This is the largest Douglas-fir tree I have ever seen (in Humboldt County). And I have never seen such ridiculous limbs. The limbs themselves are like 4′ feet in diameter and 80′ tall! The fact that it can support all that weight is a testament to the structural integrity of Douglas-fir.
What causes that swelling of limbs at the base? In general we find that tree structure is strongly correlated to its environment. Open grown trees photosynthesize more allowing for larger, more frequent limbs. And it is not uncommon to find these old, wolfy trees throughout the region with large limbs near the base. Often times these trees are hidden in younger forests that have emerged more recently, as is the case with the Grandfather Tree.
Many forests in Humboldt where previously woodlands, dotted with the occasional Douglas-fir. Prior to 1920, the forests were mostly white oak, black oak and grasslands. Of course all forests have minor smatterings of other species. All waiting for their moment. When the light or climate conditions change they may get a chance to turn the tide.
When fire was removed from the system, new forests quickly emerged. The new forests grew up in single regeneration events, so their structure tends to be uniform. Because they grow up so dense, they crowd each other out. Many die and the trees that win drop their lower limbs early, stretching upwards to out compete their neighbors.
But that is only part of the story. Genetics ultimately are the major player in tree structure, however it can be harder to notice to the casual observer. The Douglas-fir genome is very complex and after a few hours of reading about it online, I needed to take some advil! In short, conifer genomes are long and extremely complex. A product of being hundreds of millions of years old. In general the variation is subtle and difficult to notice, but occasionally you can find pockets of trees that all share some common characteristic such as sweep or taper.
All of these trees share genes that favor larger than average limbs. But it is rare to find trees with the kind of structure as the Grandfather Tree. Not surprisingly, there is a definite cohort of trees with large lower branches scattered in the surrounding forest for hundreds of acres around this tree.
In forests that have been intensively managed, logged and replanted many times, genes like this are on the decline. Much research has gone into developing Douglas-fir seedlings that will grow straight, tall trees with little taper. While this is good for wood production, it may not be the best for the trees long term strategy, which is to persist in a variety of climates and micro-sites. Not to mention the obvious value complex crown structure provides to wildlife, which has evolved along side these genetically diverse forests. Something to think about as we walk around these forests we call home.