Why don’t plants reproduce every year?
Many plants do not produce regular annual seed crops, but instead switch between years of bumper seed crops (“mast years”) and years with low seed production. This reproductive strategy is reported in many tree species, but the evolutionary drivers are still poorly understood.
Two new papers involving Dr Andrew Hacket-Pain help to shed light on why this strategy has evolved in different plant groups. The first paper, published in Nature Plants this week, analysed plant traits that co-vary with masting in over 200 plant species, distributed across the globe. The paper reveals that masting has evolved multiple times in the plant tree-of-life. The analysis also demonstrates that masting is more likely to be associated with species that are limited by nutrients. This provides new evidence to support the hypothesis that masting evolves, at least in part, as a response to strong resource limitation.
The second paper, published in the Journal of Ecology, focuses on the benefits that masting brings to one particular species, white spruce. The persistence of white spruce in the boreal forests of North America is surprisingly, because it does not possess the classic fire-adaptation strategies employed by its competitors. The paper tests the hypothesis that in this ecosystem, it is the timing of seed production in relation to wildfire which is the key to successful regeneration. Fires result in favourable conditions for seedling establishment, by exposing the mineral soil and increasing light at the forest floor – but this "window of opportunity" closes quickly. Consequently, plants must evolve strategies to rapidly reclaim sites after a fire and gain the competitive advantage.
In the boreal region, increased fire disturbance is associated with drought conditions. The paper shows that white spruce uses these same climate conditions to trigger a bumper seed crop, ensuring that seed production peaks after conditions that promote fire disturbance. In this way, the species increases regeneration success, ensuring long-term persistence alongside boreal tree species traditionally considered to be better adapted to fire.
The paper “Nutrient scarcity as a selective pressure for mast seeding” is published in “Nature Plants”, and the paper `Climate teleconnections synchronize Picea glauca masting and fire disturbance: Evidence for a fire‐related form of environmental prediction’ is published in `Journal of Ecology’ (https://doi: 10.1111/1365-2745.13308).