The effect of afforestation on water infiltration in the tropics, as ...

Infiltration change after <strong>afforestation</strong> 

in the tropics 

Part <strong>of</strong> larger systematic review 

and meta analysis on forest 

land use changes in the tropics 

and its <strong>effect</strong> on infiltration 

Ulrik Ilstedt 1& 2 , Anders Malmer 2 , Elke Verbeeten 1 and Daniel Murdiyarso 1 

• Deforestation 

• Reforestation 

• Afforestation 

• (Selective) 

Logging 

1 Center for International Forestry Research (CIFOR) 

2 Department <strong>of</strong> Forest Ecology, Swedish University <strong>of</strong> 

Agricultural Sciences (SLU) 

Swedish University <strong>of</strong> Agricultural Sciences 

Why the tropics? 

Why Infiltration? 

Important for: 

• Erosion & water 

quality 

• Groundwater 

recharge 

• Dry season flow 

• Slow/quick flow 

Key variable for understanding & modelling green 

& blue water under climate and land use change 

Types <strong>of</strong> infiltration methods 

• Steady state/saturated condition 

• Field measurements or undisturbed 

samples 

• Top soil (0-10cm) 

Systematic review is 

Protocol for: 

• Databases, search syntax and time 

• Criteria for selection 

Easy to repeat by others and in later 

follow up 

Less bias than ‘narrative reviews’ 

1

Afforestation in a broad sense 

Literature Search 

Low tree density 

• Permanent agriculture 

• Agr<strong>of</strong>orestry 

• Short fallow shifting 

cultivation 

• Grasslands 

• Savannas 

• Pastures 

Higher tree density 

• Agr<strong>of</strong>orestry 

• Plantation forests 

• Succession to ”climax” 

forests 

Databases used (30-11-2005): 

• Web <strong>of</strong> Science (1986-2005) 

• BIOSIS Previews (1989-2005) 

• CAB Abstracts (1973-2005) 

Search syntax: 

• Land uses from the objectives 

• Synonyms <strong>of</strong> infiltration 

Selection criteria 

Total search hits (3001 references) 

-Outside tropics 

Title 

-Not a comparison between any <strong>of</strong> the 

specified land uses 

References 

from experts Abstract 

-Not a field experiment/treatment 

-Articles not available 

Articles from library 

-Not in English or French 

-Flawed designs/methods 

References lists 

-Means, N and SD not possible to estimate 

Meta Analysis (20 references incl. 64 comparisons/experiments) 

Meta analysis is 

Using data from several studies to have a 

higher number <strong>of</strong> observations to get a 

more secure mean with higher confidence. 

(response means, number <strong>of</strong> observations and variance needed) 

Meta analysis is used for 

A global mean treatment <strong>effect</strong> for a larger 

set <strong>of</strong> criteria or a mean for a more 

specific treatment. 

More sound than ”study wote conting” in 

narrative reviews 

Response ratio and 95% confidence interval for individual 

experiments and the grand mean (LnR = Ln(After/Before) 

Grand mean 

Agr<strong>of</strong>orestry 

Response ratios and 95% confidence 

intervals for meta analysis 

(times increase in infiltration by <strong>afforestation</strong> and agfr<strong>of</strong>orestry) 

Afforestation 

Studies 

Exp. 

mean 

Response Ratio 

(after/before) 

lower CI upper CI 

Afforestation 2 8 3.8 2.7 5.5 

Agr<strong>of</strong>orest 2 6 1.9 1.7 2.8 

Subtotal 4 14 3.2 2.4 4.7 

2

Range <strong>of</strong> studies - <strong>afforestation</strong> 

Rejected studies 

• Two continents (Africa and 

Asia) 

• Rainfall: 850-2500 mm 

• Alfisols and Ultisols 

• 8 different tree species 

• 1 – 12 yrs after planting 

-Too few studies to analyze 

the influence <strong>of</strong> species 

and sites 

• 12 in total 

• 7 design 

• 2 methodology 

• 3 statistics 

Mostly in peer review 

journals… 

But strong pro<strong>of</strong> <strong>of</strong> soil improvement and infiltration 

increase 2 – 5 times from 3-47 mm/h shows relevance 

Conclusions 

• Meta-analysis promising tool 

• Afforestation 2 to 5-fold 

increase 

• No single study on rubber, oil 

palm, etc. 

• Too few studies for: 

-Some important land uses 

-Analyzing factors (climate, 

species, methods etc.) 

Wish list… 

• More basic soil physical data 

• Grey literature? 

• More languages (cooperation needed) 

• Multivariate analysis: soil type, texture, rainfall, methods 

etc. 

• Please make randomized designs & report statistics 

Thank you! 

Let´s widen our horizons 

Table 1. Description <strong>of</strong> the data and experiments used for a meta-analysis <strong>of</strong> the <strong>effect</strong> on infiltration from <strong>afforestation</strong> and 

agr<strong>of</strong>orestry on former deforested land. <strong>The</strong> mean infiltration, standard deviation, and number <strong>of</strong> replicates (N) before and 

after treatment is reported, as well as the country <strong>of</strong> the study, the mean annual rainfall, texture, soil type and vegetation 

before and after treatment. 

Infiltration Standard 

Source 

(mm/h) 

dev. N Country Latitude Rainfall Texture Soil Vegetation 

before after before (mm) after 

before after after before 

Tectonia grandis (12yrs) 

26 57 12 12 15 15 2500 Grass 

1. Mapa (1995) Sri Lanka 7 N Clay Ultisol 

Tectonia grandis (12yrs) 

2. Mapa (1995) 29 57 12 12 15 15 Sri Lanka 7 N 2500 Clay Ultisol Crops 

Cassia Spectabilis + 

3. Hulugalle and Ndi (1993) 3 5.5 1.0 1.0 3 3 Cameroon 3 N 1522 Clay Ultisol Crops 

crops (1yr) 

Cassia Spectabilis + 

4. Hullugale and Ndi (1993) 3.3 5.5 1.0 1.0 3 3 Cameroon 3 N 1522 Clay Ultisol Crops 

crops (1yr) 

Sesbania sesban (3yrs) 

5. Chirwa et al. (2003) 13 95 6.8 6.8 3 3 Zambia 14 S 850 Clay Alfisol Crops 

6. Chirwa et al. (2003) 13 44 6.8 6.8 3 3 Zambia 15 S 850 Clay Alfisol Crops Gliricidia sepium (3yrs) 

7. Chirwa et al. (2003) 13 37 6.8 6.8 3 3 Zambia 16 S 850 Clay 

Leucaena leucocephala 

Alfisol Crops 

(3yrs) 


Acacia angustissima 

Alfisol Crops 

(3yrs) 


Acacia + Sesbania 

Alfisol Crops 

(3yrs) 


Gliricidia + Sesbania 

Alfisol Crops 

(3yrs) 

11. Hulugalle and Kang 

Gliricidia sepium + crops 

47 152 127 127 3 3 Nigeria 7 N 1250 loamy Alfisol Crops 

(1990) 

(8yrs) 


Alchornea cordifolia + 


(1990) 

crops (8yrs) 


Leucaena leucocephala 


(1990) 

+ crops (8yrs) 


Acioa barterii + crops 


(1990) 

(8yrs) 

3

Classification <strong>of</strong> designs 

1) True time series 

2) Randomized treatments (blocked, 

factorial etc.) 

3) False time series with good 

randomization 

4) Flawed designs, e.g. no replication 

(excluded) 

Literature Search 

Databases used (30-11-2005): 

• Web <strong>of</strong> Science (1986-2005) 

• BIOSIS Previews (1989-2005) 

• CAB Abstracts (1973-2005) 

Search syntax: 

• topic=((hydraulic conductivit* or Infiltra* or 

permeabilit*) and soil* and water and (forest* or 

afforest* or reforest* or deforest* or agro$forest* or 

oil palm* or palm oil* or rubber* or tree* or 

shifting$cultivat* or slash$burn or shifting$cultivat* 

or slash* or logging* or clear$felling or clearing* or 

skid* or burn* or hauling* or woodland* or savan*)) 

Response ratios and 95% Confidence Intervals 

Afforestation 

Confidence Intervals for Response Ratio 

(after/before) 

0.00 1.00 2.00 3.00 4.00 5.00 6.00 

Stud/Exp. 

Reforestation 

Selective 

Logging 

Tracks 

Between tracks 

Subtotal 

5 11 

3 7 

6 18 

Deforestation 

Selective logging 

Reforestation 

Deforestation 

Tracks 

Between tracks 

Subtotal 

Permanent cropps 

Shifting cultivation 

Savanah 

Subtotal 

1 3 

2 3 

3 6 

5 10 

4 11 

1 2 

8 23 

Afforerstation 

Plantation 

Agr<strong>of</strong>orest 

Subtotal 

2 8 

3 6 

4 14 

higher after 

Steps <strong>of</strong> a meta-analysis 

Treatments 

Effect sizes 

Combined 

<strong>effect</strong> size 

Systematic review 

Study 1 

Study 2 

Study 3 

etc ... 

-means 

-variances 

-number <strong>of</strong> samples 

-<strong>effect</strong> sizes 

-confidence intervals 

4

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