ANOVASeminar #30

(Economic Value of Tropical Forest to Coffee Production)

Mike DeDad12/3/07

Source: http://www.pnas.org/cgi/reprint/0405147101v1.pdf

Economic Value of Tropical Forest to Coffee Production

Societal benefits are immense Not a big enough motivator

Economic value pollination services to agriculture

Purpose

To “conduct pollination experiments to examine the effects of these patterns on coffee production and quality, and to estimate the resulting economic value of tropical forest fragments to coffee farms.” Previously determined that “bee species richness

and visitation rate decline with distance from forest.”

Methods

Studied a 1,065 hectare coffee farm in the Valle General, Costa Rica

Took branches from three types of sitesNear, Intermediate, and Far

Took 4 branches from each of 5 healthy plants from each site divided randomly between hand-pollination and ambient pollination

Methods

Explanatory VariablesDistance (Near, Intermediate, or Far)Pollination (By hand or ambient)

Response Variables seed massFruit setpeaberry frequency

Methods

What are some possible confounding variables? Length of the branch number of leaves relative shade

Dismissed these because r<.19 Not significantly related

What are the hypotheses?

Null Hypothesis: population means of each response variable are equal for each explanatory variable

Alternative Hypothesis: population means differ

Two-way ANOVA

DFG= product of the two degrees of freedom for each factor Distance dfg= (I-1)= 3-1= 2 Pollination dfg= (I-1)= 2-1= 1 Two-way ANOVA dfg= 2 x 1= 2

F2,24 = 8.13, P < 0.0001 F2,24 = 2.96, P = 0.0710

F2,24 = 7.28, P = 0.0034

Reject H0

Reject H0

Borderline

Conclusions

Hand pollinating increased seed mass and fruit set for far sites while decreasing peaberry frequency (higher quality)

Ambient pollination decreased seed mass and fruit set for far sites while increasing peaberry frequency (lower quality)

Conclusions

The presence of native tropical forest increased both the quantity and quality of harvested coffee (near and int. sites)

The lack of nearby forest decreases quantity and quality of harvested coffee (far sites)

What are the consequences of committing error?Type 1: Rejecting the null hypothesis even

though it is trueConvincing farmers to not expand even though the

presence of forests has no effect on coffee productionType 2: Failing to reject the null hypothesis even

though it is falseAllowing deforestation even though forests have an

effect on coffee quality and yield

Are there any questions?