The Great BRF Tree Project: Tree Identification 101

Update, September 26, 2018: This post has been adapted into an article on BRF’s website, “The Forest in Fall: Tree Identification and Leaf Color.”

As I’ve said on this blog before, half of my work in gathering samples is finding the right trees.  Such a task may sound easy.  You just go into the woods, you pick out all the maples, and you’re out, right?  Wrong.  There are 455 species of tree native to eastern North America listed in my Peterson Field Guide, 65 of which have been documented at Black Rock.  For every tree on my list of species to collect, there are at least two or three other trees for which I could easily confuse it, on the basis of probability alone.  And that’s not even talking about the numerous shrubs (weedy and established) that I’ve added to my species list this year.

Finding my desired trees in this massive forest is like trying to find a green needle in a stack of other green needles.  The needle I’m looking for might be a slightly different shade than the other needles, or it might be slightly thinner, or slightly sharper.  But it also might be slightly wider, or slightly duller, if it’s younger or has lived in a different part of the forest.  Or it might be torn up by insects.  Or it might be just imperceptibly different from all the other needles, but is on a branch ten feet high where I can only get a closer look after wrangling my pole saw for several minutes.

All in all, tree identification takes a lot of practice and a lot of trial and error.  I’m far from an expert, but I’ve had enough concentrated practice that I trust my skills at least with common species.  During several weeks of working on this project last summer and two weeks of getting back into it this summer, I’ve used information from the Peterson field guide, online resources, and the experienced BRF staff to identify over 20 species on my own.  (Although I usually check with staff members when I’m unsure about something.)

Here are the primary markers I use for determining the identity of a tree or shrub.

Location:

A plant, like any organism, occupies a specific niche – an ecological term that describes a set of environmental conditions specific to that organism which give it a place in the larger ecosystem.  Niches can include what resources the organism uses, what it eats, when it reproduces, or where it lives.  That last category is often useful in identifying trees, as I can use my knowledge about which species live in which areas of the forest to figure out what I might be looking at.

For example: bear oak, a shrub in the oak (Fagaceae) family, is only found at high elevations, mostly on mountain tops.  Thus, even if I see a plant with similar leaves, if it’s not growing on a high point in rocky soil, I won’t expect it to be bear oak – it’s more likely a different kind of shrub.  Similarly, eastern cottonwood is an invasive species that only successfully grows at Black Rock Forest in highway regions where the native forest has been cut away.  Thus, even if I see a plant with similar leaves, if it’s not growing on the side of a large road, I won’t expect it to be eastern cottonwood.

Leaf shape:

Leaf shape is my go-to identifier for most trees.  The leaves of many species I look for have characteristic shapes: they’re rounded or pointed, simple or compound, smooth-edged or jagged.  This identifier is perhaps most useful for established species that I see often, such as the oak and maple families; trees in both families have leaf shapes that appear similar from a distance, but are distinctive up close.

 

Although red maple and sugar maple have similar leaf shapes, red maple (left; via Evelyn Fitzgerald // Flickr) has rounder, more jagged leaves while sugar maple (right; via Dcoetzee // Wikicommons) has more pointed leaves.

 

Red oak, chestnut oak, and black oak also have similar leaf shapes.  But red oak (top left; via Angela Huster // Wikicommons) has more divided leaves with sharp individual points, while chestnut oak (bottom left; via Bruce Kirchoff // Wikicommons) has leaves with rounded edges and black oak (right; via yours truly) has fewer and deeper divisions.  Black oak can also be identified by its darker-colored bark.

Leaf texture:

When leaves of different species have similar shapes, another useful means of identification is their texture.  This can be a difficult quality to evaluate, as I have to grab onto a few leaves from a tree (sometimes clipping them from a high branch) to tell if they are leathery, smooth, or soft.

For example: black gum has a similar leaf shape (rounded with one point at the end, no jagged edges) to that of ash trees, but this species’ leaves have a distinctive, leathery texture.  Slippery elm also has a distinct texture: rubbing the leaves of this species between your fingers feels like rubbing sandpaper.  Even the texture isn’t enough to confidently identify slippery elm, though, as I discovered today while talking with Katie, BRF’s research manager.  Hop hornbeam and black birch, both native BRF tree species, have leaves that are practically identical to those of slippery elm – and hop hornbeam even has a very similar texture!  Even though the three trees aren’t even in the same family!

Bark:

Bark can be a tricky identifier, because depictions in field guides and other resources usually describe the bark of older, mature trees while I often look at younger saplings in the field.  Still, by honing in on older sections of a tree (usually the trunk near its base), I can sometimes solve debates about its identity based on this outer casing.

The case of slippery elm v. hop hornbeam, for example, falls to bark: slippery elm has rough, intensely textured bark, while hop hornbeam has more regular, peeling bark.  (Black birch, another similar species, has smooth bark with horizontal stripes.)  After closely re-examining some trees from which I’d taken branches last week, believing they were slippery elm, I have now realized they’re actually hop hornbeam, based on this test.  Damn.

Another tree that can be easily identified by bark is American beech, another member of the Fagaceae family.  American beech has smooth, gray bark that can appear almost shiny compared to the other trunks in a forest of oaks and maples.

Flowers:

Flowers are useful markers when I look at shrubs.  Although it’s still early in the season and many plants aren’t yet blooming, for those that are, I can spot a particular species from many feet away by looking for specific flower shapes and colors.

Today, for example, I looked for flowers while searching for six samples of mapleleaf viburnum, a shrub with leaves similar to those of maple and clusters of unique white flowers.  I found it along road sides and near one of Black Rock’s reservoirs.

Another distinct flower is that of mountain laurel, which has recently begun to bloom in sunnier spots – on mountain peaks and around bodies of water.  This shrub has gorgeous white and pink flowers that are unforgettable once you clip a few samples of the plant’s branches.  (The flowers got absolutely everywhere in the lab when I processed mountain laurel samples yesterday, though.)

Practice, practice, practice!

Identification is incredibly challenging, and I get it wrong a lot of the time.  But I’m practicing in every way I can.  I point out species to myself when I hike around Black Rock even when I’m not specifically out to look for samples.  I bring small branches of species that I don’t recognize back to the Science Center and ask staffers if anyone knows what they are.  I hold onto small samples and stick them in my pockets for reference when I go out collecting.  After a couple more weeks at Black Rock, I’m hopeful that I’ll be – well, still very far from expert status, but at least able to distinguish between all the different oaks and maples on my own.

All photos via Betsy Ladyzhets unless otherwise specified