About lichens. Do they care about trees they grow on?

Nature Talk
1

Do lichens care about the trees they grown in or do they not?

Yesterday I took a bunch of pictures of the lichens in my project, with my cellphone. And I noticed that some trees were empty and some others filled with lichen. But I don’t know if the tree itself matters or simply is the area “air” that makes them thrive.

For examples trees that were filled with lichen were totumos, guamas and a third one i didnt identify. And trees without lichen were matarratón paloamarillo and aguacate/palta Even the old ones were fairly empty.

I want to introduce myself into the microscopic world of lichen.

And this was the first thing I noticed. Is just a coincidence or does the tree type actually influence?

Here is the link to the pictures of lichen i observed.

https://www.inaturalist.org/observations?on=2026-04-17&project_id=los-amigos-de-betania&subview=table&verifiable=any

2

Thank you for bringing lichen to attention today. I do not think I have ever made an Observation of them since I know so little, which is inexcusable since I often startle at their beauty.

I found this, which I am s-l-o-w-ly poring over. I wonder if you might also find it useful.

Saludos desde Yucatán!

3

The bark of different tree species differs in pH and this is a major decider of which trees host which lichens (he says from a position of great ignorance of lichens, but it is what I have read and been told).

4

From the link I posted:

Some lichens can grow on many type surfaces while others are confined to specific types of trees or rocks.

The growth of lichen on tree bark depends more on the physical surface of the bark than on the kind of trees. Young trees in general have a smoother bark that tends to attract crustose lichen species. As trees get older, the bark usually develops uneven broken surfaces that permit the foliose and fruticose lichens attach to the tree.

As I read it, that means “sometimes yes, sometimes no”?

But I am not sure about that. Or anything. I have however added this to my list of things to look for at the mercado:

Brodo, Irwin M, Sylvia Duran Sharnoff and Stephen Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven and London.

(There are almost 3 million Observations of lichen on iNat. Slightly better than 800K are RG,)

5

Lichens help absorb water and nutrients from the air. For example, lichens can form thalluses that store water, which can improve air humidity and create a unique microclimate around trees…

6

I think OP meant “care” as in preference, not as in care for or help. But it’s interesting to learn how they can be beneficial.

7

I was of the mind that some are selective, and some are generalists. Not that I’m entirely an expert!

Lobaria pulmonaria for example grows on a few trees.

8

So Ph (specie), bark surface, age.

Next time I take pictures of lichen. Then i will try to find an empty bark space of the host tree and also add that to the observation.

Besides the specie.

9

Funny, some people here told me they are disease and i should take it down (all the places they grow) I replied no they arent they might come after the tree is sick or is too humid to the tree they do nothing to the tree.

I guess we both were wrong as they do have an effect.

10

I updated the title slightly based on OP’s original post to make it a little clear what the topic of the thread is.

11

Lichens rarely cause harm to the trees they grow on. In some cases, they help transfer water from misty air to the tree. Many contribute nitrogen fertilizer to the ecosystem and thus to the tree. I think they add to the appearance of the tree, too.

12

Some species do, some don’t. There‘s one species I‘m aware of (Evernia prunastri) that grows (almost?) exclusively on oaks.

Other species (looking at you, Xanthoria parietina) just seem to grow, like… everywhere?

13

The single most important indicator for lichen fauna that most researchers agrees is always the exact host tree species. (another reason again that iNat should really prioritize ecological interactions recording in better way, by standardizing multiple observation fields names used for same context and providing uniform low friction ways to record such interactions readily)

well within such species reasoning, most readily call out the PH, there is bark physical structure, bark physiochemical gradients of cations and trace elements, water holding capacity of bark, tree diameter, tree crown height, elevation of the tree, geographical latitude, tree position among other trees, tree inclination …

all of these parameters are studied, albeit sadly not in a single unified way, and each are known to influence towards certain lichen preferences. if one sees closely things above are correlated too - for example a water holding capacity can be amplified by bark fissures which inturn can happen as tree matures with correlated increase of diameter … Effects of habitat quality and fine-scale spatial structure on epiphytic lichen and bryophyte communities Moller, Kaufmann, and Hauck, 2026

so even within a single tree species, lichen diversity can differ depending on these various factors, called as β dominated communities in literature - Lichen diversity and red-listed lichen species relationships with tree species and diameter in wooded meadows Thor, Johansson, and Jonsson, 2010

obviously finding such true causative agents is not just about curious science question but also a great study for real conservation policies of lichens itself, so if a goal is to retain maximal species diversities of lichens in an agroforestry business, knowing such correlations will have immediate benefits in turn - The value of information in conservation planning: Selecting retention trees for lichen conservation Perhans, Haight, and Gustafsson, 2014

and there are types of lichens within lichens too - for example, a nitrophytic lichen usually loves high PH environment than an acidophytic lichen - but the environment and pollution is blurring that lines more and more in recent decades: Is bark pH more important than tree species in determining the composition of nitrophytic or acidophytic lichen floras? Spler, Doben and Dort 2010.

Now coming to another question occurred above, are lichens harmful per se to trees?

well context matters a lot to what is harmful as with individual goals; for example even if a certain lichen species is known to reducing growth of certain trees by interefering with tree photosynthesis and cellular respiration, … (called alleopathic intereference and is pretty common among lichens) does not definitively conclude such lichen is harmful and should be immediately cleaned out, because maybe that specific tree population level reduction is inturn gonna increase other flora given time as the environment obviously has limited resources be it space or nutrients or such.

It’s easy to talk as tree vs lichen battle in those discussion but in reality its groups of specific trees+specific lichens battles even if indirect.

For example, to a pine conservator these research looks opposing but for tree lovers and not exclusively pine lovers, it feels good: Lichens and mosses promote alternate stable plant communities in the New Jersey Pinelands

Lichens Contribute to Open Woodland Stability in the Boreal Forest Through Detrimental Effects on Pine Growth and Root Ectomycorrhizal Development

14

Let’s add The importance of tree diversity and other abiotic and biotic drivers of lichen species richness in a threatened and mountainous biodiversity hotspot here: “For all lichens, analyses based on just the low disturbance sites implicated greater tree richness as the most critical factor for higher lichen richness.”

And don’t worry, we are not running out of pine trees in the Pine Barrens (although this might be quite a fire year if the weather holds dry).