BIO 111 L Environmental Science Laboratory Field Trip
	[Activities][Flora and Fauna][Questions]

The seedlings of the Rio Grande cottonwood require about 6 years of repeated flooding in order to survive long enough for their roots to reach the water table. Because flood controls have eliminated the normal flood cycle the seedlings are not surviving, sprouting few and far between, only to succumb to dryness. Tamarisk and Russian olive, musk thistle and Siberian elm are the trees which will dominate the bosque in the next century unless some remedy can be found for the lack of natural flooding. Proposals include controlled flooding of select areas of the bosque, and "pole planting", a technique which places long cottonwood cuttings into holes punched deep into the soil to reach the water table. Both of these procedures are problematic. Controlled flooding would be an engineering challenge and very costly, as would pole planting due to it being very labor intensive. And a significant fraction of pole-planted cuttings might not survive. Without something, however, the bosque we now know will eventually disappear along the Rio Grande.

Activities:

We will explore the area, identifying the dominant plants and physical features. Water tests will be done to determine the relative health of the Rio Grande and of the clearditch, and to compare these with other rivers and streams. The clearditch is part of the drainage system which helps not only in flood control but also in removing saline from the land. Unlike the arroyos and diversion channels the clearditch actually cuts down into the water table aquifer. Salt accumulated on the soil from irrigation and fertilizers will soak down into the water table and be eventually carried away by the drainage. Of course this salt finds its way to the river. But areas not having such a system must install special underground drainage pipes to prevent the land from eventually becoming too salty for agricultural production. California's Central Valley has lost thousands of acres to salinization.

Soil samples will be taken to be tested in the Field Data Analysis lab later in the semester. You should make observations about the impact of man and other characteristics of the area to be included in your habitat assessment. Often in the fall and spring semesters we hear or see the sandhill cranes flying over on the migration to or from the Bosque del Apache wildlife refuge which the class visits in December and February.

Selected Flora and Fauna:

Rio Grande Cottonwood - Populus fremontii var. Wislizenii This is the dominant tree of the bosque. But its seedlings are not surviving (see above) and the old trees are slowly dying and being replaced by introduced species (see below).

Texas mulberry, Morus microphylla - Produces a juicy edible berry in June. Several types of ornamental mulberries have been introduced into the US from the orient.

Coyote willow - salix exigua (a.k.a. red osier willow) Grows in thickets anywhere ground water is abundant and near the surface. Red to ashen gray twigs, grayish-green leaves. Its slender twigs (osiers) are favored the world over for baskets. Other willows: Arroyo willow, salix interior, Lancelot generally smooth margined leaves. Found in lower elevations along drainages. Peachleaf willow, Salix amygdaloides, is the only willow which can truly be called a tree, growing to 30' in height with a trunk diameter of a foot or more. Weeping willow: an introduction from China.

Burr reed - sparganium var. Also called cockle burr, the seeds of this common mudflat plant stick to everything.

Tamarisk - tamarix pentandra [see reference] Introduced from the Mediterranean region for erosion control, this shrub to small tree (the largest specimen is 44 feet tall and 2 feet diameter) has taken over many areas, especially along riverbanks and arroyos. It is an aggressive competitor which sucks up the water and crowds out natives like the cottonwood. This tree, together with Siberian Elm and Russian Olive, represents what our bosque will become unless measures to prevent it can be found. Efforts to combat tamarisk invasion are being tried in the Bosque del Apache Wildlife Refuge with moderate success. [see also Tackling Tamarisk]

freshwater marsh grasses - Varieties are found covering the mudflats and edging onto the shore.

Kochia-Kochia scoparia An introduced weed which has crowded out much of the native groundcover, this plant is actually used for cattle feed because of its high protein content. Has spread rapidly throughout disturbed areas.

Russian Olive - Elaeagnus angustifolia Introduced for landscape and as windbreaks. Some birds eat the seeds.

Musk thistle - [introduced weed]

Beavers, Castor canadensis - this large rodent burrows into the riverbank underwater for its den, while its mountain brethren build dams which incorporate underwater entrances. The characteristic grooved tree stumps are sign of its existence.

Other animals seen in the area: crows - large flocks visible in the fall red tailed hawks - occasionally seen in the valley, mostly during the songbird migration. red squirrel, Tamiasciurus hudsonicus. Tree squirrels are not as abundant as one expects, but there is a population of these in the central Rio Grande Valley. grasshoppers - numerous in the late spring and summer.

Questions

1) Does anything about the bosque, its trees, understory, etc., seem unusual? In what ways has the bosque changed since man began tampering with the river and with its bosque?

2) What does the future of the bosque hold? What methods would have to be used to return this habitat to what is once was?