He says that 40% of Europe’s sugar comes from Haiti and 60% of its coffee. It’s economic contributions amounted to 40% of french overseas trade. With all the spanish colonies in the Americas, and all the other Caribbean islands, how was Haiti so dense? They couldn’t grow plants on top of each other, could they? i would imagine that there simply wasn’t the flat land available to conduct much farming, but clearly there was. And if the land is so incredibly fertile there, them why is the other side of the island, modern Dominican Republic, so much less productive? Perhaps It would help to give statistics for mass or volume of crops produced?
EDIT: I’m terribly sorry, but the exact quote is “in the early 1790’s the produce of this former slave colony of 8,000 plantations was greater than all of Europe’s Caribbean and American colonies combined”. It appears as though he meant 8,000 plantations, not 8,000 people.
Your question is based on a false premise: Haiti (then colonial Saint-Domingue) was not "half an island with 8,000 people." According to Laurent DuBois in Avengers of the New World, the population of just one province of Saint-Domingue far exceeded that number:
In 1789 the Northern Province, which included Le Cap, the plain, and the surrounding mountains, contained 288 sugar plantations, most of them producing refined sugar; 443 indigo plantations; and more than 2,000 coffee plantations. The population included 16,000 whites and at least 160,000 slaves.
The figures for the entire colony were much higher:
In 1789, according to official figures, there were roughly 465,000 slaves in the colony, 31,000 whites, and 28,000 free-coloreds. Masters, who were taxed on the basis of the number of slaves they owned, had an interest in underreporting the true numbers, so that it is likely the slave population was higher, probably near a half-million. (The United States, in contrast, had a total population of 700,000 slaves in 1790).
On your point about geography: there are a number of plains in Haiti, where a good deal of agriculture was conducted. The northern plain "was an ideal place for sugar plantations" and this was where a lot of them were located. The Western Province contained two plains:
the Cul-de-Sac surrounding Port-au-Prince and, to the north, a plain traversed by the snaking Artibonite River bordered by the port towns of Gonaives and Saint-Marc. Both plains were dry, the Artibonite plain so much that one writer described it as "Egypt." During the second half of the eighteenth century, government-sponsored irrigation projects put slaves to work building canals that ultimately irrigated nearly half of the land on the Cul-de-Sac. Consequently sugar production in the area boomed.
This province contained 314 sugar plantations, while the Southern Province (which also had two plains) only had 191 plantations.
So Saint-Domingue was not lacking in either people (who, it should be pointed out, where overwhelmingly enslaved people who worked very intensely under brutal conditions) or arable land. Where arable land was lacking, as in the Western Province, the government sponsored projects to help bring it under cultivation.
To add to u/unkosan's point about scale, the other side of this equation is infrastructure.
The thing to understand about plantation cash crops generally and sugar in particular is the capital and labor investments they required. I wasn't able to find illustrative numbers on this point, but a sugar cane plantation requires a significant amount of specialized equipment. To start, the fields would have been fed by cutting edge irrigation systems backed by larger scale water infrastructure (dams, levees, diversions, etc). On the other end of production, the raw sugarcane would have to be processed - it would be milled to extract the sugars and then run through what is essentially an assembly line process of clarification to produce exportable white sugars, molasses, etc. Richard Pares said that “More than any other kind of plantation in the West Indies, sugar production combined industry and agriculture”.
Then, of course, there is slavery. Those 500,000 enslaved people provided the continuous, back breaking labor required to maximize sugar production. The death toll of that work was so high that from 1783 to 1791 (the start of the revolution), the colony imported approx. 800,000 enslaved Africans - in 1789 they were importing 40,000 slaves per year.
To give you some rough sense of scale, there were about 800 sugar plantations in Saint-Domingue in 1789, worked and maintained by those slaves, with the most advanced plantations (maybe a third) refining sugar on site using their own mills and equipment. These plantations would produce 138,616,494 pounds of sugar that year. The revolution would completely obliterate that industry with the abolition of slavery and the destruction of many of the plantations and their equipment.
Illustratively, the leaders of post-revolutionary Haiti tried to reestablish the export sugar economy, up to an including restrictive labor contracts to keep free Haitians on the plantations, but weren't able to bring back the 'Pearl' of the Caribbean. In 1804 there were approximately 300,000 free Haitians, and (according to the figures I could find) in 1802 sugar yields peaked at 56,000 pounds.
Put most simply, it wasn't that Haiti was producing so much, it was that Spanish American colonies weren't emphasizing sugar and coffee production at that time. First, to answer your question about crop space, coffee actually thrives in hilly, high-altitude areas, so it makes sense that the fertile, flat land would be used for sugar plantations while the mountainous interior would foster coffee production.
Second, Spanish mercantilism put a large emphasis on Bullion (gold, silver, and other precious metals). This made expeditions and settlement into the mainland of Central and South America much more appealing than staying on the Caribbean islands where gold and sources of indigenous labor had already dried up. For much of the 17th and 18th centuries, the Spanish Caribbean was regarded as sort of a backwater territory. Santo Domingo (Dominican Republic) had been hit by a variety of natural disasters that impeded its sugar production and although it had been an important port during the earliest days of Conquest, Havana's position on the Gulf Stream made it much more useful as a site for trade and colonial administration. The lack of indigenous labor, and Spain's relatively strict policies on importing African slaves meant, for the most part, that the Spanish Caribbean in the 18th century just didn't have the manpower to produce large amounts of cash crops. Really only in the aftermath of the Haitian Revolution did Cuba emerge as a major sugar producer and slaveholder. While Portuguese Brazil was also an early competitor in the Sugar market, its cultivation waned around the end of the 17th century and the colony switched its focus to newly discovered gold mines in the South.
With comparatively fewer New World colonies to manage (and none with the silver/gold producing capacity of the mainland territories) the French development of Saint-Domingue focused intensely on the cultivation of cash crops. The French government authorized massive imports of slaves, creating the workforce necessary for the labor-intense process of harvesting sugarcane and coffee. Thus economic and political conditions in the New World provided space for French Haiti to dominate the sugar market with relatively little competition from their Spanish and Portuguese neighbors. British Jamaica also had the land and labor available to produce large amounts of sugarcane but the island was engaged in internal (between settlers and maroon communities) and external (with other imperial powers) struggles that likely hampered its production and trade abilities.
I'm more familiar with the history than the historiography but some suggestions for further readings on the interconnectedness of the Colonial Carribbean are Havana and the Atlantic by de la Fuente , Freedoms Mirror by Ada Ferrer, and Modernity Disavowed by Sibylle Fischer
I haven't read this book so I'll admit I don't understand the context of what the author is saying, nor where this 8000 figure comes from, but I will say that saint-Domingue had steadily, throughtout the beginning of the 17th century and all the way to the Haitian revolution of 1791, imported over 900 000 slaves, 500 000 of which were still alive by the time of this survey, to work some of the ~800 sugar refineries/plantations/etc; it would as well seem that the European population at the time would also have been something around 30 000 white colonists.
So, to answer the question, first we have to sort of understand how sugar cane is refined, and why this is even important to your question in the first place. Sugarcane requires about 200cm of rainfall every year, which is unsurprisingly difficult to achieve, as they get about 140cm of rainfall per year. The volume of export had gone up from ~14 000 tonnes of sugar exports in the 1760s, to about 63 000 tonnes by 1791; point is, sugar was being farmed on unprecedented scales. How did they deal with the boom in production, when there wasn't enough water to go around, you ask? Well, it's quite simple, we've been doing it for thousands of years: you just divert the rivers. But unfortunately, that doesn't solve all the issues. You see, lumber is/was a huge requirement for sugar refinery processes; it was used to make the machinery, the juice presses, the buildings, etc., not to mention that for the extraction process to work, you have to heat up the filtered 'mulch' to about 80 degrees Celsius. Since wood has an energy conversion of about 10 mj/kg, the highest commercially available fuel until the discovery of coal and fossil fuels, you can imagine how many forests were annihilated to provide fuel for these factories. Haiti enjoyed a 60% forest coverage in 1923, but today, in 2019, they have about 0.4% of the country covered. A little taste of what "industrialisation" would've looked like for the people at the time.
It wasn't just dense farming, it was the systemic eradication of local flora in favour of unsustainable mass plantations. The colonists destroyed the forests, erected plantations all over, and then ever-increasingly expanded their lands. Farming, before the invention of the stump remover, was no easy task. You couldn't just pick a plot of land and start farming, you'd have to clear everything before you started, and then you'd have to selectively plant and crop rotate to make sure the land was still fertile. Besides, trees are abundantly necessary to prevent soil erosion from occurring, something that has been plaguing Haiti for centuries. In other words, the landscape was more suitable for the industrialisation of sugarcane growth.
So it isn't so much that their soil was more fertile - in fact, it still remains to be of somewhat lower quality due to unsustainable farming practices, it's that they were willing to cut down giant swathes of forest to process the sugar, using those accumulative 900 000 slaves to do all the hard work. The life expectancy of a freshly imported slave, according to almost all the sources I could find (because I refused to believe it), was seven to ten years. This was not a system that was designed for sustainability, and everyone paid for it.
EDIT: MY SOURCES!!!!
http://www.madehow.com/Volume-1/Sugar.html
https://anthropology.arizona.edu/sites/anthropology.arizona.edu/files/u339/*JMY%202014%20MA.pdf