This document summarizes research on the hydrologic and erosion impacts of woodland encroachment into sagebrush steppe ecosystems and treatments to remove encroaching trees. Key findings include: 1) Woodland encroachment can increase hydrologic vulnerability by reducing vegetation cover and increasing the connectivity of bare ground, leading to concentrated overland flow and amplified erosion. 2) Prescribed fire initially enhances runoff and erosion by creating more uniformly bare conditions but can effectively reestablish sagebrush vegetation in the long-term to improve hydrologic function. 3) Research at sites in Utah evaluated the short and long-term effects of woodland encroachment and tree removal techniques on vegetation, infiltration,

2. A B
C D

3. • IMPROVE UNDERSTANDING OF
HYDROLOGIC & EROSION PROCESSES
FOR WOODLAND ENCROACHED
SAGEBRUSH STEPPE,
• QUANTIFY IMPACTS OF WOODLAND
ENCROACHMENT ON VEGETATION &
INFILTRATION, RUNOFF, & EROSION,
• DETERMINE THRESHOLDS FOR INCREASED
RUNOFF & EROSION ASSOCIATED WITH
DECLINE IN UNDERSTORY VEGETATION,
• QUANTIFY SHORT-TERM & LONG-TERM
IMPACTS OF TREE REMOVAL BY FIRE ON
VEGETATION & HYDROLOGIC &
EROSION PROCESSES

4. • PHASE II-III WOODLANDS
• SITES AT TRANSITION OF WARM/DRY TO
COOL/WET SOIL TEMP/WATER REGIMES
• SANDY LOAM SURFACE SOILS
• ~25% TREE COVER; ~75% INTERCANOPY
• BARE: 50% AT MC, 60% AT ON
Marking Corral Site
Pinyon-Juniper
Onaqui Site
Utah Juniper
Pierson et al., 2010 – Rangeland
Ecology & Management
~300 mm precip
7ºC temp
~300 mm precip
~9ºC temp
Marking
Corral
Onaqui

5. Marking Corral OnaquiTREATMENTS
Pre-Treatment/Control Pre-Treatment/Control
Prescribed Fire Prescribed Fire
Sampling
Pre-treatment
1 Yr Post-Treatment
2 Yr Post-Treatment
9 Yr Post-Treatment

6. Tree Zone
Interspace Tree Coppice
Shrub-
Interspace
Zone
Shrub
Coppice
SMALL PLOT
SCALE –
0.5 M2
LARGE PLOT SCALE - 13 M2
SITE CHARACTERIZATION PLOTS - 990 M2
SITE LEVEL

7. Site Characterization Plots (990 m2)
Tree Cover
Tree and Shrub Density
Canopy and Ground Cover
Small Plots (0.5 m2) & Point Scale
Canopy and Ground Cover
Surface Roughness
Litter Depth
Hydrophobicity
Aggregate Stability
Soil Moisture
Soil Bulk Density and Texture
Large Plots (13 m2)
Canopy and Ground Cover
Canopy and Basal Gaps
Surface Roughness
Pierson et al., 2010 – Rangeland Ecology & Management; Williams et al., 2014 - Ecohydrology

8. Small Plots (0.5 m2) Large Plots (13 m2)
64 mm h-1
102 mm h-1
45 min
Oscillating Arm Simulator CSU-Type Standpipe Simulator
Walnut Gulch
Simulator

9. • 25% TREE COVER; 75% INTERCANOPY
• 16% SHRUB COVER; 12% AS SAGEBRUSH
• 7% PERENNIAL GRASS COVER
• <1% CHEATGRASS COVER
• 50% BARE
Marking Corral Site
SL Pinyon - Utah Juniper
Onaqui Site
Utah Juniper
Pierson et al., 2010 – Rangeland Ecology & Management
• 26% TREE COVER; 74% INTERCANOPY
• 3% SHRUB COVER, NEARLY ALL AS SAGE
• 8% PERENNIAL GRASS COVER
• <1% CHEATGRASS COVER
• 62% BARE

10. Interspace Tree Coppice
Shrub
Coppice
Interspace Tree Coppice
Shrub
Coppice
Marking
Corral
Onaqui
43 mm
52 g m-2
5 mm
4 g m-2
8 mm
3 g m-2
39 mm
207 g m-2
6 mm
38 g m-2
23 mm
46 g m-2

11. 5-20 mm
4-38 g m-2
39-57 mm
36-207 g m-2
38-58 mm
222-296 g m-2
Shrub-Interspace

12. Marking Corral Onaqui
34 mm
346 g m-2
Shrub-Interspace Shrub-Interspace Tree
31 mm
491 g m-2
11 mm
78 g m-2 43 mm
1893 g m-2
Tree
35 mm
41 g m-2
Interspace Tree Coppice
Shrub Coppice
Interspace Tree Coppice
Shrub Coppice
8 mm
48 g m-2
21 mm
46 g m-2
49 mm
351 g m-2
22 mm
220 g m-2
13 mm
294 g m-2

13. • 9% SHRUB COVER; 6% SAGE COVER
• 63% GRASS COVER & 1% FORB COVER
• 32% PERENNIAL GRASS COVER
• 30% CHEATGRASS COVER
• 53% BARE (13% AS ROCK)
Marking Corral
Onaqui
Williams et al., 2018 – Catena (In Press)
• 11% SHRUB COVER, <1% SAGE COVER
• 40% GRASS COVER & 14% FORB COVER
• 21% PERENNIAL GRASS COVER
• 16% CHEATGRASS COVER
• 51% BARE (22% AS ROCK)

14. Marking Corral Onaqui
58% Bare
Hydro-
phobic
78%
Bare
Interspace
Shrub Coppice
Interspace
Shrub Coppice
61%
Bare
23% Bare
Hydro-
phobic
75%
Bare 65%
Bare
Tree Coppice Tree Coppice
5% Shrub
29% Grass
77% Bare
61% Grass; 49% Litter
2% Shrub
62% Grass
51% Bare
Tree
72% Grass; 69% Litter
Tree
Shrub-Interspace Shrub-Interspace

15. Williams et al., 2018 – Catena (In Press)

16. Marking Corral Onaqui
Shrub-Interspace
Tree
Shrub-Interspace
Tree
Marking Corral Onaqui
Control Control
37 mm RO
325 g m-2 Sed 12 mm RO
20 g m-2 Sed
39 mm RO
192 g m-2 Sed 9 mm RO
38 g m-2 Sed
Shrub-Interspace
Tree
Shrub-Interspace
Tree
9 Yr Post-Fire 9 Yr Post-Fire
6 mm RO
4 g m-2 Sed 6 mm RO
4 g m-2 Sed
15 mm RO
58 g m-2 Sed 15 mm RO
37 g m-2 Sed
Nouwakpo et al., 2018 – Catena (In Review)

17. WOODLAND ENCROACHMENT
• IMPACT OF WOODLAND ENCROACHMENT ON HYDROLOGIC VULNERABILITY
DEPENDS ON THE INFLUENCE OF TREE DOMINANCE ON BARE INTERSPACE
CONNECTIVITY.
• AMPLIFIED CROSS-SCALE EROSION LARGELY RELATED TO A SHIFT TO
CONCENTRATED FLOW AS THE DOMINANT EROSION PROCESS WHERE BARE
GROUND > 50-60% IN THE INTERCANOPY.
PRESCRIBED FIRE – SHORT-TERM
• BURNING INCREASES CONNECTIVITY OF RUNOFF AND EROSION SOURCES BY
CREATING MORE UNIFORM BARE SURFACE CONDITIONS.
• RESULTS IN ENHANCED SEDIMENT DETACHMENT AND DELIVERY BY
CONCENTRATED FLOW AND SHORT-TERM INCREASED CROSS-SCALE EROSION.

18. LONG-TERM EFFECTS
• OUR RESULTS DEMONSTRATE TREE REMOVAL BY FIRE CAN EFFECTIVELY RE-
ESTABLISH SAGEBRUSH VEGETATION AND THEREBY IMPROVE HYDROLOGIC
FUNCTION.
• CAVEAT: RESULTS IMPROVE UNDERSTANDING THESE SYSTEMS, BUT LIMITED TO
ONLY A FEW SITES.

19. Williams et al., 2016 – Rangeland
Ecology & Management
Williams et al., 2017 – Rangelands
Hernandez et al.,
2017 – Water
Resources Research
https://apps.tucson.ars.ag.gov/rhem/

20.  
 
exp 6 397 8 335 3 252 3440
1 exp 6 397 8 335 3 252 3440
( 756)
. . S . bare q
. . S .
P
bare q
n
   
    


• Probability of overland flow to
concentrate, Al-Hamdan et al.
2013:
Al-Hamdan et al., 2013 – Transactions of
ASABE 56: 539-548.

21. Hydrologic Impacts of Woodland Encroachment and Tree Removal Practices
Pierson et al., 2010. Hydrologic vulnerability of sagebrush steppe following pinyon and juniper encroachment. Rangeland Ecology
and Management 63:614-629.
Cline et al., 2010. Hydrologic response to mechanical shredding in a juniper woodland. Rangeland Ecology and Management
63:467-477.
Pierson et al., 2013. Hydrologic and erosion responses of sagebrush steppe following juniper encroachment, wildfire, and tree
cutting. Rangeland Ecology and Management 66:274-289.
Williams et al., 2014. Can wildfire serve as an ecohydrologic threshold-reversal mechanism on juniper-encroached shrublands?
Ecohydrology 7:453-477.
Pierson et al., 2014. Short-term effects of tree removal on infiltration, runoff, and erosion in woodland-encroached sagebrush steppe.
Rangeland Ecology & Management 67-522-538.
Pierson et al., 2015. Short-term impacts of tree removal on runoff and erosion from sagebrush-steppe hillslopes. Rangeland Ecology
and Management 68:408-422.
Williams et al., 2016. Structural and functional connectivity as a driver of hillslope erosion following disturbance. International Journal
of Wildland Fire 25:306-321.
Williams et al., 2018. Vegetation, hydrologic, and erosion responses to mechanical tree removal in sagebrush steppe. Rangeland
Ecology and Management In Press.
Williams et al., 2018. Effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and ecohydrologic function on
woodland-encroached sagebrush rangelands, Great Basin, USA: Part I: Vegetation, hydrology, and erosion responses.
Catena In Press.
Nouwakpo et al., 2018. Effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and ecohydrologic function on
woodland-encroached sagebrush rangelands, Great Basin, USA: Part II: Runoff and sediment transport at the patch scale.
Catena In Review.
RHEM Model Development and Application
Al-Hamdan et al., 2012. Concentrated flow erodibility for physically based erosion models: Temporal variability in disturbed and
undisturbed rangelands. Water Resources Research 48:W07504.
Al-Hamdan et al., 2013. Risk assessment of erosion from concentrated flow on rangelands using overland flow distribution and shear
stress partitioning. Transactions of the ASABE 56:539-548.
Al-Hamdan et al., 2015. Rangeland Hydrology and Erosion Model (RHEM) enhancements for applications on disturbed rangelands.
Hydrological Processes 29:445-457.
Williams et al., 2016. Incorporating hydrologic data and ecohydrologic relationships into ecological site descriptions. Rangeland
Ecology and Management 69:4-19.
Williams et al., 2016. Application of ecological site information to transformative changes on Great Basin sagebrush rangelands.
Rangelands 38:379-388
Hernandez et al., 2017. The Rangeland Hydrology and Erosion Model: A dynamic approach for predicting soil loss on rangelands.
Water Resources Research 53:9368-9391.
QUESTIONS?