Last week, most of the ridges here in south-central Pennsylvania really started to show the widespread flaming colors that signify autumn has arrived.

It seems to me that glorious transformation is a tad later than usual this year. But one thing I’ve learned from decades of observing the annual cycles of the natural world is that nature surely operates on its own calendar, one that is often distinctly out of sync with the one we humans adhere to.

But sometime during October, the green leaves of summer trees will transform into yellow, red, orange, russet or bronze and bathing entire mountainsides with autumn splendor.

Some years tend to provide a much better show of fall colors than others. Some trees display their fall colors earlier than others, and each species will change in its own time slot. Timing is everything, and when most of the trees in a given area reach their peaks around the same time, the results can be spectacular for viewing fall foliage. Each species of tree also displays its own distinctive fall colors.

Beech trees turn a light bronze, while hickories will show golden bronze. Poplars will display leaves of golden yellow. Dogwood will turn a lovely purple. Red maples live up to their name with foliage of brilliant scarlet, and sugar maples will turn a beautiful orange.

Oaks are the last to show their fall colors of red, brown or russet. Oak trees are also the last to shed their leaves, often retaining them well into winter and long after they have turned dry and brown.

Predicting the timing of the onset and extent of fall foliage tends to be mostly folklore, but there is some basic science behind how and why leaves change color. The deciduous trees in our northern latitudes grow new leaves each spring, and those leaves become individual food factories for the tree throughout the spring and summer.

Leaves are predominantly green because of the pigment of an amazing substance called chlorophyll. Biochemistry is well beyond my pay grade, but to put it simply, chlorophyll absorbs the energy from sunlight and through an extraordinary chemical reaction uses it to transform carbon dioxide and water into sugars that the tree uses for food via the process known as photosynthesis. Most green plants rely on chlorophyll and photosynthesis for their existence.

As fall approaches, leaves stop their food-making processes, and the chlorophyll breaks down, allowing other pigments present in the leaves to show their color. The first of those, known as carotenoids, tends to be mostly yellow to orange in color.

Carotenoid pigments are responsible for the distinctive colors of corn, carrots, daffodils and even bananas. Carotenoids tend to be present in the leaves of many trees and shrubs, which is why many of the first leaves to change color tend be yellow hues.

Another group of pigments, known as anthocyanins, produce the bright reds and purples in fall foliage as well as apples, grapes, blueberries, cherries, strawberries, and plums. Most anthocyanins are produced in leaves later in autumn in response to bright light and excess plant sugars within leaf cells.

While weather-related factors, such as rainfall, sunlight and temperature, can have some effect on the intensity and duration of fall foliage colors, photoperiod is the primary determining factor of when leaves make their fall transition.

Photoperiod is the scientific term for the relative length of daylight and darkness for each day throughout the year. Photoperiod is also the trigger for many of the remarkable transitions in nature, and fall foliage is certainly one of those.

The shorter days of autumn start the biochemical processes in a leaf that ultimately cause the seasonal color changes. Low temperatures can enhance the formation of anthocyanin pigments that produce the bright reds in maples and other species, but an early frost can weaken the red color.

As the colors of fall start to peak here in our region, they will provide a wonderful backdrop for hikers, photographers, hunters and anglers in the next couple of weeks. The archery deer season is well underway. For small-game hunters, squirrel season started last month, and the rabbit and ruffed grouse seasons begin this weekend as well.

And for the anglers who haven’t put away their tackle yet, the cooler fall weather brings with it abundant opportunities for trout, bass and other species.