Collecting ash seeds this year may give the species a second chance
National Tree Seed Centre in Fredericton hopes to offset damage caused by emerald ash borer
The National Tree Seed Centre is asking the public to help it increase its collection of ash tree seeds this year.
Ash trees across Canada are threatened by the emerald ash borer, an invasive beetle initially found in Ontario in 2002 that has since made its way to the Maritimes. The beetle's first incursion into New Brunswick was in Edmundston in 2018, and it was found in Oromocto last month.
The tree seed centre is part of the Atlantic Forestry Centre of Natural Resources Canada in Fredericton. It serves as a seed bank for all tree species across the country.
Donnie McPhee, co-ordinator for the centre, said 2019 will be an important year for ash tree seed collection.
Black and white ash trees only produce seeds every five to seven years, while green ash trees produce seeds every year. This is because it takes a long time for trees to gather the resources to produce a healthy seed crop. It's also tied to an evolutionary tactic called predator satiation, where species will release seeds all at once to reduce the probability of an individual organism being eaten.
"Right across from Ontario through Nova Scotia the white ash and black ash are in seed this year," McPhee said. "That means it could be another five to seven years before we're going to see big ash population, seed populations in those trees.
"In five to seven years, emerald ash borer could have really exploded across the landscape, and I'm not saying too late, but we're going to have already lost a lot of genetic diversity and it'll be too late to get it into conservation storage."
McPhee said the goal of an intensive seed collection this year is to help revitalize the population once the insect is gone. To do that, the centre needs help from the public.
"We're a very small department and we're into collaborating with the general public, with parks, provincial agencies and governments to get as many ash populations into conservation as possible."
People who suspect they have a healthy ash population should check the tree seed centre's website for information on tree identification and seed harvesting.
Once they've determined that, McPhee said, they should contact the centre to co-ordinate gathering efforts.
There are three main species of ash in the Maritimes.
Black ash trees grow in swampy areas and are an important natural resource for First Nations communities. White ash are often planted in cities and are probably the most recognizable of the species. Green ash grow along riverbanks and help prevent erosion.
McPhee said it can be difficult for an untrained eye to tell the difference between an ash tree and some other species, but the seeds are the most identifiable.
Ash seeds grow in clusters on the branch and are long and thin, covered by a flat green sheath called a samara.
The best way to tell if a tree's seeds are healthy is by cutting the top off. If you see a white seed, it's healthy, where a brown seed or empty pod means it is not.
McPhee said the centre's collection of ash tree seeds from Ontario is relatively healthy because samples have been collected since the beetle arrived. However, there are few ash trees left in that province now, so this year may be the last opportunity to gather seeds in places where none have been collected.
There is less of a bank built up for trees in the Maritimes because no one predicted how quickly the beetle would arrive to the region.
"It should have taken 1,000 years by natural conditions for that insect to get here and all of a sudden in two or three years it's being transported by humans," he said.
Harvesting and storing
Seeds are harvested by using pole pruners or extendable clippers. McPhee said his team is sometimes called in to take samples when a park is cutting down an infested tree.
"A lot of times when a tree is initially infested by an insect … it'll put out a big effort into seed because it knows it's going to die," he said.
Ash seeds must mature on the tree. They turn from green to brown when they are ready to be harvested. For black ash that is around mid-September, and for white and green it is mid-October.
"If you see seed falling to the ground before this time it just usually means that the seed wasn't good in the first place."
Once the centre has the seeds, they are cleaned, dried to seven per cent moisture content, vacuum-sealed and stored at –20 C.
McPhee said a diverse seed collection is important because while the seeds from one area may look the same as those from another, they are adapted to different environments.
"When we go back to replant, we need to plant seedlings back to where they came from originally."
Eventually, the beetle will wipe out the ash population to the point where it no longer has enough food and the beetle population will shrink, McPhee said.
Once that happens, conservationists can gradually begin replanting the trees.
"Any trees that are developing now are going to be just fodder for emerald ash borer," he said.
"Our focus is 30, 40 years down the road that we have the genetic diversity of the species in conservation to go back and replant after the emerald ash borer is gone."