Epsilon Archive for Student Projects

Abstract

ABSTRACT
Rapid changes in the forest structure due to logging strongly affect lichen vegetation and can exceed tolerance of many organisms while being beneficial to others. Cladonia botrytes was supposed to be obligately lignicolous and having a high portion of the occurrences on stumps on clear-cuts. The aim of this study was therefore to clarify the ecology of Cladonia botrytes and especially how frequently it occurs on soil in clear-cuts. Scots pine Pinus sylvestris clear-cuts aged 10-12 years old were examined for the abundance of the species on stumps and exposed soil in three provinces of Sweden – Uppland, Dalarna and Västerbotten. C. botrytes was present on the soil in all the regions on two distinct substrates: humus on the ground and on boulders. There was a significant regional difference in the distribution of the lichen on the ground and on boulders (p< 0.001), indicating a trend of increasing abundance towards the north. Regional variation for the occurrence of the lichen on the stumps was significant (p < 0.001); however the distribution among the regions was more homogenous and did not have a distinct northward trend. Canopy cover of the new tree generation influenced the abundance of the lichen on all the substrates: ground, boulders and stumps. It was found that the species prefer dry conditions as it was less abundant in the plots with wet habitats. As for the occurrences on the stumps, it was found that stump size variables (height and surface area) have an effect on the presence of the lichen yet the relationship behind that is unknown. The species is positively affected by the logging activities as it provides short-term habitat. Due to the abundant presence of the lichen on soil, change in the classification as obligatory lignicolous should be considered.

POPULAR SUMMARY

Rapid changes in the forest structure due to logging activities can strongly affect the forest vegetation. Modern practice of clear-cutting, where almost no standing trees are left, clearly represents a different environment from the original forest cover, having more direct solar radiation, higher precipitation rates and amplified temperature fluctuations. These sudden dramatic changes and hostile new environment can exceed the tolerance of many organisms, while being beneficial to the ones that can adapt to them. Lichens are a group of symbiotic organisms that contain algal and fungal cells, which allows them to colonize and thrive in habitats where they could not survive separately. Response to felling can be very diverse among different lichen species, resulting in dramatic physiological changes or even extinction from the habitat. However, some species can manage to thrive in the habitat created by logging. Felling creates heterogeneity and the habitat complexity that allows occurrence of the new substrate for lichens, such as stumps. Stumps and other felling residues are important for the recovery of the species as they allow lichens to refugee while the original habitat quality is restored. Stumps can be colonized both by generalist lichen species and specialist, wood dependant, lichen species. However the reasons for wood affinity are not yet fully understood.
This study was done on lichen species Cladonia botrytes, also commonly known as the stump lichen. Despite the fact, that the species has been known to be confined to decaying or rotten wood, several findings indicate its occurrence on the soil substrate. This study aims were to clarify the ecology of C. botrytes. 180 plots in 36 clear-cuts located on the gradient from the central to northern Sweden were examined for the presence of C. botrytes on the stumps and soil, along with several ecological variables in attempt to explain the factors preceding the occurrence of the species.
C. botrytes was found to be present on the soil with an increasing abundance towards the north. As it is no longer confined to decaying wood as its only substrate change in the classification of the species is recommended. Apart from the substrate preference other factors were found to be significant for the occurrence of the lichen. Canopy cover of the new tree generation and ground moisture were found to be influential for the presence of the lichen, however there is no direct and clear relationship between these factors and abundance of C. botrytes. Same goes for the stump variables that were measured (stump surface area and height) in the field. Species occurrence is not directly connected to the size and height of the stump, although it is important for the presence of C. botrytes. Species abundance is a difficult matter affected by multiple variables with complex interactions, therefore making it hard to distinguish their direct influence.
C. botrytes is positively affected by the conditions created by clear-cutting as it assures long-term continuous supply of suitable habitat for colonization and allowes species to thrive. C. botrytes is a fast colonizer and can occur in natural habitats in similar conditions created by storms or forest fires. Despite the fact, that stumps are not naturally created substrate they host a large proportion of the species population. Therefore it is advised against stump harvest in the logging areas.