Guide to natl’s Old-Field Nature Trail

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Trail Guide to NATL’s Old-Field Nature Trail
(advanced version, 18 September 2007)

Cautions: If you wander from this trail, you may encounter unfriendly plants. Some of these have thorns (blackberry, catbrier), some have sticky seeds (Spanish needle, ticktrefoil). Many are poisonous, but only if eaten (rattlebox, Mexican tea). Ragweed is abundant and will soon be releasing abundant pollen. Fire-ant nests are frequent and occasionally encroach on the nature trail—so be careful where you stand!

Points of interest: Along the trail are 24 numbered points of interest that are explained below. Each is marked with a white plastic stake with two brown bands at top. The uppermost brown band bears a number keyed to the numbered explanations on this sheet. [All other stakes, white plastic or otherwise, are for other purposes!]

OF 1. Entering Old-Field Plot A. This plot is to be tilled every 10 years. It was last tilled in March 2002, which means that about 5½ years ago, except for the longleaf pines, it was a bare, cultivated field. [The longleaf pines were left standing to increase the genetic diversity of the pollen available to the pines in NATL’s upland pine ecosystem.]

OF 2. Ragweed (Ambrosia artemisiifolia). Ragweed can be recognized by its deeply and intricately dissected leaves. Being a common native weed in agricultural fields, it is one of the first plants to become abundant in old field succession. Ragweed is an annual--that is, it reproduces from seed each year.

OF 3. American nightshade (Solanum americanum) [marked with yellow flagging]. This species, with its small but pretty flowers and its shiny black fruits, is a member of the plant family that includes tomatoes and potatoes. [Its fruits have many small seeds that should be considered poisonous because they may contain high levels of solanine, a highly toxic glycoalkaloid.]

OF 4. Seeds looking for a ride. Beggar-ticks (Bidens alba), also known as Spanish needle, is a favorite nectar source for butterflies and a curse to nature lovers who brush against it when it is in seed. The “needles,” which are arranged in little spheres where the flowers once were, are seeds with two barbed prongs at their tips that enable them to attach securely to most clothing. Removing them is a major chore, and the discarded needles may produce a new patch of beggar-ticks the following year. [The white flowers with yellow centers are actually clusters of small flowers, with white, sterile ray florets surrounding yellow, fertile disk florets. The disk florets produce copious amounts of nectar, which attract both butterflies and bees. Each disk floret produces a one-seeded fruit (an achene), which becomes a “needle” when dry.]

OF 5. Sassafras (Sassafras albidum). This tree, usually small, has leaves of varying shapes, including leaves with no lobes, leaves that resemble right- and left-hand mittens and leaves with a lobe on either side. Its leaves are aromatic when crushed and its bark and roots have an oil that was once used to flavor root beer—until safrole, a principal constituent, was found to cause liver cancer in mice. [Sassafras trees are dioecious—that is, the flowers are unisexual with the staminate (male) and pistillate (female) flowers borne on separate plants.]

OF 6. Patch of dead cogongrass (Imperata cylindrical). Cogongrass, native to southeast Asia, is one of the most threatening of the foreign plants that are invading Florida ecosystems. If left unchecked it would form such dense stands in NATL’s old field plots that native plants could not compete. You are standing near the middle of a patch of cogongrass that was sprayed with herbicide in April 2005. The re-growth, from underground stems (rhizomes), has been sprayed repeatedly since then. As you can see, the original thatch has yet to decay completely and some re-growth is still occurring. The re-growth that is marked with fire-orange flags was left unsprayed when the rest was sprayed a few weeks ago. [A cogongrass expert recently told us not to expect to eradicate cogongrass patches such as this, treated continually, in less than five years!]

OF 7. Briar patch. Dense, thorny growths of blackberries such as this one are common features of fields that have been abandoned for a few years. This patch is of sand blackberry (Rubus cuneifolius), which bears small tasty fruit in early summer.

OF 8. Black cherry sapling (Prunus serotina). Birds and other animals eat the small black fruits of this species and disperse the seeds along with a dose of organic fertilizer. The bark on the branches and trunks of young cherry trees is distinctive. It is thin and reddish brown and has horizontal markings made up of rows of small openings (lenticels).
[Black cherry leaves (as well as twigs, bark, and seeds) are poisonous because they contain a cyanogenic glycoside that produces hydrocyanic acid during digestion. Livestock are sometimes poisoned by eating the wilted leaves.]

OF 9. Persimmon (Diospyros virginiana). This tree, when mature, bears large fruit that are mouth-puckering astringent when green but turn tasty and translucent orange when they ripen. Its leaves have reddish petioles and are dark green above and whitish below. [Persimmon trees, like sassafras trees, are dioecious: mature trees can either produce fertile pollen or bear fruit but not both.]

OF 10. Winged sumac (Rhus copallinum). This small tree, frequent in old fields, can be recognized by the “wings” between the leaflets along the stem of its compound leaves. In fall it produces clusters of small reddish berries that are eaten by many kinds of birds--which is how it colonizes abandoned fields.

OF 11. Cross into Plot B. To enable NATL to always exhibit the earliest stages of succession, at least part of Plot B is tilled every year that no other plot is tilled. The area on the left side of the nature trail through Plot B was mowed and disked twice in early November 2006. Its dense crop of ragweed illustrates how that species is often the first to dominate an abandoned field. The area on the right side of the trail was last mowed and disked nearly two years earlier (January 2005). What differences do you notice between the two sides?

OF 12. Dogfennel (Eupatorium capillifolium). Like ragweed, dogfennel is a native plant characteristic of the early stages of old field succession. Unlike ragweed, it is a perennial—that is, plants survive year after year rather than having to start from seeds each year. Dogfennel is a commonly occurring pasture weed, especially in unimproved and overgrazed pastures. At this season it can be recognized by its finely divided leaves that have a distinctive odor when crushed.

[Dogfennel leaves contain low levels of a toxin (tremitol) that causes dehydration when ingested by cattle. Cattle usually don’t feed on dogfennel but may do so when more suitable forage is lacking—as in a drought.]

OF 13. Worm remedy? Mexican tea (Chenopodium ambrosioides) was used medicinally by native Americans in a variety of ways--for example, they extracted chemicals from the aromatic leaves by boiling and mixed the extract with milk to give to children for worms.

OF 14. View Plot D [straight ahead]. Plot D is a 10-year-rotation plot and was first started in 1997. To re-start it, the plot has recently been cleared of trees, mowed, and tilled. The debris from clearing (stacked at center) will be burned, and the plot cultivated again this fall. By the end of 2007, Plot D will be left alone to show consecutively later stages of old-field succession until 2017.

The Old-Field Nature Trail will detour around Plot D until re-starting is completed.

OF 15. View Plot C. Plot C was started on its first 40-year-rotation in 2000. Its closer parts have a deep layer of clay and show few trees that have grown tall. At the western edge of the plot, no clay was dumped and tall trees are more plentiful. The southern third of the plot has a dense stand of saltbush, which is the subject of OF 22.

OF 16. Shyleaf (Aeschynomene americana) [marked with yellow flagging]. This native plant, also known as joint-vetch, folds its leaves at night and, very slowly, in response to touch. It will soon bear modest flowers and these will later be replaced with narrow pods that are scalloped below. The foliage is grazed by deer and the seeds are eaten by quail, dove, and turkey.
[In some tropical countries shyleaf is used as forage, for grazing or to “cut-and-carry.”]

OF 17. Fire ant nest. [Do NOT disturb.] Since its accidental introduced from South America to Mobile, Alabama, in the 1930’s, the imported fire ant (Solenopsis invicta) has spread throughout the Southeast and become the dominant ant in disturbed areas, including old fields. It displaces native insect species (much as cogongrass displaces native plant species). Most Floridians know how fire ants defend their nests—by mass, stinging attacks on whoever
disturbs a nest and then stands on or near it. You may notice that few ants are seen on or near undisturbed nests even on days when workers are actively foraging. This is because fire ants establish subterranean foraging tunnels that radiate from the nest and along which there are openings at intervals from which scouts issue to find food and to recruit workers to gather it and return it (via subway) to the nest.

OF 18. Wild poinsettia (Poinsettia heterophylla) [marked with yellow flagging]. Also known as Mexican fireplant, this species can be recognized by its resemblance to its larger, more colorful relative, the Christmas poinsettia. When abundant in pastures, wild poinsettia is considered a noxious weed.
[The leaves of some individuals are not “poinsettia-like”, but very narrow with smooth margins.]

OF 19. Scarlet creeper (Ipomoea hederifolia). The bright red flowers of this vine attract cloudless sulfur butterflies, which use their long tongues to reach the nectar.

[In some crops, this pretty, delicate species becomes a weed that requires control.]

OF 20. Canadian goldenrod (Solidago canadensis) [marked with yellow flagging]. The wind-dispersed seeds of goldenrod enable it to colonize abandoned fields, and, once there, it uses underground stems (rhizomes) to form dense clonal colonies. These colonies produce the beautiful, dense golden displays that characterize many old fields in the fall (and will soon be evident here).

OF 21. Don’t eat this plant! [marked with yellow ribbons] All parts of yellow rattlebox (Crotalaria spectabilis), but especially the seeds, are poisonous, whether green or dried in hay. Chickens, horses, cattle, and swine are the species most often affected. The name rattlebox is based on the fact that the seeds come loose in the black, mature pods and rattle when the pods are shaken.

OF 22. Saltbush (Baccharis halimifolia). Saltbush, also known as sea myrtle, gets its names from its salt tolerance and is a common tree of both coastal and interior wetlands. The dense stand of saltbush in the southern third of Plot C may be a result poor drainage and lots of saltbush seeds in the muck from the excavation of SEEP that was spread on portions of Plot C to ameliorate the effects of the clay dumped there in the 1970’s. Whatever the causation, saltbush is not the usual tree to first dominate succession in upland old fields in north central Florida. [Look into the open ends of the PVC stakes that mark the points of interest along this trail and you may see one or more squirrel tree frogs peering back!]

OF 23. Loblolly pines (Pinus taeda). Loblollies are usually the earliest trees to dominate upland old fields. They grow fast and soon begin to shade the early old-field colonizers, most of which require full sun. Indeed the loblollies eventually produce a shade so dense that loblolly seedlings cannot survive. This sets the stage for colonization by the tree species that dominate mature hammocks—that is, those that have seedlings that can grow in the shade.
[The Hammock Nature Trail will help you learn more about the final stages of old-field succession.]

OF 24. Two species of pine seedlings. Along this section of trail, seedlings of loblolly pines are marked with yellow flags and those of longleaf pines are marked with fire-orange flags. Loblolly seedlings grow upward rapidly but are fire-susceptible for a decade or more. Longleaf seedlings can survive most fires because the bud remains in the ground for 4 or more years; however, in the absence of fire, they soon die from being shaded by faster growing, fire-susceptible plants.
[Take the Upland Pine Nature trail to learn more about the role of fire in maintaining that ecosystem.]
At the end of this trail, you will see the kiosk at the start of the Hammock Nature Trail.
To return to the start of the Old Field Trail, take the trail that goes due north
from the kiosk toward the Cultural Complex.

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