Environmental Predictors of Deforestation: A summary

How can fateful difference be explained between Easter Island and Mangareva, two Pacific island societies who differ in the extent of their own contribution to deforestation? Rolett and Diamond (2004) examine 9 environmental variables at 81 sites on 69 islands to determine, as the title indicates, Environmental predictors of pre-European deforestation on Pacific Islands.

 Beginning with a story about the Pacific Islands in Asia, the authors provide a historical account that occurred between 1200BC and 1200 AD, when island settlers cut down trees for purposes of agriculture, firewood, and survival. However, what later early European settlers were puzzled about was the variety of the extent of deforestation as well as composition of new trees (Replacement) that had occurred between islands. So, the authors conducted a study to determine the extent that 9 IV Predictor variables had on 2 outcome variables, deforestation and replacement, that accounted for the variations between these 81 islands.

4 statistical analyses were used in this analysis:

  1. Spearman bivariate correlations, followed by bivariate regression coefficients between the two outcomes: Deforestation and Replacement
  2. Multivariate regressions to determine correlations on the 9 IV predictors.
  3.  Multivariate tree models to examine conditionally shared impacts of multiple IV variables on deforestation and replacement.
  4. Examining residuals, and looking for large discrepancies between the model and the data, and then determining other unknown variables (variables not included in the analyses) could have accounted for deforestation and replacement.

As you’d expect, The Photosynthesis Model learned in grade school partially predicts the authors’ analysis: Read on for an entertaining editorial by yours truly.

1) High Rain Fall->Replacement; and, Low Rainfall->Deforestation.

Why? Plants need water; also, with little water, plants make excellent dry firewood.

2) High Latitude (Cold Temperatures)->Deforestation (little plant growth); and High Latitude->Low Reforestation:

Why? Gotta keep them tropical plants warm and toasty; chestnuts cannot thrive in cold weather. It’s possible for only so many chestnuts roasting on an open fire high up in the mountains; probably why PA sells them at a gold brick/pound price.

3a) Makatea (raised sharp coral)->Retained forests

(b)Non-Makatea terrain->Deforestation

(c) Makatea->Low Replacement

(d) Makatea->Low Deforestation.

Why? No one wants to sleep or walk on sharp objects, so little reason to cut down or plant trees in those areas.

4) Old Island Age ->Deforestation

Old island (inconsistent) Replacement.

Why? Soil composition is a complicated mess. Eg: islands west of aerial tephras àlower deforestation

5) Tephars->lower replacement.

Why? Nutrient-dense soil stands the test of time; dust blows best, which helps to nutrify soil.

6) Dust fall off->low deforestation.

Dust fall off->low replacement.

Why? See #4. Dust adds to soil nutrients, which keeps trees thriving; it’s difficult to cut down strong, tall trees.

7) High Elevation->little Deforestation or Replacement.

Why? Good rain supply, high elevation rain catches nutrient-filled dust; high elevations are difficult to cross, so little motivation to cut down trees located here.

8) Large surface area->low deforestation and low replacement.

Why? Larger diversity, tricky terrain, and low chance of coastal water nearby supporting and inviting harmful humans. There’s a reason why FernGully was named The Last Rainforest.

Why did the characters in “Lost” ever leave the beach front, I will never know!

9) Distance from other islands->Both High Deforestation and Replacement.

Why? Ever live in a small town? There is little to do there. Might as well cut down a lot of trees and start replanting, especially if “Lost” is now off the air now.

 

So, why did Easter Island experience deforestation? 5) Lowest tephra; 6) lowest Dust Fall off; 9) second most isolated island; 3) No Makatea; 7) Low elevation. 8) Small surface area; and 1) little rainfall.

Essentially, unfavourable environmental conditions, rather than a surprisingly experienced group of tree cutters lead to Easter Island’s deforestation and little replacement. However, the authors cite unexplained variables as social pressures in Easter Island, where it is important to make way for transporting stone statues, as other contributing, and unexplained variables contributing to the island’s downfall.

To keep your trees looking their best, water them daily, keep them close the equator, elevated, in direct sunlight is best, planted around deathly spikes topped over nutrient-dense, dust-fallen soil. Keep them away from large bodies of water, which attract machete-wielding robbers, but not distanced away from civilization. If need be, supplement with more interesting activities than tree cutting, like watching re-runs of “Lost” or “The Gilmore Girls”. Better yet, throw in a television and some rabbit ears, and tune in to Hockey Night in Canada instead of cutting down those tall, habitat-supporting, and air-circulating trees.

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