According to biological theory all properly drained lands left to themselves will eventually become forested as the final phase of ecological succession. It is not the whole story as forests do change overtime but for now it will do.

Cryptoforests are:
1) Feral forests (Planted tree zones, for instance along motorways, that have been allowed to become wild to the point that their wildness is outgrowing their manmadeness.)
2) In limbo forests (Tree-covered plots that feel like forests but technically probably aren't; states of vegetation for which lay-language has no name.)
3) Incognito Forests (Forests that have gone cryptic and are almost invisible, forests in camouflage, forests with a talent for being ignored.)
4) Precognitive forests (Lands that are on the brink of becoming forested, a future forest fata morgana.)
5) Unappreciated forests (Forests regarded as zones of waste and weed, forests shaming planners, developers, and the neighbourhood. NIMBY forestry.)
But! Based on personal observation, these are pointers only, not universally valid guidelines. The cryptoforest is a cultural and not a biological way to classify nature and the recognition of a cryptoforest is a visionary act, not a mechanical operation: there is no machine vision here. In this respect the 'cryptoforest' is no different from common, but ultimately ambiguous, terms like 'weed' or 'forest'. One UN forestry position paper (1) reports finding 950 different definitions for forest, some legal, some biological, some practical, some counter-intuitive, none of them trivial. According to some definitions a suburb can double as a lush jungle and according to others a forest doesn't need to contain a single tree. The etymology of the words 'forest' is instructive, it is derived from the Medieval Latin 'forestis (silva)' or 'outside (woods)':  a forest is a wood (silva itself via 'silvaticor' leading to the word 'savage') of exclusively use to the crown, it's a kingdom inside a kingdom, a box inside a box with a licensed-to-kill royal guard at the gate. The 'for' of 'forest' reappears in 'foreigner', the forest, in other words, is a Neolithic twilight zone where social stratification is coloured green on the map. These old connotations carry over, laterally, into the cryptoforest project. Cryptoforests are social rejects, urban outsiders and cryptoforestry is an anarchic and primitivist 'art brut'. 

In the first use of the word cryptoforests named fallowed islands of uncivilization that could serve as seeds and catalysts for full urban afforestation, but that is superficial thinking right there. The entire city is already a cryptoforest on the rebound. It might not casually show but the forest is right here, in the cracks between the pavement, waiting for an opportunity to break free. Weeds accept no authority and I have counted 15 different species of plants growing through the paving of a pool that had been waterless for three months, that's almost a complete bioregional botanic garden for free. Alejo Carpentier writes about 'the worm', a speculative force threatening every city in the rainforest. At the moment the city stops to resist this force it will be composted in days. "Something like a baleful pollen in the air - a ghost pollen - impalpable rot, enveloping decay - suddenly became active with mysterious design, opening what was closed, closing what was opened, upsetting calculations, contradicting specific gravity, making guarantees worthless. One morning the ampoules of serum in hospital were found to be full of mould; precision instruments were not registering correctly; certain liquors began to bubble in the bottle; the Rubens in the National Museum was attacked by an unknown parasite immune to sprays." The cryptoforest shows that this power is also present in moderate climates, with less brute force with but with equal stubbornness.

Cryptoforests are those parts of the city in which ‘nature’, in 'secret', has been given the space and the time to create its own millennia-millennia-old, everyday-everyday-new order mysteries by using the materials (seeds, roots, nutrients, soil conditions, waste, architectural debris) and conditions (urban micro-climates, soils, pollution) at hand. Cryptoforests are sideways glances at post-crash landscapes, diagrammatic enclaves through which future forest cities reveal their first shadows, laboratories for dada-do-nothingness, wild-type vegetable free states, enigma machines of uncivilized imagination, psychogeographical camera obscuras of primal fear and wanton desire, relay stations of lost ecological and psychological states. Cryptoforests are wild weed-systems, but wildness is equated not with chaos but with productiveness at a non-human level of organization. Citoyen: the diminutive cathedral effect of the high forest is absent in the cryptoforest, long live the cryptoforest. What starts with weed ends with a cryptoforest, and in between there is survivalism, with plants eking out a living against all odds, slowly but determinedly creating the conditions for the emergence of a network of biological relationships that is both flexible and stubborn, unique and redundant, fragile and resilient. Cryptoforests are honey pots for creatures that have no other place to go. Animals live there, the poor forage there, nomads camp there and the cryptoforester who has renounced the central planning commission re-creates there (free after Henri Thoreau). In the future, young people will no longer want to play in bands and they will become guerrilla gardeners and cryptoforesters instead.

Psychologically the forest has always been an upsetting force, a place of oppressing loneliness and deep silence, a territory of unspeakable dangers and dark secrets; it is where the witches live and the outlaws hide and where, following Joseph Conrad, an implacable force broods over inscrutable intentions. The ruined clear cut landscapes of the West have deprived us of truly understanding a part of our own selves. The cryptoforest is its own psychological category, a synthetic mind-state all its own. The fallow is a living landscape, the 'edible city' is already eaten and the cryptoforest is a lacuna managed by indifference and inability. Trails appear out of nowhere and reach into nothingness. Lone tents and make-shift pseudo-forest-Eskimo dwellings of the type Ray Mears shows you how to make on the Discovery Channel are often to be found and its anonymous occupants, you never find them at home, leave huge piles of garbage and their defecation attracts clouds of buzzing flies. I have the pictures to prove it. It is said that agriculture started with the observation that many desired species of plants and trees appeared near 'dumpheaps'. Waste is everywhere, brought in by the wind or illegally dumped. All year round people come in to collect wood and chop down trees for camp-fires. Some level of maintenance may be in process, perhaps once a year a cryptoforest is checked for dangerous situations or possible damage to fences or cables; perhaps soil samples are collected every three months; perhaps the grass is partly mowed. Hey, where does that spade suddenly come from? Total neglect, in our boorish nanny-state societies, can only exist under supervision. Stressing the cryptoforest as a zone of non-human independence would turn reality into a Ballardian garden fiction. The cryptoforest is the non-intentional artefact of the city, the semi-domesticate aura of Hercynia.

The cardinal rule of cryptoforestry is that you can't search for a cryptoforest. You stumble upon them, they are already right in front of you, you find them when you get lost or when you are on your way to an area where you suspect you will find one (but don’t). This is not me being pedantic: it is just how it is. A cryptoforest always appears larger from the inside than from the outside. Again this is not a mysticism but based on the realities of the sensory apparatus. With trees blocking your view and the horizon barred from view the natural tendency is to underestimate distance and the Cryptoforest appears vast. It takes determination to enter a cryptoforest, to find your way through a dense thicket, on a small, steep slope along one of the busiest motorways in the country, there is no trail, unsure where you will end up, every wrong step may snap your ankle, derelict gloom confronts you, travelling back to the end of tourism, spider webs glued to your forehead, your face plastered with sticky forest sweat, microscopic gnats crash into your forehead, thorns rip your clothes, nettles attack your bare skin and, no, you best not worry too much about that bloodsucking dementor of the cryptoforest: the tick. You will be scratching your back for the rest of the afternoon but it is as the Fight-The-Google-Jugend savage said: "don't come here and complain to us about the mosquitoes, go back to your air-conditioned room and stay there!" The cryptoforest is not there to entertain us, and the insects and the various thorny bushes are its first line of defence against intruders. The insects are an obvious source of discomfort and a good population of them will shy away any half-hearted visitor. The aggressive, immensely fast growing blackberry, its dense clutter of branches spiked with long painful thorns are an underrated architectonic force creating pathways and blocking access to the backstage of the Cryptoforest. The willingness to confront these obstacles with a sense of good humour is the litmus test for any aspiring cryptoforester. If you are ready to confront the cryptoforest on its own terms, if you are ready to become a 'practitioner of the wild' (after Gary Snyder), you will find that all cryptoforests offer a unique experience that can translate into an ethical and artistic proposition. Find them, enter them, take your friends there, be careful, become a native. You never know what you will find. A cryptoforest is the only nature that does not need protecting.