Pennsylvania Fall Foliage Reports

This approximately 125-mile loop is the quintessential “leaf peeper” road trip. The tour closely follows the ridge offering views at every turn. Highlights include a stop at the third deepest gorge in Pennsylvania, a ride on the world’s steepest vehicular incline, a walk to a bog, and a pleasant drive through and past four state parks and a state forest. Allow a minimum of four hours to complete the tour.

• Begin at Donegal (Exit 91 of the PA Turnpike)
• Drive PA 711 North (Laurel Highlands Scenic Byway) to Ligonier
• Go around the town square (take second RIGHT) to continue on PA 711 North

The Laurel Ridge

The Laurel Ridge seen on your right is known geologically as the Laurel Hill Anticline. It spans more than 70 miles and runs in a northeast to southwest direction extending from Cambria County in the northeast to beyond Ohiopyle in the south.

When the earth’s continents collided 300-220 million years ago the layers of rock folded into alternating ridges and troughs called anticlines and synclines. This folding produced the area we call the Laurel Highlands with its prominent anticline ridges – Laurel Ridge, Chestnut Ridge (to the west), and Allegheny Ridge (to the east) with rock layers at the top that are resistant to erosion.

Due to the steep slopes of the Laurel Ridge and the difficulty of reaching some areas, it is primarily heavily forested. Seven state parks and a state forest along this ridge ensure its continued conservation. Laurel Ridge State Park with its main feature of the 70-mile Laurel Highlands Hiking Trail runs the length of the ridge. The flat crest of the ridge provides backpackers and day hikers a wilderness experience with the reward of stunning views. The elevation and the ridges provide an ideal location for ski resorts that rely on the climate for winter recreation.

As you continue, you cross the ridge several times. Look for views of the ridge, the abundance of trees, and the variety of fall color.

• Turn RIGHT at New Florence to continue on PA 711 North to Seward

Fall Foliage – Why and How Leaves Change Color

Did you ever wonder how and why leaves change color? Why a maple leaf turns bright red? Where do the yellows and oranges come from?

Leaves are nature's food factories. Through photosynthesis, plants take water and carbon dioxide and use sunlight to make oxygen and glucose. A chemical called chlorophyll makes photosynthesis happen and is what gives plants their green color. As summer ends and autumn comes, the days get shorter. Trees shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades, we see yellow and orange colors. The orange colors come from carotene pigments and the yellows from xanthophyll pigments. Small amounts of these colors are always in the leaves but we can't see them in the summer because they are covered up by the green chlorophyll. The yellow and gold colors remain fairly constant from year to year since they are always present in the leaves.

The bright reds and purples are derived from anthocyanin pigments that develop in leaf cells in late summer. Sugars in the leaf begin to breakdown in bright sunlight as phosphate and other chemicals decrease in the leaf. The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting colors of reds and purples.

The most spectacular fall foliage results when late summer is dry and autumn has bright sunny days and cool (low 40 degree) nights. A fall with cloudy days and warm nights brings drab colors. Early frosts or a wind storm will quickly end any fall color display.

• Turn RIGHT on PA 56 East and travel approximately five miles to the overlook parking on LEFT

Conemaugh Gap

You drove over the Laurel Ridge to reach this site. Travel through the region requires going over, or in some cases through, the ridge.

The Conemaugh River originates three miles east of here at the confluence of the Little Conemaugh and Stoneycreek rivers in Johnstown and flows west towards Saltsburg to the Kiskiminetas River. The river has cut through the ridge by eroding its soft, brownish-gray rock layers of sandstone, siltstone, and shale while the top of the ridge comprised of massive sandstone boulders that are erosion resistant remains. The resulting gap reveals millions of years of geologic history in the exposed Devonian age rocks.

The Conemaugh Gap receives its name from the river. Derived from the Delaware Indian word “Conunmoch” meaning otter, this river cuts a deep, narrow gap through the Laurel Ridge forming the third deepest gorge in Pennsylvania. The gorge measures seven miles long and 1,650 feet deep. This gorge is locally known as Sang Hollow because of the abundance of ginseng that once grew here.

As you leave this area, notice the topography as you wind down to the river valley.

• Turn LEFT to continue on PA 56 East to Johnstown and drive four miles following signs for PA 56/403 to the inclined plane

Johnstown Inclined Plane

Ride 900 feet above the river valley on the world’s steepest vehicular inclined plane for a view of the confluence of the Stonycreek and Little Conemaugh Rivers and the spectacular fall foliage on the surrounding ridges. Both vehicles and pedestrians can use the inclined plane. Purchase a roundtrip ticket or a one-way ticket if you plan to drive or hike back down. More information and hours of operation can be found at: www.inclinedplane.org or 814-536-1816.

• Turn RIGHT out of parking area and travel approximately 2.2 miles
• Turn LEFT to stay on PA 403
• Turn RIGHT onto PA 271 South to Waterford

The Highlands

After crossing the summit, the ridge to your left prior to reaching Waterford is the Laurel Ridge. It is one of three ridges that define this area.

This area, geologically known as the Allegheny Plateau, consists of high ridges with flat tops separated by valleys with steep sides as a result of the folding that occurred when the continents collided. This entire region was then lifted into mountains as tall as today’s Andes Mountains in South America, forming the highlands. Over the millennia, the ridges have eroded down to their present elevation.

Elevation and the ridges play a key role in the climate of the Laurel Highlands. It is often cooler and wetter than climates in the surrounding areas. On average, temperatures can be eight to ten degrees cooler. The ridges create barriers that dramatically affect the weather. As a result, one side of the ridge may receive abundant rain or snow while the other side is dry. The average temperatures for October is a high of 62 degrees and a low of 41 degrees. Snowfall in October can be one to three inches.

As you travel to your next destination, notice the characteristic terrain of the highlands as you drive over high ridges and into the valleys between.

• Turn LEFT at Kinsey Museum (log building) onto Nature Run Road to Laughlintown

Need a snack and want to try a local favorite? Stop for a pumpkin gob at the Laughlintown Pie Shoppe (on left at intersection with PA 30).

Gobs

A gob is a mining term that refers to a coal refuse pile but is also a name given to a regional dessert. These little cakes with the cream filling can be traced back to Germany and this local favorite is an adaptation of whoopee pies of the Pennsylvania Dutch. In the 1920s, the Harris and Boyer Bakery of Johnstown named these desserts gobs which proved to be the perfect lunchbox snack for the coalminers of the time. The original consists of two small devils food chocolate cakes with white cream filling but there are many variations including the pumpkin gob with its cream cheese filling.

• Turn LEFT onto PA 30 East (Lincoln Highway) and travel 4.4 miles to crest of hill
• Turn RIGHT onto Laurel Summit Road and past Laurel Mountain State Park (road becomes gravel) and drive two miles into Forbes State Forest to the Beam Rocks trailhead parking lot on LEFT. 

Beam Rocks Overlook

This popular rock outcropping on Forbes State Forest provides a panoramic view of Beam Run hollow, Somerset County to the east, and the surrounding landscape of the Laurel Ridge. Beam Rocks is easily accessible by hiking the one-half-mile, relatively flat Beam Rocks Trail.

Beam Rocks is maintained in its natural state. Some of the paths within the rocks lead to sudden drop offs. In the fall, the wet leaves can make these areas extremely slippery. Also, look for rattlesnakes that often sun themselves on the warm rocks.

This sandstone rock formation sits at an elevation of 2,657 feet. The 70-mile Laurel Highlands Hiking Trail passes along the base of this outcrop 75 feet below you. The narrow pathways through the moss-covered rock lead you to areas filled with rhododendron and hemlock. Look for the uncommon, high-elevation Mountain Ash, a small tree which can have dull red or rich yellow leaves and clusters of bright red fruits. Look overhead to see soaring hawks or eagles.

The spectacular views from here contribute to the popularity of this site for hiking and enjoying the view. A quieter view with more wildlife viewing opportunities can be found at your next destination, Wolf Rocks.

• Continue on Laurel Summit Road to Laurel Summit State Park
• Park in the lot and hike to Spruce Flats Bog or the Wolf Rocks Overlook

Spruce Flats Bog and Wildlife Area

This 28-acre bog is easily accessible by hiking the one-quarter-mile, flat Bog Trail. The trail follows the old Pittsburgh Westmoreland & Somerset Railroad that traveled across the bog in the early 1900s. A boardwalk located at the end of this trail reaches out into the bog.

Spruce Flats Bog and adjoining Spruce Flats were misnamed. Early in the 20th century, lumbermen found a forest of virgin hemlock growing on the flats which they misnamed "spruce".

The origin of the bog is obscure. Past geologic activity left a depression on top of Laurel Ridge. This depression passed through natural succession from open water to swamp, to bog, to meadow, and finally to forest. Lumberman clear-cut the forest causing the water table to rise. Transpiration, the evaporation of water from plant leaves, had been the major method by which water was removed from the depression. Devastating fires around the same time burned away the upper layers of organic matter on the forest floor above the water table. These events recreated the bog. Although the original depth of the bog is unknown, current depth is six to eight inches of peat covering almost two and one-half feet of muck. Bogs are characterized by limited nutrients, acidic soils, and large amounts of organic matter. These growing conditions determine the types of plants that can grow here. Plants found here are often more typical further north and include large cranberry, cotton grass, and the insect-eating pitcher plant and sundew. The 300 acres surrounding the bog are managed primarily for wildlife habitat.

Wolf Rocks Overlook

This little-known rock outcropping on Forbes State Forest provides a spectacular view of Linn Run Hollow and the Chestnut Ridge beyond. Wolf Rocks is accessible by hiking the two-mile, relatively flat Wolf Rocks Trail to the overlook. This trail is recommended for intermediate hikers. Although it has a gentle grade, there is rough footing. Hiking boots are strongly encouraged.

The trail follows the rocky ridge through mountain laurel and rhododendron. Wolf Rocks is maintained in its natural state. The rock formation drops sharply to the forest trees below. In the fall, wet leaves can make these areas extremely slippery. Use caution while at the rocks.

Wolf Rocks is located along the slope on the western edge of the Laurel Ridge at an elevation of 2,600 feet. The sandstone rock outcropping extends approximately 100 feet and is characterized by frost cracks, frost wedging, and slippage; evidence of its geologic formation. Most of the forest land that makes up Forbes State Forest was purchased from lumber companies. The 8,532 acres surrounding the outcrop were purchased by the Commonwealth of Pennsylvania in 1909 from the Byers-Allen Lumber Company. This land was the first parcel of state forest land purchased in the Ohio River Watershed.

Look for wildlife as you hike along the trail. Sightings include white-tailed deer, black bears, and bobcats. Note that hunting is permitted in Forbes State Forest.

• Continue on Laurel Summit Road which becomes Linn Run Road and follow Linn Run Road thru Linn Run State Park

A Transitional Forest - Melting Pot of two Forest Types

Most would agree: the sugar maple is the “King of Autumn.” Most of southern Pennsylvania is covered with Oak-Hickory dominated forests. However, the Laurel Highlands’ uniquely elevated terrain brings some of the northern hardwood forest species, like sugar maple, into southern Pennsylvania which creates a diverse splash of color in the fall.

The forest species that grow within a certain region are dictated by topography, elevation, available sunlight, slope position, rainfall, and soil characteristics. The many elevation changes in the Laurel Highlands create a melting pot of Pennsylvania’s northern and southern tree species. The highest plateaus are covered with northern hardwood species, such as sugar maple, American beech, red maple, black cherry, sweet birch, northern red oak, and white ash. The valleys, lower elevations, and side slopes are covered with the oak-hickory forest type which consists of northern red oak, red maple, black oak, white oak, chestnut oak, hickory, sweet birch, white ash, American beech, and yellow poplar.

In the Laurel Highlands, the highest ridge tops peak about a week before the valleys and side slopes. In general, fall color in the Laurel Highlands peaks around October 15-20. Black gums and some red maples peak around October 1-10. Most red maples, sugar maples, black cherries, and sweet birches peak around October 10-20. Red oaks, white oaks, chestnut oaks, yellow poplars, and beeches peak around October 20-30.

With this widely diverse mix of tree species, especially the abundance of sugar maples and red maples, some say the peak of fall color in the Laurel Highlands rivals some of the New England states in the Northeast.

• From park office, travel approximately four miles to a “T” intersection
• Turn LEFT on PA 381 South
• Turn RIGHT onto PA 31 West to return to Donegal

This approximately 70-mile loop offers meandering drives through the valleys between the ridges of the highlands. Highlights include stops within two state parks and views of the deepest gorge in Pennsylvania from both on top of the ridge and from the Youghiogheny River. Allow a minimum of two and onehalf hours to complete the tour.

• Begin at Donegal (Exit 91 of the PA Turnpike) and drive PA 31 East
• Drive PA 381/711 South (Laurel Highlands Scenic Byway) to Normalville

The Laurel Ridge

The Laurel Ridge seen on your right is known geologically as the Laurel Hill Anticline. It spans more than 70 miles and runs in a northeast to southwest direction extending from Cambria County in the northeast to beyond Ohiopyle in the south.

When the earth’s continents collided 300-220 million years ago the layers of rock folded into alternating ridges and troughs called anticlines and synclines. This folding produced the area we call the Laurel Highlands with its prominent anticline ridges – Laurel Ridge, Chestnut Ridge (to the west), and Allegheny Ridge (to the east) with rock layers at the top that are resistant to erosion.

Due to the steep slopes of the Laurel Ridge and the difficulty of reaching some areas, it is primarily heavily forested. Seven state parks and a state forest along this ridge ensure its continued conservation. Laurel Ridge State Park with its main feature of the 70-mile Laurel Highlands Hiking Trail runs the length of the ridge. The flat crest of the ridge provides backpackers and day hikers a wilderness experience with the reward of stunning views. The elevation and the ridges provide an ideal location for ski resorts that rely on the climate for winter recreation.

As you continue, you cross the ridge several times. Look for these views of the ridge, the abundance of trees, and the variety of fall color.

• Turn LEFT onto PA 381 South to Ohiopyle and Ohiopyle State Park
• After crossing the railroad tracks, turn RIGHT into the parking area at the Ferncliff Peninsula, walk along the Great Allegheny Passage Trail towards the right to the high bridge (approximately a four-minute walk) for a view of the Youghiogheny River OR
• Continue on PA 381 South into the borough of Ohiopyle and turn RIGHT into the main parking area for a short walk to the overlook deck for a view of Ohiopyle Falls

Transitional Forest - A Melting Pot of Two Forest Types

Most would agree; the sugar maple is the “King of Autumn.” Much of southern Pennsylvania is covered with Oak-Hickory dominated forests. However, the Laurel Highlands’ uniquely elevated terrain brings some of the northern hardwood forest species, like sugar maple, into southern Pennsylvania which creates a diverse splash of color in the fall.

The forest species that grow within a certain region are dictated by topography, elevation, available sunlight, slope position, rainfall, and soil characteristics. The many elevation changes in the Laurel Highlands create a melting pot of Pennsylvania’s northern and southern tree species. The highest plateaus are covered with northern hardwood species, such as sugar maple, American beech, red maple, black cherry, sweet birch, northern red oak, and white ash. The valleys, lower elevations, and side slopes are covered with the oak-hickory forest type which consists of northern red oak, red maple, black oak, white oak, chestnut oak, hickory, sweet birch, white ash, American beech, and yellow poplar.

In the Laurel Highlands, the highest ridge tops peak about a week before the valleys and side slopes. In general, fall color in the Laurel Highlands peaks around October 15-20. Black gums and some red maples peak around October 1-10. Most red maples, sugar maples, black cherries, and sweet birches peak around October 10-20. Red oaks, white oaks, chestnut oaks, yellow poplars, and beeches peak around October 20-30.

With this widely diverse mix of tree species, especially the abundance of sugar maples and red maples, some say the peak of fall color in the Laurel Highlands rivals some of the New England states in the Northeast.

• Continue on PA 381 and turn LEFT on Sugarloaf Road. Drive two miles to overlook on LEFT

Baughman Rock

The drive to the overlook takes you from river level to the steep slopes overlooking the Youghiogheny River Gorge. The path to the overlook crosses a flat tilted outcrop known as Baughman Rock. Although the access to the overlook is steep, the view is worth the walk.

The Youghiogheny River originates in West Virginia and flows 130 miles north to join the Monongahela River at McKeesport. This river, which is older than the surrounding mountains, has cut through the Laurel Ridge leaving the erosion resistant sandstone where you stand. It also lies along the top of the ridges you see in front of you.

At 1,700 feet deep, the Youghiogheny River Gorge is the deepest gorge in Pennsylvania. Look to the right to see the Laurel Ridge and below to see what was originally the Baltimore and Ohio Railroad; built in 1870. This active rail line is currently operated by CSX Railroad. The section of river, known as the “Middle Yough,” is barely noticeable from here as it meanders around Victoria Flats.

As you leave this site, you cross over the ridge and follow the river south to where it joins the Casselman River and Laurel Hill Creek.

• Continue on Sugarloaf Road for 5.6 miles. Turn LEFT at PA 281 North.
• Drive 2.5 miles then turn LEFT to continue on PA 281 North (Oden Street). Drive 0.3 miles to Confluence
• Turn Right at the stop sign in Confluence and drive 15.5 miles to a blinking light in New Centerville.
• Turn LEFT onto Copper Kettle Highway

Fall Foliage – Why and How Leaves Change Color

Did you ever wonder how and why leaves change color? Why a maple leaf turns bright red? Where do the yellows and oranges come from?

Leaves are nature's food factories. Through photosynthesis, plants take water and carbon dioxide and use sunlight to make oxygen and glucose. A chemical called chlorophyll makes photosynthesis happen and is what gives plants their green color. As summer ends and autumn comes, the days get shorter. Trees shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades, we see yellow and orange colors. The orange colors come from carotene pigments and the yellows from xanthophyll pigments. Small amounts of these colors are always in the leaves but we can't see them in the summer because they are covered up by the green chlorophyll. The yellow and gold colors remain fairly constant from year to year since they are always present in the leaves.

The bright reds and purples are derived from anthocyanin pigments that develop in leaf cells in late summer. Sugars in the leaf begin to breakdown in bright sunlight as phosphate and other chemicals decrease in the leaf. The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting colors of reds and purples.

The most spectacular fall foliage results when late summer is dry and autumn has bright sunny days and cool (low 40 degree) nights. A fall with cloudy days and warm nights brings drab colors. Early frosts or a wind storm will quickly end any fall color display.

• Drive 2.8 miles and turn LEFT onto Ream Road
• Turn RIGHT onto Lyons Road
• Turn right at the Scenic Overlook sign and follow the road to the gate. Park in the lot at the gate and enjoy a short walk to the overlook pavilion.

Scenic View at Laurel Hill State Park

Enjoy the panoramic view of the Laurel Highlands from this 180-acre property. The only evidence of development that can be seen is the top of Seven Springs Mountain Resort to your left and the old farmhouse in front of you. The farmhouse is the visitor center at Laurel Hill State Park

Return to Copper Kettle Highway and drive thru Trent where Copper Kettle Highway becomes County Line Road. Turn RIGHT into Laurel Hill State Park (visitor center on left)

Laurel Hill State Park

As you enter the park, notice the large bronze statue to your right. The CCC Boy statue represents the hard work and tremendous pride of the boys that served in the Civilian Conservation Corps.

The Laurel Hill Visitor Center contains exhibits about the Civilian Conservation Corps and its influence on the development of the park. Learn about the challenges of early logging and lumbering practices on the ridge.

The park, named for its location at the foothills of the Laurel Hill Anticline (Laurel Ridge), offers numerous views of forested slopes that make up the ridge. From the visitor center, follow the main park road to the left for approximately one-third mile to reach Laurel Hill Lake. Park in one of the parking lots on the right. Walk to the causeway that crosses the dam and admire the reflection of the fall foliage in the calm waters of Laurel Hill Lake.

• As you leave the park towards your next destination, you will begin your climb up and over the Laurel Ridge.
• Turn RIGHT out of Laurel Hill State Park to continue on County Line Road to Seven Springs Mountain Resort

Continue on County Line Road

The Highlands After passing Seven Springs Mountain Resort, the ridge ahead of you is the Chestnut Ridge. It is one of three ridges that define this area.

This area, geologically known as the Allegheny Plateau, consists of high ridges with flat tops separated by valleys with steep sides as a result of the folding that occurred when the continents collided. This entire region was then lifted into mountains as tall as today’s Andes Mountains in South America, forming the highlands. Over the millennia, the ridges have eroded down to their present elevation.

Elevation and the ridges play a key role in the climate of the Laurel Highlands. It is often cooler and wetter than climates in the surrounding areas. On average, temperatures can be eight to ten degrees cooler. The ridges create barriers that dramatically affect the weather. As a result, one side of the ridge may receive abundant rain or snow while the other side is dry. The average temperature for October is a high of 62 degrees and a low of 41 degrees. Snowfall in October can be one to three inches.

As you travel to your next destination, notice the characteristic terrain of the highlands as you drive over high ridges and into the valleys between.

• Turn RIGHT onto 381/711 North
• Turn LEFT onto 711 North/31 West

Need a snack and want to try a local favorite? Stop for a pumpkin gob at the Old General Store and Country Pie Shoppe (on the left).

Gobs

A gob is a mining term that refers to a coal refuse pile but is also a name given to a regional dessert. These little cakes with the cream filling can be traced back to Germany and this local favorite is an adaptation of whoopee pies of the Pennsylvania Dutch. In the 1920s, the Harris and Boyer Bakery of Johnstown named these desserts gobs which proved to be the perfect lunchbox snack for the coalminers of the time. The original consists of two small devils food chocolate cakes with white cream filling but there are many variations including the pumpkin gob with its cream cheese filling.

• Continue on PA 31 West to return to Donegal

Three factors influence autumn color — leaf pigments, length of night, and weather, but not quite in the way we were told as children. The timing of color change and leaf fall are primarily regulated by the increasing length of night. None of the other environmental influences-temperature, rainfall, food supply, and so on-are as unvarying as the steadily increasing length of night during autumn. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape with nature's autumn palette.

Where do autumn colors come from?

A color palette needs pigments. These molecules capture energy from sunlight to power the chemical reactions that convert water and carbon dioxide into sugars—photosynthesis. Trees in temperate zones store these sugars for their winter dormant period. Three major pigment types are involved in the production of autumn color.

Chlorophyll is the most abundant pigment. It absorbs red and blue light and reflects green giving leaves their basic color and masking lighter shades.

Carotenoids, (carotene and xanthophylls) reflect orange, yellow and brown colors in corn, carrots, buttercups and bananas. The clear yellow of tuliptree leaves and the russets shades of oaks are due to carotenoids. 

Anthocyanins give red, blue and purple colors to cranberries, apples, grapes, berries, cherries, and plums depending on their acidity. They are water soluble and dissolve in the fluids of leaf cells.

Chlorophyll and carotenoids are present in leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells.

During the growing season, chlorophyll is continually used, broken down and replaced and leaves appear green. As night length increases in the autumn, chlorophyll production slows and then stops. Eventually all the chlorophyll is destroyed. Carotenoids and anthocyanins present in the leaf are then unmasked and show their colors.

Tree species have characteristic colors. Oaks turn red, brown, or russet; hickories show golden bronze; aspen and yellow-poplar, golden yellow; dogwood, purplish red; beech, light tan; and sourwood and black tupelo, crimson. Maples differ by species — red maple turns brilliant scarlet, sugar maple glows orange-red and black maple a rich yellow. But the little striped maple becomes almost colorless. Leaves of some species such as the elms simply shrivel, turn brown and fall. 

When is the best time to see autumn color?

The timing of the color change varies by species. Blackgum begins to show brilliant scarlet branches in late August and the related dogwood is draped in brick-red by midSeptember. Maples become red and orange in late September and early October. But oaks only put on their colors long after maples have shed their leaves.

In most years, northern PA counties reach their best autumn color October 1-10. Central counties are at their peak October 10-20 and south central and southeastern PA have the most color October 20-31.

How does weather affect autumn color?

Because carotenoids are always present in leaves, the yellow and gold colors remain fairly constant from year to year. The brilliance of red colors that develop as chlorophyll in the leaves is dwindling can be affected by temperature and soil moisture in late summer and fall.

A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays. During the day, sugars are produced in the leaf but cool nights and the gradual closing of veins connecting leaves to twigs prevent these sugars from moving out. Lots of sugar and lots of light spur production of brilliant red, purple and crimson anthocyanin pigments.

Dry soils also affect the chemistry of autumn color. Like the weather, soil moisture varies greatly from year to year and place to place. So fall color will never be the same in any two years or locals. A late spring, or a severe summer drought, can affect the onset of fall color. Warm fall weather may lower the intensity of autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights typically produce the most brilliant autumn colors.

What triggers leaf fall?

In response to the shortening days and weakening sunlight, leaves begin processes leading up to their fall. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to drop.

What does all this do for the tree?

Winter is a certainty that all vegetation in the temperate zones must face each year. Perennial plants, including trees, must protect themselves from freezing temperatures and desiccation. Stems, twigs, and buds are equipped to survive extreme cold and will reawaken when spring heralds the start of another growing season. Tender leaf tissues, however, would freeze and burst in winter, so plants must either toughen up and protect their leaves or dispose of them.

Evergreens — pines, spruces and other conifers — survive by toughening up. Their needle-shaped foliage is covered with a heavy wax coating and the fluid inside their cells contains substances that resist freezing. Thus the foliage of evergreens can safely withstand all but the severest winter conditions. Evergreen needles survive for several years but eventually fall due to old age.

Leaves of deciduous plants, on the other hand, are typically broad and thin and not protected by any coating. They are tender and vulnerable to damage. The fluid in their cells is usually a thin, watery sap that freezes readily. This means that the cells could not survive winter where temperatures fall below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival. Thus, leaf fall precedes each winter in the temperate zones.

Pennsylvania is the meeting ground of northern trees that flourish only on mountain tops farther south and southern species that are at the northern limits of their range.

Northern tree species include:

• Gray and paper (white) birches
• Mountain maple
• American mountain ash 
• Quaking aspen
• Pin (fire) cherry

Southern tree species include:

• Black gum
• Black walnut
• Pignut hickory
• Flowering dogwood
• Southern red and scarlet oaks
• Sweetbay and umbrella magnolias
• Persimmon
• Pawpaw

Ohio buckeye, bur oak, and shingle oak, common to the Mississippi Valley, have eastern outposts on the Allegheny Plateau.