Arboriculture

Rare and native plant species are more likely than abundant or invasive species to be lost from an ecosystem when nitrogen is made more available. Nitrogen increases plant growth, but appears to give a competitive edge to some plants, and a disadvantage to plants that are not adapted to take advantage of more nutrition. This is the conclusion of a wide-ranging nitrogen fertilization experiment by Katherine Suding and her colleagues at UC Irvine. The study was published in PNAS.

Nitrogen in soil comes from nitrogen fixation by certain plants and microorganisms, by lightning-fixation in rainfall, and from manmade sources. The most important manmade sources include fertilizer and acid rain. While fertilizer is not applied intentionally to natural ecosystems, it can arrive in the wind from agricultural sources. Acid rain contains sulfuric and nitric acids from industrial pollution, and is adding considerable amounts of nitrogen to natural ecosystems.

The ecological consequences of nitrogen addition are made clear by this study. Increased nitrogen from anthropogenic sources will reduce biodiversity, eliminate rare species and favor aggressive, fast-growing species including invasives.

As landscaping in urban areas moves toward native plants, it is important to recognize that excess nitrogen fertilization will promote the growth of weeds and non-natives, which have been selected to do well in high-nitrogen environments.

     

There are continuing conflicts between property owners and state authorities trying to enforce ash tree removal to prevent spread of "EAB". We have previously reported several stories on these conflicts. In Port Huron, MI, property owners are trying to stave off the ash removal program by treating the trees with systemic pesticides known to deter the beetle. However, the treatments are expensive and need to be repeated annually with no end in site. State authorities have not agreed to permit treated trees to remain. Since the state has no guarantee that the property owner will continue treatment, or that the treatment is 100% effective, authorities are unlikely to permit the trees to stand. The "EAB" control program requires removal of healthy ash trees within 200 ft. of infested trees (farther in some states). Property owners often do not recognize the need to remove apparently healthy trees. It is a difficult task for agricultural authorities to sell property owners on the need to remove trees, especially prized shade trees, when there is nothing wrong with them. This is a public relations problem for the states trying to prevent spread of the "EAB".

Adult emerald ash borer, Agrilus planipennis. Photo by James Zablotny, US Department of Agriculture

     

The "EAB" has spread in northern Ohio, and is now in downtown Toledo and Maumee Bay State Park. State officials are planning aggressive ash tree removal programs for both areas. The Maumee Bay infestation is particularly worrisome: "The most disconcerting news for state officials was the discovery of infested trees at Maumee Bay State Park in eastern Lucas County. That means the beetle has moved perilously close to the Lake Erie shoreline and could spread eastward across northern Ohio - something officials have been fighting to avoid. They fear the pest will be much harder to stop if it enters wetland areas in state preserves and the Ottawa National Wildlife Refuge in Ottawa County that have limited road access. "I can confirm it has been infested," Lee Anne Mizer, agriculture department spokesman, said yesterday of Maumee Bay State Park. She refused to elaborate, indicating the state plans to discuss details on Monday." - Toledo Blade

Adult emerald ash borer, Agrilus planipennis. Photo by James Zablotny, US Department of Agriculture

The winter moth, Opheroptera brumata, was introduced into North America from Europe. Caterpillars of the winter moth are summer defoliators of maples, apples and blueberries.  Long a problem in southern Canada, the winter moth has established itself in Massachusetts and Rhode Island. Winter moth adults emerge in November and December, and many communities in Massachusetts had dense flights of the moths last fall. These areas are now seeing extensive defoliation.

Defoliated trees are weakened somewhat, but spring defoliations are generally followed by a flush of new growth and recovery. Several years of consecutive defoliation can reduce tree vigor, especially if other stressors such as drought also reduce vigor. Defoliation can severely depress fruit production. The winter moth is unlikely to become as serious a problem as the gypsy moth, and effective biological control agents are already known. In Canada, winter moths have been controlled by the introduction of a predatory wasp, Cyzenis albicans, and Massachusetts authorities are raising trial populations of the wasp. It could take several years before wasp populations are high enough to control the winter moth.

The last few years have seen major increases in defoliation from multiple causes in New England. Defoliation by native insects is at all-time high levels. Insect outbreaks are often regulated by weather. Mild winters, such as we have had in recent years, permit higher insect populations to survive. Global warming is thus a likely cause of increased insect infestations.

Florida is facing an outbreak of dendrophobia, the fear of trees, following last years spate of severe hurricanes. Property owners frightened by the amount of damage done by falling trees to roofs, cars, and power lines are removing large trees or heavily pruning them. Combined with extensive construction-related tree removal, the result could be a dramatic reduction in tree cover in Florida's urban forests. Reduced canopy cover, especially in a hot climate, increases the urban heat island effect, creates higher demand for electricity, increases storm water runoff and erosion and damages the esthetic appeal of a city.

The Orlando Sentinel says, in an editorial, that Florida cities need tree management policies and regulations. They propose five policies:

• Require permits for tree removal. Orlando and Tampa already require permits but other cities do not;
• Identify tree species that should be protected and those whose removal should be encouraged. Alien invasives such as Brazilian peppertree and Australian pine should be targeted for removal;
• Pay particular attention to "grand" trees, those well-established trees of significant benefit to the community;
• Require government departments to talk with each other to protect trees during right-of-way construction;
• Establish crisis response policies to reduce hazards quickly after a storm. This could include lifting permitting requirements for a specified period.

In general, communities need to do more to teach citizens the benefits of trees. Dendrophobia is taking hold in many communities, and the result is a loss in canopy cover throughout a community.

I have been using the term 'dendrophobia' as a way to get people's attention focused on a serious problem. By dendrophobia, I mean the fear of trees described above that leads people to make the apparently rational decision not to have large trees in their lives. However, I recently became aware that dendrophobia is a real psychological disorder, an irrational fear of trees akin to agorophobia or ailurophobia. I probably will continue to use the term in its informal sense.