Three key functions are required for the long-term persistence of tree populations in a landscape. Broadly speaking, trees must acquire and allocate resources to maintain or increase their biomass, to tolerate or resist stress, and to pass genetic material to new generations. Yet the three central resource allocation pathways of growth, defence and reproduction have rarely been assessed simultaneously nor have they been assessed across individual to landscape scales. This information is critical to identifying the physiological, environmental and genetic mechanisms underpinning resource allocation.
In a recent study published in AoBP, Redmond et al. assessed trade-offs between growth, defence and reproduction among piñon pine (Pinus edulis) trees at the individual, population, and landscape scales. They found evidence for a defence-reproduction trade-off among individuals whereby defence allocation is reduced during high cone production years. There were no trade-offs between growth and reproduction or defence at any scale measured. The results of this study suggest that a strategic trade-off can occur where investment into defence is temporarily curtailed to favour reproduction, despite the ability of piñon to simultaneously allocate resources to growth and defence. The authors hypothesise that a greater demand for carbohydrates and nutrients in reproduction necessitates a lower allocation to resin duct and terpene production during mast years, while continued allocation to growth supports continued resource allocation and transport. The next step is to evaluate the physiological mechanisms underpinning changing resource allocation between reproductive and defensive pathways within individuals.
Dr. Miranda Redmond is an Assistant Professor at Colorado State University, USA, where she teaches forest ecology and conducts research on the effects of climate and disturbances on forest and woodland dynamics. The majority of her research is focused in piñon-juniper woodlands in the US Southwest, and she also works in ponderosa pine and sub-alpine forests of the southern Rocky Mountains, USA and Afromontane forests of South Africa.