The Forests

When we think about the forests prior to European settlement, we tend to think of the dense forests we are familiar with today, only with bigger trees. This tendency is based on the assumption that all the virgin forests back then were old growth forests because they were never harvested. While the majority of New Jersey was forested prior to European settlement, as was most of the eastern US, the virgin forests back then were very different from what we would have imagined. Early settlers reported open woodlands with 10-30 trees per acre in New Jersey. Long Island had large natural prairies and savannahs, and heath hens, a grassland-shrub-dependent bird now extinct, was abundant from Maryland to Massachusetts.

Forests in northern New Jersey have been dominated by oaks for about 10,000 years, as evidenced by concentrations of both charcoal and oak pollen in the soils in that timeframe. Frequent fires helped to keep oak forests as oak forests by killing shade-tolerant, thin-barked northern hardwoods such as maples. Before European settlement, fires likely occurred at least every 20-30 years in northern New Jersey which, coupled with hurricanes and beavers, helped shape the forest into a mosaic of multi-aged semi-open canopy forests, open-canopy and young forests/grasslands, and old growth hemlock forests. Today’s forest structure are mostly mature with a closed canopy.

Forest Structure	Pre-European Settlement	Today
Multi-cohort/Semi-open	25-40%	<11%
Open/Young	10-50%	8%
Old Growth	<7%	<1%
Closed-canopy Mature	3-58%	82%

With the suppression of fire and lack of forest management, most of the mature closed-canopy forests today have northern hardwoods such as maples growing in the understory instead of oak trees. If these oak forests are left alone to become old growth, without fire or other disturbances they will become northern hardwood forests after the oaks die and require at least another 100 years before becoming old growth forests. Opening the canopy will help regenerate oaks and promote biodiversity through a complexity of habitat types while perpetuating species that co-evolved with the ephemeral nature of stand replacement natural disturbances such as fires, beavers, and hurricanes, all of which helped shape the forests in northern New Jersey prior to European settlement.

Opening the forest canopy will also help these forests be more resilient in the face of climate change and invasive pests. Oak trees, which need ample sunlight to regenerate, are drought-resistant and fire-adapted and will be favored in future climate conditions. Northern hardwoods, on the other hand, are expected to decline in future climate conditions. Reducing the density of mature trees will also reduce their competition for moisture, nutrients, and light, allowing the remaining trees to be healthier, grow faster, and be more resistant to pests and pathogens.

The Birds

Another effect of fire suppression and lack of forest management is the lack of regenerating forests, also known as young forests or early successional forests. These shrubby areas within the forest are used by a large diversity of wildlife and are home to many songbirds, including the endangered Golden-winged Warbler (Vermivora chrysoptera).

In 2019 researchers from Cornell, American Bird Conservancy, and others published an article in Science (pdf, 2.7mb) about the 2.9 billion birds that have been lost in North America since 1970. Out of the 59 forest bird species that breed in New Jersey, 31 of them are declining, and 30 of those declining species either breed in open-canopy forests filled with shrubs, saplings, and herbaceous vegetation, or bring their chicks to open-canopy forests filled with shrubs and saplings after leaving the nest. The remaining 28 out of the 59 bird species that breed in New Jersey are increasing in number, and all but 3 of them breed in mature closed canopy forests. The top 5 species that breed in New Jersey with the greatest losses and increases are below:

Species	Breeding/Post-breeding Habitat	Percentage of Global Population Lost
Northern Bobwhite	Open Forest/Savannah	78.4%
Eastern Whip-poor-will	Open Forest/Savannah	69.0%
Cerulean Warbler	Mature Open Forest/Young Forest	68.7%
Golden-winged Warbler	Young Forest/Mature Open Forest	65.7%
Field Sparrow	Early Successional/Young Forest	63.6%
Species	Breeding/Post-breeding Habitat	Percentage of Global Population Gained
Red-shouldered Hawk	Mature Closed-canopy Forest	47.8%
Blue-headed Vireo	Mature Closed-canopy Forest	47.2%
Barred Owl	Mature Closed-canopy Forest	38.1%
Pileated Woodpecker	Mature Closed-canopy Forest	37.0%
Black-throated Blue Warbler	Mature Closed-canopy Forest	37.0%

Birds suffering the greatest losses like the eastern whip-poor-will, golden-winged warbler, cerulean warbler and field sparrow have all been observed in areas where the closed-canopy forest was extensively thinned via silviculture to make an open-canopy forest. Even birds associated with closed-canopy forests, such as the pileated woodpecker and red-shouldered hawk, are seen using these areas for breeding or foraging.

Opening the forest canopy to restore young forest habitat for wildlife can only be done through cutting a lot of trees, which then allows enough sunlight for new trees, especially those that can’t tolerate shade, to grow in addition to native grasses, shrubs, and blackberries. This restoration work may seem counter-intuitive but it has demonstrated an amazing positive impact on the birds in the area. Within a few years, the average number of bird species using the managed areas during the breeding season more than doubles, and the bird species of concern (rare and declining birds in New Jersey) more than triples the average number of bird species detected before management was done.