Lichens

[mrtree]

I cannot identify the pink organism but I am willing to bet it is producing a chemical that has killed the underlying lichen. Just as there is succesion in forests their is succesion on tree bark and often a battle between organism for dominance.

[WeeDee]

Bark pH varies between tree species, ie. pines and oak are acidic and maples and elms are basic. Bark pH also varies with age and growing conditions (high rain fall can leach nutrients from bark and move pH towards basic). Lichens have certain preferences and pH is one preference we can easily identify.

 

I understand.

So the pH of a particular tree species IS significant with regards to the lichen species that may colonise its surface?

[mrtree]

I understand.

So the pH of a particular tree species IS significant with regards to the lichen species that may colonise its surface?

 

Absolutely. Certain lichens are very closely associated with certain trees.

 

Nitrogen is also a large factor. Trees near fertilized fields often are yellow/orange from Xanthoria lichens.

 

Unfortunately I do not know of a single volume that discusses lichens and trees. THere are loads of articles and chapters in books though. I would recommend reading William Purvis's Lichen book first and then branching out into other literature.

[WeeDee]

Absolutely. Certain lichens are very closely associated with certain trees.

 

Nitrogen is also a large factor. Trees near fertilized fields often are yellow/orange from Xanthoria lichens.

 

Unfortunately I do not know of a single volume that discusses lichens and trees. THere are loads of articles and chapters in books though. I would recommend reading William Purvis's Lichen book first and then branching out into other literature.

 

Thanks.

[mrtree]

OH if you want some gripping reads about lichen discovery and trees get The Lichen Hunters by Oliver Gilbert.

[BenR]

Sorry, I've been a busy boy. Again, I agree with mrtree, no idea what the pink stuff is but is clearly having some sort of influence.

 

pH is an issue.. lichens are generally grouped into nitrophytes and acidophytes. However, there was a paper from Holland which was saying that the distinction between the two is becoming blurred after finding both acidophytes and nitrophytes on the same trunk of young trees in the Netherlands. I will try to dig out the paper when I get home. I will paste the abstract here. Thanks mrtree for your continued, insightful input. Share the wealth

[BenR]

Found it anyway:

 

To study the pH preference of epiphytic lichens, the bark pH of Fraxinus, Tilia, Quercus and Ulmus trees in an urban environment was measured using a flat surface electrode. The total number of trees was 253. A survey was made of the lichens in a 40 × 40 cm quadrat surrounding the pHmeasurement point. Our data analysis using multivariate and univariate statistical techniques indicates that the tree species is the most important factor influencing lichen colonisation, and that bark pH alone is of less importance. We hypothesize that the changed pollution climate, with strong decreases in both sulphur dioxide and ammonia concentrations over the past two decades and a concomitant general increase in bark pH, has made epiphytes less sensitive to pH.

Tree species, rather than bark pH determines the occurrence of acidophytes and nitrophytes on trees.

 

L. Spier, H. van Dobben, and K. van Dort, 2010

 

It should be made clear that this hypothesis is based on urban areas only.. And it suggests that pH is important as part of a range of other factors, rather than saying simply that pH is not as important.

[BenR]

Some more interesting info from J. W. Humphrey, S. Davey, A. J. Peace, R. Ferris and K. Harding. 2002.

 

Abstract

Lichen and bryophyte communities of spruce and pine plantations in different parts of Britain were surveyed and compared to those of semi-natural pine and oak woodlands. In total, 202 lichen species and 111 bryophytes were recorded. Community composition and species-richness were related to measures of climate, stand structure and deadwood (snags, logs and stumps). Plantations had a less species-rich lichen flora than semi-natural stands related to reduced light availability and lack of old trees. Bryophyte species-richness was similar in plantations and semi-natural stands, and was positively correlated with large diameter (>20 cm), well-decayed logs and stumps. Lichens species-richness was higher on decorticate snags (especially in semi-natural Scots pine stands in the Scottish Highlands). Early successional stands were often the richest for lichens, stumps being important for Calicium and Cladonia species. Three strategies are suggested for enhancing lower plant diversity in planted forests: (1) extending felling rotations; (2) introducing alternative silvicultural systems to clear-felling (e.g. single-tree selection) to foster continuity of woodland conditions and increase deadwood volumes; (3) modifying restocking practices on clear-fells to avoid excessive shading of deadwood.

[Tony Croft aka hamadryad]

The pik stuff I am certain is the plasmodia of a fungi known a lycogala, they form tiny ball like fruits on bark and burst a geletinous liquid that often goes pink with age

[BenR]

Is plasmodia some sort of reproductive fluid Tony? Ive often seen that same pink residue/fluid and wondered what it was. Thanks