These two photos from an excellent post by Dan Carter show a part of the ecosystem that deserves more attention: the communities of lichens, mosses, bacteria, algae, and more that may play an important role in prairies and oak woodlands. Crusts may, for example, help determine which plant species reproduce and which do not.
In this first photo we see an elaborate lichen and its moss companion on the floor of an oak woodland.
In the second, of a burned prairie in early spring, zoom in to see most of the above-ground crust burned off but starting to re-emerge along with blooming yellow stargrass and Seneca snakeroot among emerging prairie betony, bastard toadflax, prairie violet, some small panic grasses, and many other species characteristic of high quality.
It would be great if we could make management decisions based on full knowledge of an area's plants, animals, fungi, lichens, micro-organisms, etc. Instead, we make decisions based as much as possible on what we know. Otherwise, brush or other invasives win out, and the rich biodiversity is lost. But let's encourage study, learning, and collaboration. We do better and better thanks to many dedicated individuals who take on detailed studies. Thanks to Dan Carter's fine blog for reminding us of the magic of crusts.
Yesterday, I took a walk to the top of a prairie kame. I looked down the south facing slope. There were no bryophytes among the recently burned area. At the top of the slope, along the edge of the trail, and on the north face of the slope were bryophytes. I think the lack of bryophytes on the south facing slope is due to more intense fire. As most people in this advocation know, south facing slopes are warmer. Fuels dry faster. Fire is hotter.
ReplyDeleteI have seen fire kill bryophytes. People studying bryophytes say the soil under them is better. If plants are the fur, then soil crust organisms are the skin. Justin Thomas has shown multiple examples of growing season fire destroying Ozark ecosystems. The mass death from fire killing the soil crust organisms leads to nutrient surges. Nutrient surges lead the the establishment of rubus and sumac. In more extreme cases, the organic layer of soil is burned off completely. Destruction of the plant community leads to soil eroding away. Soil takes centuries to develop.
Dead stem accumulation causes prairies to become increasingly dominated by tall grasses. This has been known since John Weaver observed it in Nebraska. Dead stems must be burned off to prevent prairies from being degraded. What becomes important is how this is done. Prescribed burning can be conducted as soon as the fuels are dry enough to carry fire. If fuels are allowed to dry longer, fire will be more intense. Fire can be conducted during winter. Being frozen should help protect the soil crust organisms from the heat of fire.
I do not recall any of the people conducting prescribed burns ever doing this work in below freezing condtions. I believe this needs to change.
The main culprits working against crusts in the places they belong, many / most / all dry to mesic prairies is 1) litter accumulation and 2) high fire intensity due to too long of fire return interval or warm conditions with drier, warm soil. Crusts typically survive and recover if fires are annual and conducted when soils are cool (don't have to be frozen, but it helps) in the autumn through very early spring.
DeleteI have seen soil crust present on a south facing slope. It was in the conditions you describe. The thin vegetation led to sparse litter accumulation. The site is burned annually and preferentially on the best days. When possible the site has been burned in fall.
DeleteIn locations where vegetation is more robust, I think burning when ambient conditions are below freezing would help. Burning on days below freezing would not only have the benefit of decreasing impacts to soil organisms. There are a lot of good burn days being missed because burning is not happening in below freezing condtions.
I visited the largest and best prairie kame in the area. This kame receieves the best management. I specifically looked at bryophytes and soil crusts. What was said above was generally true. Although, more than just aspect is important. Soil depth was a very important factor. As the soil depth increased, the bryophytes decreased. Increased soil depth leads to more vigorous vegetation. More vigorous vegetation leads to more intense fire. Although, at the base of the kame in a prairie reconstruction area I found bryophytes growing where fuel grows dense. The more level ground may stay hydrated longer helping protect bryophytes from the dormant season fire.
ReplyDeleteIt should be mentioned that bryophytes are important in wet prairies too. They grow in areas just above the water table or on hummocks. In one such wet prairie, yellow star grass grew like is shown in one of the images in the above blog post. This prairie has very limey soil that is wet in spring but typically drys out during summer. Unfortunately, trespassing ATV riders turned this wet prairie into a mud pit. All that now survives intact is a few square feet around which the ATV riders drove in circles. I do not know of any still surviving examples of this ecosystem. Possibly there is some in a nature preserve along railroad tracks further west.
ReplyDeleteHere is a video titled “Biodiversity and Conservation of Puget Sound Prairie Bryophytes and Lichens.” Some relevant quotes from the presentation are included in the replies below.
ReplyDeletehttps://www.youtube.com/watch?v=WnPrDGGVhFw
(18:52) … In terms of common in burn plots we see more disturbance adapted bryophytes. Ones that are shorter lived, have a shorter life cycle, and reproduce more quickly. More weedy species …
Delete(31:19) All functional categories decreased in the burn plots, except for one, which is the ephemeral mosses.
Delete(31:53) And it really helped to illustrate that some lichen populations could be at risk of extirpation from these sites. Including some rare species, with these burning practices …
Delete(50:09) Question: From a management standpoint, what frequency of burning is detrimental to the old growth lichens and bryophytes … ?
DeleteAnswer: … Some of these species can take 80 to 100 years to grow all the way back … Prescribed burning is an important part of this ecosystem …
(29:34) Bryophyte and lichen ground layer in burned plots exhibited a decrease of 72.7 percent in mean biomass and 38.8 percent in mean cover relative to the unburned plots.
ReplyDeleteNone of this tells us much unless time since last fire, fuel loads, and season of fire are addressed. Also, it may well be that lichen cover and composition had changed with past fire exclusion, favoring species that would normally be restricted to areas that fire can't/doesn't get too. While some species may take decades or 100s of years to develop, they may essentially be the sugar maples of the lichen community. We see this with reindear lichen in acid oak barrens. It can occur over wide areas in the absence of fire, but fire restricts it to refugia with too little fuel to burn--as it probably ought to be.
DeleteThat's the problem with *most* research of fire effects on any taxonomic group--post-burn vs. no burn comparisons without appreciating the huge role (often leading to opposite effects) parameters like season, time since last fire/fuel loads, weather conditions, etc. play. There is also often the assumption that more of everything native is better, which isn't the case. We know this with native plants. Well, that extends to other taxonomic groups too. This is at the root of much of the well-intentioned mismanagement of many (most?) natural areas where fire plays an important role.
DeleteThere is much I agree with – and much I’d be cautious about – in the comments above.
DeleteI emphatically agree with Dan Carter’s comments: Soil crusts very much deserve study – but not necessarily “the more the better.”
I have seen soil crusts that give the appearance of being results of long over-grazing until the soil was badly depleted – and then a long “recovery” of sorts. Some conservative species seem to reproduce in those areas, while most do not. Perhaps such crusts facilitate the recovery of some species and discourage others.
Certainly it’s common to see crusts of algae, mosses, lichens and others covering old burn scars for a while. In regularly burned areas, the species involved may well be important parts of the biota, following downed log or brush pile burns. But in the chaos of recovery from long exploitation, the species found there may, as Carter suggests, be or include species from elsewhere.
Ron Panzer’s careful studies demonstrated that a substantial part of insect species diversity at many sites consisted of common generalist species. Thus, for conservation, we needed to know which were the species of conservation concern, either because of their rarity or because they played important roles in the ecosystem. "More species diversity" was not necessarily good.
One question about crusts that seems important to me is: what happens when various conservative species are seeded into species-poor soil crust areas? Perhaps for ecosystem recovery it would be helpful to seed some species of conservation concern into them … but don’t waste the seed of others there.
Many species seem to come and go at various parts of various sites. Perhaps soil crusts also come and go and are part of the internal succession. It could be helpful to understand this better. But it’s likely unhelpful to prioritize soil crusts or any one element over all other components of the ecosystem.
As one commenter wrote: "There is also often the assumption that more of everything native is better, which isn't the case." Yes.