Forestry and Hydrology_Week_1

What is interception loss in forestry?

The loss of precipitation that does not reach the soil because it is intercepted by tree canopies.

What are the typical transpiration values for Douglas-fir in winter?

10 to 30 mm/month.

What are the typical transpiration values for Douglas-fir in summer?

50 to 100 mm/month.

What does the BACI approach stand for in detecting hydrological effects?

Before-After/Control-Impact.

What methods are used to detect the impacts of forest on hydrology

BACI (before-after control impact) study

→ ex: paired catchment study

Time series effect

→looking at the hydrology of a region before and after an event

Spatial comparison:

→ space for time substitution

What kind of Runoff process occurs in forests?

Stormflow is generated through through flow and saturation excess overland flow

What is considered hydrologic recovery post-logging?

Recovery to pre-logging forest state, though not exact due to species and stem density changes.

What is meant by 'Peak Recovery' in snowpack studies?

The seasonal peak snowpack water equivalent.

In the context of forest hydrology, what does 'ablation recovery' refer to?

Mean ablation rate during the melt season.

What typically influences transpiration rates in coastal forests?

Weather, season, soil wetness, forest characteristics (species, tree density, stand age).

Why is infiltration-excess overland flow rare in forests?

Forests have high infiltration capacity.

Alsea Watershed Oregon study

OBJECTIVE:
→ looking at the effect of forest harvesting on stream flow in rain-dominated coastal catchments

VARIABLES:
→ Annual yield
→ August water yield
→ Annual peak flows

METHOD:
→ Three water sheds were analyzed with
Flynn Creek being the control.
Needle Branch experiencing clearcut logging, hot slash burn and no buffer
Deer Creek experiencing patch logging, slash burn and riparian buffer

RESULTS:
→ patch logging has a lower impact on the hydrology of a forest compared to other kinds of logging

How are the results of a paired-catchment study interpreted?

No effect:
→ no effect is spotted when the post-harvest data falls within it is distributed above and below thepre-harvest regression within the 95% confidence interval of

CASE STUDY: Fool Creek Colorado, snow dominated

OBJECTIVE:
→ Look at how clearcutting would influence streamflow in an interior snow dominated catchment

VARIABLES:
→ Annual water yield
→ August water yield
→ Annual peak flows

RESULT:
→ Annual peak flows are happening earlier
→ Forest removal causes snow to melt faster
→ Forest removal results in more snow accumulation (this is because forests can reduce the accumulation of snow)

How to calculate hydrologic recovery at the forest stand scale?

HRi = 100% [ (x1-xo) / xr-xo)

where:
→ xr = quantity measured as a reference for forest stand
→ xi = measured process or quantity of interest for a given stand
→ xo= quantity measured at a recently harvested site

Australia case study

As trees get older, the water yield increases but interestingly soil evaporation stays the same.

What does interception depend on?

Meterological conditions
Available energy considerations ( latitude, day/night, season)
Air humidity
Precipitation amount

Wind speed