Carbon stock and tree diversity of dry zone homegardens in southern

Sri Lanka

Eskil Mattssona

Madelene Ostwalda

S.P. Nissankab

a Division of Physical Resource Theory, Department of Energy and Environment, Chalmers University of Technology, Gothenburg, Sweden

b Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka

World Congress of Agroforestry2.2. Tropical homegardens: multifunctionality and benefits

Feb 10, 2014 Delhi, India

Homegardens in Sri Lanka

• Traditionally important land usesystem – 13 percent of total land area

• Provide multiple benefits offering fuelwood, timber, food and income(Kumar and Nair 2006; Pushpakumara et al. 2012)

• Ongoing developing programs providing free seeds, fertilizer and technical advice

(Mattsson and Johansson, 2011)

Colombo

(Mattsson et al. 2013)

Homegardens in Sri Lanka – above groundbiomass (AGB) carbon stocks

Aims of study

map and assess biophysical characteristics of Sri Lankan dry zone homegardens and implications for climate change mitigation and adaptation

• investigate the amount and pattern of AGB carbon, soil organic carbon (SOC) and tree diversity

• assess present soil fertility in homegarden and rainfedagriculture (chena) lands

Study area

Beralihela – Moneragala District

- dry zone

- wet zone

- int. zone

Methodology

• Measurements of DBH, heightand species frequency in small (≤ 0.2 ha), medium (0.4–0.8 ha)and large (>1 ha) homegardens (totally n = 45)

• Soil samples in homegardens (n=45) and chena lands (n=20). Reference samples in naturalforests

• AGB carbon stock and soilorganic matter estimation usingallometric equations (Chave et al. 2005) and Walkley and Black method (Schumacher 2002)

Results – AGB carbon stocks

0

5

10

15

20

25

30

35

AG

B C

arb

on

sto

ck (

Mg

C h

a-1)

small homegardens (n=11)

medium homegardens (n=27)

large homegardens (n=7)

mean (small+medium+large)

26

98

13

Mean in AGB Kandyan forest gardens: 87 Mg C ha-1

Mean in Dry monsoon forests: 106 Mg C ha-1

Mean in Open dry forests: 22 Mg C ha-1 (Mattsson et al. 2012)

Results – soil organic carbon

Soil organic carbon (%) Max Min Mean SE Range Mg C ha-1

Homegardens 0–10 cm 1.7 0.2 1.1 0.04 1.5 15.9

Homegardens 20–30 cm 1.2 0.3 0.8 0.03 0.9 12.1

Chena 0–10 cm 1.4 0.6 0.9 0.05 0.8 14.2

Chena 20–30 cm 1.1 0.4 0.7 0.04 0.7 10.4

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1986 2013

Soil

Org

anic

Car

bo

n (

%)

Change of soil organic carbon 1986 – 2013

Dry open forest

Homegardens

Chena

Results – tree diversity

Homegarden size

Species Shannon Wiener index

(SWI)

Mean number

of species ha-1

SE Total Mean Mean SE Range

Small (0.2 ha) n=11

43 14.91 2.08 0.15 0.76 – 2.66

80 10.03

Medium (0.2–0.8 ha) n=27

58 15.52 2.07 0.09 1.08 – 3.01

23 2.13

Large (1.0–1.2 ha) n=7

37 15.57 1.94 0.16 1.52 – 2.60

15 1.78

All categories

73 15.38 2.05 0.07 0.76 – 3.01

36 4.65

Implications and needs

• large variety of AGB carbon stocks in measured dry-zone homegardens (1–56 tC/ha); less than wet zone homegardens (48 to 145 Mg C ha-1)

• Higher carbon stocks and tree diversity per unit area in small homegardens (≤ 0.2 ha) than medium (0-4–0.8 ha) and large (>1 ha)

• water accessibility improved – could improve crop diversification, carbon density and food security

• soil fertility can be enhanced through awareness creation of agricultural technologies with local participation

• harmonization with climate mitigation schemes under existing or emerging developing programs. Potential trade-offs needs further attention and food security is greater priority for farmers.

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