impacts of cattle grazing on spatio-temporal variability of soil moisture and above-ground live plant

281 Pages·2013·12.17 MB·English

IMPACTS OF CATTLE GRAZING ON SPATIO-TEMPORAL VARIABILITY OF SOIL MOISTURE AND
ABOVE-GROUND LIVE PLANT BIOMASS IN MIXED GRASSLANDS
By
Ravinder Virk
(M.Sc., M.A., B.A. (school honors))
A thesis submitted to
The Faculty of Graduate and Postdoctoral Affairs
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
Department of Geography and Environmental Studies
Carleton University
Ottawa, Ontario
(November, 2012)
© Ravinder Virk
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Abstract
Areas with relatively high spatial heterogeneity generally have more biodiversity than spatially
homogeneous areas due to increased potential habitat. Management practices such as
controlled grazing also affect the biodiversity in grasslands, but the nature of this impact is not
well understood. Therefore this thesis studies the impacts of variation in grazing on soil
moisture and biomass heterogeneity. These are not only important in terms of management of
protected grasslands, but also for designing an effective grazing system from a livestock
management point of view. This research is a part of the cattle grazing experiment underway in
Grasslands National Park (GNP) of Canada since 2006, as part of the adaptive management
process for restoring ecological integrity of the northern mixed-grass prairie region. An
experimental approach using field measurements and remote sensing (Landsat) was combined
with modelling (CENTURY) to examine and predict the impacts of grazing intensity on the
spatial heterogeneity and patterns of above-ground live plant biomass (ALB) in experimental
pastures in a mixed grassland ecosystem. The field-based research quantified the temporal
patterns and spatial variability in both soil moisture (SM) and ALB, and the influence of local
intra-seasonal weather variability and slope location on the spatio-temporal variability of SM
and ALB at field plot scales. Significant impacts of intra-seasonal weather variability, slope
position and grazing pressure on SM and ALB across a range of scales (plot and local (within
pasture)) were found. Grazing intensity significantly affected the ALB even after controlling for
the effect of slope position. Satellite-based analysis extended the scale of interest to full
pastures and the surrounding region to assess the effects of grazing intensity on the spatio-
temporal pattern of ALB in mixed grasslands. Overall, low to moderate grazing intensity
ii
showed increase in ALB heterogeneity whereas no change in ALB heterogeneity over time was
observed for heavy grazing intensity. All grazing intensities showed decrease in spatial range
(patch size) over time indicating that grazing is a patchy process. The study demonstrates that
cattle grazing with variable intensity can maintain and change the spatial patterns of vegetation
in the studied region. Using a modelling approach, the relative degrees to which grazing
intensity and soil properties affect grassland productivity and carbon dynamics at longer time-
periods were investigated. Both grass productivity and carbon dynamics are sensitive to
variability in soil texture and grazing intensity. Moderate grazing is predicted to be the best
option in terms of maintaining sufficient heterogeneity to support species diversity, as well as
for carbon management in the mixed grassland ecosystem.
Acknowledgements
I would like to extend sincere thanks to my supervisor, Dr. Scott Mitchell, for his guidance and
valuable feedback throughout my PhD program. Special thanks go to my advisors Dr. Andrew
Davidson and Dr. Elyn Humphreys for their time, helpful suggestions and comments.
This thesis was partially funded by a NSERC Discovery research grant awarded to Dr. Scott
Mitchell, as well as in-kind contribution of Parks Canada; special thanks go to Parks Canada for
providing logistics and data support. I also acknowledge the financial support in the form of
"Torrance Graduate Scholarship 2008" from the Department of Geography and Environmental
Studies, Carleton University.
I had substantial support throughout the duration of my PhD program and would like to make
special note of all the people who made this journey, both comforting and manageable. I
would especially like to acknowledge my friend Sheri Burke for reviewing my initial work and
giving me valuable advices. I would also like to thank my field assistant Benjamin Deschamps
for the long driving hours and assisting me with the collection of data throughout the field work
conducted in summer 2008. I would also like to thank all the people, especially Pat Fargey and
Rob Sissons at the Grasslands National Park (GNP) in Val Marie, Saskatchewan for providing
resources, friendly smiles and enthusiasm towards my work; and Melody Mastad from Carleton
University library for sharing her knowledge of grazing management in Saskatchewan and her
support throughout my PhD program. From my colleagues and friend during my work at
Agriculture Canada, I would like to thank Kevin Crichlow for providing help with ArcGIS. Special
thanks go to Kristie for all her support especially at the end of my PhD journey. I am forever
indebted.
I would like to thank my family for all their support and encouragement towards completion of
my PhD. My deepest appreciation goes to my sweetest mom and best friend Ehab who have
been incredibly supportive emotionally, financially and confident in my ability to accomplish
what I started.
Finally, I would acknowledge the Carleton University and all the people who have touched my
life in some way with their friendly smiles and inquisitive nature regarding my completion of
thesis, in turning my dream into reality. Big thanks to all of you.
This thesis is solely dedicated to my mom, without her love and encouragement; it would have
been an impossible task.
Table of Contents
Abstract.....................................................................................................................................................ii
Acknowledgements.................................................................................................................................iv
Table of Contents.....................................................................................................................................v
List of Tables............................................................................................................................................ix
List of Figures...........................................................................................................................................x
List of Appendices..................................................................................................................................xv
1.0 Introduction.......................................................................................................................................1
1.1 Heterogeneity: Definition, importance and factors causing heterogeneity..............................4
1.2 Importance of grazing-induced heterogeneity in Grasslands National Park, SK, Canada 6
1.3 Why is Research Required?.............................................................................................................6
1.4 Importance of Scale..........................................................................................................................8
1.5 Research Objectives..........................................................................................................................8
1.6 Dissertation Structure and Organization......................................................................................11
2.0 Historical Perspective on the Grasslands in North American Great Plains Region..................13
2.1 North-American Great Plains Region............................................................................................13
2.1.1 Grasslands in Saskatchewan...................................................................................................18
2.1.2 Grasslands National Park, Saskatchewan..............................................................................21
2.2 Dominant factors affecting the formation and maintenance of grasslands in North America
.................................................................................................................................................................24
2.2 1 Climate.......................................................................................................................................24
2.2.2 Water and Nutrient Availability.............................................................................................26
2.2.3 Fire.............................................................................................................................................29
2.2.4 Introduction of exotic or non-native plant species..............................................................31
2.2.5 Grazing.......................................................................................................................................31
3.0 Methodology....................................................................................................................................37
3.1 Study Area........................................................................................................................................37
3.2 Field Data, Experimental Design and Methods...........................................................................42
3.2.1 Field Experimental design.....................................................................................................43
3.2.2 Soil Moisture: methods and data...........................................................................................46
3.2.3 Above-ground live plant Biomass: methods and data.........................................................49
3.2.4 Weather Data...........................................................................................................................54
3.3 Satellite Data, processing, and sampling design..........................................................................55
3.3.1 Image pre-processing..............................................................................................................57
3.3.2 Identification of Grazed and Ungrazed Sites with variable grazing intensity (Gl)............58
3.3.3 Sampling design for satellite based data analyses................................................................58
3.4 Data analysis and methods............................................................................................................59
3.4.1 Geostatistical analysis using semivariograms.......................................................................60
3.4.2 Moran's I ...................................................................................................................................65
3.4.3 Measures of Heterogeneity....................................................................................................66
3.5 Modeling..........................................................................................................................................68
3.5.1 CENTURY Model.......................................................................................................................69
3.5.2 Parameterization of the model and model set-up..............................................................70
3.5.3 Sensitivity Analyses: Grazing Intensity and Soil Texture......................................................75
3.6 Research Contributions...................................................................................................................76
4.0 Detection of Spatio-temporal Variation and Pattern in Field-based Soil Moisture (SM) and
Above-ground live plant biomass (ALB): A case study of Experimental Pastures located in East
Block, GNP, Saskatchewan....................................................................................................................79
4.1 East Block experimental site characteristics................................................................................81
4.2. Results.............................................................................................................................................85
4.2.1 Soil Moisture............................................................................................................................85
4.2.1.1 Impact of local Intra-seasonal weather conditions.......................................................85
4.2.1.2 Effect of Slope Location and Time...................................................................................91
4.2.2 Aboveground live plant biomass..........................................................................................101
4.2.2.1 Impact of local Intra-seasonal weather conditions.....................................................101
4.2.2.3 Spatio-temporal variability in ALB between pastures and within pastures 101
4.2.3 Effect of Grazing on SM and ALB..........................................................................................109
4.2.3.1 Soil moisture and Grazing..............................................................................................110
4.2.3.2 ALB and Grazing..............................................................................................................I l l
4.2.4 Spatial patchiness as a result of grazing disturbance........................................................112
4.2.4.1 Soil Moisture....................................................................................................................112
4.2.4.2 ALB....................................................................................................................................114
4.3 Discussion.......................................................................................................................................115
4.3.1 Spatio-temporal variability in SM and ALB.........................................................................116
4.3.2 Short-term grazing disturbance on plot-scale SM and ALB...............................................119
4.3.3 Spatial pattern in SM and ALB...............................................................................................121
4.4 Applicability of results, limitations and research recommendations......................................123
4.5 Conclusions....................................................................................................................................124
5.0 Semivariogram Approach to determine Spatio-temporal Variability in Satellite-based Above­
ground Live Plant Biomass (ALB): Case Study of Grazed and Ungrazed Experimental Pastures 126
5.1 Data Analyses.................................................................................................................................128
5.2 Results............................................................................................................................................128
5.2.1 Local Weather Variability......................................................................................................128
5.2.2 Effect of different grazing intensities on ALB spatio-temporal heterogeneity................130
5.2.3 Spatial patterns of ALB..........................................................................................................140
5.3 Discussion.......................................................................................................................................143
5.3.1 Spatial heterogeneity in grazed and ungrazed pastures...................................................143
5.3.2 Effects of Grazing Intensity and slope location on ALB......................................................147
5.3.3 Spatial patterns of ALB overtime........................................................................................151
5.4 Applicability of results, limitations and research recommendations......................................152
5.5. Conclusions...................................................................................................................................154
6.0 Modelling productivity and soil carbon dynamics of a mixed grassland ecosystem under
variable grazing intensities: A simulation analysis..........................................................................155
6.1 Introduction...................................................................................................................................155
6.1.1 Grasslands and modeling................................................................ 155
6.1.2 The grazing history of the Study Area: Grasslands National Park, SK, Canada...............156
6.1.3 The CENTURY Model.............................................................................................................157
6.1.4 Modeled variables of interest..............................................................................................157
6.1.5 Modeling Goals and Hypotheses.........................................................................................158
6.1.6 Addressing the Hypotheses: Two Modeling Scenarios......................................................159
6.1.7 Model Evaluation...................................................................................................................160
6.2 Results...........................................................................................................................................160
6.2.1 Validation of the CENTURY model.......................................................................................160
6.2.2 Model Predictions..................................................................................................................161
6.2.2.1 Impact of soil texture on the ALB, SOMTC and TOTSYC.............................................161
6.2.2.2 Impact of grazing intensity on the grassland productivity and total soil and plant
system carbon (Scenario 1)........................................................................................................163
(A) Results for predicted SOMTC and TOTSYC......................................................................163
(B) Results for predicted annual net primary productivity (above- and below-ground) 165
6.2.2.3 Effect of light, moderate and heavy grazing intensity on the model predictions for
ALB.................................................................................................................................................169
6.2.3 Sensitivity analyses.................................................................................................................170
6.2.3.1 Sensitivity to change in soil texture parameterizations.............................................170
6.2.3.2 Sensitivity to change in fraction of live shoots (flgrem) per month during a grazing
event..............................................................................................................................................176
6.3 Effect of grazing termination (Scenario 2)..............................................................................181
6.4 Discussion.......................................................................................................................................187
6.4.1 Effect of soil texture and grazing intensity on model predictions....................................187
6.4.2 Sensitivity analysis..................................................................................................................191
6.5 Applicability of results, limitations and research recommendations......................................194
6.6 Conclusions....................................................................................................................................196
7.0 Summary and Conclusions.........................................................................................................198
Bibliography.........................................................................................................................................203
Appendices...........................................................................................................................................237
List of Tables
Table 3.1 Summary of number of experimental plots within each pasture and total number of
measurements taken per plot..........................................................................................................46
Table 3.2 Landsat TM image acquisition information....................................................................56
Table 3.3 Monthly summaries of daily data from Environment Canada climate station Mankota
(1970-2007).....................................................................................................................................72
Table 4.1 Generalized soil characteristics in experimental plots (extracted from Saskatchewan
Institute of Pedology (1992).............................................................................................................84
Table 4.2 Summarized May and June 2008 SM semivariogram results......................................97
Table 4.3 Summarized May and June 2008 ALB semivariogram results....................................107
Table 5.1 Summarized sill, range and MSH results for different grazing intensities for years
2007, 2008 and 2010.......................................................................................................................138
Table 6.1 Predicted and measured Above-ground live plant Biomass (ALB in g m'2), Grasslands
National Park.....................................................................................................................................160
Table 6.2 Effects of soil texture on ALB (g m 2): An example of June 2008 ALB under light,
moderate and heavy grazing...........................................................................................................162
Table 6.3 Range of variability in above-ground- and below-ground NPP (g C m~2 yr"1) for low,
moderate and heavy grazing intensity (2006 to 2020)...........................................................168
Table 6.4 ALB sensitivity to variability within clay loam soil texture during grazed and ungrazed
period.............................................................................................................................................173
Table 6.5 Effects of grazing intensity and grazing termination on predicted ALB (g m 2) during
2013-2020....................................................................................................................................182
Table 6.6 Effects of grazing intensity and grazing termination on predicted SOMTC (kg m'2) and
TOTSYC (kg m 2) for years 2013 to 2020.....................................................................................184