Well, as this over-caffeinated young man explains so well in the following video, that depends on what ecosystem you are thinking about.
There has been some controversy in the "forestry" world because so many academic forestry programs have transformed themselves into "ecosystems" programs over the last decade or so. That includes your beloved Penn State School of Forest Resources, which is now the Penn State Department of Ecosystems Science and Management.
The main complaint against this trend is that this new definition of "those who study the forest" is too broad for potential employers to evaluate. And the main argument for this trend is that this new definition of "those who study the forest" is broad enough to encompass all the areas of interest included in the video...and then some. So, you see, it really is a matter of perspective.
Also a matter of perspective is whether wood and wood science is part of ecosystems science, or not. Many scientists who are interested in the ecosystem energy flows as measured by the living, growing components of the system view wood as a simple product, or outflow, of the energy system. In particular, commercial lumber, engineered wood, and paper products are seen as by-products of tree harvest, and as net extractions from the ecosystem under study. In life-cycle analysis terms, these folks have framed their ecosystem "outside or before the gate", that is, the gate of the mill to which the logs are delivered.
Another type of scientist who focuses on the wood as raw material to a manufacturing process, may frame his or her system "inside the gate", as engineers usually do. This is the reason that most of our "wood products" faculty opted to move to the Department of Agricultural and Biological Engineering once the School of Forest Resources label was changed. Because of their training, they prefer to work with the wood from a process perspective, not an ecosystem perspective.
Although I was trained as a forester, I spent the majority of my career in this latter camp, working happily away inside the gate where wood is good and efficiency and quality are king and queen. As the time for a career decision neared, however, I found my interests turning back to my roots outside the gate. For over the years, I had perceived that most who spend their time and interest in the woods have little interest in what goes on inside the gate, and therefore discount wood's role in a larger ecosystem we could call human life.
And so I work to reverse that trend. Because not only is wood vitally important in the forest as a support for those carbon-dioxide consuming and oxygen producing things called leaves, and feeds the detritivores mentioned in the video who feed off all the remnant biological energy that finds its way to the forest floor...it feeds a lot of omnivores called humans competing for resources in the global ecosystem. And the question of how much wood is good in the forest versus in our living rooms is a question that folks will be discussing for a long, long time...and that is as it should be.
So, Go Wood in your ecosystem, and feel good about it.