Moss Harvest Research

Tree-moss Succession

Some of the early projects produced results that were a bit surprising.  For instance, in a comparison of sites that were thought to have never been harvested before (virgin moss) with adjacent sites known to have been harvested within the past 15 years, we saw no evidence that species richness was greater in the old-growth moss.  In fact, it was just the opposite (Peck 1997c).  A few years went by, and then in the 2004 sampling of the 10-year regrowth, we again found that richness appeared to be greater in the regrowth than in the originally harvested mats (Peck 2006b).  OK, so maybe this is real.

Come to think of it, this meshed with what we were seeing the field, too.  Over the years I had learned to identify shrub stems that had been harvested in the past partly on the basis of their species composition, although we hadn't really experimentally demonstrated that yet.  I had picked up a search image that called for a particular combination of taxa, and that combination was always species rich.  My mental image for "mature" moss mats was rather dull--domination by Isothecium.

Furthermore, the stereotype for unharvested stems, or very old regrowth, was higher richness yet again with the introduction of moisture-loving acrocarps and vascular plants.

This led to the development of the following theoretical model of tree-moss succession.  When a stem is disturbed, what will regrow is strongly influenced by what species were left as residuals on the stem and/or grow very nearby.  Thus we see two types of composition in the early colonization stage:  Isothecium-dominated, or a mixture of different early successional taxa (Claopodium, Eurhynchium, Metzgeria, Radula).  The Intiation stage can last over a decade and ends only when the stem has reached 100% cover and taxa begin to directly compete for resources.  During this exclusion stage, Isothecium out-competes the appressed early successional species and dominates the mat.  Eventually enough epiphytic soil develops that the moisture-lovers are able to move in and we again see a multi-aged mat of mixed species composition.

In an on-going project, I have attempted to validate this model using the species composition of moss mats of various presumed ages.  The colonization state is taken from years 1-2 of the regrowth study while the initiation stage is taken as year 10.  Data for the exclusion stage (15-25 years) and the multi-aged stage (>25 years) are taken from the various experiments in which the host shrub stem was aged and the supported moss mat is presumed to be no older than the shrub stem (assuming no obvious signs of recent disturbance).  What I found is this phenomenal mess!  I'll let you know if I can make any sense out of it.