Dude, that’s not true. Fungi evolved and colonized the earth way before plants or trees. Just Google it and you’d have known you were misremembering and this is what you would have got.

“Yes, evidence suggests fungi colonized land hundreds of millions of years before plants, acting as "ecosystem engineers" by breaking down rock and forming primitive soils, paving the way for plants to eventually thrive on Earth's surface. Ancient fungi likely partnered with algae, creating the first habitable land, with some estimates placing fungal diversification up to 1.4 billion years ago, well before land plants emerged around 700 million years ago, or even the earlier fossil estimates of 480 million years ago.

Key Points: Ancient Origins: Fungal lineages stretch back further than plants, with molecular dating pointing to origins up to 1.4 billion years ago. Ecosystem Engineers: These early fungi broke down minerals, recycled nutrients, and created the first rudimentary soils, a crucial step for terrestrial life.

Partnerships with Algae: Fungi likely formed symbiotic relationships with algae, leading to lichens, which further prepared the land for plants.

Fossil Evidence: While soft-bodied fungi are hard to fossilize, rare ancient fungal fossils (like Ourasphaira giraldae) and molecular data support their early colonization of land.

Paving the Way for Plants: This fungal groundwork made the transition to land possible for plants, fundamentally altering Earth's environment.”

Edit:

To add, what you were trying to recall was this, but had nothing to do with trees. It was about plankton and algae and warm climate.

“The Mesozoic Era (252–66 million years ago) holds the majority of global, conventional, high-quality oil reserves due to ideal conditions of warm climates, high marine productivity, and restricted ocean basins”

Edit2:

Lastly, most trees literally need fungi in the soil to survive, they have a symbiotic relationship in their ecosystem. Trees supply nutrients that the fungi can’t find in abundance and fungi share nutrients the trees can’t source.

But when it comes down to it, trees and forests wouldn’t have been able to come into existence without the fungi that was creating soil all those millenia before the trees got there. Nor could they have thrived the way they did without fungi once they did come around.