is the canonical age that the Talmud fixes for man, meaning that from that age on reason is completely formed; 
St. Augustin indicated in forty the product of 4 (= time) and 10 (= knowledge): 'forty' teaches therefore to live in coherence to knowledge; 
and, what is more, it took Moses forty years, after first engraving the 10 commandments on a stone slab, to deliver the Torah rolls that he wrote during the exodus through the desert. 
At Stonehenge forty stone blocks are used as columns in a circle forty paces wide, alluding  to  an astral origin. (6)

 
This is a famous symbol in ancient religions of India (Veda) and Mesopotamia (Zohar), signifying the emanation of divinity in all things living. Often it is imagined upside down with its roots in heaven and its branches on earth. Much mystification has developed around such sacred texts and its supposed benevolent influences, as in the movement of  "The Golden Dawn"  which doesn't interest us really in this pages. Even then some positive effects can be found in the net. 

I suggest this  "Tree of Life"  site,  it offers an interesting biological taxonomy: 

http://ag.arizona.edu/tree/phylogeny.html 
See also: 
http://geocities.datacellar.net/Athens/9574/kabbalah.html 
 

 Celan mentions, in his poem,  40 trunks, remnants of trees of life and as it is known that the jewish poet, amongst the different meanings of his texts, always includes the reflection about the distance between words and names, the first being  directly accessible to the senses, the other indirectly pointing at the mystical name of God, the forty trunks are in this sense forty words on the way to become names in a poem. Are there perhaps forty religions in the world as a further allusion? 

The tree of life corresponds to the 10 Sefiroth of the  Cabbala , presented as a  tree, "a tree with many branches and bearing many different fruits", the Otz Chimm, the upside down tree with its roots in En soph, the divine light, as mentioned in the Zohar  "The tree of life is extended from the top till the bottom and the sun illuminates it entirely". 
(auriel@primenet ) 

Explains the french anthropologist Gilbert Durand: 
 

"The cosmic tree of the Upanishads (The Katha-Upanishad cites: "This eternal Ashvattha,  whose roots ascend and whose roots reach down, is the pure, is the Brahma; the Brahma  is the one that is named the non death", my note)... stretches its roots in the sky and stretches its branches on earth. The image of the upside down tree can be found in the sabea tradition (yemenite civilization, V.th-I.st cent. b.C, my note), in the sepharoth  esoterism, in Islam, in Dante as well as in certain rites of the laps, australians and islanders. "(7)
At "Auriel Cabbala", where we find the following, that will help to explain the 'skinning' of the trees: 
 
"The tree of life has 10 concentric rings, the outer ring representing the forms of earthly life or klippoth.  The word "qlippah " or "klippah " (plural "qlippoth ") means 
"shell" or "husk". The idea of a covering or a garment or a vessel is common in Cabbala, where it is used, at various times and with various degrees of subtlety, to express the manner in which the light of the En Soph  is "encapsulated". For example, the Sefiroth , in their capacity of recipients of light, are sometimes referred to as kelim  , "vessels". The duality between the container and the contained is one of the most important in Cabalistic explanations of the creative moment. The word "qlippah " is an extension of this metaphor. A qlippah  is also a covering or a container, and as each sephira  acts as a shell or covering to the sephira  preceding it in the order of emanation, in a technical sense we can say the qlippoth  are innate to the Tree of Life.  Cut a slice through a tree and one can see the growth rings, with the bark on the outside. The Tree of Life has 10 concentric rings, and sometimes the qlippah is equated to the bark. The word is commonly used to refer to a covering which contains no light: that is, an empty shell, a dead husk...... The "Zohar  " attributes the primary cause of evil to the act of separation. The act of separation is referred to as the "cutting of the shoots". What was united becomes divided, and the boundary between one thing and another can be regarded as a shell. The primary separation was the division between the Tree of Life (Pillar of Mercy) from the Tree of Knowledge (Pillar of Severity). In normal perception the world is clearly characterized by divisions between one thing and another, and in this technical sense one could say that we are immersed in a world of shells. The shells, taken by themselves as an abstraction divorced from the original, undivided light (making another separation!), are the dead residue of manifestation, and can be identified with dead skin, hair, bark, sea shells, or shit. They have been referred to as the dregs remaining in a glass of wine, or as the residue left after refining gold. According to Scholem, the Zohar interprets evil as "the residue or refuse of the hidden life's organic process"; evil is something which is dead, but comes to life because a spark of God falls on it; by itself it is simply the dead residue of life. The skeleton is the archetypal shell. By itself it is a dead thing, but infuse it with a spark of life and it becomes a numinous and instantly recognizable manifestation of metaphysical evil. The shell is one of the most common horror themes; take a mask, or a doll, or any dead representation of a living thing, shine a light out of its eyes, and becomes a thing of evil intent. The powers of evil appear in the shape of the animate dead - skulls, bones, zombies, vampires, phantasms." (cited from Colin Low) 
More about the Cabbala at: 
http://www.digital-brilliance.com/kab/faq.htm<

 the forty trees are abandoned in the flow of history and they will eventually end in the ocean, which is, as Sternberger writes, like the Talmud 'vast and deep'. (8)

 
to 'count' means here, as I see it, that the exploration is done in a scientific quantitative way. 
Celan tells us here that he, though a poet, gives utmost importance to facts and the objective analysis of them. But the search is also conducted in another, alternative way 'touching' its objects, approaching them with poetic sensitivity, with feeling. 
The poem states in an obscure way, the only way explains Walter Benjamin, that the essence of poetry is the revelation of the abyss of truth and that it can achieve this only by showing the hidden depth of words and sounds and their flow of infinite possible combinations. We hide however this , sometimes unbearable, truth on a subconscious level and, worse, we use our conscious intelligence to defend us from it. Walter Benjamin calls this function the "reizschutz", the protection from irritation". Not everything is lost however because we registrar traces of  it in what Marcel Proust has called the "mémoire involontaire".(9) Benjamin in his so called "shock theory"  states that properly apparently meaningless details like amorphous fractions, parts of objects, voids between sensations, absurdities,  act as signs that can reveal shockingly utterly unexpected and therefore true allegorical meanings 

(I due time I will enter here an "embedded object" to actually let you hear the rhythm.) 

We can connect the notion of prosodic rhythm with modularity in architecture and design.