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Mammalian herbivores

Week 5 Fire-grazing synergism in grasslands

1

2 of 39

Grassland Drivers (review)

2

Mammalian

herbivores

Jayne Jonas

Periodic

fire

Mike Bowden

Climate/

periodic

drought

Jayne Jonas

Grassland Ecology

3 of 39

Grassland Drivers (review)

3

Mammalian

herbivores

Jayne Jonas

Periodic

fire

Mike Bowden

Climate/

periodic

drought

Jayne Jonas

Grassland Ecology

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Herbivory-related definitions

Plants being consumed

Herbage: all herbaceous biomass
Browse: edible leaves and twigs of woody plants
Forage: edible herbage and browse

Action of consumers

Grazing: consumption of standing forage
Browsing: consumption of browse

Society for Range Management (1998)

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Effects of defoliation

Direct

Loss of leaf area
Consumption of reproductive parts
Compensatory processes

Indirect

Increased light
Altered water and nutrient processes
Altered competition

5

P. Meiman

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Plant response depends on

Location of meristems
Growth stage/phenology
Remaining tissues

6

Evolutionary consequences

1. Avoid/resist

2. Tolerate

Source: National Range and Pasture Handbook (1997)

Elongated tillers

With intact growing points leaf material will continue to be produced.

-leaves grow from bottom up 🡪 leaf left becomes top of leaf.

If growing point removed 🡪 new growth from dormant basal buds if soil moisture is adequate, temperatures are within the plants growing range, and day length is appropriate. Leaf/stem remaining d/n continue to grow.

critical factors affecting regrowth: growing point removal, growth stage/seasonal timing (how much time is there to regrow; is plant already dormant), amount of green leaf material left following defoliation.

-more green leaves present following defoliation= faster regrowth if conditions (soil moisture and air temperature) are right.

Loss of meristems = loss of regrowth potential
Enough time to replace lost tissues, need to replace lost tissue
Loss of ability to capture energy/photosynthetic capacity

Palatability and robustness (traits of avoidance, resistance, or tolerance) both

arise from many traits and physiological processes,

notably photosynthetic capacity, growth rate and form,

leaf nitrogen, fiber, spines, and phenolic compounds. Selective

foraging in relation to these attributes filters plant species composition

at local to biogeographic scales182–186 and alters trait manifestation

at within-individual to macroevolutionary scales via

phenotypic plasticity and natural selection

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Plant response depends on

Location of meristems
Growth stage/phenology
Remaining tissues

7

Source: National Range and Pasture Handbook (1997)

Elongated tillers

Evolutionary consequences

1. Avoid/resist

2. Tolerate

With intact growing points leaf material will continue to be produced.

-leaves grow from bottom up 🡪 leaf left becomes top of leaf.

If growing point removed 🡪 new growth from dormant basal buds if soil moisture is adequate, temperatures are within the plants growing range, and day length is appropriate. Leaf/stem remaining d/n continue to grow.

critical factors affecting regrowth: growing point removal, growth stage/seasonal timing (how much time is there to regrow; is plant already dormant), amount of green leaf material left following defoliation.

-more green leaves present following defoliation= faster regrowth if conditions (soil moisture and air temperature) are right.

Loss of meristems = loss of regrowth potential
Enough time to replace lost tissues, need to replace lost tissue
Loss of ability to capture energy/photosynthetic capacity

Palatability and robustness (traits of avoidance, resistance, or tolerance) both

arise from many traits and physiological processes,

notably photosynthetic capacity, growth rate and form,

leaf nitrogen, fiber, spines, and phenolic compounds. Selective

foraging in relation to these attributes filters plant species composition

at local to biogeographic scales182–186 and alters trait manifestation

at within-individual to macroevolutionary scales via

phenotypic plasticity and natural selection

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Community composition

Detling (1988) Concepts of Ecosystem Ecology

Plant community responses

Decreasers
Increasers

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Community composition

Detling (1988) Concepts of Ecosystem Ecology

Plant community responses

Decreasers
Increasers

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Community structure

Oñatibia et al.(2018) Oikos

arid

intermediate

semi-arid

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Community structure

Oñatibia et al.(2018) Oikos

Higher productivity site

grasses less adapted to grazing
negative response to grazing

How do herbivores impact grasslands?

DIFFERS AMONG RANGELANDS – largely driven by overriding effects of climate/precipitation

Patagonian steppe – precip gradient

Looking at effects of sheep grazing pressure on vegetation structure (patches and distribution)

No diff in the number of patches with grazing pressure (low produ. Site had more patches than interm and high produc)

In

the low-productivity community, grazing (both moder-

ate and intensive) increased the frequency of small patches

in comparison to those ungrazed (ungrazed versus mod-

erately grazed: D = 0.149, p  0.001 and ungrazed versus

intensively grazed: D = 0.132, p = 0.002) (Fig. 3a) and did

not affect inter-patch-size distributions (Fig. 3d)

Finally, in the high-productivity com-

munity, there were only significant linear negative responses

to increasing grazing pressure from dominant species, indi-

cating lower total resistance in these environments. In sum-

mary, patterns found in these South American rangelands

with a similar biogeographical origin support the notion

that patchiness response to grazing pressure may depend on

the evolutionary context associated with the regional aridity,

which determines dominant species idiosyncrasy (Milchunas

et al. 1988).

Accumulated frequency (%) of patch-size (patch-size distribution) and inter-patch-size (inter-patch-size distribution) in three communities located along a regional productivity gradient (low-productivity community, intermediate-productivity community and high-productivity community), under three grazing intensities (ungrazed, moderately grazed and intensively grazed). Arrows indicate the maximum size reached by each distribution. Numbers between brackets show the number of patches or inter-patches sections in each curve. Tables indicate the D statistics and p-values resulting from Kolmogorov–Smirnov test between each pair of distribution curves: (*) between 0.05 and 0.01; (**) between 0.01 and 0.001; (***)  0.001; (ns) 0.05.

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Grassland response to grazing

Depends on:

climate
evolutionary history of grazing
productivity
plant composition
species of herbivore
grazing regime

duration
season
intensity

Milchunas et al. (1988) American Naturalist,

water ------------------🡪 light

vertical---------🡪 horizontal

Diversity peaks at low intensity grazing in areas with a short evolutionary history of grazing – change is slightly more pronounced in more productive subhumid systems (bottom row)

--upper left – favors shortgrasses

--lower right – favors tallgrasses

--lower left –favors short- to midgrasses

--upper right – favors mix of short, mid, and tallgrasses

Areas with long evolutionary history of grazing, more pronounced effects of climate

--semi-arid, less effect of grazing on species composition and maintained higher levels of productivity than those with short histories. Short stature plants competiting for water rather than light – so little change in competitive pressures, these species also typically regrow quickly after grazing.

--subhumid/higher productivity, diversity more responsive and peaks at intermediate grazing intensity.

Proposed by Milchunas et al. 1988, supported by Milchunas and Lauenroth (1993) and Diaz et al. (2007)

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Grassland response to grazing

Depends on:

climate
evolutionary history of grazing
productivity
plant composition
species of herbivore
grazing regime

duration
season
intensity

Milchunas et al. (1988) American Naturalist,

Diversity peaks at low intensity grazing in areas with a short evolutionary history of grazing – change is slightly more pronounced in more productive subhumid systems (bottom row)

--upper left – favors shortgrasses

--lower right – favors tallgrasses

--lower left –favors short- to midgrasses

--upper right – favors mix of short, mid, and tallgrasses

Areas with long evolutionary history of grazing, more pronounced effects of climate

--semi-arid, less effect of grazing on species composition and maintained higher levels of productivity than those with short histories. Short stature plants competiting for water rather than light – so little change in competitive pressures, these species also typically regrow quickly after grazing.

--subhumid/higher productivity, diversity more responsive and peaks at intermediate grazing intensity.

Proposed by Milchunas et al. 1988, supported by Milchunas and Lauenroth (1993) and Diaz et al. (2007)

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Fire vs Grazing

fire	grazing
Less selective	Preferences/selectivity
Litter, senesced biomass	Live biomass
Nutrients more evenly redistributed	Nutrients patchily redistributed
No impact on soil density	Trampling/compaction

Mike Bowden/Nancy Braker

Jayne Jonas

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Grazing vs Fire

Selectivity
Amount remaining
Redistribution of nutrients
Trampling/compaction

15

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16

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Fire x grazing synergism

Week 5 Fire-grazing synergism in grasslands

17

18 of 39

Grassland Drivers (review)

18

Mammalian

herbivores

Jayne Jonas

Periodic

fire

Mike Bowden

Climate/

periodic

drought

Jayne Jonas

Grassland Ecology

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Fire effects on forage

Scasta et al. (2016) Renew Food Agricul

Wanchuket al. (2024) Ag Ecosys Environ

Northern mixed-grass prairie

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Fire-grazing feedbacks

20

3-yr post-burn

Year of burn

Fuhlendorf and Engle (2004) J Appl Ecol

1-yr post-burn

2-yr post-burn

↓ Pr[Grazing]

Adapted based on

Scasta et al. (2016) Renew Food Agricul

↑ Pr[Fire]

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Fire-grazing feedbacks

21

3-yr post-burn

Year of burn

Fuhlendorf and Engle (2004) J Appl Ecol

1-yr post-burn

2-yr post-burn

Adapted based on

Scasta et al. (2016) Renew Food Agricul

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Shifting mosaic

Heterogeneity

Plant biomass
Composition
Habitat structure

22

3-yr post-burn

Year of burn

1-yr post-burn

2-yr post-burn

3-yr post-burn

Year of burn

1-yr post-burn

2-yr post-burn

3-yr post-burn

Year of burn

1-yr post-burn

2-yr post-burn

time

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Shifting mosaic

Heterogeneity

Plant biomass
Composition
Habitat structure

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Shifting Mosaic - Example

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Patch-burn grazing (PBG)

Disturbance-adapted grasslands

Fire and grazing
Higher precipitation

Similar or higher livestock performance
Increases diversity and heterogeneity

Oklahoma State Extension Bulletin

Scasta et al. (2016) Renew Food Agricul

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Small mammal response to PBG

Ricketts and Sandercock (2016) Ecosphere

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Grassland bird habitat needs

27

Bernath-Plaisted et al. (2023) Rangeland Ecol Manag

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Grassland bird response to PBG

Fuhlendorf et al. (2006) Ecological Applications

Abundance per point count

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Traditional ecological knowledge

29

Roos et al. (2018) PNAS

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Fire x grazing x browsing

Week 5 Fire-grazing synergism in grasslands

31

32 of 39

Grassland Drivers (review)

32

Mammalian

herbivores

Jayne Jonas

Periodic

fire

Mike Bowden

Climate/

periodic

drought

Jayne Jonas

Grassland Ecology

33 of 39

Browsers

Consume browse

Browse = leaves/twigs of woody plants

33

McNew et al. (2023)

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Woody plant survival

34

Donaldson et al. (2022) Ecology

Jayne Jonas

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Fire-grazing-browsing interactions

Source: Smit and Costsee (2019) The Ecology of Browsing and Grazing II

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Fire-grazing-browsing interactions

Source: Smit and Costsee (2019) The Ecology of Browsing and Grazing II

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Multispecies grazing

Stocking domestic grazer and browser species

Complementary diets

37

Doyle (2021) SDSU Extension

Jayne Jonas

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Fire + Multispecies grazing

Benefits

Woody plant control
Heterogeneity
Wildlife habitat
Livestock productivity
Climate smart practice

38

Wilcox et al. (2021) Front Ecol Environ

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