The Native Habitat of Redwood Trees

Coastal redwoods (Sequoia sempervirens) are some of the most iconic trees in the world. They grow taller than any other living trees and more massive than all but a handful of others. They’ve shared our planet for millions of years, and over this time, they’ve played an important role in the ecosystems they’ve played a role in creating.

But these amazing trees are not able to grow just anywhere. In fact, the entire global population of naturally growing redwoods is restricted to a 450-mile-long strip, stretching from southern Oregon to Salmon Creek Canyon, near Monterey.

Redwood Range

In total, redwoods have access to about 1.6 million acres of suitable habitat, although they are not the dominant tree species in much of this area. Redwoods represent more than half of the hardwood present in only about 640,000 of these acres. Redwoods occasionally grow at elevations of up to 3,000 feet, although most are found below 2,500 feet. Above these heights, redwoods fail to reach their characteristic size, and other trees begin replacing them in the landscape.

It actually appears that this range is shifting slightly to the north, probably in response to climate change. Fewer new redwoods are growing in the southern end of the trees’ range, while seedlings are popping up in previously uncolonized portions of the northern end of the range.

Climate and Weather

Redwood forests benefit from one of the most hospitable climates in the world. Mean annual temperatures vary between about 50 and 60 degrees Fahrenheit, and the temperatures rarely drop below 15 degrees Fahrenheit or climb above 100.

The forests literally drip with moisture. Most of the precipitation falls in the form of rain, although fog also contributes a substantial amount of moisture to the region. Like most of the Pacific Coast, the region receives most of its rainfall in the winter, with very little rain falling in the summer.

Redwood History

Redwoods were not always restricted to such a small geographic area. In fact, 100 million years ago, redwoods covered most of the northern hemisphere. However, about 20 million years ago, the climate began shifting, which allowed vast glaciers to extend farther south into North America and Asia than they previously had. Ultimately, this killed off mostthe redwoods alive at the time; only a relative handful were able to persist in small pockets of California and China.

But this range was reduced even further in the 19th and 20th centuries, as aggressive logging practices and habitat alteration removed thousands of redwoods from the gene pool. Currently, the redwood forest covers only about one-twentieth of the land that it did 150 years ago.

The Function of Fog

Redwoods reside near the Pacific Coast, penetrating inland as far as 35 miles in some places (although the forest contracts to about 5 miles wide in many areas). The primary limiting characteristic of this range is fog penetration. Fog is crucial to the health of redwoods. In fact, fog is more important than rainfall level in defining the coastal redwood forest type. While redwoods can be grown in areas without nearly constant fog, such as commercial orchards or residences, they do not do so naturally.

Nevertheless, these are still large trees with significant water needs. Large individuals may pull 500 gallons of water a day from the ground. Accordingly, while their habitat is restricted to only those areas that receive regular fog coverage, they do not grow equally well in all areas within these areas. The largest individuals and densest groves typically occur in riparian areas alongside major streams and in flat, low-lying areas – both of which have ample water stores. However, redwoods cannot grow in saturated soils, and soils carrying about two-thirds of their total water capacity are associated with the most productive portions of the forest.

The abundance of moisture in these forests (which are sometimes classified as super-humid) causes transpiration and evaporation rates to fall. Additionally, soil moisture levels remain higher throughout the year, further reducing the water stress that afflicts the trees growing in nearby but fog-free areas in the region.

The Neighbors of Redwoods

Redwoods are the dominant species in many of the forests they help create, although several other trees grow alongside them. Douglas firs (Pseudotsuga menziesii) are one of the most common species growing among the redwoods, but western hemlocks (Tsuga heterophylla) and Sitka spruce (Picea sitchensis) also occur with some regularity.

A litany of animal species live amid the towering redwoods. Small animals – including rodents, birds, reptiles, amphibians and invertebrates – represent the bulk of the local fauna, as occurs in most natural habitats. Rodents are particularly well-represented in the region, including two very large species: the porcupine and North American beaver. Nearly one-third of the country’s native bird species have been documented to occur in the redwood forest, including representatives of all major lineages, from flycatchers to owls.

However, large animals also live in the land of giant trees too. Black-tailed deer and Roosevelt elk – the largest of the United States’ native elk subspecies – browse vegetation amid redwood groves. Black bear, mountain lions and coyotes hunt through the forests, but their numbers are much lower than those of deer, elk and other herbivores, as is common in all habitats.

Frequent Fires Fuel Adaptation

Redwoods, like most other California natives, have a number of adaptations that allow them to survive the relatively frequent fires that occur in the state. Young trees – those less than about 20 years old – frequently die in these fires, but the stands rapidly regenerate in the form of clones, which sprout from the below-ground root systems. Older trees survive most fires, thanks in part to their 12-inch-thick bark. Most trees simply suffer bark damage, which is easily replaced over time.

Interested in Growing Avocados? Check Your Soil First

In the past few years, an increasing number of homeowners have been bitten by the fruit-tree bug. Instead of roses or marigolds, people are interested in growing their own citrus, pear, apple or avocado trees.

But whether you want to start producing tree fruits with an eye toward profit, or you are simply interested in stocking your kitchen with fresh fruit that you grew yourself, it makes sense to select a species and variety that warrants a high price tag. You’ll either pocket more cash while selling your crops at the local farmer’s market or save more money at the grocery store, but you’ll help your bottom line in either case.

And if you are interested in producing a high-priced tree fruit, it is hard to find a better example than the avocado. Avocados are relatively expensive fruit in the first place, but because of climate change and other socioeconomic factors, it is likely to increase drastically over the next several decades. In fact, future harvests are expected to fall by about 40 percent, which will cause the price of avocados to skyrocket.

But you must be sure that you are equipped to care for avocado trees before you start shopping for your stock. You’ll obviously need access to a reliable (and affordable) water supply and plenty of sun exposure, but one of the most critical aspects of avocado production relates to the soil you have available.

Make sure that you address the following soil characteristics before setting out to install your new trees:

  • Soil Structure: Avocados are shallow-rooted trees, whose roots are incapable of penetrating into compacted soils, so it is always best to break up the soil in the planting hole before introducing the tree. They prefer very coarse, well-drained, loamy soils, and they will struggle to thrive in heavy clay soils. Additionally, it is imperative that avocados not be planted too deeply, as this can stress the root systems and damage the trunk. Avocado trees cannot tolerate soggy soil, particularly while the temperatures are low, so it is better to err on the shallow side when you are planting these trees. Many California-based avocado farmers grow their trees on raised mounds, to help ensure adequate drainage and prevent root rot.

 

  • pH: Avocados grow best in slightly acidic soils, with a pH of between 5 and 7. Alkaline conditions limit the ability of avocado trees to absorb iron and zinc, which will ultimately lead to their demise. You can use elemental Sulphur to help reduce the pH of the soil when necessary, but you must be sure to plan ahead and address these issues before planting your avocados, as it can take six months or longer to properly adjust the pH.

 

  • Salt: Avocado trees are very sensitive to salt. Salt spray from the ocean, salt in the local water supply and salt in the soil are all problematic, so it is important to consider the salt content of these things and your geographic location before deciding to grow avocados.

 

  • Fertilization: Avocado trees respond best to small, frequent applications of fertilizer, rather than infrequent and heavy applications. Nitrogen and potassium (particularly after the trees begin to produce fruit) are the most important nutrients to supply to young avocados, while supplemental phosphorus rarely appears necessary. By the time they are about 10 years old, most avocado trees have produced a thick layer of mulch, comprised of their shed leaves. This usually eliminates the need for supplemental nitrogen.

Tree Growth Explained: The Magic of Meristems

From a macro view, trees appear to grow in many different ways through the course of a season. Their leaves unfurl and enlarge in the spring and their fruit swell in the summer.

But this is not true growth – after all, the tree will shed these structures eventually.

True growth occurs when trees produce new wood. This kind of growth produces tissue that persists from one season to the next.

But even this growth is a very location-specific phenomenon, and it only occurs in a few places throughout the tree.

These places are called meristems.

Apical Meristems

Apical meristems occur at the tips of branches and roots. They are responsible for a tree’s longitudinal growth along its axis, or, put more plainly, they are the place from which branches and roots grow longer. Arborists and botanists consider growth from the apical meristem to be primary growth.

However, apical meristems also produce the cells that will become the plant’s secondary growth center – the lateral meristems.

Lateral Meristems

Lateral meristems are found in the thin ring of tissue around the circumference of a tree’s trunk, branches and roots. These lateral meristem regions (which exist along the entire length of the branch or root in question) are responsible for increases in girth, rather than length.

Lateral meristems occur in two different tissues of each branch. The innermost ring is called the vascular cambium, while the outer meristem layer is called the cork cambium. Each produces new tissues from both the inner and outer surface of the ring.

More specifically, the cork cambium produces cork cells on its outer surface and phelloderm cells on its inner surface. The cork cells will eventually die and become the outer bark, while the phellogen is a parenchyma-rich layer of cells that serves to store starch for future use.

Further inside the tree, the vascular cambium produces phloem tissue on its outer surface and xylem cells (wood) on the inner surface. Phloem tissue transports starches along the length of the branches, while xylem transports water from the roots to the leaves and supplies support and stability to the tree as a whole.

The Arboricultural Implications of Meristems

With the understanding that trees only grow from these regions, it is important to apply this knowledge to the ways in which we prune trees. There are a number of ways to use this knowledge, but the following include some of the most important:

  • Because it removes a large number of a tree’s apical meristems, topping is a destructive practice that should be avoided. Removing a branch’s meristem often results in the branch’s death, and it forces the tree to grow from lateral branches, rather than the branch tip.

 

  • Tree branches do not move higher off the ground with time. Because trees grow from the tips of their branches, and not from the trunk’s base, limbs do not move higher with time. This means that an obstructing limb will remain in the way unless you remove it. Arborists must perform a procedure called a crown raising to deal with these types of limbs.

 

  • Narrowly spaced, co-dominant stems force material to grow inside the wood of the junction. When a tree produces a pair of trunks, the expansion in girth causes the tree to produce wood around the bark material, sandwiched between the two. This makes such junctions weak, as the bark does not attach well to the wood inside the junction.

 

Three Great Tree-Identification Apps for Your Smart Phone

There are few aspects of life that remain untouched by technology.

Even the ways we interact with the natural world have changed thanks to the technology available at our fingertips.

For example, if you wanted to identify a tree20 years ago, you’d have to break out a field guide or a dichotomous key. But in the year 2017, all you need is your phone.

A variety of different tree-identification apps are now available, each of which help users determine the identification of the trees around them. We discuss a few of the most popular products below.

Virginia Tech Tree ID

If you spend any time researching trees on the internet, you’ve no doubt stumbled across Virginia Tech’s incredible dendrology portal, that includes a wealth of photographs and high-quality information. But they’ve also produced a stellar tree-identification app, so you can access this incredible data from your phone, while you are actually looking at the tree you are trying to identify.

One of the primary “selling” features of the app (which is actually available free of charge right here or here for both iPhone and Android, respectively), is its flexibility. The app features a number of filtering options, which allow the user to narrow down the potential species in question to just those within the user’s area. In fact, users can narrow down the search criteria so much that the app effectively becomes, in the designer’s words, the “Woody Plants of Where You Are Standing.”

Another exciting feature offered by the app is the ability to send tree-identification questions to “Dr. Dendro,” who will help you distinguish between closely related taxa.

LeafSnap

LeafSnap is an electronic field guide – actually, a collection of online field guides – that help users to learn about trees. The app includes a lot of basic information about trees, including many high-quality photos of various species; but LeafSnap’s claim to fame is undoubtedly the LeafSnap feature. To use the LeafSnap feature, the user takes a photograph of a tree they wish to have identified. The application then uploads the photo to a central database, processes the image with an algorithm, and provides the user with a species identification.

LeafSnap also has several interactive features, and the information you collect is automatically shared with scientists around the world. This provides them with the chance to study an incredibly large dataset, and understand what is happening among wild populations in nearly real-time.

A diverse array of scientists, researchers and developers are responsible for the work behind LeafSnap, including representatives from Columbia University, the University of Maryland and the Smithsonian Institution. LeafSnap is available at no cost (you can download it here), but unfortunately, it only includes trees of the northeastern United States, and it is only available for Apple-based systems.

Botany Buddy

Botany Buddy is an interactive plant information app that offers helpful information to users. Botany Buddy not only helps users to identify unknown plants and trees with its 1,300-species-strong database of both native species and ornamentals, it also suggests suitable plants and trees for various situations that may confront professional landscapers or homeowners.

Unlike some other apps, Botany Buddy does not require users to be connected to the internet to access their personal dataset, which can be an important feature when you’re out on the trail, miles away from civilization. Botany Buddy is free to download, but it is only available for iPhones and other Apple products. You can download Botany Buddy at the iTunes store or here.

Meryta Trees

Native to islands in the South Pacific, most species of the genus Meryta are small, evergreen, dioecious trees. The genus contains 28 different species, but scientists routinely add, synonymize and eliminate the occasional species within the group.

Meryta trees are found on several different islands in the south Pacific, but they are best represented in New Caledonia, where 11 endemic species live. Many native cultures existing alongside Meryta trees consider them to be sacred, and protect particularly noteworthy specimens with fences or other boundaries. Among other uses, the Maori use the bark of some Meryta species to produce a dark, red dye.

Culture and Care

Meryta trees are excellent choices for many Californian properties. They’re distinctive foliage and modest size makes them both attractive and manageable in most yards, and their tolerance of salt spray means they even work well right on the coast. Further, Meryta trees do not produce thorns or prickles, require little in the way of regular maintenance and do not cause significant litter problems.

Rated for USDA Hardiness Zones 10 and 11, Meryta trees prefer full- to partial-sun exposure and well-drained, loamy soil. Although they aren’t exactly drought tolerant, they do not require as much water as is commonly supposed. Most Merytas bloom in the winter, although their flowers are relatively inconspicuous, those of some species produce a pleasant fragrance.

Important Species in the Genus Meryta

Although represented by 28 different species, only three are available on any kind of regular basis.

Broad-Leaved Meryta (Meryta latifolia)

Native to Norfolk Island, Australia, the broad-leaved Meryta is an evergreen tree that reaches heights of between 15 and 20 feet. In keeping with the theme of the genus, the leaves of broad-leaved Merytas are quite large, measuring as much as 2 feet in length and 1 foot in width.

Broad-leaved Merytas are quite rare in the wild, and few locations have many individual specimens. In total, scientists suspect that there are no more than 150 mature specimens living in the wild. Although occasionally available from specialty nurseries and similar sources, broad-leaved Merytas are not cultivated as much as Denham’s Merytas or pukas are.

Denham’s Meryta (Meryta denhamii)

Denham’s Meryta is a New Caledonian endemic, that grows to about 20 feet in height. Although noteworthy for their enormous leaves, which may reach 3 feet in length or more on mature specimens, Denham’s Merytas also bear fragrant flowers. This is somewhat unusual for (apparently) wind-pollinated species, but a pleasant treat for homeowners planting the trees on their property.

Denham’s Merytas are cultivated in parts of Australia and Florida, but given their intolerance to freezing temperatures, they are not cultivated as commonly as pukas (who are slightly more cold tolerant than Denham’s Merytas) are.

Puka (Meryta sinclairii)

Like most members of the genus Meryta, the puka bears very large, thick leaves; however, the puka is noteworthy for having the largest non-divided leaves of any New Zealand tree species. Although the puka grows as a single trunk when young, it typically begins to branch out after producing its first inflorescence. It is often the dominant tree species within its native range.

The puka has been cultivated since at least the end of the 19th century, and it remains a widely propagated tree in the modern world. Because of its tolerance to wind and ability to grow in either sun or partial shade, the puka is a common street tree in its New Zealand homeland; and it is being seen with increasing regularity in warm locations worldwide, such as California and Florida. However, as the puka is susceptible to freezing temperatures (as are most Meryta species), it is not suitable for locations in which the temperatures drop below about 28 degrees Fahrenheit.

Six WaysTrees Influence Your Business’ Security

Modern business owners cannot afford to ignore security concerns. And while most 21st century security threats are of the cyber variety, old fashioned crimes, such as burglary, theft and vandalism still occur with alarming frequency.

Savvy business owners do their best to limit such crimes. They install auxiliary lighting and alarm systems; some even hire security personnel to monitor the property. But most fail to consider the ways in which the trees on the lot influence the security profile of your retail store, warehouse or office.

Don’t misunderstand: A row of palm trees will not turn your property into Fort Knox. In fact, trees can even make your property less secure, if you install them improperly or fail to keep them pruned. But with some thoughtful planning, you can maximize the security-enhancing benefits of your trees, which will help keep you, your employees and visitors safe.

  1. Trees often act as visual barriers, which can give criminals places to hide. It is really important to reduce (or eliminate, to the extent that it is possible) the number of hiding places present on your property. Not only can criminals use these places to remain out of sight, but they may even be able to monitor your employee’s habits, as well as things like key codes or entry procedures.
  1. Trees and shrubs can be used to form dense hedges or boundaries. You probably can’t stop sophisticated or especially motivated burglars with a row of columnar trees or bushes, but you can deter most casual or opportunistic criminals by simply making your building harder to access. Dense hedges can re-route would-be thieves, and force them to travel through well-lit and monitored areas. By using trees and bushes that are armed with prickles, thorns or spines, such as honey locusts and some acacias, you can make such hedges even more impenetrable.
  1. Well-pruned trees indicate that a property is frequently maintained and (probably) under surveillance. As with criminals targeting homes, burglars and vandals often search for businesses that look neglected. Unkempt or dead trees are like a beacon to burglars, as they suggest the property isn’t regularly monitored or maintained – it may even be unoccupied. By simply doing things like keeping your trees well-pruned, you can encourage would-be trespassers to target some other business.
  1. Trees can serve as anchors for hidden security cameras. Security cameras are a great way to help protect your business, and some security professionals even recommend fake security camerasfor some situations – people are less likely to commit crimes when they believe they are being watched. However, it is sometimes advisable to mount cameras in inconspicuous places, to catch people that don’t think they are being watched. Trees provide a great way to mount clandestine cameras, as their branches and leaves will help camouflage it well.
  1. You can hang lights from trees to help illuminate the ground. Even if you have a few large street lights and some flood lights near your parking lot, chances are, your business’ property has plenty of under illuminated areas in which criminals can hide.
  1. Trees can effectively prevent local graffiti artists from accessing their canvass. Large, blank walls are like magnets to your local graffiti artists. One of the best ways to keep the walls from being covered in unauthorized, potentially offensive, language and art is to plant appropriate trees right up next to the walls. You’ll need to work with a skilled arborist to select species unlikely to produce invasive roots and an appropriately shaped canopy for the location.

Schefflera Trees

Schefflera Scheffleras are largely tropical species, found in warm and humid habitats around the world. Several species – including the umbrella tree (Schefflera actinophylla) and the dwarf umbrella tree (Schefflera arboricola) – are widely planted as ornamentals or as indoor houseplants. They are especially prized for their hardy nature and the tropical flavor they can provide your yard or home.

Classification and Composition of the Group

The genus Schefflera, as presently construed, contains about 600 different species of trees, vines and large shrubs. As you may expect for such a large collection of species, botanists and taxonomists disagree about the exact composition of the group, and changes have been (and will surely continue to be) common.

It appears that current composition of the group is paraphyletic, meaning that it is comprised of several different independent lineages. This will likely lead scientists to split the group into several different genera at some point in the future. These independent lineages appear to be more-or-less geographically clumped into four different groups, centered in Melanesia, Central and South America, Southeast Asia, Africa (including Madagascar), respectively.

Description and Care

Most of the species placed in the genus have palmately-compound (hand-like), evergreen leaves, primarily located at the apex of the branches. It is difficult to make broad generalizations about the various features of such a varied group, but the most popular commercial species exhibit a tree- or shrub-like growth habit.

Scheffleras tend to want warm, humid conditions, with ample soil moisture. Nevertheless, few Scheffeleras can tolerate having wet root zones for extended periods of time, so it is wise to let the soil dry out between waterings. Most species in the genus prefer partial shade; they will wither in exceptionally dim light and they are susceptible to burning in bright sunlight.

Unfortunately, despite making wonderful houseplants or ornamental trees, most Scheffleras contain calcium oxalate crystals in their tissues. These highly irritating crystals are toxic to dogs and cats, who may experience extreme irritation and burning in the mouth, esophagus and tongue, after eating the leaves, stems or flowers.

Important Species in the Genus Schefflera

Schefflera is a wide-ranging and species-rich genus, but only a few species are commonly seen in the marketplace.

Umbrella Tree (Schefflera actinophylla)

Also known as the Queensland umbrella tree or the octopus tree, the umbrella tree hails from the tropical portions of northern Australia, New Guinea and the island of Java. It is a medium-sized tree, growing up to 50 feet in height. It often grows as a multi-trunked tree, and occasionally starts life as an epiphyte, nourishing itself as a parasite, located high above the canopy floor. Over time, the tree will send down aerial roots, which eventually reach the ground, allowing the plant to become self-sufficient.

The umbrella tree is perhaps most notable for its spike-like protrusions (called racemes) that bear its flowers. Appearing in the early summer, the racemes may persist for several months before withering away. Particularly large racemes may contain 1,000 red flowers or more.

Dwarf Umbrella Tree (Schefflera arboricola)

The dwarf umbrella tree is named for its appearance, which resembles that of a small Australian umbrella tree. Native to Taiwan and south China, the species is grown all over the world as both a houseplant and a landscape tree. Although these trees can grow up to 30 feet in height, most indoor-maintained specimens only reach 8 or 9 feet in height.

Dwarf umbrella trees are extremely popular houseplants, if for no other reason than their incredibly hardy nature. They tolerate poor conditions and neglect in stride, and they often live for many years after becoming established. These traits also make dwarf umbrella trees very popular among bonsai enthusiasts.

Seven-Finger Tree (Schefflera digitata)

The seven-finger tree is a distinct-looking Schefflera, native to New Zealand – in fact, it is the only Schefflera native to the country. Preferring damp, cool riparian habitats, the seven-finger tree grows to about 30 feet in height. Unlike most other Scheffleras, the seven-finger tree has leaves with serrated margins.

Seven-finger trees have been important to the lives of New Zealand’s native peoples throughout history. In addition to the milky sap, which is used in a variety of medicinal applications, the wood was a popular choice for starting friction fires.

Imperiled Species

Like many other plant and tree species hailing from underdeveloped, tropical regions, many Scheffleras are struggling to cope with habitat loss. Several of the species are listed as threatened or endangered, and are unlikely to survive without increased protection, and possibly cultivation programs.

Some of the most imperiled species include the Cameroon Schefflera (Schefflera hierniana), which hails from the tropical regions of equatorial Africa; and two Indonesian species: the Javanese Schefflera (Schefflera fastigiata), from Java, and the many-leaved Schefflera (Schefflera multifoliolata), of Sumatra.

Why Do Tree Leaves Change Colors in the Fall?

AutumnThe red, gold and purple tones of autumn leaves provide a once-a-year bounty for the eyes. But this phenomenon represents an interesting biological phenomenon, that provides lessons into tree biology, the interconnection between weather and trees and the ecological interactions between trees and their predators.

Unfortunately, the fall color here in the west is not as glorious as that in New England or along the east coast, but there is still plenty of gorgeous foliage to be seen. Aspens turn bright gold, a variety of shrubs and smaller trees produce oranges and other colors, and many of trees of eastern origin produce the prototypical fall fireworks you’d expect elsewhere.

And yes, before anyone asks, you can find pretty awesome fall color in California.

The Basic Process

Trees produce three basic pigments in their leaves:

  • Chlorophyll is a green pigment that is involved in the process of photosynthesis. It is continually created, used and degraded through the growing season, which causes the leaves to appear green.

 

  • Carotenoids are yellow to orange pigments that are also found inside leaves for much of the year. However, the chlorophyll generally overpowers these pigments, and mask their presence.

 

  • Anthocyanins are reddish pigments, which are typically not produced in the leaves until the fall.

Whereas chlorophyll and carotenoids are produced in small structures called chloroplasts, anthocyanins flow through the watery material inside the leaf’s cells.

Deciduous trees become dormant in the winter, which alleviates their need to manufacture food (photosynthesis). In fact, because water is often scarce during the winter, dormant trees tend to shed their leaves. This reduces the chances that the water evaporating from the leaves will exceed that which can be drawn from the ground.

So, as the days become shorter and the nights become longer, deciduous trees cease producing chlorophyll. As the chlorophyll breaks down, the underlying carotenoids (which have always been present) and the anthocyanins (which are produced around the same time that chlorophyll production ceases), become visible.

This yields the purple, yellow, red or orange leaves that characterize the season.

A short time later, as the tree prepares for its winter slumber, the leaves form something called an abscission zone at the base of the petiole (leaf stalk). This zone effectively blocks the transport of resources between the tree and the leaf, and eventually serves as an easy point of detachment. Once the abscission zone is complete, the leaf is normally blown off the tree a short while later.

Conditions that Improve Fall Color

You’ve probably noticed that fall color intensity varies from one year to the next, but it also varies from one location to the next – even when all other factors are the same.

But if you look carefully, you’ll notice that the yellow, gold and orange colors tend not to fluctuate from one year to the next; it is the red, maroon and purple colors that are dazzling one year and mediocre the next. Part of that is because the carotenoids which yield the yellows and oranges are present all year long and in similar quantities each year. But anthocyanins are only produced during a relatively small window of time, and the amount produced varies from one year to the next.

It turns out that weather is the primary factor that leads to the differing amounts of anthocyanins. When the days are sunny, the nights are cool and the weather dry, fall color is best. This collection of conditions helps encourage the production and retention of sugars in the leaves, which promotes the production of anthocyanins.

However, a number of other weather conditions can dampen the fall color for a given year. Summer droughts typically reduce the vibrancy of the fall colors, as do warm or wet autumns.

How Do Trees Draw Water from the Ground?

Tree AnatomyMost people understand that trees require water to grow and live, and many are aware that roots play a critical role in drawing water from the ground. But this is the limit of most people’s understanding of the subject.

But by exploring the way in which trees accomplish this surprisingly tricky feat, you can learn a wealth of information about tree biology and you’ll surely appreciate the intricate engineering Mother Nature accomplishes.

Basic Tree Anatomy

Trees pack a whole lot of function into relatively featureless-looking tissues. For example, the wood is actually a complicated type of tissue called xylem. Made from a combination of living and dead tissues, the xylem provides the tree with support and serves as the pipeline for water to travel up the tree.

Xylem contains a number of specialized structures called vessel elements. Comprised almost solely of dead cell walls, the vessel elements form an unbroken tube from the roots, through the trunk and to the leaves. The vessels eventually connect to small pores in the leaf surface, called stomata (singular: stoma).

Another set of plumbing-like tubes are found immediately under the bark of trees in a tissue layer called the phloem. The phloem is tasked with the responsibility of transporting the sugars produced in the leaves to needy tissues throughout the tree. Unlike xylem, which transports water in one direction, phloem is capable of bi-directional flow.

Plumbing and

Percolating

So far, this all seems pretty intuitive. Trees have long “pipes” which carry water from the roots up through the tree. But the truth is more complicated. Consider, for example, that it usually takes energy to pull the water up from the ground. Just think about how much effort you have to apply to suck a soda through a straw. Trees accomplish similar feats, except that they are often required to draw water for much greater distances.

People often view trees as relatively inanimate objects. They may bloom in the spring and exhibit glorious color in the fall, but people rarely consider the energy required by a tree to grow, produce new tissues and repel invaders. Using energy to draw water up their trunks would increase their energy needs drastically.Fortunately, trees have devised a way around this problem.

The solution relies on a few different physical phenomena or properties.

  • Osmosis begins the process. Simply put, water tends to move from areas with relatively low levels of dissolved substances to areas with relatively high levels of dissolved substances. The fine hairs on the outer surface of absorbing roots contain liquid that has very high levels of solvents. This causes the water surrounding the roots, which are relatively solvent poor, to flow across the root hair’s cell membrane and into the xylem.

 

  • Now that the water has been drawn into the tree’s xylem, capillary action — the tendency for the water to flow into a narrow tube – becomes important. This occurs when the molecules in the water are more attracted to the vessel walls than they are to each other. This causes some of the fluid to “climb” up the sides of the vessel elements inside the xylem. However, capillary action cannot draw water very high up the tree, so it is only one part of the solution.

 

Now we have drawn water into the roots via osmosis, and capillary action has helped draw it up to perhaps the level of the trunk (give or take). But to understand the manner in which the water completes its journey, we need to move to the leaves at the canopy’s limit.

Moving On Up

As we said earlier, the vessels inside the tree’s xylem eventually connect to holes in the surface of the leaves called stomata. These pores serve as an exit-point for the water, which evaporates from the pores, diffusing into the air. This process is called transpiration.

But there’s a problem with this – it should be impossible to create this much negative pressure (a fancy way of saying “sucking power”) without causing the water inside the vessels to boil. Trees get around this problem by ensuring that vessel elements are very narrow and 100-percent full of water. Without air bubbles to serve as nucleation sites for the water to start boiling, the water remains in the liquid state. Accordingly, trees are able to use transpiration to achieve high negative pressures, which draws the water from the bottom of the trunk all the way to the leaves at the edge of the canopy.

As you can see, there’s a lot to the process by which trees draw water from the ground. This is a simplified version of the steps, so be sure to check out this great video if you’d like to learn a little more about the process:

 

Hollies (Ilex spp.)

HolliesHollies are familiar trees, easily recognized by their glossy, dark green foliage and beautiful bright red berries. But hollies are a diverse and varied group, and several species break from this mold. Although the vast majority of holly species are evergreen, a handful shed their leaves annually; some have spiny leaves, while others bear smooth, round foliage; and while bright red berries are iconic, some species bear yellow or black fruit.

Hundreds of species have been described worldwide, but a few – notably the American holly and European holly – are the most commonly used in ornamental plantings.

Wildlife Interactions

While holly fruits (technically, holly fruits are drupes, rather than berries) are toxic to humans and some domestic animals, a variety of wild creatures rely on them for a food source. Insects also feed on the nectar produced by holly flowers, and play an important role in fertilization.

Holly fruits develop from the late summer to the early winter, but most wild animals eschew the drupes until they’ve been through multiple freeze-and-thaw cycles. This appears to soften the previously hard fruits and make them more palatable.

In addition to providing value as a food source, hollies provide very dense cover to rodents and birds foraging amid their boughs. Nesting birds will also set up shop in these dense, often spiny, foliage.

Ornamental Use and Culture

Hollies are quite popular in the ornamental plant trade, and they are available as both wild-type plants and numerous human-created hybrids and cultivars.

Because most hollies are dioecious (plants occur as distinct male and female individuals), it is wise to plant representatives of both sexes to ensure the best possible fruit set. Additionally, while American hollies and a few other forms grow well in the shade, they will produce more fruit when grown in full sun.

Most hollies prefer well-drained, slightly acidic soils, but they are relatively flexible and will adapt to many different growing conditions. Different forms grow best in different places, and most locations have at least one species (typically many more) that will thrive in the area and climate. Taken collectively, hollies thrive in U.S.D.A. Hardiness Zones 3 through 11, which encompasses most of the country.

One down side to their ornamental use is the tendency of some to select non-native species. Most hollies, regardless of their point of origin, produce fruits that are attractive to local birds, who consume the drupes and deposit the seeds elsewhere. This often leads to the spread of invasive holly species, typically at the expense of native hollies and other understory species.

Selected Species Accounts

Species richness estimates for the genus Ilex vary widely. Some authorities recognize only 400 or 500 species, while others recognize nearly 800.

  • American holly(Ilex opaca) – The American holly is an understory species of the southeastern United States, which occasionally grows to about 60 feet in height. When they are grown in open areas with full sun, American hollies often become impressive, pyramid-shaped trees. However, like many other hollies, American hollies are slow-growing trees that take a decade or more to reach maturity. A number of cultivars have been developed, including dwarf forms that make excellent hedges.
  • European holly(Ilex aquifolium)– While European hollies are native to the warmer portions of Europe, their native range also extends into north Africa and southwest Asia.
  • Winterberry (Ilex verticillata)–Winterberry is a large (occasionally reaching 15 feet in height or more), deciduous shrub, native to the Northeastern United States. Celebrated for its glorious red fruit, which are especially conspicuous given the lack of winter foliage, winterberries are a favorite of gardeners. A variety of cultivars are available, with varying tolerance for soil conditions.
  • Mountain holly (Ilex mucronata) –The mountain holly was formerly called the false holly, and placed in the genus Nemopanthus, but recent molecular data has caused taxonomists to place it with the true hollies in the genus Ilex. A North American native, the mountain holly is a shrub that only rarely grows taller than 10 feet. It is sometimes grown as an ornamental shrub or in groups as a hedge.