Monday, April 20, 2015

Amphibian Project (I): From twigs to amphibians

Wood frog (Lithobates sylvaticus)
The exercise of studying winter twigs over the last few weeks was very rewarding and as the first leaves begin I wanted to begin another mini project. With a late start to spring this year, the amphibian season is just getting started. Only in the last week have vernal pools begun to fill up with the froggy croaks of wood frogs and the high pitch peeps of spring peepers. It seemed a good fit to focus in on amphibians and to start recording my observations of amphibian breeding locations in Burlington on a more systematic basis.

Video above is from May, 2012

To do so, over the next few weeks I'll be somewhat systematically traveling to different sites around Burlington where I expect there to be breeding amphibians (and hopefully find places where I don't while exploring those). If anyone knows any good places, feel free to email more or leave a comment below. I've decided to use's project interface to start recording where these different breeding sites/courtship locations are. This also means that anyone else can contribute to the data set. Citizen science! I would love your help, so please feel welcome to contribute to the project by submitting observations through the project page. You may also pass along the link to your friends, neighbors, or Front Porch Forum communities. If teachers would like to be involved that would be great too. I planning on returning to this map annually. I'd like the project to fill in as much of the map as possible, so submit away, naturalists. 

Some good resources for amphibian identification and information can be found here:

Wednesday, April 15, 2015

Dichotomous key (VII.d) - The world of internodes cont'd (Adornment)

Adornment - thorny parts
A twig at its most basic form, is rather helpless against predators. Fortunately, trees do not leave them unaided. For example, sap can contain a range of chemical defenses (like the toxic orange sap of staghorn sumac) - this is particularly prominent later in spring when the sap gets, as they say in the sugaring world, buddy; I've written about that previously. Many plants, however, have figured out clever solutions by remolding different parts to serve a more spiky purpose; we only have a scant few trees in our area that have these spikes along their stems - though there are a number of delightfully delicious plants that have thorns (e.g. raspberry, blackberry, roses). These sharp projections derive from three different parts of the plant, the stem, leaves, or epidermis. Also good to remember that the terms below are botanical terms and are vernacularly often used interchangeably.

Chickadee flies from buckthorn branch
Spines are projections that form from the stem of the tree, arising from buds. In buckthorn, as shown above, they form at the tips of branches, or rather these spines are the tips of the branch. Hawthorn has very prevalent spines, as do honey locust and osage orange.

Thorns are modified stipules or leaves. The sharp projects on barberry and black locust, for example, are thorns. Above are the paired thorns of black locust, or pointed ears of Marrowzodufia Blugly the Dwarf, as you'll remember from my posting on bud scars.

Multi-flora rose thorn
Blackberry thorn with a scar just above it from where another thorn fell off
Prickles derive from the epidermis and are not vascularized (hence the can be popped off quite easily). Roses, raspberries, and blackberries all have prickles. Tracing the stem of a blackberry, rose, or raspberry, it is easy to find a number of scars dotting the stem from where thorns have fallen (or been ripped) off.

Tendril anchoring a grape vine to another twig. 

Showing adhesive pads on the ends of Virginia creeper
Adornment - clasping parts
Since vines put very little investment into their stem for structural support, and therefore need some mechanism by which they can cling to other objects as they wend their way up to the top of the canopy. Grape vines and Virginia creeper (both in the grape family, Vitaceae), have tendrils, which are highly specialized anatomical features for vining, originating from the stem. Virginia creeper, which is in the grape family Vitaceae, even has adhesive pads at the tips of the tendrils. 

Zoomed in view of a sharp and grippy bud of a bittersweet vine
Bittersweet climbing a sugar maple sapling
Tumurous growth of a sugar maple in response to a bittersweet vine
Other vines, like hardy kiwis and oriental bittersweet, accomplish this task with pointy buds that anchor the vine as it spirals and wraps around a substrate, often strangling and killing its unwilling host over several years. The constricting force around the stem of the tree being strangled cuts of circulation in new conductive tissue, effectively cutting off the host's supply chain. We also have a number of perennial herbaceous vines that encircle the substrate as they climb up it (e.g. deadly nightshade, morning glory, bindweeds, hops).

Poison ivy vine attached to white pine trunk. Image is from August 2012
Poison ivy vines have thousands of root hairs that anchor the stem to a surface. No other vine in our woods have this. This paper provides a good synthesis of different strategies of vining plants and unanswered questions concerning vines.

Monday, April 13, 2015

Dichotomous key (VII.c) - The world of internodes cont'd (Color)

Color - To start, everyone should read through this beautiful portrait of colors through the seasons. This time of year can come with color changes nearly as drastic (though not as abundant) as in the fall. The bark of aspens begins to take a strong green hue, red-osier dogwood bark deepens in red, and the boxelder twigs have taken on a stronger purple. The primary reason for the color change is photosynthesis. This early into spring, it's still a bit risky to produce leaves for fear of a hard frost. This is particularly true for species with compound leaves, which have a lot more energy invested in a single leaf than trees with simple leaves (and indeed ash is one of the last to leaf out).

Color change - While color can be important in distinguishing one species from another, it can also be helpful in determining the age of a section of branch. The two photos immediately above show this color change over time in sugar maple. At the bottom of each section you can see the terminal bud scale scars that wrap completely around the branch (they kind of look like Jane Fonda's bunched up socks). In total, the whole branch was 6 years old, the brownest on the left was the youngest and progressively getting older to the right. The photo above it is the branch before I cut it. The color changes as the bark thickens and cork is added. As the bark thickens on a branch or stem, photosynthesis is inhibit and that section of the plant may no longer exhibit the dramatic shift in color in the spring.

In some species this color change indicates response to ecological conditions. The photo at the very top is a shrub willow, which I unfortunately do not know which species. Each of the sections is from just a single year's growth - the stem was about four and a half feet! The stem greens as photosynthesis in the bark ramps up (the green is due to the production of chlorophyll). The response of the plant that results in the gradation to red is from the production of anthocyanins in the bark. These accessory pigments, which give red maple and many other leaves their red or purple fall colors, act as protection from the sun (see below for more details). 

Photosynthetic, greenish bark of quaking aspen with a snow flea! (first warm day of the year, 65deg)

Green: I always remind my students that when you see green on a plant it means photosynthesis is happening there. More precisely it indicates the presence of chloroplasts, which are the site of photosynthesis. Regardless the important thing to remember is that where you see green, that part of the plant is harnessing sunlight to make sugars. So whether it's a ripening green banana photosynthesizing energy to help itself grow rather than siphon all its energy budget from the leaf production or a vibrant green twig of boxelder photosynthesizing in the early spring before leaf out, the color is always due to the presence of chlorophyll. Above is the yellowish green bark of a mature quaking aspen. It maintains thin bark to continue photosynthesis along the stem for many years by having the bark turn to powder. If you rub the bark you're hands will feel soapy and you can see the white of the bark on your hands. This can actually be used as sunscreen!

White pine twig. When wet shows more dramatically the yellowish hue of its bark
Plants with dramatically green bark include:
  • boxelder
  • aspens, cottonwoods, willows
  • striped maple (at maturity, twigs are purplish)
  • white pine

Red: There are many other colors besides green. Some plants on red all the way around and up and down the stem, as in red-osier dogwood, while others are facultatively red, as in the reddish pigment in raspberry branches. On raspberries, you'll often see a stark contrast from the red color on the top (exposed to the sun) surface versus the green color on the bottom, shaded part of the stem. I have a hunch that in dogwoods the red is also a warning to would-be predators of the toxicity of the plant. Since, as shrubs, their stems are always within munching range of most herbivores mouths, it would behoove them to have strong defenses and strong warnings.

Plants with vibrant red bark:
  • Red-osier dogwood
  • Silky dogwood (above)
  • Raspberry

Alt-leaf dogwood showing controst between the lighter bottom of the stem and the darker, exposed portion. 
Purple in trees is caused by the same process as reds, though in purples there is a higher concentration of chlorophyll. The following plants have a purplish tint.
  • boxelder (kind of gets a lot of dramatic color)
  • alternate-leaf dogwood (pictured above and below)
  • striped maple

Yellow: The dead twigs of alternate-leaf dogwood (Cornus alternifolia) turn yellow. I haven't been able to find any corroborating evidence of this, but I would assume that the branches of alternate-leaf dogwood, which are a deep purple when alive, are rich in carotenoids, accessory pigments that allow a plant to capture a wider range of wavelengths of light. When the twig dies for whatever reason, the cholorophyll dies too and is it breaks down reveals the beautiful hidden palette of oranges and yellows. 

Thursday, April 9, 2015

Dichotomous key (VII.b) - The world of internodes cont'd (surface texture)

Aging bark on speckled alder
Surface texture
Surface texture is highly variable between twigs, though some features are common not between taxa, but rather due to convergent evolution. Most forest dwelling twigs are rather bland in terms of texture on the surface. Sugar maple, American beech, and red oak are all generally glabrous and without epicuticular wax (though red oak does have a light sheen to it). Beyond the boring twigs, a tree can have a papery filament coating its surface, a thin white bloom (boxelder, aspen), or it can be fuzzy to furry (as in speckled alder, staghorn sumac, and slippery elm).

The species that do have specialized features coating their epidermis (bark will protect species later in life, but when young the twig needs a boost from the epidermis to do the protecting), are trying to solve the problem of protection against harsh desiccating winds, insect predators, harsh UV radiation (the wax on succulents like dudleyas are known to be have the highest reflectivity of UV radiation of any biological substance), or material that might build up and clog pores or block photosynthesis (see my post on jewelweed). 

Forsythia twig
Epicuticular wax
Forsythia twigs have a whitish hard sheet that encrusts the bark of twigs and younger branches. As it ages, it cracks and sloughs off in flakes. Most of the twigs show a sharp contrast of between the surface exposed to the sun and the shaded surfaces, with the exposed surface being coated in the protective white layer. 

Boxelder has a similar adaptive strategy, but the white bloom is much more of a waxy coating. On a side note, I've often noticed when burning boxelder twigs that oils seem to surface and the heated twigs become glossy and oily to the touch. 

Fuzzy twig of speckled alder (c.f. top image of maturing speckled alder bark)
fuzzy of staghorn sumac twig, which is absent by 3rd year of growth
Fuzz: A twig can be either glabrous (smooth) or pubescent (fuzzy). As with most things, there is more than one way to skin a cat. I've mentioned the boundary layer before (here), and it comes into play again while talking about a twig's fuzziness. In order to prevent drying out, one way to solve the problem is to prevent drying via convective cooling. If you lick your finger and hold it up to the wind, it feels cold on the side the wind is blowing from. The wind evaporates the liquid, drawing away heat. Now say you licked your finger, put on thin gloves and then held it up to the wind. It would take much longer for the saliva to evaporate - longer still the thicker the glove. The tiny (or large on sumac) hairs prevent wind from wicking away moisture for lenticels. 

Monday, April 6, 2015

Dichotomous key (VII.a) - The world of internodes (Lenticels)

Older lenticels on sugar maple (with gouge from squirrel), kind of looks like a monkey face
This along with the next 3 posts will be heavy on the photographs, a way of representing the variation in morphology of lenticels, textures, "accessories", and color. Enjoy!

Velvet mite on bizarre ridges of hackberry. Lenticells are a yellowish color and rather non-descript as they age
In his 1921 book, Trees of New York State, Harry Philip Brown writes that lenticels are "of minor value in identification." I would agree, sort of. In twigs many species have small whitish lenticels that all kind of look the same. But when we look closely, particularly at older branches, we find them adeptly telling us a great deal. Because bark is impervious to both water and gas, no exchange can happen through this part of the tree's body. Lenticels, like the stomata of a leaf, are the mouth holes, pores, or excrescences that erupt through a tree's bark, allowing the exchange of water and gas (especially oxygen). Without oxygen, the living cells of the bark would die.

Diamond shaped lenticels of quaking aspen bark, looks like a punk's studded belt
I have a hypothesis that primary succession species should have a total surface area of lenticels per node than more shade tolerant species to fuel the rapid growth of cells. While I found several research papers that document shifts within a species over different growing conditions (like this one, which shows that red-osier dogwoods growing in wet conditions have more lenticels than those growing on drier sites), I haven't found any research pointing to a corresponding link between lenticel abundance on a species and photosynthetic rates, growth rates, or shade tolerance. The red-osier paper makes me wonder if perhaps a greater abundance of lenticels is allied more with wetland species that with speed of growth. The paper states that lenticels are able to provide roots with oxygen to a certain degree in anoxic conditions.

Orbiculate lenticels of staghorn sumac bark

Vertical orientation of lenticels on Glossy Buckthorn twig
Punctate lenticels on red oak
Variation in lenticels from one species to another fall into the following categories:
  • The shape of the lenticels can be spotted or punctate (most species), rounded or orbiculate (boxelder, sumac) or linear/elongate (cherry, birch, glossy buckthorn)
  • Their orientation either vertically or horizontally (transverse or perpendicular) to the branch. In thinner barked species, the lenticels will remain active over a longer period of time. As the tree's trunk/branch thickens, the lenticels expand and on something like paper birch, the lenticels can be quite long.
  • The color of the lenticels can be in sharp contrast to the twig or roughly the same hue; they can be white, yellow, orange, brown, red, or black (the vast majority are in the white range)
  • The texture can be fuzzy, or powdery and break apart when rubbed.
  • Lenticel abundance can be great or small 
  • Placement can be distributed evenly over the bark or concentrated on the underside of the twig or nearest the nodes.
  • As a tree ages, lenticels become distorted in different ways. 
Far fewer lenticels were on the underside (left) of alternate-leaf dogwood than on upper surface (right)
The enormous elongate, horizontal lenticels on paper birch, with my thumb for scale
Twig and mature bark of glossy buckthorn, showing distortion of aged lenticels from vertical to horizontal orientation

In black cherry the lenticels elongate horizontally as the tree matures. As the bark thickens the lenticels eventually close off. Over time the plates (people describe them as potato chip-esque) fall off. The exposed surfaces are a deep burnt orange before fading to a darker gray, and lack any visible sign of lenticels. The image to the right is of the backside of the "lenticeled" plate on the left. It lacks any sign of the horizontal lines. 

Contrast this with paper birch bark. The lenticels continue to elongate as the tree ages and the bark thickens. Rather than having a thicker, corky bark, paper birch sheds barks in sheets (each layer of bark represents one year of growth). In the image above you can see the lenticels marking the inner bark beneath a relatively thin outer bark. The tree was about 16" in diameter.

Friday, April 3, 2015

Dichotomous key (VI) - A nod to nodes before moving on to the space between

So when not looking at the buds themselves, there's a lot that a branch can tell us both in terms of what we're looking at and the ecology of the plant. A node is a point at which a bud (and subsequent leaves, fruits, branches) emerge from a twig. Depending on the branching pattern of the twig (phyllotaxy describes arrangements of leaves on a stalk) there can either be one, two, or a whorl of buds, etc. emerging from a given node. If thar be one, tis alternate, but if a pair as in two, then opposite, and any mar it be a-whorled with branches (as in many conifers and catalpa). 

The space along the branch or twig between each node is called the internode. Rather than an empty desert stretching the gap between our beautifully relevant little buds, who are oh so helpful in identification, the internode is rich repository of information about the twig and the ecology of the tree. This post started as just one, but quickly became three.

I wrote earlier about sub-opposite branching patterns, the forth option to bud arrangement at a node. One of the things I had read in Peter Thomas's Trees: their natural history, which I can't recommend enough, is that in opposite branched trees the faster that tree is growing the more likely its buds are to be slightly offset from one another. This is often readily apparent in common buckthorn branches, where two buds are slightly offset from one another followed by a much wider gap before the next pair of offset buds.

White ash, typically opposite, showing distinctly alternate branching at the tips of its rapid growth

In an open field at Rock Point, one which receives regular hair cuts every few years, there are a number of white ash saplings growing. The trees probably grow for several years, get cut back, and then sprout up again from the same root stock. With an abundance of stored energy, the new growth is extremely vigorous. I found the above seemingly alternate branched twig on one such sapling. Pretty impressive that the growth was fast enough to result in opposite buds offset enough from one another that this distance was equal to the distance between the nodes!

When thinking about ultimate causes of branching patterns, it is a tricky nut to crack. Researchers studying phyllotaxy - or the spatial arrangement of leaves - of rice, wrote in their paper: "the mechanism responsible for this extremely regular pattern is one of the most fascinating enigmas in plant biology." So while we may not fully know what controls phyllotaxy, observing patterns of conditions that result in changes to a plants norm is beginning to illuminate what factors impact phyllotaxy (Here's another really fascinating article about auxin's role in controlling growth patterns in plants, not just with branching).