Tuesday, August 9, 2011

Reforestation Thoughts

 Old growth loblolly pine at Congaree NP

A few years ago, we travelled in the South, visiting old cypress swamps and sandy longleaf pine savannas. A few of the swamps were old growth and were thick with the rot and renewal of centuries. I remember one pine with great big fissured plates of bark like stegasaurus skin and a massive trunk. Nearby was a stand of pawpaws in maroon fetid bloom, laurel oaks and horse sugar and redbay and baldcypress and great tangles of unknown flowering vines.

I also remember driving down country roads through miles and miles of timber plantations-- dense, isolating, more-or-less lifeless. Pines growing like corn, row after row, nothing above or below them. The great pulpbasket of America, future toilet paper and plywood and post-it notes occupying the better part of an entire biome.

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I've been thinking a lot about reforestation lately. I'll be planting about 8 acres worth of reforestation this fall, and am involved in various ways in a few other projects to convert fields to forests. The underlying goals of these are generally "closing gaps" in otherwise contiguous forests. The utility of trees in sequestering carbon has also played into the funding for a few projects.

I wonder about planting trees, sometimes several hundred per acre, into what are essentially "disturbed" habitats - old farm fields, capped dump sites, and the like. When all of those successfully-planted trees reach canopy height in a great dense sward, will we have a forest? Or will we have something that looks, structurally and biotically, a lot more like those pulpwood plantations down south, or the derelict christmas tree plantations one passes on country roads here in the Northeast? I've walked through old "reforestations"- generally coniferous, it's true - red pine, Japanese larch, Norway spruce - even in places as otherwise intact as the great Catskills park. Like the plantations of the South, there's not much doing in the understory.

It seems to me that many of our native forest herbs, and understory trees and shrubs, are dependent on small-scale canopy gaps for recruitment. I figure it takes a tree fifty years or more before it has the girth to create a significant canopy gap such as would recruit spicebush or flowering dogwood or hornbeam- or stoneroot, black cohosh, or wild ginger.

Many of the reforestations I am involved with are being done, partially, to create larger areas of habitat for birds that thrive best in large acreages of contiguous forest. They are "closing gaps" in otherwise largely forested areas.

Yet many of the birds that depend on "contiguous forest" utilize the understory, not immature canopies. There are plenty of biologically depauperate post-agricultural forests around here that bear that out-- even age stands of red maple and ash, with nary an ovenbird or Kentucky warbler or veery in earshot. Why? The understory is lacking.

What about our ancient forest herbs, the rich, rainforest-like layer of broadleaved wildflowers and ferns that run thick and waist-high in the most intact of our local forests? Black cohosh, horsebalm, bloodroot, wild ginger, wood nettle, purple-node Joe Pye Weed, interrupted fern, round-lobed hepatica...

These are the essence of the Eastern forest, and are everywhere declining. They seem generally unable to recruit in second-growth forests. Many (not all) have extremely limited seed dispersal distances, relying primarily on clonal growth in their relatively undisturbed habitats. Some may need evenly moist conditions through the summer to survive as seedlings. These species may have thrived in a Northeast with higher groundwater levels and more frequent precipation; maybe we see merely relics of a former age in the remaining populations. Some of these species need thick organic duff; others need sheltered micro-habitats, nurse logs, the heterogeneous topography of a habitat wild and abundant.  Is soil biology an issue?

Will our reforestations recruit these conservative plant species? Can we recreate, from scratch, an honest eastern forest with forest herbs, dense shrubs, and a structurally varied canopy? In a "reforestation", when will the mycorrhizal fungi arrive that network so many of the root interdependencies of the forest?



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In many ways, I'm doubtful. Our primary tools in doing ecological restoration are often modes of disturbance. Chainsaws, loppers, herbicide, tractors, augers. The system ("forest") we are trying to re-assemble is the most complex and interdependent ecosystem type we have in the Northeast -- and, relatively, the least disturbed -- what they used to call "climax", though that kind of religiously teleological science is thankfully out of vogue now.

Perhaps we should focus ecological restoration more on creating high-quality meadows, savannahs, grasslands. These are highly productive habitat types, on a par with any other. They are also among the most threatened habitat types in the world, right up there with tropical rainforest. They are critical for many species of birds, and for most native pollinators. Although meadows and areas of scrub-shrub are often accused of "fragmenting" forests when they lie in between even the crappiest of second-growth parcels, I'm skeptical of this notion. I suspect that patches of open habitat within a forested matrix probably keep many native pollinators viable adjacent to woods that are so stripped of flowering plants by deer that the woods can no longer support its on suite of pollinating insects.

I'd be so bold as to say that meadows and scrub-shrub are forest, just very young forest, and that the forest fragmentation we hear of in studies is often that created by lawn, factory farm, mall, and parking lot.

I wonder if, by creating good meadows now, we might set the stage for a good forest in the future, whereas if we just plunk a bunch of trees into a field a few years out of corn production or hay, we're locking our planted site into 50 to 100 years or more of depauperate tree plantation.

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What about a hybrid approach? This is what I'm thinking for some of our reforestation projects:

1. Keep the trees in the planting mix, but leave large gaps between densely treed areas. Into these gaps, plant native shrubs which thrive in full sun (for the early years) but also transition successfully to shaded habitats. Blackhaw, winterberry, arrowwood, highbush blueberry, maleberry, even spicebush... rather than waiting several decades or more for gap dynamics to naturally recruit the beginnings of an understory, it'll already be in place, and thriving, as the canopy closes (hopefully unevenly).

2. Plant trees that will die soon. Gray birches, Virginia pine, sassafras -- these pioneer trees are the land-healers. When they give way, the young forest will be shady and no longer ruderal. These trees will die and in their places will recruit shade-tolerant species -- whether they are the next generation of (mid-successional) trees, or native herbs, or forest shrubs -- rather than mugwort and chinese lespedeza and, if fenced from deer, rather than multiflora rose and autumn olive, too.

3. Plant meadow plants that can transition from sun to part shade. Own the ground with boneset, hollow-stem Joe Pye weed, ironweed, Indian grass, swamp milkweed, etc. These plants serve two purposes -- first, to pre-empt recruitment of invasive plants by filling niches, and second, to mimic natural meadow successions. There is much that we have little control over in the realm of the soil, and I believe that it is these herbs that prepare the agricultural soils for a transition to forest soils -- bacterial to fungal, nutrient-lossy to nutrient conserving. These herbs also support pollinator communities that could make the difference in successful recruitment of mid-successional herbs -- plants like solomon's seals and the like which bridge the gap from thicket to forest.

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We ecological restorationists are much like healers, with similar responsibilities towards our work, and a similar imperative to "do no harm". Yet our tools are largely borrowed-- from agriculture, from forestry, from landscaping. What sets us apart are the plants -- our healing herbs. We need to observe natural habitats, and unnatural habitats, very closely, and consider how to use the plants in our palette to best effect. If we simplistically interpret forest as "trees", and leave the rest of the forest system to time and chance, my bet is that our future forests will be structurally and biologically impoverished. We risk creating habitats that are more like forestry plantations or monocultural farms than indigenous natural habitats.

Driving by a southern pine plantation 

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