffer for soil carbon
Enter '1' if the land use footprint type creates a buffer for soil carbon. Enter '2' if it does not. This input defines which carbon pools are to be included in carbon pool dynamics analyses. Although the model tracks carbon in each of the listed pools, output will only be tabulated for those turned on by entering a value of 1.
14. FT buffer width affecting soil carbon
Enter the width (m) of the buffer within which soil carbon is affected for each land use footprint type.
15. Initial soil carbon values and assorted metrics
- Enter the proportion (0 - 1) of soil carbon lost to fire in each landscape type.
- Enter the average litter loss rate (proportion, 0 - 1).
- Enter the proportion (0 - 1) of litter decomposition to fast and slow soil carbon pools.
- Enter the size (tonne / ha) of the fast and slow carbon pools in each landscape type at the start of the simulation period.
16. Average number of years for debris decomposition
Enter the number of years required for debris decomposition. When a disturbance event occurs (i.e., the building of roads, rail lines, seismic line, inblock features, acreages) on the landscape, the model calculates the amount of phytomass and carbon created as organic debris. An example would be a 1 ha wellsite clearing in a forest. Even though the model considers this 1 ha area to be a wellsite immediately upon its completion, the decomposing phytomass of the preceding plant community is still tracked. This decomposing phytomass enters a pool that decomposes at a user-defined rate expressed in number of years to accomplish full decomposition. These data are best identified from the literature.
17. Phytomass component switches
For each phytomass component, enter '1' if to include the phytomass component in carbon budget analyses. Enter '0' to exclude it.
18. Exotic / invasive plant invasion metrics
- Enter the average average spread rate (m/yr) of invasive plants in each landscape type.
- For each landscape type, enter the average age of anthropogenic features at the start of the simulation period. This information is used to estimate the historic spread of invasive plants.
- For each landscape type, enter '1' if the landscape type can be invaded by agronomic plant species. Enter '0' if it cannot.
- Enter the proportion (0 - 1) of land use footprints built in each landscape type that were reclaimed prior to the simulation period.
- Enter the proportion (0 - 1) of each landscape type into which invasive plants can become established.
19. Stand breakup rates of oldest seral stage
Enter the proportion (0 - 1) of the oldest seral stage in each forest type that reverts to the first seral stage as a result of gap dynamics processes.
20. Which forest seral stages represent old growth?
For each forest type, enter '1' for seral stages that represent old growth. Enter '0' for seral stages that do not.
21. Do footprints remove aboveground and belowground vegetation?
- For each land use footprint type, enter '1' if the footprint removes aboveground living vegetation from the landscape type on which it is built. Enter '0' if it does not.
- For each land use footprint type, enter '1' if the footprint removes litter from the landscape type on which it is built. Enter '0' if it does not.
Graphic inputs
Precipitation modified tree production
This graphic input device makes it possible to explore relationships between long term changes in annual precipitation and tree growth. For example, relative to initial tree growth and yield curves, a 20% (1.20) increase in precipitation may cause a 20% (1.20) increase in tree phytomass at a given seral stage. The relationship is applied only if the accompanying switch is on, and annual precipitation is permitted to vary in a random fashion. For this function to work, the meteorology module must be switched on.
Switches
Precipitation modified tree growth
When this switch is on, tree growth is modified by precipitation according to the relationship specified in the accompanying graphic input device. Also, the switch may be activated only if annual precipitation is permitted to vary in a random fashion.
Precipitation modified shrub growth
When this switch is on, shrub growth is modified by inter-annual variation in precipitation. The switch assumes a linear relationship exists between primary production in a given year and the ratio of actual to average precipitation during that year. Also, the switch may be activated only if annual precipitation is permitted to vary in a random fashion.
Precipitation modified herb and agricultural growth
When this switch is on (green), herb growth and production of agricultural crops are modified inter-annual variation in by precipitation. The switch assumes a linear relationship exists between primary production in a given year and the ratio of actual to average precipitation during that year. Also, the switch may be activated only if annual precipitation is permitted to vary in a random fashion (Panel 5).
Arthropod outbreak modified crop growth
When this switch is on (green), production of agricultural crops is modified by inter-annual variation in arthropod outbreaks. The switch assumes a linear relationship exists between crop growth in a given year and the ratio of actual to average insect outbreak during that year. Also, the switch may be activated only if arthropod outbreaks are permitted to vary in a random fashion (Panel 6).
Invasive plants expansion switch
When this switch is on (green), invasive plants may expand.
Rangeland Community Structure Dynamics
Grassland and shrubland communities are not constant in structure (physiognomy), but express dynamics that are driven by numerous agents including fire (wildfire or prescribed fire), drought, and herbivory caused by livestock, native herbivores, and arthropods. The current approach to modelling the dynamics of rangelands in ALCES is heavily influenced by Barry Adams, Range Management Specialist with Public Lands of the Alberta Government who has been studying the dynamics of Alberta's rangelands for several decades.
In ALCES, native plant communities age (advance along seral stages) unless a pertubation agent (fire, herbivory, drought) of sufficient magnitude occurs to reset the community back to a "younger" development stage. This post-disturbance community may or may not be the "youngest" development stage. The graphic input devices in this panel make it possible to define the relationship between intensity of livestock stocking rate, drought and fire and the relative loss of successional age of a given landscape type.
When conducting grassland dynamics simulations in ALCES, note that herbivory, fire and drought events, when they do occur with sufficient magnitude to affect seral stages, do not express themselves until the following year. This is because ALCES reports the status of each grassland community type at the beginning of the growing season, whereas fire, insect, and drought events occur during the middle portions (summer) of the annual time step.
Graphic Inputs
Effects of precipitation on successional dynamics
In the graphic input device, enter the relationship between the ratio of actual/average precipitation and the relative loss of structural age that a landscape type will experience. For example, a User may suggest that a year experiencing 25% (=0.25) of average precipitation may result in a loss of 50% of the successional age of a given grassland type.
Effects of livestock stocking rate on successional dynamics
In the graphic input device above, enter the relationship between the ratio of actual/average livestock stocking rate and the relative loss of structural age that a landscape type will experience. For example, a User may suggest that a year experiencing 125% (=1.25) of recommended average stocking rate may result in a loss of 50% of the successional age of a given grassland type.
Effects of fire on successional dynamics
Based on the User-defined average fire rate (either constant or stochastic), fires return a portion of the plant community to the youngest development stage.
Successional patterns in non-forest structure
Structural changes generally accompany changes in successional stage. These graphic inputs make it possible to describe how overall structural complexity of various plant communities changes with seral stage. Enter the relationship between development stage of this plant community and its structural complexity.
LFH & soil organics gradient x seral stage
The amount of organic material stored in the soils of rangeland and shrubland landscape types can change depending on recent and historic disturbance regimes. Relative to average LFH and soil organic levels, measured in tonnes/hectare, the graphs below allow the User to express the relationship between seral stage and LFH/soil organic levels relative to the mean value. For example, a RSS of 0.2 may have a Soil Organics/LFH level of 0.1, indicating that it contains 90% less soil carbon that the landscape average. In contrast, a RSS of .9 may have a organic level of 2.3, indicating that advanced seral stages have 230% more carbon than the landscape average.