Germination of the federally endangered Michaux's sumac (Rhus michauxii)

The federally listed Michaux's sumac (Rhus michauxii Sarg. [Anacardiaceae]) is one of the most endangered shrubs in the southeastern US. The endangered status of this fire-adapted species may be primarily attributed to fire suppression. Many hard-seeded plants in fire-adapted ecosystems can survive high temperatures and germinate in response to scarification caused by high fire temperatures. Unfortunately, little is known about the germination strategy of Michaux's sumac. Using seeds collected from Virginia Army National Guard, Maneuver Training Center, Fort Picket, that were subsequently manually scarified, we discovered that imbibition of intact seeds was prevented by endocarp impermeability. We then examined if dry heat, as an analogue for wildfire, could be used to break this physical dormancy. Replicated (n = 3) dry heat treatments applied at 60, 80, 100, 120, and 140 °C (140, 176, 212, 248, and 284 °F) for 5 and 10 min durations, as well as a nontreated control, yielded no germination after 4 wk. All seeds were subsequently manually scarified. During the next 4 wk, a range of 47.8 ± 4.8 to 56.7 ± 12% germination was observed for scarified seeds of the 60 and 80 °C (at 5 and 10 min) treatment groups, not significantly different than the 61.6 ± 6.2% germination observed with scarified control seeds. Very low germination was observed when seeds were exposed to 100 °C for 5 min; all longer duration and higher treatment temperatures were lethal.