Are we at critical moss?

I’ve spent the last two weeks looking into moss conservation around the world– how are mosses faring? have we taken conservation action? do we need to? And I feel like the most common response I found in literature dated as recently as nine years ago was ‘We don’t have enough information to judge.’ This is definitely a concern- if mosses are struggling, we need to know this so we can take steps to support populations. If mosses are fine, let’s take our limited conservation resources and focus on organisms that are in trouble. If we don’t know what is going on, that puts us in a difficult position.

Mosses can be some of the first plants to colonize bare substrate, like these lava beds- they provide important habitats for other organisms to colonize, but they can be very sensitive to changes in habitat.

Mosses can be some of the first plants to colonize bare substrate, like these lava beds- they provide important habitats for other organisms to colonize, but they can be very sensitive to changes in habitat.

How blurry is the situation? While there are definite gaps in our knowledge, I think several general trends are emerging which suggest some mosses could use our help.  Researchers working on a number of continents have recognized that mosses are impacted by both global and local habitat changes. At the global scale, increasing levels of air and water pollution impact mosses more than some of the other plants we are familiar with (Söderström et al. 1992, Cleavitt 2005). Part of this has to do with moss anatomy- as non-vascular plants they absorb a lot of things from their environment directly through leaves and stems with less of a filter for harmful substances. Part of this has to do with habitat- mosses are typically found in wetter habitats and that means that they may sit in acid rain or polluted run-off after a storm.

At the local level, mosses are very sensitive to changes in microclimate, for example humidity (Lõhmus et al. 2006) or light (Rothero 2003). Researchers in Sweden found that mosses near newly-logged areas were less-impacted by a thinned forest if they were growing in concave depressions on the ground than if they were growing on mounds and had less access to groundwater (Hylander et al. 2005). Mosses in the boreal forest were more numerous and diverse on hardwood than softwood debris, probably because of the higher acidity of softwoods like pines (Mills and Macdonald 2004). Since logging in general creates changes in microhabitat through less plant cover, greater wind and light exposure, and soil disturbance, we should expect that logging can be a big challenge for moss populations. And a lot of forest management in colder climates involves pines and other softwoods, so mosses may be losing habitat in that respect, too.

If we combine those issues with moss harvest, we are impacting mosses both directly and indirectly. Researchers in West Virginia reported that moss harvesters were collecting more rock-based mosses because log-growing mosses were less common in managed forests (Studlar and Peck 2007)- a change in collection could impact community structure. And a switch in moss harvesting in the Pacific Northwest from harvesting scattered patches to stripping whole sections of forest slowed moss regrowth by taking all adjacent mats together and reduced populations of late-successional species because harvest was so often (Peck and Frelich 2008).

So we do know mosses are facing challenges even if we don’t know all of the details. For my next post I’ll look at more recent research and options for mitigating negative impacts on moss communities.

Works cited:

Cleavitt, N.L. 2005. Patterns, Hypotheses and Processes in the Biology of Rare Bryophytes. The Bryologist 108:554–566.

Hylander, K., M. Dynesius, B.G. Jonsson, and C. Nilsson. 2005. Substrate Form Determines the Fate of Bryophytes in Riparian Buffer Strips. Ecological Applications 15:674–688.

Lõhmus, P., R. Rosenvald, and A. Lõhmus. 2006. Effectiveness of solitary retention trees for conserving epiphytes: differential short-term responses of bryophytes and lichens. Canadian Journal of Forest Research 36:1319–1330.

Mills, S.E., and S.E. Macdonald. 2004. Predictors of Moss and Liverwort Species Diversity of Microsites in Conifer-Dominated Boreal Forest. Journal of Vegetation Science 15:189–198.

Peck, J.E., and L.E. Frelich. 2008. Moss Harvest Truncates the Successional Development of Epiphytic Bryophytes in the Pacific Northwest. Ecological Applications 18:146–158.

Rothero, G. 2003. Bryophyte conservation in Scotland. Botanical Journal of Scotland 55:17–26.

Söderström, L., T. Hallingbäck, L. Gustaffson, N. Cronberg, and L. Hedenäs. 1992. Bryophyte conservation for the future. Biological Conservation 59:265–270.

Studlar, S.M., and J.E. Peck. 2007. Commercial Moss Harvest in the Appalachian Mountains of West Virginia: Targeted Species and Incidental Take. The Bryologist 110:752–765.