After taking a break during the recession, gentrification is back with a vengeance in Greater Boston, as middle-class capes and ranches get bulldozed in increasing numbers to make room for ever-larger homes.

The number of teardowns is on the rise again, with some key western suburbs on track for dozens over the coming year. It’s a trend that may mark the beginning of modest-sized, middle-class homes in increasingly affluent communities like Lexington and Needham.

And in a part of the country where broadly affordable housing is scarce, this can’t be good news. But it’s a trend for which there is no easy solution, with larger economic forces at work.

Changing Economy, Changing Market

Overall, Greater Boston has seen a steady and at times stealthy transition over the past three decades from a blue-collar economy to a white-collar one in which research and finance are king, not manufacturing.

And the magnitude of the changes for the local housing market – seen in the wave of teardowns – is just now becoming glaringly obvious in the suburbs.

The first hints that something was changing came back in the 1990s, amid furor over what were quickly dubbed McMansions – outsized new homes in older neighborhoods of more modest, post-war homes.

At the time, it was a startlingly new phenomenon, more easily dismissed then as an explosion of bad taste driven by new wealth derived from the stock market and the high-tech world.

But that shock value has faded over the years, and teardowns, after dipping during the recession, are rising relentlessly once again.

Lexington is on track for more than 60 teardowns this year, a marked increase from 34 back in 2010, when the real estate market was in the doldrums. Meanwhile, Needham saw 82 teardowns last year. Newton (58) and Wellesley (48) also recorded sizeable increases from the recession years. Concord is seeing an uptick as well, with 21 last year, according to demolition permits filed with the towns.

One factor clearly driving the surge is a scarcity of land for new construction, with available land either already built up or under conservation restrictions.

In towns like Lexington and Wellesley and Newton, teardowns have become the norm when it comes to new construction, with single-family construction on undeveloped lots now the exception, not the rule.

Aggravating matters, new home construction – especially new subdivisions – has been on the decline now for decades in the Boston area. That, in turn, has forced buyers to compete for a largely aging pool of homes, or, if they are wealthy enough, shell out $1 million or more for a new house where an old one once stood.

But the bigger factor is growing wealth. Greater Boston’s booming biotech and high-tech sectors are steadily importing highly paid talent, with salaries big enough to buy the kind of homes they want – big, shiny and new.

Middle-Class Squeeze

It makes sense that new homebuyers would have little appetite for fixing up and old cape or ranch when they may have been living in a 4,000-square-foot colonial somewhere else.

Nor is it just the 1950s-era capes biting the dust – one prominent Lexington builder recently shelled out over $800,000 for a nice looking split-level that he promptly tore down. In its place he’s building a $3 million, 6,000-square-foot house for a wealthy buyer.

What’s being lost here is the broad middle of the housing market in these towns – the older $400,000 to $600,000 house in need of some work.

But even these “modest” prices are a stretch for many buyers. And the number of families that can afford the homes taking their place, routinely priced at more than $1 million, is much smaller.

And of course, there are the ripple effects. Middle-class buyers, squeezed out of towns like Needham and Lexington, are in turn bidding up home prices in other more affordable, middle-class communities across the western and southern suburbs.

So what’s to be done?

The debut of the McMansion back in the 1990s sparked a backlash in a number of Boston suburbs, but practically speaking, whatever rules resulted have proven to be ineffective.

Needham imposed restrictions, but exempted lots of 10,000 square feet and smaller. Wellesley imposed a review system, but reserved it for monstrously sized homes. Builders quickly learned to build around whatever restrictions were put into place, while townspeople, worried about hurting their own property values, left too many loopholes.

But it’s not clear that town officials, even if they had the will to do so, could stop this trend.

We are dealing with much larger, historic forces that are transforming some markets, including Greater Boston, New York, Washington and San Francisco, into elite hubs in our increasingly knowledge-based, innovation-driven economy.

That’s driving up real estate prices and putting the squeeze on middle-class buyers everywhere.

Sadly, teardowns are here to stay, putting capes, ranches and other modestly sized homes on the list of endangered species in our more affluent ’burbs.