On compression forks and axioms

Abstract

Dear Editor In Slater (2016), the “axiom of uniform stress” of Mattheck and Breloer (1994) is rightly questioned. And also in Drénou, Restrepo, and Slater (2020), a fine biomechanical approach to bark-included forks can be found, where they, rightly, question the “compression fork” model of Mattheck and Breloer (1994). However, simple reasoning and common sense might also shed light on this controversy, which has been subject of funded research, methodologies, scientific publications and the perhaps unfounded felling of many trees over the last three decades. According to the “axiom of uniform stress” (Mattheck & Breloer, 1994), a tree lays down extra wood where it is needed, for instance around a mechanical defect, to maintain a uniform stress level and to compensate for the biomechanical defect. However, another idea in the arboricultural scene, is the one that says that “crotches with included bark push each other apart as they grow in diameter”, which is the “compression fork” model, also by Mattheck and Breloer (1994). But . . ., if the branches were really pushed apart by “compression forks due to included bark”, would that stress then not be easily compensated by the tree by laying down extra wood (“axiom of uniform stress”), at the outer side of the fork and at the same time? There is something that is called “compensation wood”. Compensation wood is built where the tree experiences more stress or strain than biomechanically interesting for itself, and this being the result of experimented loads, structural inner defects, and so on. This process, even though not well understood yet, is called thigmomorphogenesis or the response by plants to mechanical sensations. Thus, and again, if thigmomorphogenesis really exists (which it does), would it not compensate for the “pushing apart” (if it really existed) of the branches at the height of the “compression fork”? And as the first (thigomorphogenesis) is a truth, the second (compression forks) could then be just a myth. Hence, accepting both the “axiom of uniform stress” and the “compression fork” model, both by the same authors, is impossible. The herein presented simple reasoning shows that the “compression fork” model by Mattheck and Breloer (1994) invalidates the same author’s “axiom of uniform stress”. If one accepts the first, the second can then only be rejected, and vice versa. Therefore, both their claims seem untenable.