Dynamic allometric scaling of tree biomass and size

These organs, growing up together and overtaking each other.

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The structure of the tree is relatively simple. Like animals, the growth of the various organs of the tree also obeys allometry. We often use allometric rules to estimate, predict, and calculate the carbon storage of forests, their ability to absorb CO2, and their response to climate change. But unlike mammals, fishes, birds, insects, and microbes, the difference between the weight of an individual sapling and a mature tree for woody plants has reached an astonishing degree. This has made modelling trees more difficult. In order to obtain an allometric model, people have been destructively measuring tree biomass using hard work for decades and may have developed thousands of allometric biomass equations as a result. However, it is difficult to get a general model for all different-sized trees, even for the same species. The biomass equations developed for estimating forest carbon have large errors, especially for large trees (e.g. in tropical rain forests).

The structure, main parts, major organs, and estimable biomass components of a tree

In a field measurement a few years ago, when I was looking up at the sky through the canopy, once in a while, I thought about the difficulties of modelling. How many trees will we need to cut to explore the truth? It might never be possible to find a black hole by observation with an astronomical telescope, but it is possible to do so using theory. Fortunately, in terms of woody plants, the huge differences between individual trees can expand the researcher's scope of observation. The weight difference can reach several million (even billion) times from seedlings to overmature trees tens of meters high. This is beneficial for generating hypotheses and improving theories.

Based on these considerations, we use an asymptotic allometric biomass equation to describe a dynamic growth relationship. As we can often observe, some organs grow very fast when they are young but are later surpassed by other organs. They are growing up together and overtaking each other but no one may be in the lead all the time. The dynamic allometric coefficient may be a universal law for understanding the relationships between body size and the weight of each organ. All in all, this is an interesting issue of metabolic scaling. In any case, it may be difficult for the field observers of forest ecosystems to accept an expression with an exponent as a simple and fixed fraction, which is used to conveniently represent the allometric scaling for the complex natural world. A lot of work remains to be completed, and various organs need to be estimated and examined.

A long way...

Xiaolu Zhou

Professor, Hunan Normal University (Special-term)