(This was copied and modified from the Facebook page of Felton League.)

Warm and humid weather is an uncomfortable change for an otherwise mild summer. It also causes spontaneous limb failure among trees, particular those in riparian areas or irrigated landscapes. What sounded like muffled firecrackers was the (slow but steady) fracturing of another cottonwood limb in Felton Covered Bridge Park. (Another incident of spontaneous limb failure was mentioned a few days ago.) (https://tonytomeo.wordpress.com/2018/07/01/spontaneous-limb-failure/) This one was over the picnic area adjacent to the playground. The fallen portion of the limb was less than a foot in diameter, although it was slighter wider than a foot wide where the fracture originated. It fell onto the middle of a group of picnic tables, with the fractured proximal end remaining suspended and attached to the originating tree. Because it remained attached and fractured slowly, the limb did not fall with enough inertia to damage the picnic tables. It was removed very efficiently.(continued)

Cottonwood, sweetgum, coast live oak, valley oak, Chinese elm, California bay, California sycamore, willow and various eucalypti are particularly susceptible to spontaneous limb failure. The oaks and eucalypti are particularly dangerous. Oak limbs are extremely heavy, and tend to break away cleanly and suddenly rather than fall slowly while still attached. Eucalypti limbs likewise break away cleanly, and then fall from great heights without many lower limbs to slow them down. As they start to fracture, Chinese elm and willow limbs might stay attached to the main trunks or the larger limbs from which they originate, which might slow them down somewhat.

Sadly, spontaneous limb failure does more than damage whatever the falling limbs land on. It can also disfigure the affected trees so severely that they must be removed rather than salvaged.