Hybridization is the main cause of extinction and biodiversity loss in Cannabis.
Indigenous Asian populations hold the vast majority of Cannabis biodiversity.
Bringing foreign seed to ancient centres of biodiversity such as India or Cambodia has set in motion an irreversible process known as genetic swamping. This is when regional genotypes are replaced by hybrids, permanently annihilating millennia of irreplaceable genetic diversity.
In post-Hippie Trail South and Southeast Asia, this mostly involved Westerners introducing Indicas (var. afghanica). The technical term for the resulting ecological nightmare—as it is in the context of indigenous Cannabis—is introgressive hybridization.
The rise of Internet commerce means that process has rapidly accelerated, with an unprecedented influx of hybrid seed to countries such as India and Pakistan. Compared to traditional Asian domesticates (“landrace”) and wild-growing plants, these modern Indica–Sativa hybrids have an utterly narrow and homogeneous genetic base.
Short-sighted and uncontrolled hybridization is not merely a catastrophe for Cannabis itself, but also destroys the heritage and wealth of impoverished farming communities and their nations. Without real landraces there can’t be real Nepali charas or Thai ganja, for example. Lost too is the possibility of a multitude of future indigenous cultivars—cures and creations which we haven’t even begun to conceive of yet.
Here’s an important and freely available ecological study by Judith Rhymer and Daniel Simberloff, Extinction by Hybridization and Introgression. A key focus of the paper is loss of biodiversity by hybridization within a single species, as now threatens the future of Cannabis.
For a recent overview of hybridization and extinction, including genetic swamping, see this talk by renowned professor of botany and plant evolutionary genomics, Loren Rieseberg: