BOSTON, MA—“The trees are certainly shorter out here,” said Luke.

The East Coaster in me bristled instantly. “Well, sure, nothing’s going to measure up to a Redwood,” I said, “but these guys along the road are hardly the best that Massachusetts has to offer.”

As Luke mused out loud over the tall trees that could be found in his home state of Oregon, I thought about what the forests of the Northeastern United States would have looked like centuries before the highway we now cruised was constructed.

I grew up in the heartland of the deciduous tree, embedded within the wedge of our country whose rainfall and temperature regime are ideal for colorful broadleaf trees. The backyard of my childhood home was packed with red maples, sweet gums, and hundred-year-old oaks, towering overhead in their climatological niche. Yet even these trees didn’t represent a Northeast forest at its prime: Our neighborhood was built on old farmland, cleared of its forest during colonial times centuries before.

Since the Mayflower made landfall in Plymouth, Massachusetts, in 1620, we’ve cut down one quarter of the 4 million square kilometers of forest that covered our country. Much of the initial land-clearing occurred along the Eastern seaboard, as each new resident of the future United States carved out a hectare or two of farmland. The land that wasn’t cleared was often selectively logged – particularly for tall, straight-as-a-die trees like Atlantic White Cedar, a popular choice for ship masts.

The wood did not go to waste. It built, furnished, and heated homes. It fenced in pastures and supported plows. Eventually, however, the land lost its appeal. Farmers moved West, chasing a new frontier, or to cities, chasing a different career, leaving their hard-won farmland to lie fallow.

But in the Northeast, old fields do not remain fields for long. Slowly but surely, they undergo the ecological process of succession, transitioning from weedy pasture to shrubland to pine forest to hardwood forest.

The trajectory of this reforestation varies dramatically across locations. Each tree has its own habitat preferences, evolved over millennia. Differences in things like topography – which can render one spot boggy and an adjacent one dry – and soil type – for example, the relative proportions of sand and clay – can produce dramatic shifts in the set of tree species inhabiting a site. Meanwhile, disturbances like wildfires and storms provide an additional environmental filter – selecting for species with special tolerances or that bounce back quickly – and press an occasional reset button on succession. And, to add another layer of complexity, random processes – like the casual arrival of an unusual seed at the right place at the right time – can sometimes dramatically alter the course of a plant community’s development.

That’s why, as a group, ecologists have moved away from the old concept of “climax communities” – the idea that a group of plants and animals would eventually converge on some regional average and remain there indefinitely.

Yet we still use terms like “old growth” and “primary forest” to describe the few remnants of Northeastern forest that remain relatively untouched by man. These are our icons – our vision for what the forests were, what they could yet be, and my benchmark to contradict Luke’s West Coast snobbery. Red oaks soar well past the height of ten-story buildings. Hemlocks stand equally tall, some more than 500 years old. Sugar maples run sweet in the spring and flush red with the fading of summer. The ground rolls gently underfoot, flowing over the hummocks of old logs and into the hollows between.

On our two-day whirlwind trip back East, Luke and I won’t get a chance to stop by any of these forests or (as Luke would prefer) hunt for salamanders in their cool, dark recesses. Even if we had, we wouldn’t really have seen a glimpse back in time. The American Chestnut tree has vanished from the region, victim to a foreign disease. Passenger pigeons no longer crowd the branches. Some changes are here to stay.

 Yet the forests themselves – and their up-and-coming relatives springing up alongside highways or on abandoned fields – remind us that, at least in this system, recovery is possible. Understanding this recovery, and its varied suite possible trajectories, helps us understand the limits to ecosystem resilience. And witnessing the sheer amount of time it takes – hundreds of years to even approach the look and feel of “old growth” – reminds us to safeguard the uncut forests that remain, like Luke’s beloved, towering Douglas-fir.