Scasta John Derek, Engle David M, Harr Ryan N, Debinski Diane M
Department of Ecosystem Science and Management, University of Wyoming, Laramie, 82071, WY, USA.
Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK, USA.
Bot Stud. 2014 Dec;55(1):80. doi: 10.1186/s40529-014-0080-4. Epub 2014 Dec 24.
Symphoricarpos, a genus of the Caprifoliaceae family, consists of about 15 species of clonal deciduous shrubs in North America and 1 species endemic to China. In North American tallgrass prairie, Symphoricarpos orbiculatus (buckbrush) is the dominant shrub often forming large colonies via sexual and asexual reproductive mechanisms. Symphoricarpos shrubs, in particular S. orbiculatus, use a unique sexual reproductive mechanism known as layering where vertical stems droop and the tips root upon contact with the soil. Because of conflicting societal values of S. orbiculatus for conservation and agriculture and the current attempt to restore historical fire regimes, there is a need for basic research on the biological response of S. orbiculatus to anthropogenic burning regimes.
From 2007 through 2013 we applied prescribed fires in the late dormant season on grazed pastures in the Grand River Grasslands of Iowa. From 2011 to 2013, we measured how S. orbiculatus basal resprouting and layering stems were affected by patchy fires on grazed pastures, complete pasture fires on grazed pastures or fire exclusion without grazing for more than three years. We measured ramet height, ramet canopy diameter, stems per ramet, ramets per 100 m, and probability of new layering stems 120 days after fire. Height in burned plots was lower than unburned plots but S. orbiculatus reached ~ 84% of pre-burn height 120 days after fire. Stems per ramet were 2x greater in the most recently burned plots due to basal re-sprouting. Canopy diameter and density of ramets was not affected by time since fire, but burned pastures had marginally lower densities than plots excluded from fire (P = 0.07). Fire triggered new layering stems and no new layering stems were found in plots excluded from fire.
The mechanisms of both basal sprouting and aerial layering after fire suggest S. orbiculatus is tolerant to dormant season fires. Furthermore, dormant season fires, regardless if they were patchy fires or complete pasture fires, did not result in mortality of S. orbiculatus. Dormant season fires can reduce S. orbiculatus structural dominance and maintain lower ramet densities but also trigger basal resprouting and layering.
接骨木属是忍冬科的一个属，由北美约15种克隆落叶灌木和中国特有的1种组成。在北美高草草原，圆叶接骨木（buckbrush）是优势灌木，常通过有性和无性繁殖机制形成大片群落。接骨木属灌木，特别是圆叶接骨木，采用一种独特的有性繁殖机制，称为压条繁殖，即垂直的茎下垂，顶端接触土壤时生根。由于圆叶接骨木在保护和农业方面存在相互冲突的社会价值，以及当前恢复历史火灾模式的尝试，因此需要对圆叶接骨木对人为火灾模式的生物学反应进行基础研究。
2007年至2013年，我们在爱荷华州大河草原的放牧牧场上，于休眠后期进行了规定火烧。2011年至2013年，我们测量了圆叶接骨木的基部萌蘖和压条茎在放牧牧场上的局部火烧、放牧牧场上的完全火烧或三年以上不放牧的火烧排除处理下受到的影响。我们测量了分株高度、分株冠幅直径、每个分株的茎数、每100米的分株数以及火烧后120天新压条茎的概率。火烧地块的高度低于未火烧地块，但圆叶接骨木在火烧后120天达到了火烧前高度的约84%。由于基部萌蘖，最近火烧地块中每个分株的茎数增加了一倍。分株的冠幅直径和密度不受火烧后时间的影响，但火烧牧场的密度略低于火烧排除地块（P = 0.07）。火烧引发了新的压条茎，而在火烧排除地块中未发现新的压条茎。
火烧后的基部萌蘖和空中压条机制表明圆叶接骨木对休眠季节火烧具有耐受性。此外，休眠季节火烧，无论其是局部火烧还是完全火烧，都不会导致圆叶接骨木死亡。休眠季节火烧可以降低圆叶接骨木的结构优势，维持较低的分株密度，但也会引发基部萌蘖和压条繁殖。
