Acton Nature Center Nature Walk September 11, :00 a.m. Grasses Leader: Billy Teels. Introduction:

Transcription

1 Acton Nature Center Nature Walk September 11, :00 a.m. Grasses Leader: Billy Teels Introduction: This nature walk is sponsored by the Acton Nature Center (ANC) and Rio Brazos Master Naturalists (RBMN). The Acton Nature Center was established in 2004 by a donation from the U.S. Department of Interior to Hood County through the Federal Lands to Parks Program. The responsibility for stewardship and development of the area was subsequently given to Hood County Development District #1, and with the help of organizations such as ours (RBMN) the area is currently being developed and managed as a natural area. The RBMN is a chapter of Texas Master Naturalists, whose mission is to provide education, outreach, and services for the beneficial management of natural resources and natural areas within the community. The RBMN was getting started about the same time as the ANC was becoming established, and one of the first big projects of the organization was to help plan and develop the Center. RBMN volunteers have spent over 2000 hours to help manage the ANC trails and vegetation, conduct plant and animal surveys, conduct nature hikes and field trips for local schools, day care centers, garden and civics clubs, and home schooled children. The ANC is approximately 74 acres in size. Prior to its transfer to Hood County, the land was used by the Federal government as part of a nationwide system to help track aircraft location. Although radar equipment was a prominent feature of the property, the land was also leased to private landowners for grazing. According to local sources, livestock grazed the property continuously without periods of rest or rotation for many years. Although there has been significant recovery since livestock were removed at the onset of acquisition, the land still shows signs of grazing abuse. Today we will discuss grasses and the effects of grazing and fire on the plant community, and how those influences have contributed to create the plant community that exists today. 1

2 Stop 1. Introduction to grasses Importance of Grass: Of all the plants of the earth the grasses are of the greatest use to man. To the grasses belong the cereals, sugarcane, sorghum, and the bamboos; and, since they furnish the bulk of the forage for domestic animals, the grasses are also the basis of animal industry (A. S. Hithchcock, 1935, Manual of the Grasses of the U.S.). There are over 6,000 species of grasses in the world. At the ANC we have identified 325 species of plants of which 52, or about 16%, are grasses. The grass family can be generally identified be identified by 3 characteristics---reduced flower parts, long narrow leaves, and rounded stems with joints. Other grass-like families are sedges and rushes, but sedges do not generally have rounded stems and rushes do not have joints. Although they occur on all continents and in different habitats, grasses are the dominant plants in most semi-arid areas. In fact, the term prairie is often defined as a grass dominated landscape. Grasses are also extremely tolerant of natural grazing and are thought to have evolved along with grazing animals. Describe how grasses grow. Grass structure, and terminology: Grass Identification: 2

3 Grass ID: Grass ID is difficult unless the plant is in flower. Most keys use minute characteristics that have to be observed with a hand lens or dissecting scope, rather than the overall appearance of the plant, as a means of species identification. Today we are going to look at the macro-features, rather than the micro-features to identify. Stop 1 grass species: Hairy Grama (Bouteloua hirsuta) Tall Grama (Bouteloua pectinata) Silver Bluestem (Bothriochloa laguroides) Little Bluestem (Schizachyrum scoparium) Little Bluestem (Schizachyrum scoparium) Side-oats Grama (Bouteloua curtipendula) 3

4 Texas Purple Grama threeawn (Bouteloua (Aristida purpurea) rigidiseta) Rough Tridens (Tridens muticus) Stop 2. The prairie plant community and invaders. Pose the question: Can you imagine what this place looked like 200 years ago, at the onset of European settlement? An endless prairie from the Rio Grande all the way to the Boreal forest in Canada. Here at the ANC, the plant community would have been classified as a tall grass prairie ecosystem, with big and little bluestem, switchgrass, and Indiangrass as the dominant species. All are considered warm season grasses, and collectively, with the other components of the tall grass community, about 4,000 pounds of forage per acre per year were produced. North American bison historically grazed these grasslands for eons without ill-effects. In fact, tall grass prairie can withstand periods of heavy grazing, much like the buffalo did. However, if the community is overgrazed, by removing too much of the top growth (stems and leaves) by continuous grazing, the plant community is damaged. More than half of the annual growth of grass has to be left or there will be a reduction in the plant s root system and energy reserves, resulting in lower plant vigor and eventual replacement of tall grasses with species that are more tolerant of heavy, continuous grazing, known as increaser species. Heavy, continuous grazing combined with the lack of fire has transformed the plant community here at the ANC. The mechanism for the various increaser species that invade overgrazed grassland varies. For example, tree seeds that would not normally germinate under the shade and duff of tall grasses can now reach mineral soil, germinate, and grow. Likewise, plants that are less palatable, or even poisonous, are released due to the lack of competition. And, plants with shallow root systems, that were formerly minor components of the plant community, can now compete with compromised roots systems of tall grasses for moisture and nutrients, whereas they could not before. 4

5 The root system of the 4 principal tallgrass prairie grasses compared to turf grass (e.g., Bermuda grass). 5

6 Stop 2 species (all increasers). Ashe s Juniper (Juniperus ashei) Red-berry Juniper (Juniperus pinchotii) Honey Mesquite (Prosopsis glandulosa) Western Ragweed (Ambrosia psilostachya) Snow on the Prairie (Euphorbia bicolor) Texas prickly pear (Opuntia engelmannii) 6

7 Stop 3. Plant community recovery and the concept of ecological site. Pose the question: Once grazing has stopped, how long does it take for the plant community to recover. It depends on how damaged the plant community is, the physical characteristics of the site, and climate. Describe the concept of range condition--- excellent, good, fair, or poor range condition depending on how close or far apart the plant community is to the potential natural plant community for the site---the composition and relative abundance of species that would be there under natural conditions (e.g., without overgrazing). Obviously, a community that is compromised (e.g., composed mostly of increaser species ) would take much longer to recover than one that still had some tall grasses and other decreaser species remaining. Decreaser species are those species that decrease with heavy grazing. However, remember nature is resilient and the community will recover if it is not continuously abused. In this part of the world, with nearly 30 inches of precipitation, 50 percent recovery from poor condition can take place in 10 years on most sites (unless the top soil is eroded away). However, it may never be exactly the same; invasion of exotic species, long-term damage to the soil, and new human impairments all have adverse effects. Obviously all sites are not the same in their ability to support grasses and other plants. Physical characteristics (e.g., soils) also influence the species composition and productivity of the site. To account for this variability, ecologists have conceived the concept of ecological site, in which each site with different physical characteristics is acknowledged as having its own distinctive natural plant community and its own unique capability for production. For example, shallow, droughty soils may not support tall grasses at all, and therefore would not be classified as the same site as a deeper, more arable soil capable of producing tall grasses. Also, recovery of the plant community from poor condition may take longer on shallow, droughty sites than on better sites. Stop 3 ecological site examples. Stop 3 species. Japanese brome (Bromus japonicus) Texas wintergrass (Nassella leucotricha) 7

8 King Ranch Bluestem (Bothriochloa ischaemum) Azure blue sage (Salvia azurea) Stop 4. Rest Stop. Water, grazing distribution, and invasive exotics. The windmill was inherited with the property, along with the concrete tank. However, it had been abandoned for some time and was restored soon after the property was acquired. It is currently used to provide drinking water to wildlife and pets. The farmhouse was donated to the ANC by a local landowner in 2009 and will be the site for a future information center featuring the Center s flora and fauna, and will contain a bird observation deck and a butterfly hatchery. The butterfly garden was planted by the RBMN and the Master Gardeners and is currently maintained by RBMN volunteers on ANC monthly workdays. Bathrooms with running water have been a feature of the property for nearly a year. Grazing distribution is never the same over any landscape. There are always favored places where grazing animals like to frequent, such as around water. Here around the windmill, where livestock watered daily, the area was heavily overgrazed and currently contains a greater density of invasive species than anywhere else on the property. Stop 4 species. Bermuda grass (Cynodon dactylon) Johnsongrass (Sorghum halepense) 8

9 Vine mesquite (Panicum obtusum) Silverleaf Nightshade (Solanum eleagnifolium) Stop 5. Wet meadow site Grasses, and other plants, have different tolerances to wetness. Some, like rice, can grow directly in water, whereas as others, like corn or wheat, will die if they have only a few days of wet feet. The area in front of you is seasonally wet. Seldom does it pond water, but it is saturated to the surface for much of the winter and spring. Because it drains so poorly, it accumulates alkaline salts at or near the soil s surface. So, plants growing here must be tolerant of both water and salt. Like using a species degree of tolerance to grazing pressure to indicate range condition, a species tolerance to wetness can indicate how wet a site is. In fact, one of the measures of a jurisdictional wetland is whether or not a site has a prevalence of hydrophytic (water loving) vegetation. Stop 5 species. Buffalo Grass (Buchloe dactyloides) White Tridens (Tridens albescens) 9

10 One-seeded Croton (Croton monanthogynus) Common Ragweed (Ambrosia artemisiifolia) Stop 6. Erosion and channel head-cutting. In addition to altering the species composition of the plant community, overgrazing also results physical damage to the land by causing soil erosion. In certain instances, vegetative cover is so reduced by overgrazing that mineral soil exposed over much of the pasture. In such cases, sheet and rill erosion occurs on grasslands just like it does on cropland. Overgrazing also causes erosion of stream banks and channels, which not only causes soil loss, but also causes downstream sedimentation. In addition, channel erosion (head-cutting) can drain adjacent water tables, which causes loss of subsoil moisture and reduces the productivity of the site. Site 6 species. Seep Muhly (Muhlenbergia reverchonii) Fringeleaf Leavenworth s Wild Eryngo Petunia (Ruellia (Eryngium humilis) leavenworthii) 10

11 Switchgrass (Panicum virgatum) Indiangrass (Sorghastrum nutans) Common Broomweed (Gutierrezia dracunculoides) Narrow-leaf Sumpweed (Iva angustifolia) 11