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

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