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

Florida Native Grassland Sites

Fresh Water Marsh and Pond

Florida Native Grassland Sites

South Florida Flatwoods Range

Fresh Water Marsh and Pond

Florida Native Grassland Sites

North Florida Flatwoods

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

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)

Example of Bahiagrass

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

Questions