The history of plants on Dartmoor is known from only a handful of studies which have been conducted on Dartmoor. Each of the studies has taken a sliver of dirt, and then examined it under a microscope to find the pollen from the plants that have grown here over time. Interestingly, these studies have shown that Dartmoor has been shaped by humans for as long as they've lived here. The pollen record shows variation of plants at different locations studied. This makes sense: the plants in my backyard are not the same as what grown on the open moor a few metres away.
We cannot say, with authority, "this tree was everywhere on Dartmoor as of this date". We can only say "this tree was here at this date". It would be convenient if the pollen record was tidier, but the truth is more interesting than convenience.
Here are a few highlights from the pollen record of Dartmoor for the trees we work with (and a few we don't).
Wind pollinated
These are the plants that most commonly appear in a pollen record. This means, the pollen is distributed by the wind, splashed about in hopes of being blown into another tree's flowers. If you're a hayfever sufferer, like me, you know exactly how well the wind can blow the pollen straight into your nose and eyes.
Willow
Willow pollen appears more than 9,000 years ago — almost as old as the post-glacial record itself. There's only one problem. When you and I picture willow, we don't picture the dwarf willow shrubs (6cm!) that enjoy the environment that would have been here as the glaciers retreated. The pollen from the dwarf shrubs, and willow trees we see today, is identical. It's impossible to know for sure what was here first. But I do know the willow we work with today is a hybrid that lives behind the village pub and is frequently damaged. We use this windfall to make our inks.
Oak
Oak pollen appears in the Dartmoor record around 8,785 years ago. It was probably at lower elevations first, and then gradually climbed the hills.
Hazel
An early arrival, first showing up at the same time as oak, approximately 8,785 years ago.
Alder
The "first" for alder can vary as much as 1,000 years between the different studies. It's another of the trees that shows how varied the moor has been – with little pockets of things happening differently in one location to another. The earliest of all the reports is 7,490 years ago at Black Ridge Brook.
Insect pollinated
These trees need a helping insect to move their pollen from one flower to another. They show up more rarely in the pollen record, although their absence from the record doesn't mean they weren't there.
Hawthorn
The earliest record of hawthorn in the Dartmoor pollen record was around 5,000 years ago. It appears as part of a brief increase in willow and holly shrubs.
Holly
This tree doesn't appear in great quantities on the high moor of Dartmoor in any part of the pollen record; however, the 1964 study from Ian Simmons includes it in one of the diagrams for the 7,000–5,000 years ago zone in the pollen record. This study is before carbon dating was normalised, so the years are "an educated guess" rather than a calibrated radiocarbon date.
Rowan
Again, the studies are sketchy at best for a "first known" date. The 1964 study from Ian Simmons makes a brief reference to rowan-like pollen 8,000 years ago, but he isn't sure.
As a reminder: the earliest record doesn't mean the tree was everywhere. It simply means this was the first time the pollen shows up in the sliver of dirt taken from a specific location on the moor.