by Roland D. Hallee

Have you ever noticed during the summer, especially when we head into the more humid days, that trees begin to drip on you? It isn’t sap, just water.

Well, the simple answer is the tree is “sweating.”

Now, for the more scientific explanation.

According to the United States Geological Survey, the process is actually called transpiration, and it is the process of water movement through a plant and its evaporation from aerial parts, such as from leaves but also from stems and flowers. Leaf surfaces are dotted with pores, similar to our skin, which are called stomata, and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells and their accessory cells that open and close the pore. Transpiration occurs through the stomatal apertures, and can be thought of as a necessary cost associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants – again similar to our sweating – changes the pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots.

Mass flow of liquid water from the roots to the leaves is driven in part by capillary action, but primarily driven by water potential differences. In taller plants and trees, the force of gravity can only be overcome by the decrease in water pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem (the woody portion of the plant).

Plant transpiration is pretty much an invisible process, since the water is evaporating from the leaf surfaces, you don’t just go out and see the leaves “sweating.” Just because you can’t see the water doesn’t mean it is not being put into the air, though. During a growing season, a leaf will transpire many times more water than its own weight. An acre of corn gives off about 3,000-4,000 gallons of water each day, and a large oak tree can transpire 40,000 gallons per year.

The rate of transpiration is also influenced by the evaporative demand of the atmosphere surrounding the leaf such as humidity, change in temperature, wind and incident sunlight.

Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate. The amount of water lost by a plant also depends on its size and the amount of water absorbed at the roots. Transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the cuticle of the leaves and young stems. Transpiration serves to evaporatively cool plants as the escaping water vapor carries away heat energy.

Transpiration rates go up as the temperature goes up, especially during the growing season, when the air is warmer due to stronger sunlight and warmer air masses. Higher temperatures cause the plant cells which control the openings (stoma) where water is released to the atmosphere to open, whereas colder temperatures cause the openings to close.

As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air.

Increased movement of the air around a plant will result in a higher transpiration rate. This is somewhat related to the relative humidity of the air, in that as water transpires from a leaf, the water saturates the air surrounding the leaf. If there is no wind, the air around the leaf may not move very much, raising the humidity of the air around the leaf. Wind will move the air around, with the result that the more saturated air close to the leaf is replaced by drier air.

When moisture is lacking, plants can begin premature aging, which can result in leaf loss, and transpire less water.

So, if anyone asks you why the trees are dripping, you can go into the long, scientific explanation, or you just simply say, “the tree is sweating,” and watch for the looks you will get.

Roland’s trivia question of the week:

Who played for both the Boston Red Sox and the Boston Celtics?

Answer can be found here.

Fireflies in a forest.

by Roland D. Hallee

One night last week, after I did my usual bedtime reading, and my wife was playing the mind games on her tablet, I turned out the light and rolled over to get some sleep. Suddenly, my wife said, “there’s a lightning bug in here.” I looked up, and sure enough, there he was on the ceiling.

I didn’t want to crush it, because we are seeing fewer and fewer of them. So, I managed to corner it, pick it up with a piece of paper, and send it on its way, outdoors.

Now we rewind to a year ago when we were sitting by a campfire when we noticed a lightning bug. Notice I said “a,” like in one, uno, solo. It was the first lightning bug I had seen in a while. I remember when I was growing up, we used to go visit relatives in Canada, and sometimes go to a camp where we would see hundreds of lightning bugs flying around in a field. We used to capture them in a jar. You just don’t see that anymore.

Anyway, lightning bugs can make summers magical, but there is more to learn about these beauties.

First off, lightning bugs are actually fireflies. Fireflies are cute and elegant by day, but downright dazzling after darkness falls. But behind their charming facade, fireflies are fascinating little insects. Consider the following facts:

Firefly

They are beetles, not flies. Fireflies are nocturnal members of Lampyridae, a family of insects within the beetle order Coleoptera, or winged beetles. Yes, they are officially beetles.

They are alchemists, poetically speaking at least. While they don’t actually turn base metals into gold, they do create light as if by magic. When a chemical called luciferin (note the same Latin root as Lucifer) inside their abdomen/tail combines with oxygen, calcium and adenosine triphosphate, a chemical reaction occurs that creates their spectacular light.

Firefly light is incredibly efficient. The light produced by the firefly is the most efficient light ever made. Almost 100 percent of the energy in the chemical reaction is emitted as light; in comparison, an incandescent light bulb only emits 10 percent of its energy as light, the other 90 percent is lost as heat.

The main reason lightning bugs flash is to attract mates. Among most but not all species of North American lightning bugs, males fly about flashing while females perch on vegetation, usually near the ground. If the female sees a flasher and she’s ready to mate she responds by flashing right after the male’s last flash. A short flash dialogue takes place as the male flies closer and closer, and then, if all goes well, they mate.

They come in a rainbow of colors. Well maybe not the whole spectrum, but they do come in yellow, light red, green and orange.

They taste disgusting. Not that we were planning on snacking on fireflies anytime soon, but for predators that might like a light meal, beware the lightning bug. Firefly blood contains lucibufagins, which sounds like something out of a Harry Potter book but is actually a defensive steroid that tastes really awful. It is similar to that found in some poisonous toads. Predators associate the bad taste with a firefly’s light and learn not to eat bugs that glow.

However, their numbers are declining. If you’re seeing fewer fireflies each summer, you’re not alone. Evidence suggests that firefly populations may be on the decline, most likely due to a combination of light pollution, pesticide use and habitat destruction. For example, according to Smithsonian.com, if a field where fireflies live is paved over, the fireflies don’t migrate to another field, they just disappear forever.

What’s going on? Bees are on the decline; butterflies are suffering, could fireflies be facing tough times as well?

The scientific and citizen consensus is “yes.” Malaysia even holds an international symposium dedicated to conservation of the firefly. Scientists have for years been warning that the world’s estimated 2,000 species of fireflies are dwindling.

And is it any wonder? As the manmade environment continues its undying march into the natural world, where are these things supposed to live? Fireflies breed and exist in the woods and forests, along lakes and streams, in dense gardens and unruly meadows. Where are they supposed to do their firefly things when those places are paved over and built upon?

All of it doesn’t bode well.

“Fireflies are indicators of the health of the environment and are declining across the world as a result of degradation and loss of suitable habitat, pollution of river systems, increased use of pesticides in agro-ecosystems and increased light pollution in areas of human habitation,” notes the Selangor Declaration, a firefly advocating document. The decline of fireflies is a cause for concern and reflects the global trend of increasing biodiversity loss.”

Fireflies are part of our heritage; they are an iconic creature and have played a role in many, many cultures. They are the epitome of summer evenings, for many of us they served as an introduction to the wonders of nature. If we lose the fireflies, we lose an important invisible thread that connects us to the magic of the natural world. And as a species, we can’t afford to lose that right now.

Roland’s trivia question of the week:

Complete the golfing adage: “You drive for show, but putt for….”

Answer can be found here.