Developing an agroecological approach to biomass scaling and branching architecture using orchard trees

Background/Question/Methods

In modern agriculture, fruit trees are modified from a natural state where a tree fills vertical volumes competing for light to an alternate state providing for the highest fruit yield and highest economic return for the least amount of wood. Conversely, in natural forest ecosystems, biological constraints influence scaling relationships (i.e., relationships between size and biological characteristics) among tree species, but little is known how these relationships are maintained in response to human manipulation or how an understanding of these mechanisms could inform the future development of more economic and sustainable horticultural programs. I test if scaling relationships differ when the assumed evolutionary forces are opposed by artificial selection. Additionally, I provide the first application of scaling theory to an agricultural system to inform management decisions for sustained and improved production. I believe human manipulation fundamentally opposes evolutionary forces on natural trees by modifying them to maximize reproductive yield and economic efficiency while eliminating the survival requirements of a forest ecosystem. Theoretically, optimization of resource transport and structural allocation results in an optimal branching ratio of 2:1, though most natural trees fall between a ratio of 2:1 (deciduous trees) and 5:1 (coniferous trees). This research asks: Do biological constraints derived in natural forest ecosystems hold up in human dominated orchard systems? Do deviations from the relationships derived in natural forest ecosystems demonstrate a deliberate human manipulation (e.g., pruning) on the system? Using data from fifteen 24 year-old individuals in a tart cherry (Prunus cerasus, mahaleb) block at the Kaysville Experimental Orchard, Utah State University, I establish biomass scaling relationships for leaves, stems, and roots, and digitally reconstruct the trees’ branching architecture. The model developed from this exercise tests the consequences of various horticultural management strategies (i.e., water management, pruning, etc.) on growth and architecture of tart cherry trees.

Results/Conclusions

It appears that terminal branches, which are pruned less, maintain volume filling patterns (2:1); however, the trunk and primary branches strongly deviate towards a higher ratio (5:1). The model developed is instrumental in defining growth characteristics of tart cherry trees under various management and environmental conditions. Additional politico-economic parameters will be included in the model to suggest sustainable management practices for breeders and growers as well as a complementary analysis which compares these domesticated fruit trees to wild-type congeneric species.