HISTORY, COMPOSITION AND STRUCTURE IN MATURE SECOND-GROWTH ACADIAN FOREST STANDS MANAGED WITH IRREGULAR SHELTERWOOD SILVICULTURE

HISTORY, COMPOSITION AND STRUCTURE IN MATURE SECOND-GROWTH ACADIAN FOREST STANDS MANAGED WITH IRREGULAR SHELTERWOOD SILVICULTURE

By Nalbert T. Tero

Thesis Advisor: Dr. Robert S. Seymour

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Forest Resources)

August, 2010

Harvesting wood, while maintaining natural forest structure and biodiversity, is a difficult tradeoff in forest management. Cutting methods based on patterns of tree mortality in natural, old-growth forest have been proposed to avoid this conflict. In Maine’s Northern forest, studies in old-growth show mortality patterns dominated by deaths of one or a few canopy trees at a time, leading to complex multi-aged forest structures. In Baxter State Park, Maine, managers have begun harvesting trees in some stands with a system that resembles these small-scale events. We investigated the ages and structures of these stands to evaluate the outcomes of their work.

We paired managed stands with unmanaged benchmarks. Benchmarks had not been cut since the sawlog harvesting in this region in the 19^th century. Managed stands had been entered 15-20 years ago with ‘establishment cutting’ to harvest mature trees and open space for seedlings and saplings to develop. More recently, groups of trees were removed from the stands in ways that created discrete gaps that approximated patterns of old-growth tree mortality

Benchmark stands had multi-aged population structures dominated by two large groups of trees which established at different times: the first after harvesting during the late 19^th century, and the second following the 1913-1919 outbreak of spruce budworm (Choristoneura fumiferana Clem.). Although these two cohorts dominated tree populations, trees established in nearly all decades from 1870 onwards, indicating that overstory tree mortality is a common occurrence. In the managed stands a recent group indicates that establishment cutting allowed new trees to establish. But the older age classes were much reduced, probably because they were preferentially removed during cutting.

We found no difference in species composition between harvested and benchmark stands, but both harvests affected stand structure. Establishment cutting reduced total volume of trees while preserving standing dead trees and adding small dead wood, and allowed seedlings and saplings in the stands to grow. Gap creation removed all standing dead trees while leaving only scattered living trees. The taller saplings in gaps were damaged. Harvest gaps were much larger than natural treefall gaps, though, so natural conditions were not perfectly recreated.