A graphic depicting the spread of Yamnaya ancestry over time over a period of around 8,000 years

We did not find that NEOL ancestry had a strong association to changes in vegetation. One possible explanation is that this association was too minor or localized for us to clearly detect an effect in our model. Earlier studies have shown that Neolithic communities did, in fact, alter their local environments (Mercuri et al. 2019 Holocene) and had a local effect on vegetation to a certain extent, at least in northwestern Europe (47, 51, 52). In particular areas, such as northern and northwestern Europe, there was a very minor decline in broad-leaf forest that coincided with the increase in NEOL ancestry, but this was not observed at a continental level (Fig. 6). A much more pronounced reduction in broad-leaf forest occurred later on throughout western and northwestern Europe and coincided with the increase in YAM ancestry. It is important to note that cultivated tree types (olive, chestnut, and walnut)—which are pervasive in the Mediterranean—also fall into the category of broad-leaf forest. Thus, our capacity to infer changes in forest types in regions with this type of cultivar (e.g., the Mediterranean; ref. 53) is limited.
https://www.pnas.org/content/early/2.../30/1920051117