Academic journal article The American Midland Naturalist

Effects of Temperature on Seed Viability of Six Ozark Glade Herb Species and Eastern Redcedar (Juniperus Virginiana)

Academic journal article The American Midland Naturalist

Effects of Temperature on Seed Viability of Six Ozark Glade Herb Species and Eastern Redcedar (Juniperus Virginiana)

Article excerpt

Introduction

Grasslands provide a variety of ecosystem services but are among the world's most fragmented and degraded ecosystems (Bond and Parr, 2010). Prescribed fire has become one of the most commonly used tools for promoting native plant establishment and reducing encroachment by undesirable invasive and woody plants (Briggs et al., 2005) but without fully appreciating the myriad of effects that fire has on altering ecosystems. Understanding which species are affected by fire and whether certain species that are impediments to restoration are more susceptible to deleterious effects of burning relative to grassland species, will ultimately enhance the utility of prescribed fires in a restoration and management context (Pyke et al, 2010).

Using Ozark glade grasslands as a study system, we examined the relative effect of heat on the viability of six herbaceous species, that are indicators of glade grasslands, as well as the problematic woody species eastern redcedar (Juniperus virginiana). We focused on seed viability for two reasons. First, because establishment of many grassland species is limited by the presence of viable seeds (Clark et al, 2007), recruitment from the seed bank may be important for determining plant population dynamics and community composition following prescribed burning. Second, although the Ozark glades are a fire-maintained system (Batek et al, 1999; Ware, 2002) and fire can have profound effects on seed viability and germination (e.g., Baskin and Baskin, 2001), little is known about how heat affects the viability of many native glade species. Our goal is to test the relative effects of heat on the seed viability of six species that are characteristic of Ozark glade plant communities (Baskin and Baskin, 2000) and the undesirable woody shrub J. virginiana (Briggs et al, 2002).

Methods

STUDY SYSTEM

Ozark glades are highly diverse grassland ecosystems found on shallow soils surrounded by hardwood forests (Baskin and Baskin, 2000). Herbaceous forbs, including several endemics, constitute a significant fraction of glade plant diversity and are considered of high conservation value (Ware, 2002). Historic fire return intervals (pre-1940s) ranged from 1 y to 2 dec (Batek et aL, 1999), where shorter fire return intervals maintained herbaceous vegetation (Ware, 2002). More recently, fire suppression has been a primary mechanism of glade conversion to shrubland, particularly by Juniperus virginiana encroachment (Briggs et aL, 2002), because frequent fires generally kill J. inrginiana seedlings and saplings (Ortmann et aL, 1998).

HEAT SHOCK EXPERIMENT

We purchased seeds from commercial suppliers: Allium canadense L. and Ruellia humilis Nutt. (Prairie Moon Nursery, Winona, MN), Echinacea simúlala R.L. McGregor (Easyliving Wildflowers, Willow Springs, MO), Lespedeza virginica (L.) Britton, Oenothera macrocarpa Nutt., Silphium terebinthinaceum Jacq. (Hamilton Native Outpost, Elk Creek, MO) and Juniperus virginiana L. (Sheffield's Seeds, Locke, NY). Nomenclature follows the USDA, NRCS (2012). Seeds were stored at room temperature and ambient relative humidity. The native species were selected based on their status as indicator species of Ozark glades habitat (see Baskin and Baskin, 2000). We heated seeds on aluminum trays (ten seeds per tray) in an oven for 15 min at four treatment temperatures: 24 C, 50 C, 100 C, and 150 C. We selected our treatments to represent temperatures and duration near the soil surface during grassland fires (Archibold et aL, 1998; Wally et aL, 2006), which are most likely to affect seeds near the soil surface. Grassland fires can reach temperatures upwards of 400 C for short durations (a few min or less) in grass and shrub canopies (Gibson et aL, 1990; Archibold et aL, 1998) but tend to be lower (50-200 C, depending on litter substrate) and of longer duration (>5 min, depending on litter substrate) at the soil surface (Archibold et aL, 1998; Wally et aL, 2006). …

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