The REPLANT Act, which was introduced in July 2020, provides money for the US Forest Service to plant more than a billion trees in the next nine years.
The World Economic Forum also aims to help plant a trillion trees around the world by 2030 in an effort to soak up some of the excess carbon dioxide in the Earth's atmosphere.
But a University of Vermont (UVM) study has found that US tree nurseries don't grow nearly enough trees or have the species diversity needed to meet the ambitious plans.
"Trees are this amazing natural solution to a lot of our challenges, including climate change. We urgently need to plant many millions of them," said UVM scientist Tony D'Amato, who co-led the new research. "But what this paper points out is that we are woefully underserved by any kind of regional or national scale inventory of seedlings to get the job done."
The team studied 605 plant nurseries across 20 northern states. Only 56 of these grow and sell seedlings in the volumes needed for conservation and reforestation, and only 14 of them were found to be government-operated.
They also discovered an "overwhelming scarcity of seedlings" from different species and "seed collection zones", which are trees adapted to local conditions and climate.
Forest nurseries tended to maintain a limited inventory of a select few species, electing to prioritise those valued for commercial timber production over species required for conservation, ecological restoration or climate adaptation.
Many areas had no locally adapted tree stock available and, within the seedlings available, there were not enough types of trees and "future-climate-suitable" genetics to meet goals for conservation and forest restoration in a hot future.
"The world is thinking about a warming climate – can we plant towards that warming climate? We know we're losing ecologically important species across North America and around the world. So, the goal is: can we restore these trees or replace them with similar species? It's a powerful idea," said UVM's Peter Clark, lead author of the study.
"But despite the excitement and novelty of that idea in many policy and philanthropy circles, when push comes to shove, it's very challenging on the ground to actually find either the species or the seed sources needed."
Red spruce, for example, is an ecologically important species that lies along hundreds of miles of eastern North America. It has been under stress from climate change, pests and land clearing for decades.
In their survey, the team only found two tree nurseries that had inventory of red spruce – a species from which many millions of seedlings are needed to meet restoration goals.
The team argues that dramatic increases in both seedling production and diversity at many regional nurseries will be central to any successful campaign to address climate change with tree planting.
The study calls for expanded federal and state investment to boost both public tree nurseries and seed collection efforts, which could boost production from private nurseries once a stable demand is secure.
In 2023, the federal government made an investment of $35m (£27m) in expanding federal nursery capacity.
"However, given the existing (and growing) reforestation backlog, declines in nursery infrastructure and complex needs for diverse seeds and seedlings, it is likely that substantially more public investment in the form of grants, loans and cost-share programs will be needed to reinvigorate, diversify and expand forest nurseries," the study states.
