Bishop Pine Health at the Mendocino Coast Botanical Gardens

May 28, 2006

An ever present reason for the decline of a tree is old age. The age after which trees decline varies with species and site quality. In forestry terms, some identify this age as being synonymous with the culmination of mean annual increment (CMAI), which is defined as the age at which the stand volume production rate is maximized. Although we like to call it the "Golden Years" for ourselves foresters offer the term "senescence" for this stage in the life of a tree.

What got me thinking about senescence was my visit in April to the Mendocino Coast Botanical Gardens to see the bishop pine, which was prompted by one of the volunteers. He wanted to have more information for patrons when they asked about the health of the bishop pine, which he said they often do.

Of the 47 acres that comprise the Mendocino Coast Botanical Gardens, several acres support a relatively even aged overstory of bishop pine, some of which have died and been topped or removed for safety. Several bishop pines display dead brown branches within the living crown, otherwise known as flagging and many of the crowns appear to be thinning.

Typically, the number of years a tree has lived, alone, will not cause flagging or death. Instead age yields a weakened state that invites a myriad of biological agents and when combined with harsh environmental conditions and animal damage may lead to the demise of a tree.

Too much water can also tip the balance. For example, shore pine on the west side of Highway 1 just north of the Albion River Inn started dying several years ago. According to Jack Marshall, Forest Pathologist at the California Department of Forestry and Fire Protection, the mortality agents are the pine engraver beetle and sour sap beetle. The shore pines follow a watercourse, which is likely receiving increased water due to a change in the water drainage pattern.

If the bishop pine at the Mendocino Coast Botanical Gardens will run their course in the next few decades the question becomes how can the next generation be encouraged without the benefit of fire, which bishop pine needs to regenerate. Bishop pine seeds are stored in closed cones until the cones are opened during fire or very hot conditions when large numbers of seeds are released to inhabit the disturbed ground.

A portion of this production was gleaned from the website: http://en.wikipedia.org/wiki/pine.

I welcome responses as well as ideas for future Tree Tips. You can also get an email version by contacting me at thembi@mcn.org.

Thembi Borras is a Registered Professional Forester living and working in Mendocino County, CA USA.