Statistical relationships between urban populations and deforestation

By Sofia Linden and Kyla Husted

Background

Forest vegetation serves various ecological functions.  Trees sequester carbon, provide habitats, provide food, and while living, release large amounts of Oxygen.  Trees help sustain myriad trophic levels and maintain biodiversity, while also playing an important role in biogeochemical cycles and holding carbon that would otherwise speed up the process of global warming.  It’s thereby important to understand what factors in human civilizations contribute to deforestation.  Densely populated urban areas tend to alter the land that’s settled on the most.  Does the size of urban populations influence the amount of deforestation the occurs in given countries?

 

Hypotheses

Our hypothesis is that as urban populations increase in nations, deforestation increases in that country.  Our alternative hypothesis is that as urban population increases in a country, deforestation decreases in that country (or that as urban populations decrease in a country, deforestation increases).  Our null hypothesis is that the increase of decrease in urban populations in a nation has no effect on deforestation rates.

 

Procedure

First we downloaded data on the national statistics of urban populations and deforestation from between 2005 and 2010 (UNEP (2016).  The statistics we used to observe deforestation rates covered the forest area for each nation annually.  The forest area was measured by the thousand hectares (UNEP (2016): The UNEP Environmental Data Explorer, as compiled from Food and Agriculture Organization of the United Nations (FAO)).  Our urban population data recorded the average percent of the total population that was urban for each country (UNEP (2016): The UNEP Environmental Data Explorer, as compiled from United Nations Population Division).  We then had to clean up the Excel spreadsheets by deleting columns with information not needed and countries that did not have data.  We kept the columns with data from the years and the country name.  We then merged the spreadsheets for each data set by copying and pasting the data into a new spreadsheet.  We grouped the data into quartiles by assigning each country in the dataset a number from 1-4 based on the independent variable, urban population.  The first 25 countries were labeled 1, the second 25 countries were labelled 2, and so on for 3 and 4.  We then used the RAND() function to create a random sample of 100 countries.  From there we opened the data in SPSS Statistics.  We used SPSS to do an independent samples T-test using the first and last quartile, because those two had the largest differences.  We then created a bar graph on SPSS comparing the percent national urban populations average to the national forest areas. Finally, we ran a correlation test in SPSS to see if there is a correlation between urban population and forest area.

 

Results

Looking at the first and last quartiles in the sample of 100 countries we found that the mean of each quartile in the Urban Population data set was 22.73882800 (1st quartile) and 89.4060000 (4th quartile and the standard deviation for the first quartile was 6.87491865 and for the fourth quartile is was 6.16782320. For the Forest Area data the mean for the first quartile was 8102.62800 and for the fourth quartile was 12115.3761. The standard deviation was 15750.4498 and 31466.9061 respectively. As seen in the chart below the p value or 2-tailed significance for Forest Area was around 0.57 for Forest Area and zero for Urban population.unnamed-2unnamed-1unnamed

Discussion

There are multiple factors that in the future would need to be taken into consideration if we were to re-conduct this study.  To notice a correlation, we would need to take into account the size of each country, which would affect how much forest area is able to exist.  We also should consider the different biomes in the nations, and the different histories of how forests have been used in different geographical region.  Therefore, this study cannot properly determine whether or not there is truly a correlation between urban populations and deforestation in different nations.  There is still great importance in discovering such a correlation.  Forests play large ecological and biogeochemical roles that must be maintained for the health of human populations and other species that exist on earth.  Understanding the relationship between urban populations and forests areas gives greater insight to the scale of impact that large dense populations can have on ecosystems and resources.

 

Bibliography

UNEP (2016): The UNEP Environmental Data Explorer, as compiled from United Nations Population Division. United Nations Environment Programme. http://ede.grid.unep.ch.

 

UNEP (2016): The UNEP Environmental Data Explorer, as compiled from Food and Agriculture Organization of the United Nations (FAO) – FAOStat . United Nations Environment Programme. http://ede.grid.unep.ch.