The miracle of spring and the endless beauty of evolution

The natural world is reborn every spring as flowers bloom and animals return like clockwork, but beneath the surface each species’ unique evolutionary history gives this rebirth an endless, almost magical variety.  In New Jersey, there are some 2,100 varieties of plants alone, each similar and unique in how they respond to the coming of summer.

The world is coming alive again in the Northeast.  Temperatures are rising, the sun is shining longer each day, and with both nature comes back in bloom, repeating what seems to be a miracle that occurs almost like clockwork on an annual basis.  One day, brown, scrubby, dried out grass turns bright, verdant green and starts growing fast and furious, thick and lush.  Over the course of a few days, what begins as tiny buds on the limbs of bare, lifeless trees, hardly noticeable at first, become flowers, and then leaves.  Perennials that were completely withered, like dead weeds in the soil, or aren’t even above ground at all, pop up in all their rainbow variety of colors, practically overnight.  The animal kingdom reemerges just as quickly:  Deer are common in my area in the winter, but just about everything else hides until spring.  Then, squirrels, rabbits, birds, even bears, and of course insects are suddenly everywhere, picking up precisely where they left off in the never ending search for mates and sustenance.  Mornings are now filled with song, emanating from every tree and rooftop though the birds themselves aren’t easy to spot.  Days are broken up with the buzzing of bees as they collect pollen from every available flower.  Sometimes at night you can hear a much larger creature, like the bear that was outside our bedroom window a few weeks ago toppling over the garbage can.  I didn’t see it, but our alert greyhound heard it and sprung into action to defend the household.

On the surface, it can appear like this happens all at once, everything coming back into bloom according to the same schedule, but if you look carefully and watch closely year over year, every different type of plant flowers in its own unique way, on its own time frame.  The front of our yard, for example, is lined with trees that seem very similar to the type lining the next block.  They are the same general size and take the same general shape, but they aren’t the same species and do not follow the same pattern.  The trees out front bloom a full two weeks earlier and flower in an off-white before the leaves form.  The ones around the corner are reddish and much slower to sprout.  Right now, I have flowering trees in front and barely sprouts to the right.  In a couple of weeks, they will look close enough it would take a horticulturist to tell the difference between the two. Likewise, the trees in my backyard all take somewhat different approaches to growing their leaves.  One goes from buds straight to almost glowing green leaves that are close to fully grown already, as if this species want a head start on summer.  Others start with helicopter seeds that have yet to fully emerge, and before they do they turn a dull brown almost like dead leaves in the fall.  A few still seem dead, though we know they are just slow starters and they’ll be back in their good time.

According to the state of New Jersey, there are some 2,100 native plants to the region, a number they claim is “comparable to states that are three to four times greater in size.”   Each of these plant species has their own evolutionary history, sharing some features while diverging in others. Thus, they all have similar mechanisms to identify the change in seasons.  They are equipped with a light sensitive chemical, phytochrome, that allows them to determine the amount of daylight.  They are also sensitive to the temperature of the soil.  The combination of the two governs when they shed their leaves in the winter and bloom again in the spring, but the details are not the same for each and some of the subtleties remain a mystery.  Sibum Sung, a molecular biologist at the University of Texas, studied the process in a small cabbage-like plant known as Arabidopsis.  Dr. Sung and a colleague discovered a molecule required for the plant to flower, and that the molecule was either produced or not produced by another gene activated based on temperature.  If the molecule is present in the plant’s cells, it blooms.  If it is absent, it does not.  The production of this molecule is dependent on both the temperature and the duration, but it’s not as simple as an on/off switch.  The molecule is produced after around 20 days of frigid temperatures, which signals another set of genes that actually produce the flowers.  This process takes 10-20 days as the Arabidopsis primes itself for spring.  Dr. Sung refers to this molecule as COLDAIR, and believes it enables plants to remember the duration of the coldest period of the year before beginning the process of blooming again.  At the same time, we remain unsure how plants know it is cold in the first place, much less for how long.

It’s also likely that each species does it a little bit differently because flowering plants evolved 150 million years ago when the earth was much warmer and winter wasn’t a concern.  They didn’t begin adapting to colder climates until the last 100 million years when the planet cooled, and each family of plants evolved differently according to their own unique circumstances in a classic case of convergent evolution.  Winter required all flowering plants to adopt some type of strategy to cope with the cold weather.  Generally speaking, that strategy is to cease production of chlorophyll for a period, and flower again in the spring when the days are long enough and the angle of the sunlight is direct enough to generate enough energy to support complex structures like leaves.  The details of each plant’s unique strategy aren’t the same, however.  While they all follow the same general pattern, the underlying processes vary and hence even trees and plants that look the same, bloom on a different schedule, in a different way, and possibly via a different genetic mechanism.  Some of these differences we can see by observing the outward show, others are much harder to determine, especially across some 2,100 unique native species in a single state.

The situation is even more complicated when you consider that the term “native species” is largely a misnomer.  No one knows for sure, but a large number of the plants we now consider “native” to New Jersey didn’t arrive here until after Columbus discovered America, setting off a chain reaction that resulted in the first truly global exchange of goods, services, and wildlife.  The weeping cherry, a beautiful tree that bears pink flowers, for example is native to Japan, as are Japanese maples popular in my area.  The saucer magnolia is from China.  The Douglas fir from the other side of the country, and the Norway spruce from the other side of the Atlantic.  Even Jersey’s famous corn came up from Mexico sometime before Europeans arrived in the Northeast, having been cultivated in Central Mexico some 7,000 years ago, derived from a wild grass known as teosinte in a way we aren’t fully aware of.  This is not unique to New Jersey.  Potatoes are actually from South America and Europeans didn’t start eating them until the 1500’s, changing the primary food source for an entire continent and, some say, setting off the Enlightenment.  Yams, while commonly known as sweet potatoes, are a different species entirely.  They originated in Africa before traveling to Asia and the Americas.

This isn’t to say that there aren’t invasive species.  In my area, the spotted lantern fly has been steadily moving east after arriving in Pennsylvania from China in 2014.  Three years ago, they hadn’t made it to my backyard.  Two years ago, they were swarming by the end of the summer, attaching themselves to the trunks of trees practically in sheets, as though the bark had become a living, breathing thing.  Last year, they were still present, but in much lower numbers, though they had made it even further east and south to my hometown in Central New Jersey.  Who knows what this year will bring?  The US and local governments consider them a serious threat to our “grape, orchard, and logging industries” as reported by the USDA.  So far, I haven’t seen anything on that scale, but the sudden emergence of anything you’ve never seen before, a strange new insect with bright red eyes, is disconcerting to say the least, making it easy to believe the world is changing around us for the worse. Plants can also take a long time to die. There have been several trees in my yard that are mostly dead, though a few of the leaves don’t seem to know it. They bloom and sprout while the rest of the branches lay bare and barren. This process can continue for several seasons, each year the poor tree tries to come back to life, but there aren’t enough leaves to sustain it. The changes introduced by something like the spotted lantern fly can take years or even decades to fully determine.

Of course, the world has always been changing.  The abundance of life right outside my window is an amalgamation millions, hundreds of thousands, thousands, and yes hundreds of years in the making.  It emerges every spring, both different and the same and I expect it will continue to do so in all the beauty evolution produces.