Norway Maples, and Seeing the Future

One purpose of this blog is to help people to look at nature now and see where it's headed. Every gardener imagines the harvest while planting the seeds. In science, one extrapolates from past and current trends to predict the future. With practice, one can look at a woodland and see not only the present but past and future as well. As a land manager, one envisions two futures--one without intervention, one with. Because we've altered local habitats so much--through altered hydrology, past farming, introduced species, banishment of important forces like fire and predators like mountain lions and wolves--intervention can help restore functionality that no longer happens naturally.

Autumn is the easiest time to divine a woods' future, because each species shows its colors, making trends easy to spot. For instance, learn the Norway maple's brand of yellow this time of year, and you'll start seeing them all over town. Unpalatable to deer, they rise unnoticed until they become full-sized trees, mostly along backyard fencelines.

That's what's happening on a larger scale in the hidden valley between the Princeton University chemistry building and Washington Road. That mix of yellow and lingering green indicates that the Norway Maples are taking over the top of the valley,

and extending downstream. This is the perfect time of year to see the extensive invasion by this nonnative tree. Why have I on multiple occasions urged the university grounds staff to cut or girdle these trees, despite their attractive yellow in autumn?

The problem is an ecological one. This forest, one of Princeton's oldest, is steadily shifting from native trees that feed local wildlife to nonnative vegetation that does not. As the shade-tolerant Norway Maples push up into the native canopy above, their competition for water and nutrients weakens the giant oaks and black gums, hastening their decline and increasing their susceptibility to wind storms. Young native trees--preferred by deer and less shade tolerant--can't compete with the Norway Maples, which grow quickly, green up sooner in spring and drop their leaves later in the fall. This photo shows a 1-2 centuries old oak with a sea of Norway maples rising underneath.

Fortunately, most Princeton woodlands have not been invaded by Norway maple, though it would be worth it for land managers to take a walk through the woods to see if they are starting to get established elsewhere in Princeton's open space.

Except in that Washington Rd. gorge woods, they have proven invasive only in people's yards, showing highly localized invasiveness much like Japanese maples and Rose of Sharon. This photo, taken along North Harrison Street, shows the classic problem with ignoring the silent ascent of Norway maples, in this case under a powerline. Chances are they grew unnoticed by the homeowner, and now will require repeated pruning to keep them from threatening the wires.

At least the half of the tree closer to the street shades the pavement in the summer,

but another annoying aspect of the species--their dense shade and aggressive roots that leave little sun or water for the lawn--has made it impossible to grow grass on the steep slope.

Like climate change and the nonpoint pollution of our waterways, the Norway maple silently transforms the world, undermining food chains and biodiversity, while our attention is elsewhere.

Women and Wildlife Awards Event Today

The Conserve Wildlife Foundation is having its annual awards event today in Stockton, from 2-5pm. My group, the Sustainable Jazz Ensemble, will be performing as part of the event. Information about the three women receiving awards for their work to preserve New Jersey's threatened wildlife can be found at http://www.conservewildlifenj.org/getinvolved/women/.

One of the women, Jackie Kashmer, has been doing heroic work to save bats, which are being devastated by White Nose Syndrome. The fungus, which was recently determined to have been introduced some years back from Europe, disturbs the bats' hibernation, causing them to run out of stored energy before spring arrives.

Jackie's 16 hour days devoted to helping bats survive the winter, detailed in a conservewildlifenj.org blogpost, are an example of the extraordinary amount of work and devotion required to counteract to any extent the destructive impact of imported organisms.

By coincidence, the NY Times article reporting on the fungus's European origins was accompanied by an article on the reintroduction of the American chestnut in Appalachia. It has taken many decades for breeding programs to develop native chestnut trees resistant to the Asian fungus that began wiping out the American chestnut tree more than a century ago. These are the sorts of quiet, awe-inspiring efforts that seldom make it into the news, but make all the difference in what sort of world we'll have in the future.

Trees On the March

Something's going on in the field down next to Faculty Drive, across Washington Road from the boathouse at Carnegie Lake.

The troops are assembled, like high-stepping Clydsdales poised for the Arbor Day parade. Ready, forward, march!

But where to? The man assigned to water these 20 foot tall specimens said they're all headed into the woods to grow in the shadow of their granddad's generation, just across Faculty Drive, where the university is finishing up its stream restoration in the valley next to the new Chemistry building. (To see a history of the project, type "stream" into the search box at the upper left corner of this website). The university had to take down a few big trees last year (some possibly 200 years old) as part of the restoration of the heavily eroded stream corridor, and looks determined to give their replacements a head start.

The stream restoration is extraordinary in terms of how they created a lovely and hopefully durable streambed, but the botanical side of the project would have been more enlightened if it had included rescue of high quality native wildflowers prior to construction, and invasive species removal on the adjacent slopes.

And though they're putting in the same species of trees they took out--tupelo, pin oak and white ash--the chances the white ash in this photo will survive for more than a decade are pretty remote, given the near certain arrival in coming years of the exotic Emerald Ash Borer now spreading eastward through Pennsylvania.

I was craning my neck to see the thick, paired twigs that identify the tree as an ash, when I realized I could just look at the tag.

Planting the Shore

If St. Patrick's Day is the traditional day for planting peas, then March 8th must be the traditional date when rushes are planted next to a pond. The dredging of the upper Mountain Lake in Princeton left the shoreline bare. A fence effectively kept the geese from congregating, but didn't quite do the trick appearance-wise.

FOPOS board member Tim Patrick-Miller at some point realized that the solution was growing just downstream, where thousands of native rushes and sedges had sprouted in the drained lakebed of the lower lake. Clark Lennon and Tim are working with new FOPOS natural resources manager AeLin Compton to transplant the natives along the shoreline.

Soft rush (Juncas effusus) is a very tough native plant whose evergreen stems and vaselike shape give it an ornamental appearance once it's established.

Repairing the Towpath and Nature Along the D-R Canal

For years, the towpath was a given, a high quality crushed-stone pedestrian and bicycle thoroughfare stretching more miles than most anyone has time to explore, up and down the DR Canal. That changed last August as the unprecedented flooding of Hurricane Irene--tearful after having been downgraded to a tropical storm--deposited a thick layer of silt over the trail. The gift of fertility, reminiscent of the ancient Nile, would have been more welcome if the valley's investment was in agriculture rather than transport.

I inquired last fall and was surprised to hear that there were no funds available for repair, and if and when they become available, the northern portion's washouts, up towards New Brunswick, would get the first attention. Some repair in the Princeton area, by the water authority rather than state parks, has taken place. The photo shows a patch job just up from Turning Basin Park.

I called Stephanie Fox at DR Canal State Park today, and was told that more extensive repairs are waiting on FEMA money from the federal government. In addition to trail damage, some of the park's historic buildings were also damaged in the flood. Though the crushed stone surface is still intact in most places underneath the mud, repair will involve bringing in additional stone. Cost for repairing just one mile of minimally damaged trail could run $10,000, so overall cost will likely be very high.

Near Harrison Street, where the nature trail branches off, the towpath is in relatively good shape, at least when it is dry. The trail loop was built by parks personnel after I "discovered" the meadow there where the land between Carnegie Lake and the towpath broadens out. At the time, the park crews were mowing the meadow weekly during the summer. When I pointed out that they were mowing not grass but a field of beautiful native wildflowers, they agreed to limit mowing to once a year in late winter. Everyone was a winner with this arrangement: less work, more habitat, more flowers.

In winter, at the trailhead, the switchgrass leaves are an attractive legacy of last year's growth.

Word is that the bluebirds have hung around all winter, it being so mild.

One reward of exploring the nature trail this time of year is an encounter with fragrant honeysuckle (Lonicera fragrantissima), whose small white flowers live up to their name. This is the one exotic bush honeysuckle species that I've never seen spreading into wild areas. A line of the shrubs remains from maybe 40 years ago when that ribbon of land between the canal and Carnegie Lake was carefully tended as part of the grand entryway into the university.


Each year, with no assistance other than annual mowing, the meadows have become richer with wildflowers like joe-pye-weed, ironweed, tall meadowrue and cutleaf coneflower. It seemed time to relax, sit back and enjoy the fruits of less labor.

But a trained eye will see in this very plain-looking photo a web of vines. Porcelainberry, a grape-like exotic vine that has covered forest edges at Princeton Battlefield with stifling kudzu-like curtains of growth, has been spreading down the canal corridor. A light infestation noticed a few years ago is now exploding, threatening to permanently overwhelm the wildflower meadows.

Park crews are busy elsewhere along the canal, dealing with invasive Japanese knotweed and hops. We'll have to see if there's anything that can be done this year.

In the meantime, there are sweetgum balls serving as natural tree ornaments next to the trail,

the resident geese, and, if one can negotiate with the geese for access to the shore,

trout to be caught.

The Story a Spicebush Tells

You can still find a few of these dead stems of spicebush standing in Princeton's preserves, pockmarked with holes reminiscent of cholla cactus wood we used to find in the deserts of the southwest. They tell a remarkable story of a forest understory's rebirth.

Seven years ago, instead of this cluster of healthy stems you would have seen one old stem too tall for the deer to reach, and a dense cluster of tiny stems eaten nearly to the ground. Soon, those old stems, which singletrunkedly kept the shrubs alive back when deer browsing pressure was high, will have rotted back into the ground amidst the crowd of younger stems that now, with reduced deer numbers, can grow to maturity. The many healthy, multi-stemmed spicebush serve as monuments to those single stems that kept the bushes alive through a period of ecological imbalance.

Update on Dam Restoration at Mountain Lakes

I haven't heard anything official, but it looks like the lower dam at Mountain Lakes Preserve is nearly complete. The wooden posts in the foreground mark where a ramp once was located for hauling chunks of ice out of the pond and hoisting them into the 3-story ice barns that used to rise behind the dam to the right.

The ice operation closed down around 1930, as refrigerators became more widely available. The stone wall extending the length of the dam is completely new, designed to mimic the original wall that now lies buried under the expanded earthen portion of the dam. For safety reasons, the dam is now broader and several feet higher than previously.

At the other end of the dam stands the newly restored spillway. As far as I know, the informative signs that were there prior to restoration will be reinstalled, describing the decades during which Mountain Lakes supplied Princeton with ice for its iceboxes.

Meanwhile, upstream of the two Mountain Lakes is another dam that was added onto the project, funded by the same anonymous donor. I had long argued in favor of restoring this "upper settling pond", also known as North Pond--an argument that was going nowhere until funding became available. It's located on one of the two tributaries feeding the lakes, and was built in the 1950s by the Clarks, who also built Mountain Lakes House around the same time.

The pond is called a catchment basin for good reason. Water rushing downstream from Witherspoon Woods drops its sediment in this pond, thereby greatly reducing the amount of sediment that would otherwise have continued into the Mountain Lakes. It played this role very effectively, completely filling up over the past 50 years. There must be 8 feet of very rich sediment here, which this week is being trucked away, perhaps to a topsoil business.

With the catchment basin trapping sediment, at least on that one tributary, the upper Mountain Lake will last much longer before it once again will require dredging.

This is my favorite vista, standing at the northwest, upstream end of the lakes, looking down.

Fire's Ecological Role

Fire is an important and beneficial ecological force. Writers like Stephen Pyne have documented how it was in past centuries an important tool for maintaining meadows and open woodlands even along the east coast. Many native plant species have evolved adaptations to and even dependency on periodic fire. In  past years, living in the midwest and later the piedmont of North Carolina, I was fortunate to participate in controlled burns of some small prairies. One prairie was right in the city of Ann Arbor, Michigan, where they regularly burn native prairie grasses and woodlands in their parks, in a very controlled way, of course. Controlled burns are being done at a few preserves in New Jersey, as described in a previous post about Schiff Nature Preserve 30 miles north of Princeton, and more widespread use would undoubtedly benefit habitat and ecological health.

This storyline is seldom encountered in news reports, which focus on war-like responses to wildfires out west.   A post at another website of mine speaks to the gap in people's knowledge perpetuated by this unbalanced reporting: Rethinking News Coverage of Wildfires.

Big Changes Come to a Hidden Valley

 There's a hidden valley in Princeton that everyone drives by but no one sees. Just over this ridge is Washington Rd, with athletic fields beyond. Down to the left is Faculty Road and Carnegie Lake.

Despite being sandwiched between a busy road and Jadwin Gym, the valley's rich soil sustains old oaks, tupelo, beech and ash that reach improbable heights.

This year, big changes have come to this long-hidden valley. Approached from Faculty Road, stacks of boulders and heavy equipment suggest some sort of road construction.

 A pile of stumps looks less than auspicious.

Further up the valley, more boulders, bales of hay, and orange fencing.

Giant trees, some a yard thick, have been cut down. How could this be anything but bad news? But wait, this post is getting depressing, so let's start from the top of the valley and work our way down.

The valley, which is to say the remnant of valley that was never developed as campus, begins at the new bridge over Washington Road. In the distance is the new chemistry building and the football stadium.

Looking downhill from the bridge, a lovely little stream meanders peacefully down the valley.

Starting farther up towards Nassau Street, the stream runs underground through campus, then emerges (or "daylights") from a big pipe just below the bridge.

The water immediately encounters what looks like an olympic luge track, attractively armored with stones.

 Further down, the narrow channel flows through a broad floodplain.

All of this--the pleasing meanders, the floodplain for stormwater to spread out into, the series of riffles and little waterfalls over stones--is manmade.

Why would anyone want to remake a stream? After a hundred or two years of flash floods caused by all the impervious surface on campus, the stream channel had eroded the ground around it, and was threatening to undercut Washington Road (beyond the green fence on the right) if nothing was done.

Here's a portion of the old streambed, broad and ill-defined. More photos of the old streambed can be found in a post one year ago when members of the Princeton Environmental Commission were given a tour of the proposed project.

A group from Rutgers developed the plans. In this photo, you can see the hoses used for pumping water around the section of stream being worked on. The "V" of stones at the left is called a "cross-vein". Water flowing over the rocks converges to scour out a pool just below them. Pools, riffles, and a narrow stream bed to focus flow are all characteristics of a healthy stream.

The stacks of boulders, then, are materials used to direct water in such a way that the streambank will survive the flash flooding coming from the hardened landscape of campus.

Lots of digging is required to form an adequate floodplain to accommodate the massive infusions of water during storms. The disturbed areas will be restocked with native plants, and though they had to take down some large trees, many were spared.

So that gets us back to the downed trees. This section of white ash is 36 inches in diameter. I counted roughly 200 annual rings, which are caused by the alternation of light-colored fast spring growth followed by a darker band of slower growth later in the season. The tree, and others in the valley, standing or cut, could well date back to the Revolutionary War. Visitors to Mount Vernon may remember the giant white ash trees in the circular drive approaching the house.

 About 160 years back, this ash began to grow very slowly, as can be seen from the very narrow rings on the left. Perhaps it was shaded heavily by another tree, which apparently fell 120 years ago when the rings began to spread out again.

It is unsettling that such old trees have been cut down, and all the more remarkable that few even know about it in a town that loves and protects its trees. But there are extenuating circumstances, tradeoffs made, factors that mitigate, at least partially, the loss. Erosion from campus has been undermining some of the majestic trees, and this project is meant to reduce that erosion.

Time will tell if the trees that were saved will survive all the disturbance around them. Tree roots are very sensitive. And the carefully designed channel is not necessarily immune from the powerful erosive forces of repeated floods.

One useful pursuit at this point would be to study the rings of the fallen trees to see what they might tell us of Princeton's past.

I had recommended a pre-construction rescue of rare native plants like horsebalm, but the idea probably got lost in the mix. Not everyone has learned to make a distinction between rare wildflowers that have survived for centuries in a valley, and whatever natives one can buy in pots at a nursery.

I had also encouraged them to remove the Norway Maples (mottled green/yellow in this photo and next) that have invaded the valley, since the invasive maples are competing with the old growth natives, and their dense shade will threaten the newly planted natives over time.

Overall, though, there's reason to believe this stream restoration--rare in New Jersey--will validate its good intentions. The project leader spoke excitedly last year during the tour about how he hopes students will find the valley an attractive place to visit, rather than merely serving as a traditional shortcut for athletes heading to practice.

This long-sheltered space, with so many stories to tell of past centuries, is beginning a new chapter worth reading.

Talk Tonight, 7pm, About New Mid-Atlantic Native Seed Bank

Here's a chance to hear about an exciting and timely new collaboration between the NY City parks dept. and DR Greenway, to develop native seed production locally and elsewhere along the mid-Atlantic. Plant species exhibit genetic variation across their ranges, and there is an effort to preserve the distinct traits of local populations. One approach is to have multiple nurseries along the eastern seaboard, each of which grows natives drawn from local wild stock. Ed Toth of NY City Parks will be the speaker. More info here, and below:

"DR Greenway's St. Michaels Farm Preserve is host to a new pilot project in native seed production that could change the future of conservation. The 13 species of native seeds being grown at the site, with support from the Natural Resources Conservation Service, will be used to restore landfills in New York City and will contribute to a Mid-Atlantic Native Seed Bank. New York City Parks is our partner in this project, led by naturalist Ed Toth, Ph.D.

Seed is a critical natural resource that has been largely unrecognized, unprotected, and undermanaged. Locally adapted seed sources are widely acknowledged as critical for habitat restoration because they do not pose a genetic risk to surrounding native plant populations. However, our seed resources are in danger of being lost from misuse of non-local source seeds.Learn how to begin to wisely manage resources through seed banking and seed networks to prevent the extinction of these critical natural resources."

Stuart School and FOPOS Collaborate

The forests of Princeton and Central America both got a boost on a recent Saturday, when volunteers met behind Stuart School to clear trails and remove invasive plants. The afternoon's work was preceded by a presentation by leaders of a Fair Trade coffee collective, who explained how the purchase of Fair Trade Certified coffee works to improve the lives of coffee growers. Camila T., a Stuart School student who has been very active in promoting Fair Trade products in Princeton and beyond, served as translator for farmer Angelina Espinosa.

Afterwards, more or less bravely oblivious to the arrival of onagainoffagain rain, we headed into the woods to improve boardwalks and cut invasive shrubs like privet and Asian Photinia. A collaboration has been long in the works between Friends of Princeton Open Space and Stuart School, which is directly upstream of Mountain Lakes. Impetus to finally set things rolling came from Sophie Glovier and Stuart School science teacher Eric Anderson.

Coffee with the Fair Trade emblem on the package, competitive in taste and price, can be found at McCaffery's and no doubt many other locations in town.