Gareth Evans: Oi! Who are you calling shorty?

Don't be sizest about your movies, says Gareth Evans, short films are still up there with the best

My first memories of going to the cinema involve a short film. The place was the cavernous single-screen Embassy picturehouse in Harpenden. It wasn't a matinee cartoon or Disney featurette, a newsreel or Children's Film Foundation outing. Instead, it was about a black bull being winched aboard an open fishing boat off the Scottish coast. This creature, the titular "Duna Bull" (as I remember it), was making the rounds of the islands for reasons of insemination, and the short documentary – part of a mixed supporting package for the main feature (long since forgotten) – followed the animal on its work.

I will never forget the image of this jet-black bull hanging in space between quayside and vessel. It seems, in a quietly pivotal way, to contain the essence of cinema and its raisons d'être. It revealed something previously unseen (to me at least), it located its subject in the material world without removing its mystery. It generated a brief intimacy while simultaneously suggesting great scale, great stories only glimpsed. And, as a neat dovetail with the chronology of cinema itself, it seeded my encounter with film at a scale that is the medium's founding one. After all, shorts are cinema. They were its birth, when the Lumière Brothers' train arrived on screen. Then came Meliés' man in the moon, the first appearance of Mickey Mouse, Un Chien Andalou, the chilling footage of the Warsaw Ghetto (or Alain Resnais' Night and Fog), Humphrey Jennings' Night Mail, La Jetée, Kenneth Anger's Scorpio Rising, Jack Smith's Flaming Creatures, right up to The Simpsons.

And so it goes, a lineage of constant exploration. However, considered now, my memory signals the moment (the early Seventies) when most viewers' experience of short films as openers to the movie itself began to be threatened by changing policies in theatrical programming. This struck a body blow to widespread viewing of short film from which we have only recently recovered. But this shift can be seen as much more than mere recuperation. An entire short-film industry is now acting globally to generate new products – from supporting acts through to internet-based work.

Many factors have contributed to this filmic fecundity, including the development of the music promo, the generally forbidding cost of full-length production and the attendant need for "calling card" evidence of talent. Which is not to claim that shorts are technical exercises notable only for the promise they suggest will be realised later. Consider short films by Martin Scorsese, Lynne Ramsay, David Lynch, Roman Polanski and Jane Campion for evidence of achievements within the form by directors famed more for features.

In Britain, the short film has a particular and gleaming tradition. It has always felt most at ease with a heightened realism. The social world is there but filtered through personal stories, impacted lives and domestic spaces rather than in grand, unanchored gestures of empowerment and betrayal. This creative lifting of daily business into empathetic and imagined realms of fine attention is exemplified by the "childhood" trilogies of Bill Douglas (1972-78) and Terrence Davies (1974-83). They imbue their triptych narratives of hard lives and losses with singular authorial intensity.

For Douglas, the setting is the Scottish mining village of Newcraighall in the 1940s. The memories are hard and unflinching, but the scenes in My Childhood, My Ain Folk and My Way Home, delivered in stark monochrome, keep sentimentality at bay and provide an enduring document of lives too often overlooked.

For Davies, the milieu is urban, working-class Liverpool, but add in the spiritual confusions engendered when Catholicism meets an emergent gay identity and the journey of protagonist Robert Tucker through Children, Madonna and Child and Death and Transfiguration becomes a stirring account of dignity quietly triumphant, observed in a way that is exacting, occasionally surreal and finally transcendent.

Screen these masterpieces of memory alongside the Borgesian structures and artifices of Peter Greenaway and it would be hard to believe that these directors hail from the same celluloid islands. However, the latter's idiosyncratic reels are in their own way as British as those by Douglas or Davies. His dry and mordant wit and strong strain of landscape romanticism, evident in works like A Walk Through H, Vertical Features Remake and Water Wrackets, support a vision of the world quite as compelling as their more explicitly realist approaches.

These three directors all benefited enormously from imaginative public funding. There is still money in the coffers, but institutional support structures have altered considerably. Now a latte lounge is as likely to host a video projection of scattergun titles, missives from the first minutes of the future, as any recognisable "cinema".

The internet has spawned demented and entirely unpredictable additions to the genre, shards thrown up, as it were, by the machinery itself. At Sheffield's Lovebytes Media Art Festival this year, Ben Slater and Jon Harrison presented "Search Engine Cinema", a subversive, often no-budget trawl through the subcultural fringes of the system, taking in Hungarian remakes of Star Wars, dynamited whale carcasses and the delights of tofu shooting ranges.

These pieces proved fragile and often insubstantial, yet somehow terribly poignant. And shorts, in their proximity to the sketch or notebook entry, reveal a similar vulnerability and hope. Inevitably they can only aspire, only suggest, but in this lies their continued strength.

'Brief Encounters: Bristol International Short Film Festival', Watershed and Arnolfini, Bristol (0117 927 5100/0117 929 9191) Wednesday to 24 November. 'In Short: a guide to short film-making in the digital age', is published by the BFI