When I started looking at the literature on endangered plants, it seemed that many of the issues being faced by these species could be summed up by four main problems:
- Invasive species outcompeting and/or altering the habitat
- Loss of habitat through development (and this has particularly hit species with already small ranges- Leavenworthia torulosa, for example, is a species found in Kentucky, Tennessee, and Alabama. Of the two sites in Kentucky where it was known in the late 1970s, one had been reduced by 90% because bulldozing in the area led to soil becoming deeper as it washed down from upslope [Baskin & Baskin 1977]. As a result, other species were able to outcompete it.)
- Human management of the system changed annual environmental regimes (for example, suppressing regular fires)
- Loss/potential loss of pollinators
I’ve already spoken a bit about invasive species in previous posts, and loss of habitat is such a regular part of my blog that I feel I should give it a spot as guest editor. I haven’t focused as much on losing crucial elements of an ecosystem which keep processes going, and I think that’s a pretty typical failing of conservation education- we spend a lot of time looking at individual species that are in danger, and sometimes neglect to point out that any species in an environment is likely to be dependent on and required by others for survival. When it comes to endangered plants, there’s an even greater tendency to look at them in isolation because they are plants– they seem to grow quite efficiently in one place, produce many seeds, and produce their own food, so what could they possible need from the rest of the ecosystem?
Lomatium bradshawii populations were reduced by land development and fire suppression
But plants, like us, depend upon a complicated web of species and abiotic factors (like water flow and geology) to survive, and humans have done a very good job of altering some of the processes that had previously sustained plant (and, by extension, general) biodiversity. In some ways, the distribution of endangered plant species in the US echoes large human population movements (with accompanying land development and introduced species)- a 1997 report found that the states with the largest number of endangered plants were Hawaii, California, Florida, and Arizona (Dobson et al. 1997). In Florida alone, by 2003 407 species were considered endangered, a further 114 were threatened, and it was believed that 10 had become extirpated (Ward et al. 2003).
One of the big changes that we have made in a variety of habitats is to alter water and fire regimes. Whether it’s diverting water for irrigation of agricultural fields or suppressing fires to protect our property, we haven’t directly set out to put plant species on a path to extinction, but the ramifications of our actions have put a variety of species in peril. One example of this is Lomatium bradshawii (also known as Bradshaw’s desert parsley), an endangered plant found in only 16 locations in 1999, 15 of them in Oregon’s Willamette Valley (Pendergrass et al. 1999). These populations were both separated by a dense agricultural patchwork and deprived of regular fire events which help promote population growth (Kaye et al. 2001). When fall burning was reinstated in some plots, plant populations responded positively.
Environmental changes we’ve made (and that will continue to evolve into the future) have also interrupted the processes needed for some plant species to survive. Concerns over changes in timing and range of insect populations in response to climate change extend to pollinators needed by endangered plants. Clematis socialis, for example, is found in Alabama and Georgia with a flowering schedule that is linked to local temperatures (Wall et al. 2003). There are five insects that pollinate the flowers, but the two bees are particularly important. However, since climate change is expected to alter the timing of both plant flowering and peak insect populations, managing the ecosystem to sustain simply the plant and the most effective pollinator species may not be enough- the entire system needs to be preserved so that it can adapt to future changes. The idea of pollinator sustainability was also brought up by researchers focused on the endangered Eriogonum ovalifolium var. vineum in California- it’s not enough to give the plants space, we also need to keep the insect relationships going as well (Neel et al. 2001).
What I’m trying to illustrate here are some of the big patterns that scientists were looking at a decade or two ago with regard to endangered plants. In my next post, I’ll look at newer developments, both good and bad. As I move into more recent research, I have no doubt that new issues will arise, but I’m also pretty confident that these same problems will be perennial. Hopefully we’ve gained new understanding and new tools in addressing these issues, too.
Works cited:
Baskin, JM and CC Baskin. 1977. Leavenworthia torulosa Gray: an endangered plant species in Kentucky. Castanea 42: 15-17.
Dobson, AP, Rodriguez, JP, Roberts, WM, and DS Wilcove. 1997. Geographic distribution of endangered species in the United States. Science 275: 550-553.
Kaye, TN, Pendergrass, KL, Finley, K, and JB Kauffman. 2001. The effect of fire on the population viability of an endangered prairie plant. Ecological Applications 11: 1366-1380.
Neel, MC, Ross-Ibarra, J, and NC Ellstrand. 2001. Implications of mating patterns for conservation of the endangered plant Eriogonum ovalifolium var. vineum (Polygonaceae). American Journal of Botany 88: 1214-1222.
Pendergrass, KL, Miller, PM, Kauffman, JB, and TN Kaye. 1999. The role of prescribed burning in maintenance of an endangered plant species, Lomatium brawshawii. Ecological Applications 9: 1420-1429.
Wall, MA, Timmerman-Erskine, M, and RS Boyd. 2003. Conservation impact of climatic variability on pollination of the federally endangered plant, Clematis socialis (Ranunculceae). Southeastern Naturalist 2: 11-24.
Ward, DB, Austin, DF, and NC Coile. 2003. Endangered and threatened plants of Florida, ranked in order of rarity. Castanea 68: 160-174.