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Ecosystem Services of Florida Grasslands
Lynn E. SollenbergerAgronomy Department
University of Florida/IFAS
Outline• Definition of grassland ecosystem
services
• Brief description of the range of ecosystem services provided by grasslands
• Focus on carbon sequestration of Florida grasslands
Ecosystem Services
• Definition
–Services from grasslands beyond providing a source of livestock feed,
–particularly those that enhance environmental quality and ecosystem sustainability
Grassland Ecosystem Services• Include:
– Wildlife habitat
– Species conservation
– Preservation/enhancement of water quality
– Preservation/enhancement of soil quality including soil carbon sequestration
Grassland Ecosystem Services
• Wildlife habitat
– In an increasingly urban state like Florida, grasslands provide habitat for 2/3s of our wildlife
Grassland Ecosystem Services• Species conservation
– Native grasslands are one of Florida’s natural ecosystems, preserving many plants and animals (332 native grasses in FL)
Grassland Ecosystem Services
• Species conservation
– More than 100 different plant species can be found on a single range unit of longleaf-slash pine-wiregrass range type (biodiversity)
Grassland Ecosystem Services• Water quality
• Water capture, minimizing particulate flow to surface water
• Filtration, removing potential pollutants from shallow ground water
• Reduce likelihood of ground water contamination from agricultural, industrial, or municipal effluent irrigation
Secondary Services• Soil quality
– Grasses reduce erosion, preserving topsoil needed to produce food for current and future generations
– Adding bahiagrass in rotation with a peanut-cotton system (Katsvairo et al., 2007):
• Increased earthworm populations
• Resulted in greater water infiltration
• Increased plant residues and soil moisture
Grasses & Soil C Sequestration
• 90-95% of the C in grassland systems is below ground, most occurring as soil organic C (SOC; Wedin, 2004)
• 22% of total global SOC resides under grasslands (Jobbagy and Jackson, 2000)
Grasses & Soil C Sequestration
• Jobbagy and Jackson (2000) state:
– SOC increases with precipitation for both grasslands and woodlands, but the rate of increase is 2.6 times greater for grasslands
– Based on a worldwide survey of soil profiles, woodlands predicted to have 43% less SOC than grasslands when annual precipitation is > 1000 mm
Grasses & Soil C Sequestration
• Three primary ways in which C sequestration can occur (assumes SOC has reached equilibrium in natural ecosystems)
– Changes in land cover or land use (most common and best understood)
– Altered management within an ecosystem type
– Altered ecosystem function
Grasses & Soil C Sequestration
• Changes in land cover or land use
– Bermudagrass establishment on previously continuously cropped land increased SOC (top 6 cm) by 1.4 tons C/ ha/yr when grazed (Franzluebbers, 2007).
Grassland Use & Soil C Sequestration
Grassland use Increase in SOC in 0-6 cm soil layer (ton/ha/yr)
Hayed 0.3
Unharvested 0.6
Grazed – low intensity 1.4
Grazed – high intensity 1.4
Soil C Sequestration
• Changes in land cover or land use
– Increase in soil C sequestration under grassland of 1.86 tons/ha/yr over 23 years (Trumbore et al., 1995)
– 90% of depleted soil C due to continuous cropping was restored after 9 yr of pasture (Romkens et al., 1999)
Characteristics of Florida Grasses
• Grasses of warm-climate origin (C4)
– Photosynthetic pathway has 2X the nitrogen efficiency compared to temperate grasses
– Results in large C:N ratios in plant litter and especially in roots and rhizomes, thus degradation is slow.
Example of Bahiagrass
• Bahiagrass – approximately 1 million ha (2.5 million acres) in Florida
• The most widely planted grass in the state
Bahiagrass Fraction MassN rate (kg/ha)
Herbage (Mg/ha)
Litter (Mg/ha)
Roots + Rhizomes (Mg/ha)
40
120
360
Interrante et al. (in review)
Bahiagrass Fraction MassN rate (kg/ha)
Herbage (Mg/ha)
Litter (Mg/ha)
Roots + Rhizomes (Mg/ha)
40 2.9 2.0 19.0
120 3.0 2.0 15.6
360 3.8 2.1 16.8
Interrante et al. (in review)
Bahiagrass Fraction MassN rate (kg/ha)
Herbage (Mg/ha)
Litter (Mg/ha)
Roots + Rhizomes (Mg/ha)
% of mass below ground
40 2.9 2.0 19.0 79
120 3.0 2.0 15.6 76
360 3.8 2.1 16.8 74
Interrante et al. (in review)
Bahiagrass Fraction [N]N rate (kg/ha)
Herbage (g/kg)
Litter (g/kg)
Roots + rhizomes
(g/kg)
40 11 12 9
120 12 13 8
360 17 18 13
Interrante et al. (in review)
Bahiagrass Fraction C:N RatioN rate (kg/ha)
Herbage Litter Roots + rhizomes
40 38 33 44
120 33 29 51
360 24 21 30
Interrante et al. (in review)
Carbon Distribution in Various Pools (Point in time) in a Florida Bahiagrass Pasture (Dubeux, 2004)
PoolCarbon
kg/ha (% of total C pool)
Leaves 2,100 (3)Stems 420 (1)Roots + rhizomes 22,600 (32)Litter 2,030 (3)Manure 1,620 (2)Soil A layer (0-15 cm) 15,500 (22) Soil E layer (15-33 cm) 9,460 (13) Soil Bt layer (33-90 cm) 16,960 (24) Belowground 91%
Predicted Degradation of Pool DM
0102030405060708090
100
0 21 42 63 84 105
126
147
168
189
210
231
252
273
294
315
336
357
Days after incubation
% D
M re
mai
ning
Leaves
Stem
Root + rhizomes
Cow manure
Litter
Predicted Degradation of SOMSOM mineralization per layer
98.298.498.698.8
9999.299.499.699.8100
0 28 56 84 112
140
168
196
224
252
280
308
336
364
Days
% S
OM
rem
aini
ng
A layerE layerBt layer
Over Time
• SOC accumulates under bahiagrass because of:
– The slow mineralization of existing SOM
– The high proportion of plant biomass that is belowground
– The slow rate of degradation of this high C:N material
Conclusions• Grassland ecosystems provide vital services
to the Florida environment
• Grasslands play a critical role in long-term C storage
• Grasslands sequester large amounts of new C, particularly following land-use changes
• Sequestration occurs regardless of grassland use, but is greatest when grazed