Pawpaw Tree

A couple of different species in the genus Asimina go by the name pawpaw, but the common pawpaw (Asimina triloba) is far and away the most commonly encountered species.

Whereas the common pawpaw is found throughout much of the eastern United States, all other members of the genus are restricted to Florida, Alabama and Georgia. Authorities differ on the number of species in the group, with some only recognizing two and others recognizing as many as 10.

While pawpaw trees are somewA Favorite Fruithat interesting looking (especially when contrasted with most other native trees), they offer little value in an ornamental context. Their primary claim to fame is their highly unusual fruit.

A Favorite Fruit

Pawpaw fruit defy easy description. Reaching up to 6 inches in length, they are the largest edible fruit that native to the United States.  Although they start out green, they often bear browns, yellows or even purple tones upon ripening. Technically a type of berry, pawpaw fruits contain a number of hard, inedible seeds.

Most people describe their taste as being similar to that of a banana (they are, in fact, used frequently in place of bananas in desert recipes), while others liken their flavor to that of a mango. Some note hints of papaya or strawberry. Their texture is better characterized as extremely soft and custard-like.   

Those who enjoy the taste often prize them greatly, as they are not easy to acquire via commercial means. Pawpaw fruits are not easy to store for extended periods of time and shipping them is equally problematic – they turn to mush in short order. Some small-scale farmers have begun growing them for local markets, but short of the development of a storable cultivar, they are unlikely to become commonplace in your local grocery store.

However, pawpaws are sometimes available in frozen or preserved form. Some manufacturers have even started creating pawpaw ice cream.

A Taste of the Tropics

Pawpaws look somewhat out of place in eastern forests. Instead of the small, thin, finely toothed leaves of maples (Acer spp.), elms (Ulmus spp.) and birches (Betula spp.), these bottomland-inhabiting trees have large, smooth-edged leaves that look like they belong in a tropical rainforest. Although they can grow to proper “tree-sized” proportions, most wild specimens are rarely more than scraggly denizens of the understory.

While their physical characteristics are partially a manifestation of their habitat adaptations (for example, their large leaves are an adaptation that enables them to collect as much light as possible in the dim forest understory), they are also a manifestation of their evolutionary relationships. Pawpaws are members of the family Annonaceae, which primarily contains trees with tropical distributions. Some of its closest relatives living in the same forests include the magnolias (Magnolia spp.) and tuliptrees (Liriodendron tulipifera).

Funny-Looking Flowers

Pawpaw flowers are very interesting-looking. They bear six petals arranged in two rows – one outside row and an offset inside row. Somewhere between maroon and brown in color, the medium-sized flowers may occur singly or in groups. They’d be relatively inconspicuous were it not for their size.

They are also relatively scent-free, which is good; what smell they do emit is not terribly pleasant. In fact, the primary insects that pollinate the flowers (several beetle species) are those attracted to the smell of decay. Because these are not very effective pollinators, pawpaws produce relatively few fruit relative to the number of flowers they bear.  

Subpar Seed Dispersal

Fruit-set is not the only thing with which pawpaw trees struggle: They are also poor seed dispersers. While plenty of animals also find pawpaw fruits to be delicious — raccoons, coyotes, foxes and opossums eagerly consume the fruit – few of them ingest, and ultimately disperse, the seeds.

To help cope with this evolutionary challenge, pawpaws often reproduce by forming large spreading colonies in hospitable locations. Some scientists have suggested that the poor dispersal pattern of pawpaws is the result of the extinction of a former predator (most likely a big herbivore that could ingest the fruit whole). Once these creatures died off, humans became the primary means by which pawpaw seeds have traveled ever since.

 

Poison Sumac

Michael Green Now a Registered Consulting Arborist

Michael Green became a Registered Member of the American Society of Consulting Arborists. He joins his father, Ruben Green, as a Registered Consulting Arborist in the southern California and greater Los Angeles area. A registered consulting arborist is trained to appraise and/or evaluate trees, provide expert witness testimony, and provide guidance for other tree related issues. Learn more about Evergreen Consulting arborist services at www.greenarbroists.com. Congratulations Michael!

 

Cashew tree

Cashew Trees

Most famous for the delicious nuts they produce, cashew trees (Anacardium occidentale) are medium-sized evergreen trees, historically native to Brazil.

Aside from their well-known and commercially important tree nuts, cashew trees also produce an edible accessory fruit, commonly known as a cashew apple.

In a culinary sense, cashews work in the same contexts as most true nuts do, so they are often referred to as such. However, in the botanical sense, cashews are seeds, not nuts.

Traits of the Tree

Cashew trees are medium-sized, evergreen trees that reach heights of about 20 to 40 feet. Their foliage is quite dense and attractive, and typically forms a spreading crown.

The leaves are smooth, leathery and rounded at the distal end, with prominent veins. Cashew trees produce a well-developed network of roots, which help them to survive during times of minimal rainfall. When grown in areas with deep, loamy soil, cashew trees produce a large taproot, which helps them access deep-water reserves. This dense network of roots makes transplantation somewhat problematic.

Cashew trees produce relatively small, pink- to magenta-colored flowers, which emerge from the current season’s growth. The flowers may be male, bisexual or female, although female flowers are relatively rare on the trees.

Poisonous Relatives

Although it seems surprising, cashews are not-too-distant cousins of poison ivy (Toxicodendron radicans) and poison oak (Toxicodendron diversilobum). Accordingly, some parts of cashew trees contain urushiol – the problematic compound found in the sap of these and other, related plants.

One part of the tree that holds a significant quantity of the toxic compound is the seed’s outer shell. This makes shelling the nuts difficult, and most commercial operations rely on special equipment to shell and clean the nuts. In fact, the University of Florida discourages private individuals from trying to harvest home-grown cashew nuts, as the caustic fluid can cause severe blistering if it contacts the skin.

Geographic Range and Preferred Climate

Cashew trees require relatively warm temperatures and they are very susceptible to frost damage. They are primarily grown between 25 degrees North and 25 degrees South latitude. The trees require a minimum of about 40 inches of annual rain, although 60 to 80 inches of annual rain is ideal.

Although native to northeastern Brazil, cashew nuts are now grown in several countries around the world. Vietnam produces more cashews than any other country, but India, Nigeria, Cote d’Ivoire and Benin also produce significant amounts of the nuts.

Growing Your Own

In spite of the problems associated with harvesting the seeds, many people like growing cashew trees as attractive ornamentals (although you can harvest the cashew apples produced by the trees, which, due to their short shelf life are typically not available in American markets). Cashew trees are most commonly grown in this fashion in south Florida, but they may thrive in southern California if nurtured.

The commercial harvest of cashews requires a long-term commitment, as it typically requires eight years for the plants to produce an economically significant harvest. However, dwarf varieties have been developed recently, which become economically viable at the end of their third year. Additionally, these dwarf varieties produce more than three times as many seeds per acre as wild-type cashew trees do.

Amid California drought, fears rise of trees dying, falling

APTOPIX California Drought Trees

TreePeople volunteers water a tree at the Los Angeles Equestrian Center Martinez Arena in Griffith Park, Friday, July 31, 2015, in Los Angeles. As Californians and the communities they live in cut back water usage and let lawns go golden, arborists and state officials are worrying about a potentially dangerous ripple effect. Nearby trees are going neglected and becoming diseased or dying. (AP Photo/Nick Ut)

LOS ANGELES (AP) — As Californians and the communities they live in cut back water use and let lawns turn brown, arborists and state officials are worrying about a potentially dangerous ripple effect: City trees going neglected and becoming diseased or even falling.

With cities ordered to reduce water use by 25 percent during the state’s four-year drought, many residents are turning off sprinklers — not realizing that trees can be permanently damaged by a sudden reduction in the amount of water they receive.

“You don’t want to be cutting back the water to the trees,” said Ruben Green, an arborist with Evergreen Arborist Consultants in Los Angeles. “The tree can’t adjust.”

Across the state, 12 million trees died over the past year due to lack of water, according to the U.S. Forest Service. While the bulk of those deaths occurred outside urban areas, conservationists and officials are now focusing on cities, where mandated water reductions are becoming visible in drying limbs and scorched leaves.

Fears that parched trees could pose a danger were heightened this week when a 75-year-old, 75-foot-tall pine tree fell on a group of kids from a camp at a Southern California children’s museum, leaving a boy and girl hospitalized with serious injuries. An independent arborist and another from the city of Pasadena are conducting an investigation into the cause, which has not been determined to be drought-related.

Green visited the site of Tuesday’s tree collapse and said it appeared unlikely the drought was to blame because the area around the tree looked well irrigated and its root system appeared compromised — a sign of rot, decay or injury, not necessarily the drought.

Still, the collapse highlighted concerns about the health of urban trees. Los Angeles alone has more than 25 square miles of parks and some 327,000 trees.

Green and other arborists said they have seen an increase in the number of diseased trees in the city. As they get less water, they become more prone to illness caused by pests. In addition to bark beetles, Green has seen a newer pest drilling tunnels in the trunks of “dozens and dozens of trees.”

Arborists say the number of falling trees and limbs does not appear to have risen in Los Angeles, but there are concerns that could be next. They also are worried that if a strong El Nino brings a wet California winter, already distressed trees will collapse when a storm hits.

“We’re really right on the brink of starting to face more serious issues,” said Cindy Blain, executive director of California ReLeaf, a nonprofit network of urban and community foresting groups around the state. “This is a critical time.”

A new six-person crew removes potentially hazardous trees from Los Angeles parks. So far this year, it has moved out 550 trees — surpassing the 300 removed in an average year.

“They are starting to fail due to the drought, and we want to make sure these trees don’t potentially pose a hazard to the public,” said Laura Baurenfeind, principal forester with the city parks department.

Turf areas in city parks are being watered three times a week, down from at least five when drought regulations were not in place. To help nearby trees compensate, the city and nonprofits are installing makeshift basins to filter water to trees.

Meanwhile, a public education campaign is underway. California ReLeaf has partnered with Save Our Water, a coalition of the California Department of Water Resources and Association of California Water Agencies, to better inform residents about proper tree care during the drought.

Blain said many of the people she’s spoken with say they have forgotten about their trees or gotten worried and began watering at the tree’s base. Trees should be watered from the edge of their canopy.

If a tree goes too long without enough water, it will become unable to soak up liquid at all.

Like many Californians, Bruce Birkett has reduced lawn watering at his childhood home in Los Angeles in response to the drought. Recently, though, he’s watched in grief as the giant cedar in the front yard became brittle and brown.

“That was hard,” he said, “watching this lovely tree looking poor.”

Critical Condition: Protect the Roots to Protect Your Trees

tree rootsA tree’s fate is largely tied to the health of its roots and the state of the surrounding soil. Unfortunately for many homeowners and arborists, the bulk of the tree’s roots are out of view. Without taking drastic or invasive investigative steps, the health of the tree’s roots must be inferred, rather than directly observed.

Accordingly, the best way to protect your tree is to protect enough of the tree’s roots to sustain it through any damage. With luck, the tree will survive the trauma, generate new roots and thrive for years to come.

The Basics

Roots perform four key functions for trees. Drawing water from the ground is among their most important duties, but roots also absorb essential minerals from the soil. Roots support the weighty trunk, branches and canopy; serve as a conduit for the transport of different substances; and store energy for future use.

When roots sustain damage, the leaves often wilt or drop prematurely. This reduces the amount of water and minerals that can travel up the tree, and it reduces the amount of food that the tree can produce. If enough of a tree’s roots suffer damage or disease, death is all but certain.

Just as a tree’s branches do not all perform the same functions; a tree’s roots delegate different tasks to different portions of the root system. While the large, woody roots at the base of the trunk help stabilize the tree and serve as a shared conduit for the transfer of water and minerals, the fine, white roots absorb most of the tree’s water and minerals.

The Damage Done

A variety of traumatic events can compromise a tree’s roots, but construction damage is one of the most common culprits. Heavy vehicles and foundation work cause soil compaction, which damages roots and alters the soil structure. Grade changes are also damaging — raising the grade buries the tree’s roots too deeply, while lowering the grade exposes the roots, which can lead to further damage and decay.

Trenches dug for utility lines may cut large swaths of a tree’s root system, and landscaping equipment may slice through surface roots. Even if the tree is capable of coping with the reduced water and mineral uptake caused by such events, it is more likely to fail in high winds.

Because few treatments can help repair damaged roots, preemptive strategies are of paramount importance.

Critical Root Zone

Not all root damage is deadly. Trees can survive with some portion of their existing roots – they do not need the entire network. Over time, trees recover from root damage by generating more roots. However, some portion – a critical portion – of these roots is necessary for the tree’s survival.

Tree care professionals call this portion of roots the tree’s critical root zone. Although the tree’s entire root system may extend two to three times farther from the tree than the critical root zone does, this area must be protected at all costs.

Measurable Maps

Different authorities calculate the critical root zone of a tree in different ways. A 1991 study by Patricia Lindsey and Nina Bassuk, published in the Journal of Arboriculture, recommends allowing 2 cubic feet of root zone space for each 1 square foot of canopy spread. (Bassuk, 1991) This usually translates to a circle with a radius of about 1.5 times the radius of the drip line.

Another formula in common use requires 1-foot of critical root radius for every 1-inch of diameter at breast height (4.5 feet above the ground). In other words, a 6-inch thick tree requires a critical root radius of 6 feet. Other tree professionals recommend allowing 1.25 feet for each inch of trunk diameter.

The critical root zone varies with species, site and soil conditions, so determining the critical root radius of a tree accurately requires extensive knowledge and experience. However, by using the formulae above, you can determine the general size of a given tree’s critical root zone.

References

Bassuk, P. L. (1991). Specifying Soil Volumes to Meet the Water Needs of Mature Urban Street Trees and Trees in Containers. Journal of Arboriculture.

fire_prone

Tending Trees in Fire-Prone Areas

fire_prone

The distances between trees significantly affects the extent of the damage incurred. Photo Credit: NASA

No matter how natural recurrent fires are, it is hard to appreciate Mother Nature’s majesty while watching your worldly belongings burn to a crisp.

Do not wait idly while politicians and professors debate policies for managing wildfires; instead, take proactive steps to help protect your home and family.

In addition to keeping potential fuels at least 30 feet away from your home, you can employ several strategies that will confer some protection on the trees in your yard. Although it is impossible to shield your home from catastrophic fires, a few techniques and strategies can greatly improve the chances that your trees – and therefore your home – emerge from low-intensity fires unscathed.

Crown Control

Crown raising is the process of removing the lowest limbs of a tree. Although often carried out for aesthetic or logistic reasons (such as to allow access under the tree or improve sight lines), crown raising can help reduce the tree’s risk to fire, as ground-traveling fires will have fewer opportunities to climb into the tree’s crown. For best results, the University of California, Division of Agriculture and Natural Resources, advises homeowners to raise all crowns a minimum of 15 to 20 feet above the ground. (Glenn Nader, 2007) While the removal of a tree’s bottom limbs may not save it from a high-intensity fire, the lack of bottom limbs may prevent a low-intensity, surface fire from climbing up to the tree’s canopy. It is important to have an ISA-certified arborist perform such tasks, as crown-raising procedures alter the way that trees respond to wind.

Clean the Crowns Regularly

To clean a tree’s crown, arborists remove all of the dead and troublesome branches from the crown. This not only helps to protect the tree from pests and infection, but it helps reduce the amount of fuel in the canopy, which reduces the tree’s risk to fire. Additionally, dead branches represent a safety hazard, and should always be removed when they occur over people or property. Additionally, always be sure to have branches near your home trimmed back at least 10 feet from the roofline and chimney, which will reduce the paths by which the fire can reach your home.

Plant Fire-Resistant Species

Given the right conditions, all plants will burn. However, some trees are more resistant to fire than others are. Whenever possible, use such species around homes and buildings to help reduce the overall risk of fire. In general, broadleaf, deciduous species are superior to evergreen conifers because their leaves (when present) contain more moisture, and they often lack oily and waxy substances, which are often highly flammable. Horse chestnuts (Aesculus hippocastanum), redbuds (Cercis canadensis), red alder (Alnus rubra), flowering dogwoods (Cornus floridana), river birches (Betula nigra) and many maples (Acer sp.); make excellent choices for fire-prone areas. (Pacific Northwest Extension, 2006) While many of these species are not native to the state, they have a relatively low potential for becoming invasive.

Space Trees Appropriately

Because fire uses branches and vegetation to travel from one tree or plant to the next, tightly clustered trees and shrubs are more susceptible to fire than isolated specimens are. Accordingly, it is important to space your trees well to provide them with the greatest chance of emerging from the fire intact. Pay attention to the spacing between not only the trunks of trees, but – more importantly –  consider the spacing of their canopies. In addition to spacing the trees in the horizontal plane, it is important to space trees and plants vertically as well. For example, a group of shrubs directly under the canopy of a tree may allow the branches of the tree to catch fire as embers rise from the flaming shrubs.

Be Careful with Mulch

While mulch is an important tool for tree care (particularly in drought-prone regions), it represents a fire hazard. Fortunately, many different types of mulch exist, so you can select a variety that is not as likely to burn as some others are. Rocks, gravel and other inorganic mulches will not ignite, yet they will still prevent the soil from drying near the plants roots, so they make excellent choices. By contrast, many organic mulches represent a serious fire hazard. According to a study conducted by the University of Nevada, Cooperative Extension, pine needles, shredded cedar bark and shredded rubber are the most dangerous types of mulch for fire-prone areas. (University of Nevada, Cooperative Extension, 2011)

References

Glenn Nader, G. N. (2007). Home Landscaping for Fire. University of California, Davis.

Pacific Northwest Extension. (2006). Fire-Resistant Plants for Home Landscapes. Pacifi c Northwest Extension.

University of Nevada, Cooperative Extension. (2011). The Combustibility of Landscape Mulches. University of Nevada Cooperative Extension.

aphids on a green leaf. macro

Aphids that Infested Her Birch Trees

Evergreen Arborist Consultants recently received a call from a homeowner regarding aphids that infested her birch trees.  She was very concerned about treating the aphids without harming her pets.  The aphids were damaging the birch tree leaves and staining her concrete from the honeydew.  Honeydew is a sticky black liquid, secreted by aphids as they feed on plant sap.  Ants were also attracted to the sugar-rich substance and were as much of a nuisance as the aphids.  Aphids are among the most destructive insect pests on ornamental plants.  Aphids are small, soft-bodied insects with long slender mouthparts that they use to pierce stems, leaves, and other tender plant parts and suck out fluids. The damage they cause to plants has made them enemies of farmers and gardeners.  Large populations can turn leaves yellow and stunt shoots.  Aphids may transmit viruses from plant to plant on certain vegetable and ornamental plants.

When considering whether to apply insecticides for aphid control, remember that many larger plants can tolerate light to moderate levels of aphid infestations.  Larger aphid populations typically decline due to hot weather.  One method of controlling aphids is spraying a high volume of water to the underside and tops of leaves.  If that’s not effective, apply water-soap solution insecticidal soap.  The insecticidal soap uses potassium salts of fatty acids.  The potassium salts weaken the insect’s waxy protective outer shell.  Be sure to follow the label’s directions.  Insecticidal soap is highly preferable to chemical pesticides because it possess toxins that can kill beneficial insects which don’t cause long-term detrimental effects on the environment.  Repeated application may be necessary as these pesky bugs tend to return if left untreated.

tree with holes

Arborists Help by Identifying Insect Problems in Tree Growth

Arborists like the professionals at Evergreen Arborist Consultants are called on every day to make appraisals and to offer expert testimony in various cases.  However, sometimes professional arborists need a bit more knowledge than what they use in their regular work.  For example, an arborist may easily recognize that a tree has insect invasion issues but may not be completely familiar with a particular insect species.  When something like this happens, it is important for a professional arborist to know where to go for information. Read more

ISA_cert_arborist logo

Certified vs. Qualified: International Recognition of Credentials

The International Society of Arboriculture offers two levels of recognition for arborists:  qualification and certification. The experts at Evergreen Arborist Consultants hold certification from the ISA, one of the highest levels to which an arborist can aim.

What Is The Difference Between Certification and Qualification with the ISA?

While both qualification and certification by the ISA represent an achievement of education and experience, they are not the same distinction.  An ISA-certified arborist, such as those at Evergreen Arborist Consultants, has passed stringent examinations over a broad body of knowledge.  Certification also requires periodic renewal after showing that the arborist has updated his or her knowledge in the field.  Certification is considered the best base for an arborist who may be confronted with a variety of situations. Read more