Reading about “old-growth” in the news probably elicits many emotions, especially regarding trees. What do we mean when using the term though? It’s our responsibility of providing context and defining the term. Welcome to my #timbertalks on old-growth. #SciComm 1/15

There are SO many definitions of old-growth. Commonly relating to specific forest types, regions, or applications. Even the professional dictionaries are not consistent. @foresters define old-growth as “the late successional stage of forest development”. 2/15

Are we talking trees, stands, or forests? Effectively communicating about old-growth requires consideration of spatial or scale issues + distinguishing among old-growth tree, stand and forest. 3/15

I have observed some technical issues with the term. (1) Age - It’s an inherent attribute, but arbitrary and varies with species. It’s hard to verify it too, so an alternative to defining specific age is to use a range. 4/15

(2) Tree size - Large trees are commonly associated with old-growth. Note that old trees can be small when suppressed or growing on sites of low productivity. 5/15

My recommendation - focus on composition, function and structure. Old-growth trees can be described by characteristics like bark, branches, and crowns. Old-growth stands + forests have structural elements, such as crown layers, snags, and down logs. 6/15

There’s also this issue of human disturbance. Some definitions of old-growth are restricted to attributes of biological development, and others include either the absence of or limitation of human disturbance. This offers its own problems. 7/15

Most of the world’s forests have had some human influence. Excluding it may exclude forests that could in time develop old-growth characteristics. 8/15

Perfectly segues into restoration. Those forests manipulated as part of landscape restoration efforts may be left out if we’re confused on what old-growth is. 9/15

With all of that being said is there a single definition? I’ll leave you to answer that specific question. I do believe though in professional, ecological, administrative, regulatory, or legal contexts, more precision is needed. 10/15

Check this out, “old-growth tree: a tree within apprx 20% of maximum observed age for a particular species, site, and location” ... this recognizes species and that a given species may not have the same lifespan at different locations/sites of productivity. 11/15

“Old-growth stand: a contiguous group of trees forming a canopy characterized by old-growth trees and in the late-successional stage of development” ... this encompasses the stand or patch of trees, shrubs, and ground vegetation in age class and cover. 12/15

“Old-growth forests: A contiguous group of stands characterized overall by old-growth trees and in the late successional development” ... we’re permitting forest contain stands of trees varying in age class as well as other features. 13/15

Hint: These definitions of course don’t resolve all problems. What do you think is missing #ForestryTwitter & #ScienceTwitter? 14/15

Key take away - mature, over mature, or climax are not to be used synonymous of old-growth! Like I said before, as professionals we should provide leadership in determining the most appropriate definition of terms like old-growth. 15/15

Thread inspired by John A. Helms paper “Old-Growth: What is it?”