While I was writing the first draft of Hild I did my very best to make sure I didn't contravene what was known to be known. Given the peripatetic nature of the royal court, this meant I had to know a lot about many different places. (Wolds, rich farmland, rocky seacoasts, high moorland; isolated farms; busy ports...) Given the turbulent nature of the times, technology, fashion, and mores changes constantly.
This care applied to language, technology, culture, fashion, and nature. So, for example, I wouldn't have anyone in York (though it wasn't called York then) writing anything until Æthelburg arrived with Paulinus, James the Deacon, and others. No one there spoke Latin--though Hild most probably would have encountered varieties of that language when in more British parts of the country (where Christian priests could still occasionally be found). In some parts of the country there was primitive coinage from fledgling mints; in most others, not; in still others, old and exotic coins were strung and used as jewellery. Most of the country didn't use ploughs. Riders didn't use stirrups (no charging at the enemy; you'd just fall off). Their attitudes to dogs would depend on their position in society.
To my surprise, the thing I've found hardest to keep track of is trees. I waxed lyrical about sycamores in a couple of places, felt pleased when I figured out dairymaids would use sycamore for milk buckets because it wouldn't leave an aftertaste in the milk--only to discover that sycamore is a neophyte: it wasn't introduced to Britain until Hild was many hundreds of years dead. So, huh, okay, I thought, I'll use maple. But UK maples are little, nothing like massive sycamores, nothing like the broad-leaved maples of the US. So then I thought, alright, how about horse chestnuts. Ooops. Nope, also neophytes--and even more recent. Then, dammit, sweet chestnuts. Except those were introduced by the Romans, and so wouldn't be ubiquitous.
I know of a zillion different trees I could put in instead, if I just want a big tree. But none of them have the kind of leaves I wanted. All those lyrical passages about leaves like hands? Gone. Phht. Sigh.
Did you know that in a crowded forest, during a storm the trees most likely to fall are the ones in the middle, while the ones at the edge almost invariably stay standing? That's because crowded trees have smaller root plates. Trees alone in a field, or at the edge of a wood, grow roots that go on for days, because they can. And that kind of tree can take a huge amount of root abuse--you can hack off more than half the roots and it'll be just fine.
Trees, basically, can survive almost anything, given time.
I just thought you might like to know all that.