Population Viability With Fire in Eryngium Cuneifolium: Deciphering a Decade of Demographic Data

Abstract

We analyzed and modeled the demography of Eryngium cuneifolium, an herbaceous species endemic to the fire‐prone Florida scrub, using 10 annual censuses (1990– 1999) of 11 populations at Archbold Biological Station. Nearly every aspect of the demography of this plant is affected by time since fire. Year, time since fire, life history stage, and plant age affected survival, growth, and fecundity of E. cuneifolium, but time since fire and life history stage had the most consistent effects. Survival, flowering stem production, and early seedling survival were highest in recently burned sites. Long‐term survival, growth, and fecundity were highest for yearling cohorts recruiting recently after fire, with the largest contrast between plants recruiting two years postfire and those recruiting more than a decade postfire. Prior (historical) stage also affected individual plant fates. For example, plants with prior stasis or regression in stage subsequently died in greater numbers than plants with prior advancement in stage. Historical analyses did not suggest any cost associated with the initiation of flowering. We used a matrix selection approach to explicitly model Eryngium cuneifolium population viability in relation to fire. This simulation strategy included preserving observed data and variances within projection matrices formed for individual combinations of population and year. We built 54 of these matrices, each with six stages (seed bank, yearlings, vegetative plants, and three reproductive stages). Each of these matrices also represented a specific time since fire. In building matrices, we minimized the use of pooled data while retaining specific matrices whenever possible. In this way, we preserved both the correlation structure within individual matrices (populations, years) and protected patterns among matrices across the time‐since‐fire gradient. To deal with less‐detailed data on recruitment processes, we evaluated 13 fertility and seed bank scenarios that bracketed a range of outcomes. All scenarios were similar in showing the positive effects of fire on the demography of E. cuneifolium. The scenario with high seed bank survival (0.5) and low germination rates (0–0.005) was the best predictor of observed postfire years of peak aboveground population size (∼8 yr) and aboveground population disappearance (30–34 yr), and also did a good job of reproducing observed population trajectories. Finite rates of increase (λ) were >1 only during the first decade postfire but then declined beyond a decade postfire. Although prior (historical) stage affected most individual demographic parameters, it did not significantly influence finite rates of increase. Elasticities were highest for stasis and germination from the seed bank. Elasticities for survival increased with time since fire, while growth and fertility elasticities decreased. In historical models (those with information on stage from the second‐to‐last year), the elasticities for stasis were higher and the elasticities for growth lower, compared to models witho...

Fire Increases Invasive Spread of Molinia Caerulea Mainly Through Changes in Demographic Parameters

“…Despite higher seedling and juvenile densities, these conditions also resulted in lower mortality rates of seedlings and juveniles (data not shown). Using 10 years of demographic data, Menges and Quintana-Ascencio (2004) found similar decreases in composite elasticities for the seedling stage with time since fire, and increases in elasticities for stasis of the largest reproductive individuals.…”

“…Fire may dramatically affect population dynamics of plants (reviewed in Noble and Slatyer 1980). Indeed, for most species, population dynamics have been shown to be very different in burned and unburned sites (e.g., Silva et al 1991, Canales et al 1994, Caswell and Kaye 2001, Garnier and Dajoz 2001a, Satterthwaite et al 2002, Quintana-Ascencio et al 2003, Menges and Quintana-Ascencio 2004. Fire has been shown to increase population growth rates by increasing seed production (McConnell and Menges 2002), seed germination rates (Canales et al 1994, Menges andDolan 1998), or growth (Lamont and Wiens 2003).…”

Moss Species Benefits From Breakdown of Cyclic Rodent Dynamics in Boreal Forests

“…Similar elasticity patterns are found in some vascular plants for which elasticities for the seed-to-seedling transition are higher in variable environments than in more stable environments (van Groenendael and Slim 1988). Furthermore, some modeling studies (e.g., of fire-dependent vascular plants [Hoffmann 1999, Menges and Quintana-Ascencio 2004, Liu et al 2005) report a tendency for poorer population development in response to change of the disturbance pattern from regular to less regular, and the sequence of environments, like crop rotations, is known to influence population growth rates (Mertens et al 2002).…”

Genetic Variation in Past and Current Landscapes: Conservation Implications Based on Six Endemic Florida Scrub Plants

“…This is likely particularly true for short-lived species that undergo continual population fluctuations. Many of our study species show substantial fluctuations in relation to fire [48,49], and lack of fire history data across our study populations may hamper our ability to understand geographic patterns of genetic variation. Past events such as bottlenecks, founder events, low effective population sizes, and local extinctions may also have affected patterns of genetic variation in idiosyncratic ways [89,90].…”

“…The study six species Warea carteri Small (Brassicaceae) [52,61], Eryngium cuneifolium Small (Apiaceae) [49], Hypericum cumulicola (Small) W.P. Adams (Clusiaceae) [50], Dicerandra frutescens Shinners (Lamiaceae) [48], Nolina brittoniana Nash (Agavaceae) [44], and Liatris ohlingerae (S.F.…”