Fire and synchrony of flowering increase reproductive success in two tallgrass prairie perennials

In the prairie, fire used to be a frequent ecological disturbance that has been suppressed in recent decades. Ecologists hypothesize fire is important for prairie communities because it can retard woody growth and affect nutrient availability, allowing native prairie plants to maintain a competitive advantage. But fire might also be directly influencing the population dynamics of plants, especially if fire is associated with better reproductive opportunities for native plants. Fire is associated with greater reproductive biomass for a couple prairie species, but there aren’t too many studies documenting the extent of reproductive increases following fire. Even if fire stimulates more flower production, individual plant reproductive success in terms of viable fertilized seeds may tell a different story. In this study, I examine how fire affects the timing of flowering and reproductive success of Liatris aspera and Solidago speciosa, two relatively common prairie species living in an extremely reduced and fragmented habitat. I present evidence that fire influences reproductive outcomes to differing degrees in the two species by mediating the timing of flowering. I suggest that fire can directly influence plant population dynamics which is useful information from a basic ecological perspective and for land managers conducting prescribed burns. I also show that the timing of flowering has important effects on plant reproductive success; a relevant consideration given that the timing of flowering is shifting for many species across the world due to climate change and altered disturbance regimes. My research also lends new insights into how fire benefits the prairie community – plants could produce more offspring following fire, and species that rely on plant seeds in their diet also benefit from having a greater food source following fire. 

Pollen flow and plant reproductive success depends on the community of co-flowering plants

The floral neighborhood, or community of co-flowering plants surrounding an individual plant, could influence plant reproduction by affecting pollination. Plants in highly fragmented habitats already risk poor reproduction due to mate-limitation, so understanding how community dynamics further impact reproduction is especially critical. To gain a mechanistic understanding of how floral neighborhood influences reproduction in a fragmented landscape, we characterized the floral neighborhood surrounding flowering Echinacea angustifolia (a common tallgrass prairie perennial), including the species richness and diversity of all insect-pollinated flowering plants, and the proximity to potential mates other flowering Echinacea. Four stages in pollination are useful for understanding pollen flow from source to seed: 1) pollinator visitation rate, 2) pollen load on pollinators, 3) pollen on stigmas, and 4) reproductive success of plants. Following pollen flow of a single plant species in this fashion is underutilized but useful for revealing mechanisms of plant reproductive success – especially for obligate outcrossing species. In this study we examine how community context of a model prairie species’ co-flowering plants and pollinators influence its pollen flow and reproductive success. 

Spatial and temporal dimensions of fitness in CA annual plant communities

Growing up in southern California, I occasionally had the opportunity to witness breathtaking “superblooms” where hills would be blanketed in small wildflowers. I was always enchanted by historical descriptions of wildflowers, such as this 1850 account by Jeff Mayfield,

“As we passed below the hills the whole plain was covered with great patches of rose, yellow, scarlet, orange, and blue. The colors did not seem to mix to any great extent… and some of the patches of one color were a mile or more across…”

Imagining the perspective of an individual plant in such a patch makes me wonder what attributes of its position in time and space are most important for growth and reproductive success. Is reproductive success higher for individuals situated in the middle of a dense patch, or in a sparse area? Are individuals surrounded by the same species more or less successful than those surrounded by different flowering species? Does flowering synchrony influence reproductive success? Is reproductive success for self- incompatible plants more dependent upon being in the right time and place than for self-compatible plants? We know competition between and within species influences plant growth, and competition for pollination influences reproductive success, but few studies have incorporated experimental manipulations of flowering timing, spatial density of flowers, and diversity of flowering neighborhood to understand which of these biotic environmental factors could be most important for predicting reproductive success. To address these gaps, I will create a common garden containing experimentally manipulated populations of four native species. Self-incompatible species, Lasthenia californica and Layia platyglossa and self- compatible species with mixed mating systems, Collinsia heterophylla and Phacelia tanacetifolia are distributed across California known to coexist in natural communities. Quantifying the contribution of an individual’s position in time and space to its reproductive success is worthwhile because differences in individual reproductive success drive species evolution and influence coexistence within communities.