1. Vegetation and
Energy Balance

2. So what is that net radiation (Rn) used for?
Rn = LE + H + M + G
where LE is latent energy, H is sensible heat,
M is biochemical energy, and G is ground heat flux

3. Daily Radiation Budget

5. Blandy Experimental Farm, north-central Virginia
LOW – Terrain Complexity
HIGH – Precipitation

6. LATE SUCCESSION MIDDLE SUCCESSION
Here is an aerial photo of part of my study sites to give you a general idea of how it looks like. The foreground is middle succession, the background is late succession. The early succession is not shown in this pic, but it is right there. You can see a clear vegetation gradient in here, from densely wooded late succ. To a more open mid-succ.
Plant elementary(algorithm) relationships: from aboveground biomass to estimate root biomass Nicklers & Enq(v)uils
MIDDLE SUCCESSION

7. Study Site Blandy Experimental Farm Early Succession: ~10 yr
VIRGINIA
Early2
Late1
Late2
Early Succession: ~10 yr
Mid-Succession: ~25 yr
Late Succession: >90 yr
Mid2
Mid1
Early1
Here is my study site at the Blandy Experimental Farm. It is located at Shenandoah Valley in northern Virginia (39.06oN, 78.07oW, elevation 183m). It has a temperate climate with annual rainfall of 940 mm, the average January T is -1.0 oC, and the average July T is 23.5 oC.
Because succession usually happens in a long temporal span, at least lasting for decades. Researchers use space to substitute time when studying successional systems, meaning to use several sites that are at different successional stages and under the same climate.
That’s the method I used to study succession at BEF. I chose 6 sites that are of 3 successional stages, early, mid, and late. Each succ. Stage has 2 sites. So naturally it forms two series of succession by location.
Blandy Experimental Farm

8. Late
Middle
Early
Here are my six succ sites. The early successional sites are dominated by goldenrod, thistles, and some grass species. The middle succession sites have herbaceous species similar to the early successional sites, and shrubs like bittersweet, buckthorn, and honey suckle; trees such as honey locust, osage orange, and tree of heaven. The late successional sites are deciduous forests composed mainly of oak and hickory with some understory shrubs and forb species.

9. Summer Soil Temperature at 2cm
Soil temp has dominant control on Rs, so I will talk about the temp effect first.
This is the hourly soil T in the summer of early mid and late successional stages.
The dashed lines are average soil temperature of each successional stage.
The average soil T is about 2 degrees higher in the early and mid succ stage than in the late succ stage. And the peak daily soil T difference among sites is up to 6 degree C
In addition the thermal amplitude of early successional sites is greater than the late successional sites. The soil of early successional sites is warmer during the day and cooler at night. The forest offers greater buffer to the soil and causes smaller diurnal temperature shift at late succ.
Wang et al. (2010)

10. Vegetation and Water Balance Atmosphere E P E Plant Canopy R S Surface
This can be relatively
large in systems with
numerous small rainfall
events or with large plant
canopies.
Plant
Canopy
Surface
Water S
throughfall / stemflow
Runoff/
Runon R
P = precipitation
E = evaporation

11. } T T Root Zone Water (W) D Atmosphere E E P E Plant Canopy
throughfall / stemflow R
0-10 cm
Water S
Surface
Water
10-? cm
Water
gravity
small }
Root Zone
Water (W)
infiltration
Runoff/
Runon
High concentration of roots in
upper soil layers.
Minimal evaporation from lower
soil layers under unsaturated
conditions.
Groundwater D

12. So, our relatively simple water balance is:
S + W = (P + Ron) - (Roff + D + E + T)
What are the factors that control different aspects of the
water budget?
Climate/Weather
Soil texture and structure
Vertical plant canopy structure
Vertical rooting distribution
Horizontal plant community structure
Topography

14. Hydraulic Lift

15. Vegetation and Wind
Alters roughness length
Affects shear stress on the surface
Traps wind-blown material