Shocks that phloem is heir to

The sap that sweetens our pancakes, preserves dinosaur blood in resined insects, and provides chewing gum, optical cement and incense evolved to serve many of the same purposes as our own blood and lymph, and a few besides. Injuries to bark and deeper layers lead to spillage of the vital fluid which (as with us) acts to flush away contaminants before “clotting” by various mechanisms to close the wound. (–Except in case of the most extreme literal shocks, which can leave perfectly dry wood scattered all about or aflame.)

The assaults that lead to grievous trunkily harm are diverse, including all sorts of mechanical impacts, incision, abrasion, avulsion, snow load and other bark-biting events, here wind flexion from nor’easters

and sun-scald/frost cracking from winter thaws

(here shown in cross-section after felling a year later due to excessively healthy growth despite the damage),

not to mention collision with cars and lawnmowers, and attacks from bucks rubbing terrain- and status-marking scent from scalp glands

(a particular issue with fragrant-wrapped magnolias), diverse smaller nibblings and peckings, down to micro-invaders like the dread phytophthora family. Our native Eastern red cedar, shown above and here,

provides not only berries for the cedar waxwing, but a higher-calorie food for sapsuckers that drill, depart, and return in time to harvest the amber ooze,

leaving dry holes in sometimes-neat array:

Thin-skinned species, including many within the lovely and fruitful genus Prunus, often exhibit a gelatinous “gummosis”

—recovery from which depends on both nature and depth of attack: in this case minor cambium scrapes that will heal, in others the result of and/or entry point for fungal infection. P. spinosa (blackthorn, or sloe), for example, is prone to this nasty-looking gall,

which the prudent will prune and burn or discard where it cannot release millions of spores to infect other specimens. A more menacing ’50s B-movie view of the same blob:

Both economic and ecologic consequences can be significant. Where a desirable (hence oft-planted) species hosts—in obligate sequence or facultative dispersion—a disease fatal to an even more-valuable species, the former may be banned by statute:

White pine blister rust is not a serious disease of currants and gooseberries; however, it is a very serious disease of white pines (Pinus strobus). Currants and gooseberries serve as an alternate host for the rust fungus that causes white pine blister rust. Therefore, planting currants and gooseberries in areas where white pines are present can lead to serious losses of white pines. … White pine blister rust causes significant damage in pine forests by forming cankers on the branches of white pines. These cankers ultimately kill the trees. … To protect white pine forests, several states have enacted laws concerning planting of black currants.

This restriction does not apply equally to all Ribes species and cultivars, or in all parts of all states. (For an interesting resume of the relevant history in Massachusetts, including a list of towns with active bans, see this article.) It is a salutary reminder of interdependence and co-origination generally, and in particular of the risks we engender through inattention to an ever-so-broadly shared genetic heritage.

Some cankers may appear benign, and even attractive, in their earlier stages, like cedar apple rust, Gymnosporangium juniperivirginianae. With our area rich in both cultivated and “wild” apples, this pest finds an ample supply of both its alternately required hosts, and produces more or less harmless perennial galls like this:

When spring rains arrive, spore-bearing “telial horns” are produced, of size, shape and profusion scaled to the originating gall: from minute

to cute

to monstrous:

Here depleted, having killed twig but not tree,

and apparently nibbled by creatures unknown:

They live among us…