Management and Restoration Ecology of the Federal Threatened Mead's Milkweed, Asclepias meadii (Asclepiadaceae)

Abstract

The federal threatened Asclepias meadii Torr. (Aselepiadaceae) is a perennial, self-incompatible prairie fori) imperiled by habitat destruction and population fragmentation. Many large populations persist in prairie haymeadows in Kansas and Missouri despite removal of seed pods by annual summer mowing. Only a few small populations remain in Illinois. Iowa, and northern Missouri. Recovery of these small populations and restoration of new populations are recovery objectives lor this species. This study was conducted to determine habitat differences among populations, to understand how hay mowing and fire management affect the structure of A. meadii populations, and to test the effects of different management treatments on restoration of this species. Soils analysis showed a geographic gradient, with southern populations on acid, nutrient-poor soils, and northern populations on calcareous, nutrient-rich soils. Milkweed ramet densities were lower in fire-managed prairies than in haymeadows; but burned sites had 68% (lowering ratnels while haymeadows had only 19% flowering ramets. This suggests that burning has selected for greater resource allocation toward sexual reproduction, while annual hay mowing has selected for greater resource allocation toward clonal spread. The Morton Arboretum is conducting experimental restoration of Asclepias meadii in the eastern part of its range, an objective of Federal Recovery Planning. In greenhouse and garden experiments, competition from oats significantly reduced seedling growth, with greater growth in artificially outcrossed seedlings. At seven restoration sites in Illinois and northern Indiana, significant variation in milkweed germination, survivorship, and growth was caused by weather, differences among sites, and site management. Seedlings were vulnerable to drought, with greater survivorship when rainfall was 2<K)% of normal. Planted juvenile milkweeds had greater survivorship than seedlings, and less sensitivity to drought. (Greater growth and survivorship also occurred in burned than in unhurried plots at three sites, bul not in all life-stages. Propagated plants from Missouri seed sources were larger than Kansas plants in the garden, but not in the field. Continued work is needed to determine if restored populations can become viable, and if there are negative effects of crossing and translocating genotypes.Managing for viable populations of endangered history stages (Fenster & Dudash, 1994; Weller, species requires knowledge of their life-history and 1994;Pavlik, 1994 Pavlik, , 1996 Guerrant, 1996). This habitat requirements, reproductive biology, and the paper examines factors that affect the management demographic, genetic, and ecological traits that and restoration ecology of Mead's milkweed (Asclemake them vulnerable to extinction processes (Gil-pias meadii Torr., Aselepiadaceae), a federal threatpin & Soule, 1986; Lande, 1988;Menges, 1986, ened (Harrison, 1988) plant essentially restricted 1991. Similar information is required to re-to the virgin tallgrass prair...

Influence of Seed Characteristics and Site Conditions on Establishment of the Threatened Prairie Milkweed Asclepias meadii

“…Previous studies of A. meadii favored juveniles over seeds as restoration units because the observed germination and seedling growth rates were higher in the greenhouse than the field Bowles et al, 2001), patterns also seen in this study. A. meadii appears to require a threshold size before it begins to flower (Bowles et al, 2001). As a consequence, plants started in the greenhouse may have a quicker path to maturity than those in the field.…”

“…5 53). Previous work by Bowles et al (1998) noted a correspondence between higher than average May-Jul. rainfall and increased seedling survivorship.…”

An Adaptive Decision Framework for the Conservation of a Threatened Plant

“…Bowles et al (2001) reported an average survival rate of 0.35 (survival to the end of the first growing season) for planted seeds at seven prairie sites. At three of these sites, Bowles et al (1998) observed greater survivorship and larger individuals in burned sections of the sites than in unburned sections, with effect size of 0.85 (logit scale) being the largest observed. In our model, we specified a 0.35 juvenile survival rate in any year that the site was not burned and 0.56 in any year that it was burned, the difference corresponding to this effect size (Table 1).…”

“…Average fecundity is consistently reported around 60 seeds per pod (Betz 1989;Betz and Lamp 1992;Bowles et al 1998;Row et al 1999), with no evidence of firerelated differences. In our model, we used the range provided by Betz (1989) and permitted fecundity to vary uniformly between 55 and 68 seeds per pod on both burned and unburned sites (Table 1).…”

“…In light of this, we focused attention on parts of the model involving the juvenile stage. This stage has proven the most difficult to observe and experimentally manipulate in field settings (Betz 1989;Bowles et al 1998), and many of the important parameters in this stage are speculative and based on incomplete or anecdotal information. Burning of Mead's milkweed sites is considered to be a positive management strategy with a net effect of boosting population growth (Betz 1989;Bowles et al 2001).…”