# Six Decades of Forest Inventory Data Highlight Decline of Sugar Maple (Acer saccharum) Sapling Abundance in Eastern Canada

## TL;DR

Sugar maple saplings in eastern Canada have declined significantly over six decades, likely due to increased American beech sapling abundance.

## Contribution

This study reveals a long-term decline in sugar maple saplings and identifies American beech as a key factor.

## Key findings

- Sugar maple sapling abundance decreased significantly between 1970 and 2022.
- American beech sapling abundance negatively affects sugar maple sapling abundance.
- Harvesting had no significant impact, suggesting other interventions may be needed.

## Abstract

Six decades of temporal changes in the abundance of sugar maple (
Acer saccharum
Marsh.) were investigated using a network of multi‐agency ground plots (MAGPlots) located across Ontario, Québec, and New Brunswick, Canada. Based on a composite dataset of nearly 400 plots mainly composed of sugar maple trees (≥ 50% basal area, m2 ha−1), results showed that the relative abundance (% total sapling basal area) of sugar maple saplings declined significantly over time. On average, the relative abundance of sugar maple saplings decreased significantly between 1970 and 2022. Out of a wide range of potential explanatory variables, including stand conditions, harvest intensity (0%–92% basal area removal), regional ecozones, and climate variables, the relative abundance of American beech (
Fagus grandifolia
Ehrh.) saplings was the only variable that had a negative effect on the relative abundance of sugar maple saplings. The plot‐specific distribution of change between the final and initial measurements over time revealed that many plots showing a decline in relative sugar maple sapling abundance also experienced an increase in relative American beech sapling abundance. The lack of differences between harvested and unharvested plots suggests that beech sapling control in the understory and soil liming treatments may be required to help promote sugar maple regeneration and development.

Approximate (±10 km) geographic location of the 390 plots among the Atlantic Highlands, Mixedwood Plains, and Boreal Shield ecozones of eastern Canada. Six decades of forest inventory data showed a significant decline in the relative abundance of sugar maple (
Acer saccharum
) saplings between 1970 and 2022.