WHAT IS A GOOD INDICATOR OF THE HEALTH OF A GIVEN HABITAT?: Today a very old post by Prasad popped up on my screen through efloraofindia so I felt like sharing my thoughts on this matter.

Just wanted to share this with all..For me what is a good indicator of a habitat’s health?
Find a plant which depends on more than one plant for its survival.
For example, Orchids. They need a particular mycorrhiza to help them germinate whether its terrestrial or epiphytic and then a particular host on which they prefer to live if they are epiphytic.
Lichens as suggested by you are a good example too. But according to my perception, the best examples are mycoheterotrophic plants (earlier known as saprophytes) are the best examples for monitoring health of a
terrestrial ecosystem. If the concerned plant is an Orchid then they need atleast three or more associates. FIRST, a MYCORRHIZA which will help the seed in germination. SECOND, another MYCORRHIZA that will
help it make connection with a host tree or shrub or herb to extract its food material. THIRD is the plant from which it will extract its food. So here FOUR different biological entities are envolved for the survival of this orchid. Please rememebr I am not counting those insects which will help in pollination of the orchid and at the same time i am not counting those organisms which will help in pollination (if required) of the host trees and also in fruit and seed dispersal.

You are right at a deep level..
but study of MYCORRHIZA would need dedicated lab etc…

but lichen colonies can be seen and detected by a lay man/woman even when just strolling thru a garden… for example… at the hort there is only one small are where lichen is present on the tree bark, and only in one third to a little more of the girth in one particular direction on those trees, regardless of the species… no where else
in the hort’s garden are there lichens? our ethnobot teacher many years ago … thought it must be the “clean” microclimate in that miniforest …
I was more interested in hormonal mimicry in the lichens in those days… so my notes only reflect that… not the environmental imperatives,,,cause and effect and hence the question…

BY the way.. I have not seen any orchids growing spontaneously on any of the trees at the hort… sometimes a dendrobium pops up on old mango or pepul trees in odd places, even road side… but never at the hort..wonder why…

Your questions could be answered by him only because i have no idea if he undertook the project or he is working on any aspect related to it. I have no idea if any other member is working on similar issues. I
work on orchids. Ask me about orchids and if I am unable to answer, then its my mistake.
As for my knowledge and head which never forgets, I remember of people working on the aspects of considering lichens as indicators a lot previously. But there is an issue. You consider a good Sal tree. Many
lichens will grow on it. But then somehow due to some reasons the tree dies but it still stands in the forest. Still you can see many more lichens growing on it, because the new ones like more light. Lichen grows on bare rocks to trees int he moist rain forests as well as in alpine areas where the Musk Deer feed on these lichens. Same thing goes to the orchids.
There are orchids on trees, you remove the canopy and the orchids will flourish more, they may not give flowers but if climate is moist, it grows luxuriantly in the availability of more light and cover the whole tree.
If I have to find an indicator then I will have to choose a or some particular taxa to sudy. I cant do it with all lichens or orchids.
Some plants are generalists where are some are very specific to their habitats. This habitat specificity is due to dependency on one or more than one associate species along with the climatic factors.
Hope I am understandable….