1. Chapter 5 Stand Dynamics & Gap Models
I work at large to global scale.
When we use bgc models over large scales we use static landcover maps.
If we project into the future a static landcover map is not accurate because as climate changes the potential vegetation community changes which can greatly influence factors such as carbon stocks, npp, c sink/source strength, nutrient demand and cycling, et, ect.
In addition, we still only simply represent disturbance which is the mechanism that can reset vegetation structure, free up resources, and act as a catalyst for large-scale vegetation composition changes.
NRSM 532, BIOS 534
Spring 2014

2. Tree Growth (live fast, die young)
Height 25 50
100
Age (years)
Douglas fir (Montana)
Southern Pines
Cottonwood
What biophysical gradient are these strategies occurring along?
Southeastern trees grow faster initially and mature earlier
foresters take advantage of this
for commercial logging
Montana trees end up growing bigger

3. The Stages of Succession
Stand Initiation Stage: high resource availability (water nutrients light), top competitors dominate while some under story facilitation can occur
Stem Exclusion Stage: overstory reaches its maximum. Growth efficiency or the wood increment per unit leaf area due to growth suppression.
Understory Reinitiation Stage: mortality creates gaps that allow understory species to establish
Old Growth Stage: dominant tree show little to no height increase, variable canopy height due to mortality and gap filling.

4. Restricted Growth (uneven walls)
This trees also has the same potential shape as the first one.
The wall is at irregular distances from the tree
asymmetric crown
Wall stops rising – what happens to the crown as the tree grows
above it?
Crown size increases with tree height since the base no longer
recedes.

5. Site Index
Age
Height 25 50
100
SI25 = 40
SI50 = 60
SI100 = 90

6. Stand Density LAI / NPP 100 1000 Stand Density (trees ha-1)
How does basal area change from 100 to 1000 trees ha-1?
100
1000
Stand Density (trees ha-1)

7. Stand Density (Self-Thinning Rule)

8. Inter-tree Competition
Light
Canopy
Water
Interception
Inter-plant species competition: in this simple schematic we see a few types of abiotic resources species must compete for.
-light, water, and the main missing factor is nutrients.
Mention competition, complementarity, facilitation
Soil Water

9. Carbon Allocation
A main factor determining plant adaptive strategy is carbon allocation or how plants chose to partion the CO2 fixed from the atmosphere.
Options include shoot growth, root growth, reproduction, defense, mycorrhizae etc.
In figure a which species is most likely to have a more developed root system??

10. Growth Efficiency (Gst-limited)HW HW 5 HW 5

11. Growth Efficiency (Gst-limited)
Hypothesis: hydraulic limitation on photosynthesis and the amount of lai that can be supported are sufficient to account for most observed decreases in tree and stand growth.

12. Growth Efficiency

13. Growth Efficiency (Ntr-limited)
Hypothesis: areduction in the rate at which nutrients are recycled explains decreased tree and stand growth with age.
Go back two slides and ask which mechanism is limiting LAI?

14. Biogeochemistry & Gap Models

15. Biome-BGC

16. Forest-BGC

17. If you own forest land, you are taxed based on this.
Used to be based on standing volume
Champion and International cut down all
their trees = no taxes
Based on fundamental principles of tree growth
Not a single formal challenge to this
Doesn’t require presence of trees
Good for land swaps (1:1, 3:1?)

18. Gap Models
Represent the regeneration in a forest based on the ‘gaps’ generated by the mortality of large trees

19. Individual Based Models

20. Gap Models Individual-based models of forest growth and succession
Simulate the establishment, growth and mortality of each tree in the plot ‘individually’
Overtopped trees are suppressed by canopy dominant trees as a function of light interception

21. Competition for light Based on Beer’s Law
“The taller the glass, the darker the brew, the less light gets through”
Simply put, farther down from the top of the canopy means less light for growth i.e. The glass is taller

22. Difference between transmitted and absorbed

23. Simple Gap Model Establish Establish Establish Grow Grow Grow Die Die

24. Gap model interactions
Most important factor is shade tolerance
Models have been expanded to incorporate other competition effects that are locally important
Nutrients
Water availability
Soil temperature (Phenology)

29. Example of a scaled up individual-based model (ZELIG)

30. What can you get from an individual-based model?

31. Best Known Models JABOWA
Botkin, D.B., J.F. Janak, and JR. Wallis. (1972).J. Ecol., 60:
FORET – the ‘GAP’ model from the JABOWA family of models. Simulates growth and competition for resources, particularly light, on patches of 1/10 Ha
Shugart et al. (1977) J. of Eviron. Man. 5:

32. JABOWA FOREST III
Ngugi et al., Ecol Mod (2011)

33. Hybrid Models

36. 3-PG Acronym Physiological Processes Predicting Growth
Simple, process-based model to predict growth and development of even-aged stands.
Uses basic mean-monthly climatic data, and simple site factors and soil descriptors.
Runs on monthly time step.
Parameterized using stand-level data.
Deterministic

37. 3-PG Flow Chart

38. Main Components of 3-PG
Production of biomass – Based on environmental modification of light use efficiency and constant ratio of NPP to GPP.
Biomass partitioning – Affected by growing conditions and tree size.
Stem morality – Based on self-thinning rule.
Soil water balance – A single soil layer model with evapo-transpiration determined from Penman-Monteith equation.
Stand properties – Determined from biomass pools and assumptions about specific leaf area, branch+bark fraction, and wood density.

39. Environmental constraints on photosynthesis for Douglas-fir vary seasonally in the Pacific NW, U.S.A.
soil water
evaporative
demand
suboptimal
temperature
Frost limitations
Autumn
Summer
Winter
Spring

40. 3-PG Uses
Stand dynamics for single age, monoculture stands of mostly evergreen trees
Generates:
foliage (Leaf Area Index), woody tissue and root biomass, conventional stand attributes (volume, BA, stocking),
soil water content and water usage.

41. ( )

42. Predicted stressed (red) and improved areas (green) since 1950-75 period

43. StandCarb Gap Model Multi species Has neighboring effects
Can mimic different types of Disturbance
Can model succession

44. StandCarb
Spatially explicit interactive cell structure, multiple species, allows for various disturbances.
StandCarb
Harmon and Moreno 2009

45. StandCarb Limitations: Much slower to run than BiomeBGC
Impractical over large landscapes.
Harder to use real data over large areas or long times.
Not a lot of documentation
Hard to learn how to use correctly
No nutrient cycling

46. Ecosystem Deomgraphic (ED) Model