Southern Trees; Southern Live Oaks with Spanish Moss

Oaks are common both in Minnesota and Louisiana. Like pines, oak species are different in the north vs. the south. Southern Live Oak (Quercus virginiana ) is a distinctive and beautiful oak species found along the Southeastern Atlantic Coast from Virginia to Florida, and along the Gulf Coast from Florida to Texas. Live Oaks retain their leaves nearly all year, which is why they are named “Live”. They are not true evergreens because they shed their leaves in the spring just prior to emergence of next year’s leaves.

Spanish Moss (Tillandsia usneoides) is draped across the branches of the oaks in the pictures below. It actually is not moss, but rather a flowering plant in the Bromeliad family. While Spanish Moss uses trees like Live Oak and Bald Cypress for physical support, it is not parasitic. Plants like this that have no roots but absorb nutrients and water from humidity and rain are known as epiphytes.

The pictures above show a majestic Live Oak along the shoreline of Lake Pontchartrain in Mandeville LA. The largest Live Oak registered by the Live Oak Society is only a few miles from this oak. It is known as the Seven Sisters Oak, and has a trunk nearly 40 feet in diameter.

The pictures above show the “oak alley” located in Fontainebleau State Park, a few miles east of Mandeville LA. These oaks were planted around 1850 when the site was a plantation and sugar mill owned by Bernard de Marigny de Mandeville.

Southern Trees; Pines

Pine trees are prevalent in the Southeastern USA, but the species are completely different from those native to Minnesota. The Southern Pines native to St Tammany Parish, Louisiana are Loblolly, Longleaf, Shortleaf, Slash, and Spruce Pine. However, locally I’ve only identified Loblolly Pine (Pinus taeda).

Loblolly Pine is the most common tree in Louisiana, by far. According to a survey by the Southern Research Station of the US Forest Service, Loblolly Pines in Louisiana numbered about 2 billion in 2005, twice as many as the second place tree, the Sweetgum. The only other pine in the top 20 Louisiana trees was the Slash Pine, which Loblolly outnumbered by about 6X.

Loblolly Pine is the most important commercial tree in the Southern US, planted extensively for lumber and pulpwood. It grows fast, about two feet per year, in a wide range of environments.

Loblolly, like most of the Southern Pines has three needles growing from each fascicle. Pine trees in Minnesota have either 2 needles/fascicle (Red, Jack) or 5 needles/fascicle (Eastern White). The cone of the Loblolly Pine has distinctive protruding barbs. The bark of the Loblolly is rather thin in comparison to other pines, such as Longleaf. A consequence is that Loblolly is less able to withstand fire than other pine trees.

Loblolly is a word of Southern origin that refers to a swampy area, or a mudhole. Its name reflects that Loblolly Pine thrives best in wetter settings.

Southern Trees; Bald Cypress

We have returned south to Louisiana for the winter, so this blog will have to change a bit. To start, there will be a few posts that compare trees in the south to counterparts that grow in Minnesota. The first tree to be featured is the state tree of Louisiana, the Bald Cypress (Taxodium distichum), which is a deciduous conifer, like Minnesota’s Tamarack.

The native range of Bald Cypress stretches south along the Atlantic Coast from southern New Jersey to Florida and west along the Gulf Coast from Florida to Texas; it also extends north along the Mississippi river valley to southern Missouri. The picture on the left above is a Bald Cypress at the northern edge of its range, near New Madrid, MO, while the picture on the right is a specimen much further south, in Mandeville, LA.

Like the Tamarack, the Bald Cypress is one of the rare conifers that loses its leaves (needles) in the fall/winter. Around this time of year in Louisiana Bald Cypress needles change from green to yellow and orange before falling off. This does not happen uniformly, as shown by the trees in the two pictures above. They were both pictured on November 13 and are only about 50 steps apart. The tree shown on the left may be staying greener longer because of better access to water or less sun exposure.

In their preferred swampy environment, Bald Cypress trees commonly grow cypress “knees”

Lumber from the Bald Cypress is valued for its toughness (another similarity to tamarack). Remarkably, in the Gulf of Mexico divers recently found a well-preserved forest of Bald Cypress 60′ below the sea, 15 miles off the coast of Alabama. It is thought that these ancient trees had been buried by sediment, but then uncovered by Hurricane Ivan.

The forest is a relic from 50-60,000 years ago, when sea-level was considerably lower than now — this was during a period of colder global climate, when much of Earth’s water was tied up by extensive glaciation. There is much more to this story, and it is well told in a web page provided by the Alabama news site “Al.com”.

Winter Survival; Insects

Remarkably, tiny insects survive weeks and months of sub-zero cold each year. This post provides brief descriptions of how three common bugs manage this; Woollybear Caterpillars, Mosquitos, and Ticks.

Woollybear Caterpillar (Pyrrharctia isabella)

The woollybear hatches in the fall and overwinters in its caterpillar form, when it nearly freezes solid. Their bodies produce glycerol, a fluid that acts like antifreeze to product their organs from being damaged by freezing. Woollybears thaw in the spring and metamorphose into the Isabella Tiger Moth. To compensate for short growing seasons, the closely related arctic woollybear lives through several winters before changing into the moth.

Mosquitos (Order Diptera, Family Culicidae)

There are 51 species of mosquito in Minnesota, ~24 of them bite humans. Winter survival strategy varies among the species, but most survive as eggs laid in soil. These eggs enter a dormant state known as diapause in response to colder temperatures and shorter days. Eggs in diapause do not hatch until environmental signals are detected, like increased temperature or increased moisture. Typically a consistent temperature above 50 degrees Fahrenheit is needed before mosquito eggs hatch.

Ticks (Family Ixodidae)

There are about a dozen species of ticks in Minnesota, the two that are most common and of concern as disease carriers are the American dog tick or wood tick (Dermacentor variabilis) and the black-legged tick or deer tick (Ixodes scapularis). Ticks have eight legs, and so are actually arachnids (like spiders), not insects.

These Minnesotan ticks are quite resilient to cold temperatures. The American dog tick is typically not active below 45 degF, but the black-legged tick is quite active as long as temperatures are above freezing. Both ticks survive the coldest temperatures by staying beneath cover, like leaves, near to the ground. Even in bitter cold snaps, near the ground temperatures are usually warm enough for these ticks to survive.

American dog ticks are carriers of Rocky Mountain spotted fever, while the smaller black-legged ticks are the main carrier of Lyme disease. Transmission of disease typically requires the tick to have been attached for more than a day. Frequent checking for ticks is recommended to help people avoid these diseases.

Ticks position themselves at the tips of low-lying grasses and bushes, waiting to grab onto passing animals or people. So, their “landing spot” is usually near ground level. They crawl up to find an exposed spot to attach. Therefore, use of a repellent like permethrin on shoes, socks, and pant legs can be an effective guard against ticks.

Fall Colors; Tamaracks

The tamarack is unusual because it is the only conifer native to Minnesota that is not evergreen. The photos below show how local tamaracks have changed color from September to October prior to dropping all their needles.

A disadvantage for deciduous trees is that they must expend considerable resources to make new leaves each year. During summer these leaves are very effective in capturing solar energy for the tree, but they are shed in fall because they are not suitable for winter. In contrast the leaves (needles) of evergreen trees are not as good at capturing energy in the summer, but they are made for winter survival and last several years before needing to be replaced. Plus, evergreen needles capture solar energy year-round.

Tamaracks have developed a survival strategy that is a mix of deciduous and evergreen traits. Like the evergreen conifers, tamaracks have needles. However its needles are “cheaply made” — thin, flimsy and not meant for winter survival. The open architecture of the tamarack tree maximizes the sun exposure for each needle, which somewhat compensates for the fact that the needles are only available to capture energy in the summer. Dropping needles is also advantageous to the tamarack because it helps the tree avoid structural damage caused by clinging heavy snow.

Another North American conifer that drops its leaves each fall is the Bald Cypress, the state tree of Louisiana. It is an interesting coincidence that both of these deciduous conifers prefer swampy environments. Perhaps a plentiful water supply is also key to their survival strategy?

Tamarack trees near Laporte, Minnesota are still green on September 23. Their characteristic scraggly form is evident in the picture on the left above.

The picture on the right above shows a tamarack beginning to turn from green to yellow. This tree is near the Shingobee River on the Paul Bunyan Trail, October 9.

Tamaracks that have turned yellow in fall are very striking trees. These tamaracks photographed on October 18 are near Williams Lake in Hubbard County, Minnesota.

Winter Survival; Trees

Gentle snow fell in Northwestern Minnesota in early October this year, providing a wintertime preview. Surviving winter temperatures far below freezing is a big challenge for plants and animals. Today’s post focuses on how trees make it through — with some scenic pictures of the recent snow.

Trees are largely comprised of water, a critical issue for trees in the winter is to prevent water within living cells from freezing to crystalline ice. An important consideration is that most of the cells within trees are not living; freezing dead cells within trees happens commonly with no harm. Living cells avoid freezing by expelling water into the space between cells, increasing the sugar content of their remaining water, and transitioning this intracellular fluid to a viscous glass-like state.

Another winter-time issue for trees is water loss. To avoid excessive water loss, deciduous trees drop leaves with their large exposed surface area. Needles on evergreen trees minimize water loss because of their smaller surface area and their waxy outer coating.

Despite these coping mechanisms, extremely cold temperature does damage trees. If the water-bearing sap within trees freezes, the resulting expansion can literally cause trees to explode. Issues are also caused by swings in temperature. A warm spell, or prolonged sun exposure, can cause sap to flow, exposing the tree to damaging freeze in a subsequent cold snap.

Thanks to Tom Rongen for suggesting the topic of winter survival.