Most hazardous tree signs are visible from the ground, if you know where to look. Large dead branches. Cracks in the trunk. A trunk that splits into two tight stems. Mushrooms or soft wood at the base. Pinholes weeping stain on the bark. A new lean with cracked soil. And fresh digging or heavy pruning near the roots. The International Society of Arboriculture lists most of these in its Recognizing Tree Risk guide, and UC IPM covers the borer holes. One sign isn’t a verdict. A tree risk assessment weighs the defect against what sits under it: a roof, a driveway, a kid’s swing. Here’s how each sign looks on the trees we work on across the San Fernando Valley.
1. Dead or Hanging Branches
ISA calls dead branches “probably the most obvious potential hazards.” Their risk depends on size and on how close they hang to people or property. Over an empty slope, it’s a note. Over the driveway, it’s a Tuesday appointment.
On a fire-adjacent lot, deadwood is also fuel. LA County Fire asks for branches cut back 5 feet from the roof and 10 feet from a chimney, though oaks are exempt from the chimney rule. A Burbank customer wrote that the Dario Tree Trimming crew finally did the dead-wooding job they’d put off.
2. Cracks and Splits
Look for long, vertical cracks in the trunk, in major limbs, or where a branch meets the trunk. ISA flags these “longitudinal cracks or splits” as a defect worth an arborist’s eye.
3. A Split Trunk and Long, Heavy Limbs
Two stems rising from one point are called codominant stems. ISA says they “can often be failure points.” So can limbs with their weight piled out at the tips.
Oaks add a local twist. UC Master Gardeners describe summer branch drop: big limbs falling on hot, calm afternoons with no wind at all. It shows up in oaks, eucalyptus, elm, and ash. The break usually comes 3 to 12 feet out from the trunk, and the limb can look sound. UC’s advice: lighten long horizontal limbs, and don’t park under older oaks.
4. Mushrooms, Cavities, or Soft Wood at the Base
Fungal growth and cavities are among ISA’s most obvious decay signs. In California yards, one culprit has a familiar name: oak root fungus. UC IPM describes clusters of light brown mushrooms at the base and white, fan-shaped sheets under the bark.
The fungus also decays roots and the base of the trunk, which raises the chance of failure. Summer water around established native oaks favors it. So a coast live oak sitting in a watered lawn deserves a closer look. And mushrooms don’t always show.
5. Tiny Holes, Wet Stains, or Gumming on the Bark
This is where a tree disease assessment earns its place. By early 2023, invasive shot hole borers were established in seven Southern California counties, including Los Angeles and Ventura. Their holes are about 1/32 inch wide, the size of a ballpoint pen tip. Look for wet staining, fine sawdust, gumming, and branch dieback around them.
UC lists California sycamore and box elder among the trees this beetle can kill. On coast live oak, the damage often concentrates in branches, and pruning them out can help. UC also warns that weakened branches on badly infested trees are hazardous to people and property.
Oaks have a second pest to watch. The goldspotted oak borer leaves D-shaped exit holes in coast live, canyon live, and black oaks. LA County asks residents not to move firewood, and to report suspected damage to its Fire Department forestry unit.
6. A New Lean, or Soil That Cracks and Lifts
A lean the tree has held for decades is one thing. The warning is a change. ISA says cracks or separations in the soil can mean the roots are moving, “especially if the tree is leaning.” After a Santa Ana wind event, walk the ground on the side opposite the lean. Raised soil on that side is a call-today sign.
7. Recent Digging, Grade Changes, or Hard Pruning
Some of the riskiest defects are human-caused. ISA lists root loss and soil compaction from construction, grade changes, and poor pruning. Its checklist also asks: “Has the tree been topped or heavily pruned?” New pavement, a trench for a pool line, or fill dirt over the roots can hurt a tree well before the canopy shows it.
What Happens During a Tree Risk Assessment?
ISA leaves the call on how serious a defect is to a professional arborist (ISA). Its options include pruning the bad limb, cabling and bracing, routine care, and removal. We work through them in that order. We look at the tree, name the defect, and tell you what’s under it. Removal only comes up after the alternatives do.
Written reports get the same straight talk. We prepare and sign tree health and risk reports for homeowners across incorporated cities in Los Angeles and Ventura Counties. Permit reports for construction work a little differently. Every city sets its own rules on who signs them, and those rules can change from one street to the next. Give us your address, and we’ll tell you what your city asks for before you pay for anything.
Frequently Asked Questions
How close can tree branches be to my roof before fire season? LA County Fire asks for 5 feet from the roof and 10 feet from a chimney, with oaks exempt from the chimney rule. Inside the City of Los Angeles, LAFD asks for 5 feet above the roof and 10 feet from a chimney outlet. Check which department covers your address.
Are mushrooms at the base always a sign the tree is dying? Not always. But light brown clusters at the base of an oak can point to oak root fungus, which decays the roots. Have the base checked before deciding anything.
What’s the difference between a tree disease assessment and a tree risk assessment? A disease assessment asks what’s wrong with the tree. A risk assessment asks what happens if it fails, and what it lands on. Ask for both.
Do I need a permit to trim or remove an oak? It depends on your city. In the City of Los Angeles, native oaks with 4 or more inches of trunk diameter are protected. Unincorporated LA County and many cities have their own oak rules. Ask before the first cut.
Stand Under Your Biggest Limb
Here’s a two-minute test. Walk out and stand under the heaviest limb on your property. Then look down.
What’s there? A parked car. A patio table. The corner of the roof where the kids’ rooms are. ISA’s own checklist asks if you’ve seen large dead branches, cracks, or mushrooms. If you spotted even one of those hazardous tree signs, it’s worth a tree risk assessment before the next hot afternoon or Santa Ana night. Call us today. We will walk the tree with you and tell you straight what it’s doing.
