About the SFMGA

Tuesday, May 05, 2009

Urban Forestry

By Joran Viers

Humanity Has a Long History With Trees
  • Some scientists theorize our long distant ancestors’ two-legged stance evolved while still arboreal;
  • Most major religions have strong, central themes that involve trees;
  • Trees provide lumber, fiber, food, beauty, windbreaks, and ecosystem services related to air and nutrient cycling.

Humanity is Urban
  • Many people live in dense cities;
  • People tend to plant trees near their homes;
  • Thus, many trees live in cities:
    • “Artificial” ecosystems;
    • Degraded soils of limited volume;
    • Poor water infiltration;
    • Heat stress;
    • “SPD” – stupid people disease.
  • Urban trees need special understanding.

Random thoughts on trees…
  • Trees have secondary growth – they get wider and taller over the years.
  • Trees are long-term investments:
    • Don’t try to save the runts of the litter!
    • Get it off to a good start.
  • Don’t: under-water, over-prune, apply weed-n-feed herbicides.
  • Trees will face, and may survive, threats by environment, insects, diseases and people.

Root architecture (1 of 2)
Trees begin in the soil…
  • As seeds;
  • In terms of overall health and growth – root system functioning is critical;
    • Very dynamic – up to 8 flushes of root hair growth per season;
    • Soil compaction and degradation hinder and thwart root function;
  • If the roots don’t work, the rest won’t either!

Understanding root architecture and function is critical to understanding trees.

Root architecture (2 of 2)
Trees “belong” in forests
  • Mutual, multiple canopy controls branching and structure – tall, narrow trees are natural.
  • Urban trees are often broader than their wild cousins – this often results in “over-branching” and poorly attached branches.
  • Urban trees are often planted well outside their comfort range – the wrong plant in the wrong place.

Functions of Urban Trees
  • Shading:
    • Cools buildings, lowers energy needs;
    • Cools landscapes, increases outdoor comfort:
      • Leads to greater community interaction in common spaces, increases quality of life.
  • Windbreaks and visual screens;
  • Aesthetics:
    • Form, blossom, fall color, etc.;
    • Subjective but subject to reality check.

Back to the Soil
  • Physical and chemical properties influenced by parent material (texture, pH);
  • These are very hard to change.
  • Can vary greatly over short distance;
  • Human activity can degrade, or improve, a soil’s structure;
  • Structure has more to do with biology than geology.
  • Soil alkalinity leads to iron and zinc deficiencies. This condition is chronic and must be addressed every year, maybe more than once a year: acidify the soil or add chelated micronutrients.

Soil Compaction
  • Decreases ability of soil to hold water and air;
  • Increases bulk density of soil; root can’t penetrate through soil;
  • Can occur quickly on damp soils – even walking across the grass can do it;
  • Can be alleviated to some degree with mulch, water and rest, with core aeration, with vertical mulching.
  • Under pavement, roots follow interface between soil and concrete.

Buying and Planting a Tree
  • Know what species (singular or plural) you want – don’t buy something just because it’s for sale!
  • Buy the smallest container size you have the patience for; quicker establishment, faster growth, lower cost.
  • Select one with single, straight trunk, no bark damage, no dead stubs, no drying, yellowing leaves.
  • Best to plant in fall, or spring.

Planting a tree
Keys to Planting
  • Add no soil amendments or fertilizers.
  • Set plant high in the soil – make sure the root flare is visible!
  • Dig broad, wide hole and settle tree into native soil.
  • Prune it while you can reach it!
  • Water well, and often enough. Take soil type into account!

The Potted Root System
  • Artificially confined, watered and fed.
  • Often has too much soil in pot – tree too deep.
    • Find first lateral root – this is important at planting.
  • May have circling roots:
    • These must be straightened, if possible…
    • Cut off if not.
    • If too many, put it back.
  • Will go through a transition once planted in your landscape, but this takes time.

  • Water well – deeply and regularly;
  • Mulch basin, but keep mulch off trunk;
  • Don’t stake, unless absolutely needed, and then:
    • Stake loosely to allow trunk movement;
    • Remove stake after one year
  • Don’t fertilize for at least 2-3 years (if at all);
  • A few judicious pruning cuts may be in order…

  • All pruning is injury and costs energy, so have a real reason;
  • Formative pruning during early growth is best value and effect;
  • Central leader, permanent scaffold branches, crossing and weakly attached branches, subordinate lower branches, dead and damaged branches;
  • Leave low leaves for more efficient trunk growth.

Branch attachment

Branch Attachment: In spring, first flush of growth comes on the branch – lays down a ayer of wood; later growth of trunk lays down another, overlapping layer of trunk wood.

Compartmentalization Of Decay In Trees.

Best Pruning Cuts:
  • Outside the branch collar, not into the branch bark ridge.
  • Three-step cut to remove weight before final cut.
  • Use the proper tool:
    • Bypass pruner;
    • Pruning saw.
  • All pruning hurts the tree;
  • Pruning cuts over 3” in diameter should be avoided when possible (increased chance of decay prior to compartmentalization);
  • Dormant season is preferred, but summer pruning has less regrowth;
  • Never take out more than 30% of leaf canopy in one season!

Maintenance and Hazard Pruning
  • Done to more mature trees;
  • Prevent hazards by thoughtful anticipation;
  • Trees can cause many thousands of dollars of damage and even take lives; don’t push things too far.
  • Leave this to the professionals, they’re trained and have insurance!

Tree critical root zone
Root “Pruning”
  • Sometimes done on purpose…
  • Mostly and accident, caused by excavations of some sort.
  • Damaging large roots deprives the tree of much water, increases likelihood of blow-down, and can lead to infections by wood decaying and vascular system plugging fungi.
  • Protect the critical root zone!
  • Radius of CRZ = 1.25’/1” diameter-at-breast-height (dbh).

Tree Pests
  • Environmental considerations most likely cause of tree health problems, but…
  • Under stress, trees are more vulnerable to attack by opportunistic organisms:
    • Insects;
    • Diseases.
  • Start by alleviating the stressors;
  • Treatment requires identification and knowledge about potential damage.

Leaf Attackers
  • Insects: honeylocust plant bug, aphids, cottonwood leaf beetle, grasshoppers, spider mites, etc.
    • Generally not terribly damaging, though very noticeable;
    • Action threshold is roughly 30% defoliation.
  • Diseases: phomopsis, anthracnose, powdery mildew, etc.
    • As with insects, usually not strongly damaging, but very noticeable.

Vascular System Attackers
  • Insects: bark and twig beetle
  • Diseases: verticillium wilt, cytospora
  • Generally very threatening to tree health.
    • Interruption of xylem and phloem flows;
    • Inconspicuous start of problem, so not noticed for awhile
  • Don’t be tempted by injected rescue chemistry – that relies on a functional vascular system!

  • Humans are the biggest threat to urban tree health:
    • Ignorance;
    • A little knowledge can be dangerous.
  • SPD begins at planting, continues through pruning, watering, fertilizing, pest control.
  • Humans are also the best (only?) cure for SPD.
  • Knowledge through education.

Trees for the Albuquerque Area

The Good, The Bad, The Ugly…
  • Many trees planted in the city ought not be!
  • Many good trees are hard to find.
  • These are my own opinions, and you are free to disagree.
  • Don’t forget we live in a desert!
  • Water is key for tree survival.

“Good” Trees
  • Grow reasonably well in our soils and climate;
  • Have relatively few pests and diseases;
  • Come in a variety of sizes and shapes;
  • Require a minimum of extra fuss to keep healthy;
  • Can be hard to find.

“Bad” Trees
  • Suffer in our soils and climates – Too hot, too alkaline, too dry
  • Are planted in sites to small for their ultimate growth;
  • Are abused and mistreated from the nursery onward;
  • Slouch and spit gum at passers-by.

Words of Caution…
  • Plant the youngest specimen you have the patience for;
  • Know most nursery stock has been poorly pruned and will need your correcting touch;
  • Saving the runt of the litter leads directly to unhealthy trees in the landscape;
  • Just because someone sells it, doesn’t mean you have to buy it.

Small Evergreens
  • Singleseed juniper* (Juniperus monosperma)
  • Utah juniper* (Juniperus osteosperma)
  • Texas madrone (Arbutus texana)
  • Chinese windmill palm (Trachycarpus fortunei)
  • Bristlecone pine (Pinus aristata)
  • Pinyon pine (Pinus edulis)
  • Black hills spruce (Picea glauca densata)
  • Joshua tree (Yucca brevifolia)
  • Palm yucca (Yucca torreyi)
  • Soaptree yucca (Yucca elata)
  • Arborvitae (Thuja & Platycladus species)
  • * Prohibited in Albuquerque – pollen.

Large Evergreens
  • Atlas cedar (Cedrus atlantica)
  • Deodar cedar (Cedrus deodara)
  • Arizona cypress* (Cupressus arizonica)
  • Alligator juniper* (Juniperus deppeana)
  • Eastern red cedar* (Juniperus virginiana)
  • Rocky Mountain juniper* (J. scopulorum)
  • Afghan pine (Pinus elderica)
  • Austrian pine (Pinus nigra)
  • Italian stone pine (Pinus pinea)
  • Japanese black pine (Pinus thunbergiana)
  • Ponderosa pine (Pinus ponderosa)
  • Scotch pine (Pinus sylvestris)

Small Deciduous
  • Arizona ash (Fraxinus velutina)
  • Raywood ash (Fraxinus oxycarpa)
  • Western chokecherry (Prunus virginiana)
  • Netleaf hackberry (Celtis laevigata)
  • Bigtooth maple (Acer grandidentatum)
  • Mountain ash (Sorbus aucuparia)
  • Paper mulberry (Broussonetia papyrifera)
  • Apricot (Prunus armeniaca)
  • Desert willow (Chilopsis linearis)
  • Mexican elder (Sambucus caerulea NM)
  • Bradford pear (Pyrus calleryana)
  • Purpleleaf plum (Prunus cerasifera)
  • Golden rain tree (Koelreuteria paniculata)
  • Vitex (Vitex agnus-castus)

Large Deciduous
  • Valley cottonwood (Populus fremontii ‘wislezeni’)
  • Chinese elm (Ulmus parvifolia)
  • Ginkgo (Ginkgo biloba)
  • Honey locust (Gleditsia triacanthos)
  • Horsechestnut (Aesculus hippocastanum)
  • Japanese Pagoda (Sophora japonica)
  • Black Locust (Robinia psuedoacacia)
  • Zelkova (Zelkova serrata)
  • Bur oak (Quercus macrocarpa)
  • Texas oak (Quercus texana)
  • Pecan (Carya illinoiensis)
  • Chinese pistache (Pistacia chinensis)
  • Mimosa (Albizia julibrissin)
  • Arizona sycamore (Platanus wrightii)
  • Arizona walnut (Juglans major)
  • Carpathian walnut (Juglans regia)
  • Kentucky coffee tree (Gymnocladus dioica)

Trees to Avoid
  • Aspens, other Populus; Willows; Sweet gum; Leyland false cypress; Green ash; Catalpa; Chitalpa; Most maples…