Science Tuesday: Burning the Late Bloomers
Authors: Lenya Quinn-Davidson
The first thing I did at work last Thursday was smash my ring finger in the door of a truck. I got out to open a gate, and my finger decided to stay with the door as I slammed it shut with my other hand. I didn’t know it was possible for a door to latch when a full knuckle is in its way, but indeed it is!
Thursday was my third day in the field last week, monitoring invasive grasses as part of a small research project I’m working on with some colleagues at University of California Cooperative Extension. The first two days we were baking in 102 degree weather in California’s Central Valley, but by Thursday, we were back in the cool fog of Humboldt County, searching out plot locations and joking about which of us should pound the t-posts for our transects: me, with my freshly crushed ring finger, or my coworker Jeff, who has a dislocated thumb. Such an impressive field crew!
For this project, we are testing the effectiveness of prescribed fire for the control of medusahead (Taeniatherum caput-medusae), an annual grass from the Mediterranean that is considered one of the worst invasives in western rangelands. Medusahead has earned that reputation thanks to a number of unlikable traits, including its ability to rapidly spread throughout an area, suppressing growth of desirable grasses and forbs, and its high silica content, which not only makes it highly unpalatable to livestock for most of the year, but also results in the development of a persistent, silica-rich thatch that further precludes growth of other plants. Unfortunately, medusahead is also quite versatile, enjoying not only intense heat and thin, rocky soils like those in The Nature Conservancy’s Dye Creek Preserve (where we started our field work last week), but also the cool climate and relatively rich soils afforded by coastal Humboldt County. Like many non-native invasive plants, medusahead is easy to please and very hard to control.
Previous studies have tested various control options for medusahead, including grazing, herbicides and fire. Grazing has the benefit of trampling, which can (at least temporarily) reduce cover of medusahead, but the grass is so distasteful that control via consumption is not a realistic option. In a grazed pasture, you can often tell where the medusahead is by looking for islands of untouched grass amid areas that have been fully grazed. Last week, we actually saw trails of grass that had been bitten off and then spit out—immature medusahead that caught the cattle by surprise.
Herbicides have been shown to be effective, especially when used in conjunction with prescribed fire. One study showed that medusahead in a sagebrush-steppe ecosystem was best controlled with burning followed by the application of imazapic, an herbicide that targets broad-leafed plants and grasses (Davies 2010). This treatment not only controlled the medusahead, but it also resulted in greater establishment of perennial bunchgrasses.
But fire alone also appears to be a promising approach; several studies have shown that it can greatly reduce medusahead cover, at least in the years immediately following the fire. A 1996 paper by Pollak and Kan showed that late spring burning on the Jepson Creek Preserve in central California successfully reduced the cover of medusahead and other non-native annual grasses, and increased the cover of native species and important range forbs, like filaree (Erodium species). Another paper from northern California showed that the successful control of medusahead was related to the amount of non-medusahead biomass in the unit before the burn (Kyser et al. 2008). More productive sites provided more combustible fuels, allowing for increased fire intensity and better effects.
Timing is also a very important consideration when using prescribed fire to control medusahead. It is a late-season grass, meaning that it flowers and goes to seed long after most of its neighbors have turned brown. In an unburned system, this gives medusahead an advantage — it can continue to grow and produce seed without competition from the early-season grasses that share its space. But there is also a window when it is vulnerable to fire and nothing else is; other plants have dropped their seeds, but medusahead seeds are still on the plant and surrounded by dry fuels. I think this late-season quality may be medusahead’s only likable trait!
Our current research trial will offer some new insights, especially for more coastal rangelands that haven’t previously been the focus of medusahead research. We’re considering similar work on star thistle, another nasty, late-season invasive that plagues western grasslands. These studies are exciting because they remind us of the nuance involved in using fire — we have to take the time to understand the physiology of the individual plants we’re managing, and how we can use fire to shape the composition and structure of our landscapes. (In this case, I also had a solid reminder of how important it is to move my hand before slamming a heavy truck door — learning opportunities abound!)
Davies, K. W. (2010). Revegetation of medusahead-invaded sagebrush steppe. Rangeland Ecology and Management, 63(5), 564-571.
Kyser, G. B., Doran, M. P., McDougald, N. K., Orloff, S. B., Vargas, R. N., Wilson, R. G. and DiTomaso, J. M. (2008). Site characteristics determine the success of prescribed burning for medusahead (Taeniatherum caput-medusae) control. Invasive Plant Science and Management, 1(4), 376-384.
Pollak, O. and T. Kan. (1998). The use of prescribed fire to control invasive exotic weeds at Jepson Prairie Preserve. Ecology, Conservation and Management of Vernal Pool Ecosystems. Proceedings of 1996 Conference. California Native Plant Society, Sacramento, California, USA, 241-249.