Is Amazonian tree biodiversity / species distribution a product of past landscape domestication?

News of recent studies has revealed that an estimated 390 billion trees are growing in Amazonia today, consisting of an approximate 16,000 species. 227 of these species are termed “hyperdominant”, because they represent about half of the total number of trees, while the rarest 11.000 species make up only 0.12% of the total.

Why only 227 species make up such a disproportional percentage of overall trees remains unknown.

“We knew that, normally, a few species dominate ecosystems, but if you have a system that has 16,000 tree species but just 227 make up half of the trees, that was pretty surprising even for us,” said lead author Dr Hans ter Steege from the Naturalis Biodiversity Center in the Netherlands.”

“In the paper, Dr. ter Steege and the team of more than 100 scientists wrote that there was no evidence that two key functional traits for trees – seed mass and wood density – played a part in determining what species dominated the landscape.” Read full article on BBC

Although the long and highly-involved history of human-forest habitation/impact/modification in Amazonia was not mentioned in the article(s), I am curious if the researchers have begun to look into the possible correlation between the 227 hyperdominant species and their ethnobotanical significance among past and present populations of Amazonian indigenous peoples. My guess is that the 227 hyperdominant species also have a wide range of human uses.

With recent findings confirming that sophisticated human societies inhabited the Bolivian Amazon 10,400 years ago, and that human habitation of the region likely dates back as far as 30,000 years, coupled with our firmly established understanding that Amazonian peoples have managed highly complex, large-scale domesticated landscapes (massive agro-silvo-pastoral systems), it seems inevitable that long-term human presence in the Amazon has played significant role in determining present day biodiversity and species distribution.

We’ll see what answers science comes up with.

Here are a few relevant articles on the subject of pre-Colombian Amazonian history, Amazonian agroforestry, and anthropogenic landscapes in the Amazon:

Clark Erickson: Culture amidst the Pristing: The Anthropogenic Forests of the Bolivian Amazon

NPR Article: Amazon was once home to advanced civilizations

Discovery News: Did humans arrive in the Americas 30,000 years ago?

New York Times: Once Hidden by Forest, Carvings in Land Attest to Amazon’s Lost World

Science Daily: Pre-Colombian societies in the Amazon may have been much larger and more advance then thought

Agroforestry and the Built Environment by: Spencer Woodard (Anthropogen):

New Yorker: Under the Jungle by David Grann

PDF: Amazonian Agroforestry and Homegardens

Psychotria viridis - Chacruna

OVERVIEW

Psychotria viridis is a perennial shrub of the Rubiaceae family. In the Quechua languages it is called chacruna or chacrona. In Quechua, chaqruy is a verb meaning "to mix". P. viridis grows to a height of approximately 5 m (16 ft). Its branches span a diameter of about 2 m (6 ft 7 in)

ORIGIN AND DISTRIBUTION

Neotropics. Amazon basin, South America. 

USES AND ETHNOBOTANY

This species of Psychotria is used by indigenous peoples of western Amazonia, primarily as an additive in the preparation of a hallucinogenic drink ayahuasca, also called yage, employed for healing and divination. Although in some instances ayahuasca can be prepared in the absence of Psychotria, the addition of the plant greatly enhances the visionary effect of the brew due to the significant amounts of DMT present in its leaves. DMT, or N, N-dimethyltryptamine, is a tryptamine alkaloid.

Other plants with significant quantities of DMT include: Mimosa tenuiflora (=M. hostilis), Anadenanthera peregrina, Acaciapolyacantha, A. cornigera, A. maidenii, A. nubica, A. plebophylla, A. polyantha, A. senegal, A. simplicifolia), Calliandra spp., Desmodium spp. Mucuna pruriens (Fabaceae), Virola peruviana, V. elongata (=V. heiodora) Epenña, Yakeé (Myristicaceae); Banisteriopsos argentea, B. rusbyana (Malpighiaceae); Prestonia amazonica (Apocynaceae); Psychotria peoppigiana, adn P. psychotriaefolia (Rubiaceae); Arundo donax, Phalaris arundinacea, Phragmites austraiis (Poaceae) and Zanthoxylum spp (Rutaceae).

PROPAGATION

Psychotria viridis is hardy in USDA zone 10 or higher. The plant is fairly easy to propagate from seeds, stem cuttings, or leaf cuttings. Some resources state that the plant is extremely difficult to propagate from seed (as low as 1%!), but I have not found this to be the case. I would probably note that treating the seeds in their own fermenting fruit pulp can improve germination. 

The plant does, however, reproduce most readily from fresh leaf cuttings. I have looked for evidence of leaves dropping off the plant and self-propagating as such. I have noticed that some plants will produce seed heavily for a while, then the bulk of the shrub will slowly die off, sending up a few new shoots in succession from the base of the trunk. 

P. viridis leaf cutting propagation.

Eugenia stipitada - Araza

Thought to be native to the Peruvian and Brazilian Amazon, still not very widely cultivated. Araza is typically consumed fresh, used to prepare excellent juices. The flavor and texture is considered to be superior to the guava. The most notable benefits of this species are, A) that it is shade loving. Unlike most fruit trees, Araza prefers at least partial shade. I have seen it growing and producing fruit in the dappled shade of understory, below two canopies. B) Given the right conditions the tree can bear fruit within a year and a half or two years of growth. Once a tree begins bearing it can be depended up on to flower and fruit fairly consistently. C) Fruit are large, seeds are easy to separate. D) The fruit is versatile. Excellent as a base for sauces, juices, and so forth. Usually used for juices. Consumed with Miracle Fruit it is almost disgustingly sweet. Araza is extremely rich in carbohydrates (7%) and vitamin B1.

The tree thrives in humid tropical climates, adapted to at least 2,000 mm annual rainfall and to poor, acidic soils.