Soil moisture impacts of redcedar encroachment
in the Cross Timbers ecoregion
Chris Zou, Lei Qiao, Elaine Stebler, Bharat Acharya Department of Natural Resource Ecology and Management
Oklahoma State University
Multiple million acres of redcedar encroachment in Oklahoma
OSU Rangeland Research Station (OSURRS)
10 – 30%, 44,522 ac.
30 – 70%, 27,289 ac.
> 70%, 8,420 ac.
Modified from Mark & Dickinson 2008 Frontiers in
Ecology and the Environment
“In areas where
natural runoff is less
than 10% of mean
annual precipitation,
afforestation can result
complete loss of
runoff.”
“Water levels going back
to 1925 for four of
Texas’s biggest rivers”
revealed “Rivers on the
Edwards Plateau are not
disappearing, but they
are increasing in flow.” Wilcox and Huang 2010 Geophysical Research Letter
E grass T grass
Recharge
Runoff
E grass T grass T cedar
Runoff
Recharge
Cedar trees
E cedar
ECH2O Station
ΔSoil ⌫ ⌫
⌫ Sapflow Unit
⌫
⌫
⌫
⌫
Acknowledgement
Jenny Hung Amanda West Shujun Chen Giulia Caterina Elaine Stebler
Dave Engle Don Turton Rod Will Sam Fuhlendorf Kim Winton
Funding sources
• South-central Climate Science Center
• Oklahoma Agricultural Experiment Station
• USGS/NWRI grant (G09AP00146)
• NSF DEB-1413900
• NSF EPSCoR (NSF-1301789)
Use of temporal soil moisture data to
interpret streamflow responses
High resolution soil moisture data to
constraint and parameterize hydrological
model
Infiltration excess overland flow
Saturation excess overland flow
Subsurface runoff
Streamflow generation in rangeland
E01
E02
G01 G02
G03
E03
F01
F02
F03
H flume
Soil moisture station
Watershed boundary
100 m N
E1
E3
E2
F1
E04
E05
E06
E07
E08
E09
G04
G05
G06
G07
G08
G09
G1
G2
G3
• 3 grassland watersheds and 4 redcedar
watersheds;
• 3 EC-5 swc arrays for each watersheds
(a total of 21 stations);
• Add 9 stations in oak watersheds in 2015
from NSF EPSCoR
Soil water content (SWC) and Water Depth
• Grassland watersheds (n = 9)
• Encroached watersheds (n = 12)
• Water content at 4 depths every 15 min
• Soil water storage (1 meter soil)
= SWC5 * 0.1+SWC20*0.2+SWC45*0.3 + SWC80*0.4
Streamflow
Grassland watersheds Redcedar watersheds
Construction of flumes and weirs
Volu
metr
ic w
ate
r conte
nt (m
3 m
-3)
0.0
0.2
0.4
0.0
0.2
0.4Grassland
Encroached
0.0
0.2
0.4
0.0
0.2
0.4
Date
6/09 12/09 6/10 12/10 6/11 Wate
r depth
(mm
)
150
300
450 Grassland
Encroached
B4:80 cm
C2: 0 - 100 cm
B3: 45 cm
B2: 20 cm
B1: 5 cm
6/09 12/09 6/10 12/10 6/11
Pre
cip
.(m
m)
0
50
100
150
200
-500
50
A1: Monthly rainfall
A2: Divergence from mean (P - P)
DormantActive
Juniper trees
Grasses
C1: Phenology
Zou et al. 2014. Hydrological Process
Ru
no
ff d
ep
th
0
2
4
6
8
10
12
14
16
Grassland
Encroached
Pre
cip
itati
on
0
10
20
30
40
50
2010 20112009
86 10 12 2 4 6 8 10 12 2 4
Wa
ter
de
pth
0
100
200
300
400Saturation excess runoff threshold
A.
B.
C.
Coupling of runoff and soil water storage
Precipitation = 915 mm
G E
An
nu
al
run
off
de
pth
(m
m)
0
40
80
120
160
2008 15%
2%
G E G E
2009 2010
Precipitation = 902 mm Precipitation = 668 mm
15% 14%
2% 5%
Do water retreat when redcedars move in?
Use of temporal soil moisture data to
interpret streamflow response
High resolution soil moisture data to
constraint and parameterize hydrological
model
• Models mostly developed for cropland, grassland
or forest
• Lack of species specific parameter for eastern
redcedars
• Lack of long term streamflow data from large
eastern redcedar watersheds for calibration and
validation
• Limited runoff events from experimental
watersheds
Challenges in simulating redcedar impact on streamflow
Wu et al. [2001]: (SPUR-91) model: 200 mm
increase of streamflow assuming woody cover being
reduced by 40%.
Afnowicz et al. [2005]: SWAT modeling within the
Edwards Plateau. ET reductions ranging from 31.94
to 46.62 mm/yr by removing juniper.
Bumgarner and Thompson [2012] suggested water
yield increase by an average of 36 mm by removing
juniper.
SIM
. Woody encroachment impacts on water budget: Uncertainty
High resolution soil moisture data to constraint
and parameterize hydrological model
Daily Stats
Model Validation in lower Cimarron River Basin Sim 1 Sim 2
Gauge
#1
Gauge
#2
Gauge
#3
Gauge
#4
Sim 1
Sim 2
Spatial and temporal swc data holds the key to
interpret streamflow response, especially in water-
limited system
Local swc network is effective in improving
hydrological models
Summary and future research opportunities
Summary and future research opportunities
Subsurface flow and recharge
Summary and future research opportunities
Integration of local, regional swc network (such as
Oklahoma Mesonet) with COSMOS, SMAP,
AirMOSS should provide new opportunity to
improve or build ecohydrological models