First the American chestnut, then the elm.
Forest experts say New York will soon add another well-known species, the ash, to the list of trees nearly wiped out by aggressive insects and diseases imported from elsewhere.
"It's probably more realistic to ask when it's going to happen rather than if it's going to happen," said forest consultant Bruce Robinson.
Invasive species, such as the beetle that is gobbling up ash trees in nearby states, the virus that Niagara County growers fear will destroy certain fruit trees, and plants that crowd out competitors in forests and lakes, continue to alter area ecosystems.
These newer unwanted visitors join already established invaders, such as the zebra and quagga mussels that proliferate in area waters, the purple loosestrife that lines area roads, and Eurasian milfoil, an ornamental plant that has become ubiquitous in many area lakes.
The presence here of these organisms -- some based on land, some in the water -- is the byproduct of a world where goods and people move from one continent to another at an accelerated pace.
"We're a mobile society in a global economy," said Deborah I. Breth, with Cornell Cooperative Extension's Lake Ontario Regional Fruit Program. "That makes the pests have the potential for being global."
Breth is dealing with one such unwanted intruder, called plum pox virus.
The virus, which has already decimated orchards in Europe, was detected for the first time in New York -- and just the second time in the United States -- last summer in three trees in Niagara County. The virus is spread by small insects, and it attacks trees producing peaches, apricots, plums and nectarines.
Last summer's discovery prompted federal officials to quarantine the area where the trees are located. Plant matter cannot be transported out of the quarantine area, which includes parts of the towns of Wilson and Porter, nor may additional trees be planted in the area.
Breth said that the fruits from those trees, even from the quarantined areas, are perfectly safe for human consumption.
Although just three infected trees have been discovered, growers are concerned -- and for good reason, Breth said.
"It's very slow in developing, but once it gets in, you can't get it out," she said.
That's been the case with the emerald ash borer, an insect that has killed many of Michigan's ash trees and continues to affect ash trees in surrounding states. Last month, it was discovered in Pennsylvania.
Ash trees make up 5 percent to 10 percent of Western New York's forest stock, according to Robinson, who is urging all of his clients to harvest their ash trees before the borer's arrival here.
"The forest with the greatest impacts will be the green ash [and] silver maple stands across New York," he said. "It's a hugely important ecosystem, but it exists, and where it exists, it's going to be totaled."
The bottom line for many of these intruders is that once they are established, they become difficult -- if not impossible -- to remove.
The zebra mussels are a prime example. Brought here in the ballast water of trans-oceanic ships, they have colonized lake bottoms and shorelines and stripped the waters of micro-organisms that are at the base of the lakes' food chain.
"They've certainly changed the lakes from what they used to be," said Mike Goehle in the Buffalo office of the U.S. Fish & Wildlife Service.
There is potential for even more change in the lakes if the Asian carp, several species of aggressive fish with voracious appetites now clogging the Mississippi River basin, make their way any further north.
The fish, known to leap out of the water at unsuspecting boaters, are not believed to have advanced past a unique electrical barrier installed to stop them at a canal that connects the Illinois River to Lake Michigan.
But that barrier is nearing the end of its life span, and a more permanent one awaits activation.
The good news, according to Marc Gaden of the Great Lakes Fisheries Commission, is, "We're still ahead of the carp."
The bad news is the threat to the lakes is tremendous if the fish, known to eat almost continuously, make it past the barrier.
"Without that electrical barrier . . . it would basically be a straight shot from the Mississippi system into Lake Michigan," Gaden said.
There are connections between all of these events, said Anthony Ricciardi, a professor at McGill University who studies invasive species.
"This is the biological result of globalization," he said, noting that planes and ships crisscross the globe, often inadvertently carrying unwanted pests in ballast water and packing crates. "This is a form of human-induced global change."
Ricciardi is also studying how these newly introduced species interact with existing species and with other introduced species.
For instance, scientists now believe the botulism outbreaks that have killed thousands of birds along the lakes in recent years can be traced to the zebra and quagga mussel explosion.
"[The mussels] have created conditions for the [botulism] bacteria to thrive, and are accumulating the toxins," Ricciardi said.
The round goby, another invasive species, is one of the few fish species that consumes the mussels. The gobies become sluggish from the bacteria and are easy prey for waterfowl, which in turn are weakened by the bacteria to the point that they can no longer hold their heads up and drown.
"There is an example of the interaction between a couple of exotic species," Ricciardi said. "If you took out the round goby, most of this wouldn't happen."
That's why he said he believes there is a compounded benefit from keeping the next invasive species out.
"Even though we can't turn the tap off completely, we stand to benefit from every invader we keep out," he said.