Distribution of Arboreal Lichens Relative to Snowpack Zack Schubert EBIO 4100-570: Winter Ecology Spring 2011 Mountain Research Station, U. of Colorado, Boulder

Outline Background Methods Results Interpretation Conclusion

Background

Background How does snowpack affect the distribution of arboreal lichens? Sun, wind, moisture, temperature My initial question in pursuing this study was: Does the level of snowpack influence the distribution of lichens on trees? If so, how? Environmental factors that may affect this are wind exposure, solar radiation exposure, moisture availability, and temperature.

Advantages of supranivean Availability of sunlight Being above the snow surface may give greater advantage to lichens if sunlight is the limiting factor in their growth.

Advantages of subnivean Availability of moisture Lack of exposure (wind, cold) Being below the snow surface may give greater advantage to lichens if moisture, wind exposure, or exposure to the cold are the limiting factor(s) in their growth. My hypothesis was that the cold and wind exposure of the superniviean environment would be too much for most lichens and so a statistically significant majority would be found below the snowpack.

Current Research Long-term burial leads to mortality (Benedict 1990) Majority of moisture from snowmelt (Campbell 2001) Lichen abundance decreases with the host tree’s distance from water (Rambo 2010) Current research in this area shows that long-term burial under snow results in the mortality of lichen (Benedict 1990), that lichens in this season get the majority of their moisture from melting snow (Campbell 2001), and that lichens are more abundant on trees closer to water (Rambo 2010). The Benedict study transplanted lichen-covered rocks to an area beneath semipermanent snowpack. The Campbell study investigated the vertical zonation of hair lichens in a subalpine spruce-fir forest. The Rambo study investigated the growth of arboreal lichen transplants in trees of a mixed-conifer forest at varying distances from streams. He attributes this to a decreasing vapor pressure deficit (VPD) closer to the stream. (Rambo 2010)

Methods

Methods One 15 m x 6 m transect Random selection from satellite image of area Mainly aspen with some pine All trees sampled The transect (15 m x 6 m) was in an location that had been randomly selected from a grid superimposed on a satellite image of the area. The composition of the transect was mainly aspen trees with a few conifers. Both types were investigated for the presence of lichen. Snow depth usually fell around 0.85 m. MRS

Methods Visual inspection for lichens Snow dug away on lichen-positive trees Height above or below top of snowpack No measurements on second trip The area was visually inspected for arboreal lichens (limiting initial selection to trees with lichens above the snow surface). Once a lichen-positive tree was identified, the snow around its trunk was dug away and it was inspected for subnivean lichens. Lichens were measured for their height above or below the surface of the snowpack. A second field trip was taken, but no numerical data was collected. This was because the goal of the second trip was to collect more qualitative data about the lichens and to acquire more images for this presentation. Limitations in this design include: The transect, being largely aspen, may not be indicative of the area. The transect was small, and there was only one due to time constraints. Only trees that were observed to have lichen above the snow were investigated for lichen below the snow; consequently, a 50% split between above- and below-snowpack lichens would have been the maximum possible.

Results

Few lichens below snow Only one group of lichens (pictured, right) were found in the subnivean, and then only on the second trip. The left picture shows a deposit of lichens on an aspen tree, while the right shows lichens on the dead branches of a conifer.

Due to the more observational nature of the second field trip, lichens observed there (including the subnivean lichen) are not included in this graph.

Disturbed bark of aspens The majority of lichens were found to occur on areas of “disturbed” aspen bark. These areas were darker in color and had greater texture than other areas of the aspen. Such areas occurred where something had disturbed the bark’s regular growth, such as a dead branch from the aspen (such as is pictured on the right) or some past impact. Lichen-negative Lichen-positive

Bare branches of conifer The only location on coniferous trees on which lichen was found was on branches in areas that had no needles. Some of these branches seemed to be entirely dead, while others had needles on either side of the lichen area.

Interpretation

Few lichens in the subnivean Insufficient sunlight Insufficient substrate Age Too much moisture (Campbell 2001) Decomposition (Coxson 2002) The fact that there were drastically fewer lichens observed in the subnivean can stem from several things: Not enough sunlight to sustain the algae in a lichen makes it deeper into the snowpack There is not enough suitable habitat – apparently sections of disturbed bark on aspens – to support lichen. The disturbed bark may be less abundant below the snow because the lower parts of the tree are older and will have had more time to heal any damage There is too much moisture beneath the snow. The amount of decomposition that occurs and the duration of a lichen’s burial show a positive relationship (Coxson 2002) Some lichens show an intolerance to prolonged wetting (Campbell 2001)

Further Research Different lichens at different heights (Campbell 2001) Occurrence on conifers Preference for disturbed aspen bark Color/Temperature Texture There could be a great deal of further research done into lichens in this environment exploring their characteristics, much less the causes of these characteristics: Do different lichens occur at different heights on a tree? This was found to be the case in Canada in a different study (Campbell 2001). What types of lichen occur on conifers? Does the lichen harm the tree, or does it just take hold where needles have already been removed? Why do lichens prefer disturbed aspen bark? Perhaps: The dark color absorbs solar radiation better and warms the lichen The heavy texture makes it easier for a lichen to deposit initially

Conclusion

Lichens in Relation to Snowpack Lichens prefer a supranivean environment Lichens prefer areas of disturbed bark on aspen trees Questions? The most important findings of this investigation were that lichens prefer a supernivean environment and that they prefer areas of disturbed aspen bark.

Literature Cited Benedict, James B. 1990. Lichen mortality due to late-lying snow: results of a transplant study. Arctic and Alpine Research 22: 81-89. Campbell, J., D.S. Coxson. 2001. Canopy microclimate and arboreal lichen loading in subalpine spruce-fir forest. Canadian Journal of Botany 79-5: 537-555. Coxson, D.S., M. Curteanu. 2002. Decomposition of hair lichens (Alectoria sarmentosa and Bryoria spp.) under snowpack in montane forest, Cariboo Mountains, British Columbia. Lichenologist 34-5: 395. Rambo, T.R.. 2010. Habitat preferences of an arboreal forage lichen in a Sierra Nevada old-growth mixed-conifer forest. Canadian Journal of Forest Research 40-6: 1034-1041.