Deciduous Woodlands

Paper birch (Betula papyrifera), quaking aspen (Populus tremuloides) and black cottonwood (Populus balsamifera) stands form the canopy over deciduous woodlands at MPG North. Healthy aspen stands propagate multi-aged tree colonies from root sprouts of a single underground clone. Young and middle-aged saplings provide energy for the clone as older trees fade and die. Birch and cottonwood communities arise after disturbance events. Stands of these species comprise many separate individuals that emerged from seeds. Depending on soil composition and disturbance regimes, the understory in healthy deciduous woodlands supports multiple shrub and herbaceous layers or a simple herbaceous layer.

Healthy deciduous woodlands and their shrub understories at MPG North support a diverse avian community, and ungulates depend on young shoots for nutrition. Healthy stands grow fast enough to compensate for ungulate browsing and damage from antler rubbing. Over time, stem density and size further reduces ungulate damage.

Unhealthy conditions arise in deciduous woodlands when disproportionate ungulate browsing reduces sapling recruitment. These conditions produce a "recruitment gap" where all stems belong to a single older age class. Conifer encroachment and increased canopy closure results until the deciduous trees and understory shrubs die out. Alterations to typical disturbance events (fire suppression and flood control, for example) allow closed conifer forests to persist and deciduous woodland habitat declines.

The desired future condition of unhealthy deciduous woodland habitat at MPG North is multi-aged stands of deciduous trees with sufficient density to facilitate expansion despite browsing and other damage by ungulates. We use fences or "exclosures" to keep ungulates out for a time and allow the stands to recover. Hand planting of deciduous species supplements stem numbers in areas with poor recruitment. Managed disturbance events like prescribed fire, soil surface scarification and conifer thinning will encourage deciduous woodland expansion after the exclosures are removed.

Upon discovering bronze birch borers in the crowns of dying paper birch trees last summer we began efforts to control the beetles. We applied insecticidal tree implants and ground coverings to reduce water stress. We searched for relationships between environmental conditions and the degree of damage to the trees. The relevance of the findings to future actions is discussed in this report.


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