ZARUJA, Portugal — This is a land that has seen its enemy, and he drinks red wine from a screwcap bottle.

For this is cork country. Silvery green cork oaks dot the dry, straw-colored landscape. Factories for trimming, boiling and binding cork into bundles surround the whitewashed villages. The free-ranging hogs that yield the region's characteristic hams and sausages fatten on cork oak acorns. Corks pop from bottles of the local Alentejo wines that wash down virtually every meal. Local entrepreneurs hand out business cards with their names printed on slivers of cork.

Cork, cork and more cork has brought a measure of prosperity to what has otherwise been a dirt-poor region of south-central Portugal.

Teresa Ortigão Ramos, a diminutive, silver-haired woman who is descended from the counts of Galveias, invites a visitor into a chapel on her property that is lined with votive paintings depicting the ordinary lives of local cork growers, the earliest from the mid-18th century, about the time her family settled here. That was only a century or so after a French monk, Dom Pérignon, first plugged a round piece of cork into a bottle of bubbly. Before that, wine bottles were stopped with things like cloth and wooden pegs.

Just how many cork trees does she have? "Thousands," she replied. "I should know. But I don't."

Eduardo Silva, 61, the manager of her lands, estimates that there are roughly 49,000 of them on about 1,700 acres.

"Here in this village, we always had cork factories, so starvation was never so deep as elsewhere," he said later over a lunch of boiled meats, cabbage and potatoes — and, of course, an Alentejo region wine topped with natural cork. Tugging his mustache, he added: "I don't understand why we're not in paradise: good wine, good weather, good cork."

Indeed, cork arguably is to Portugal what crude oil is to Saudi Arabia.

More than half of the $2 billion worth of corks produced every year originate here; nearly all the rest comes from nearby Mediterranean countries. Scrap cork goes to making floor coverings, insulation and the like. Roughly 16,000 Portuguese work in the industry.

But as the global wine industry has grown, so has the spread of stoppers like screwcaps and plastic corks.

Natural corks sometimes leak, sometimes crumble. They can impart a musty odor, called cork taint, spoiling the wines they are there to protect. They are also getting expensive. In the last five years, Mr. Silva said, raw cork has gone from $41 or less for a standard 33-pound bundle to as much as $58.

So wine growers in Australia, California and even premier regions of France, like Bordeaux, are resorting to alternatives. In Switzerland, half the wine is now sold without natural corks.

The battle lines between the cork producers and their rivals are clearly drawn.

On Web sites and in professional journals, the screwcap industry points up natural cork's shortcomings. Blind taste tests and consumer surveys showing a preference for — or at least lack of hostility to — the screwcap are highlighted.

The cork manufacturers have been equally busy picking at the makers of screwcaps and pressing their own case. When the Australian Wine Research Institute recently found that rubbery odors in bottled white wines were more notable in screwcap bottles than those with corks, for example, the cork manufacturers trumpeted the results.

Cork people also accuse the screwcap people of spreading lies — for example, that harvesting cork bark kills the trees, which it does not. In fact, they say, if cork forests die out because demand for cork drops, ecological disaster will befall the cork-growing regions.

Both sides snipe at the synthetic-cork makers, saying their products are hard to extract from bottles and may impart a chemical taste to wines. And the plastic-cork makers echo the criticisms of natural corks, but say that wine lovers want their bottles to open with a pop, not a twist.