How quickly can you regrow a forest?

Apparently, 20 years.

Here’s evidence from Brazil:

reforestation….. Salgado was to take over his family’s sprawling cattle ranch in Minas Gerais—a region he remembered as a lush and lively rainforest. Unfortunately, the area had undergone a drastic transformation; only about 0.5% was covered in trees, and all of the wildlife had disappeared. “The land,” he tells The Guardian, “was as sick as I was.”

Then, his wife Lélia had an idea: they should replant the forest. In order to support this seemingly impossible cause, the couple set up the Instituto Terra, an “environmental organization dedicated to the sustainable development of the Valley of the River Doce,” in 1998. Over the next several years, the Salgados and the Instituto Terra team slowly but surely rebuilt the 1,754-acre forest, transforming it from a barren plot of land to a tropical paradise.

Now a Private Natural Heritage Reserve, hundreds of species of flora and fauna call the former cattle ranch home. In addition to 293 species of trees, the land now teems with 172 species of birds, 33 species of mammals, and 15 species of amphibians and reptiles—many of which are endangered. As expected, this rejuvenation has also had a huge impact on the ecosystem and climate. On top of reintroducing plants and animals to the area, the project has rejuvenated several once dried-up springs in the drought-prone area, and has even positively affected local temperatures.


Here is the Guardian story.

Perhaps there is hope for countries like Nigeria (see graph) to eventually reverse the deforestation trends across the Continent over the last five decades.

Urbanization might help in the medium-to-long term, although its effects will be moderated by what happens to agricultural productivity. Climate change will matter, too. Finally, Kenya and Ethiopia provide suggestive evidence that the Continent’s ongoing population explosion might not decimate its forests after all. On Nigeria, it would be interesting to determine if the decline in forest cover is due to population growth or climate change effects in its central and northern regions.

On Africa’s Demographics

This is from The Economist:

Screen Shot 2018-09-20 at 12.03.13 PMSub-Saharan Africa’s dependency ratio (the population younger than 20 and older than 64 versus the population between those ages) is 129:100, compared with 65:100 in Europe. Sub-Saharan Africa is expected to have a worse dependency ratio than Europe even in 2050.

… There is nothing inherently African about large families. Botswana’s fertility rate is 2.6, down from 6.6 in 1960. South Africa’s rate is 2.4. And although the UN has a good record of predicting global population growth, it has got fertility projections badly wrong in individual countries. Sudden baby busts in countries like Brazil, Iran and Thailand caught almost everyone out. Could Africa also spring a surprise?

Read the whole thing here.

On balance, I am less alarmed by population growth in Africa than most observers. Female gross secondary school enrollment is at an all time high. Urbanization is apace. Family sizes are most likely to shrink at faster rates than anticipated by current models.

Population trends and the potential for a demographic dividend in Africa

Bloom, Kuhn, and Prettner write:

We assess Africa’s prospects for enjoying a demographic dividend. While fertility rates and dependency ratios in Africa remain high, they have started to decline. According to UN projections, they will fall further in the coming decades such that by the mid-21st century the ratio of the working-age to dependent population will be greater than in Asia, Europe, and Northern America. This projection suggests Africa has considerable potential to enjoy a demographic dividend. Whether and when it actually materializes, and also its magnitude, hinges on policies and institutions in key realms that include macroeconomic management, human capital, trade, governance, and labor and capital markets. Given strong complementarities among these areas, coordinated policies will likely be most effective in generating the momentum needed to pull Africa’s economies out of a development trap.


Dependence Ratios Across Different Regions