Emile DeVito asked that we post this to the stewardship roundtable. A pdf version of the signed letter can be found by clicking here. Feel free to comment!
July 2, 2012
Mr. Richard Boornazian
Assistant Commissioner for Natural Resources
Department of Environmental Protection
401 East State Street
P.O. Box 402
Trenton, New Jersey 08625-0402
You had asked Michele Byers if I would forward my thoughts regarding habitat restoration at Bull’s Island.
I would like to preface my comments by placing the Bull’s Island project in context. New Jersey Conservation Foundation has been advocating for protection of the Delaware River and its island habitats for decades, and has been helping state, county, and municipal governments acquire and protect many of them, from Petty’s Island near Camden, to Burlington and Bordentown Islands near Trenton, to the many islands in Hunterdon County. These Delaware River islands have had all sorts of varied uses over the last few centuries, but now many are forested and contain important migratory bird habitats. The forest at Bull’s Island is the most ecologically significant of any of the Delaware River islands, and it is also one of a handful of sites in all of New Jersey where old-growth characteristics are present in the forest. Finally, it is a unique breeding location for two rare warbler populations.
My conclusions are derived from 33 years of experience in examining and measuring forest structure in floodplain forests along major rivers from the Raritan and Delaware River in New Jersey to the Mississippi and Wisconsin Rivers in Wisconsin:
- If clear-cut, restoration in any of the relatively flat portion of the floodplain forest at Bull’s Island will almost certainly fail. Once the camping facilities are removed, the forest area should be added to the Bull’s Island Natural Area.
- Low-cost restoration can be attempted along a few of the severely eroding or bare riverbanks, especially at the D&R Canal inlet, but even in these places the intensity of the floods is likely to render any restoration work moot.
The basis for my conclusions is as follows:
Habitat restoration can only be considered in the context of a full ecological understanding of habitat life history and the physiognomy of floodplain forests. The floodplain in the northern portion of Bull’s Island State Park is a unique natural feature, being one of the few places left anywhere in New Jersey where a mature forest is expressing old-growth ecological attributes. The ecology of a mature floodplain forest on sand and gravel levees, like at Bull’s Island along a major river in the northeastern US, is controlled by 2 kinds of natural floods:
- yearly spring floods that are somewhat predictable in scope and frequency based on snowmelt, and often contain damaging ice floes.
- random floods from extreme storm events that can be incredibly violent and even create new sand and gravel levees and change the shape of floodplain islands.
On occasion, a few years without a scouring flood will allow for the establishment of forest trees, whose roots reach down through the sand and gravel of the levee into the water table of the river. Although the brief periods of quiet, stable soil conditions that allow for the establishment of forest are infrequent, once established these forests grow quickly since their deep roots have access to the water table. Individuals of these species can persist for long periods of time, as they either have the ability to send up multiple sprouts to recover from flood damage, and/or buttressed trunks that are resistant to toppling.
The tree species that are the most tolerant of deep flooding and periods of anoxic conditions, scouring and/or deposition of soil, and extended drought at and near the soil surface are those that form the canopy at Bull’s Island today, especially American sycamore, silver maple, hackberry, and other typical floodplain species. The forest is characterized by widely-scattered giant trees with very wide crowns, numerous herbaceous perennial and annual species like smartweed and jewelweed, but a relative scarcity of true woody shrubs, since short, shallow-rooted woody species cannot resist scouring floods and ice floes. Box elder, a smaller, multi-stemmed tree, is the only common woody plant that persists low in the flood damage zone, as it can tolerate incredible damage near ground level.
Vines replace low-growing, woody shrubs and small trees in the floodplain ecosystem, as flooding is the dominant influence on the architecture of the floodplain forest. Floods scour away woody shrubs and tree seedlings, but typically vine species may successfully reach a supporting tree where they sometimes persist through a scouring flood and become established. The giant, deep-rooted floodplain-adapted trees with wide canopies and multiple trunks host many species of vines; in fact most tree species with exfoliating bark worldwide, like the American sycamore at Bull’s Island, are floodplain species. The exfoliating bark trait is thought to be an evolutionary response to resist colonization by vine species.
As discussed on page 152 of “The Vegetation of New Jersey” (Robichaud & Buell, 1973), the mature, old-growth characteristics on display in the Bull’s Island forest have been held in special regard for decades. Rare birds that require the high, mature riparian canopy breed there (albilora race of the Yellow-Throated Warbler, extremely rare in the northeast and a disjunct, evolutionarily-important population, and the declining Cerulean Warbler). As a result of the unique forest structure and species assemblage, the southern half of Bull’s Island was designated as a state Natural Area. Had the public campground not pre-dated the New Jersey Natural Areas System designation, it is likely that the northern section of Bull’s Island would have also been designated a natural area.
Now that the campground will be removed, the asphalt roadways should also be removed and allowed to proceed through natural succession. The northern portion of the island should be added to the Bull’s Island Natural Area. Hiking can easily be accommodated along the adjacent D&R Canal Towpath, and if camping is in demand, many new state park acquisitions in the immediate area can be utilized in safety, outside of the Delaware River floodplain.
We do not support the removal of the mature forest at Bull’s Island. We do not believe that any restoration plan for the island has a reasonable or decent chance of success. As described above, floods will dictate what happens at Bull’s Island, and restoration efforts will be futile. Plantings cannot be protected from deer, as any attempt at fencing will be destroyed by floods. The droughty sand and gravel soils will make successful establishment of plantings highly unlikely, as there are extended droughts and heat waves every summer. Deep raging floods will likely scour away any plantings before they are established.
Inexpensive attempts at stabilizing the eroding riverbanks at Bull’s Island, especially at the inlet of the D&R Canal, could be considered. Since repeated severe floods limit the chance for any restoration success, the re-establishment of vegetation on steep banks must be low cost. Along the steep banks of the D&R Canal, shoots of native willows (genus Salix) could be inserted in an attempt to stop soil erosion. With luck, a window of time might pass and allow the willows to establish. Eventually, if a fairly stable willow thicket were to form, plenty of sun could still filter through the narrow leaf blades of the willows, providing appropriate habitat for the native trees at Bull’s Island to colonize the riverbanks. This process would mimic the natural ecological succession that takes place when sand and gravel islands are either swept clean or form anew in raging rivers like the Delaware.
The existing forest at Bull’s Island is the best possible habitat for protecting significant rare elements of our native New Jersey biodiversity, keeping the dynamic island as stable as possible, resisting erosion and sedimentation in the D&R Canal, and regenerating itself naturally with locally-adapted species as gaps form. The forest is mature; a tree will topple occasionally due to the natural stresses of living in a dynamic floodplain, as they have been doing for at least half a century. In 2011, a series of severe storms resulted in high rates of trees falling all over central, western, and northern NJ, creating incredible havoc. In comparison, Bull’s Island fared well, as few large trees fell despite the tumultuous conditions. This is because major floods have been removing trees at a relatively constant rate for decades at Bulls Island. Despite having buried roots and other stresses, the canopy trees at Bull’s Island are well-adapted to the physical stresses of living along a major river floodplain.
Once the campground facilities and asphalt paths are completely removed, except for the access road required for work along the D&R Canal, the remainder of the northern portion of Bull’s Island State Park should be added to the existing Bull’s Island Natural Area.
Thank you for considering our comments regarding Bull’s Island. We would be happy to discuss our conclusions with you further.
Emile DeVito, Ph.D.