Canoga Creek Farms & Conservancy Canoga Marsh Enhancement Project:
Vegetation and Wildlife Surveys Assessment, 2008.
Frank Morlock and Jim Eckler, NYS DEC Bureau of Wildlife
Introduction
Twenty wetland enhancements (shallow-water potholes and associated level ditches) were constructed in Canoga Marsh in April of 2007 (Appendix A: Before and after aerial images). Work was done under the Natural Resource Conservation Service Wetland Restoration Program and the goal was to increase interspersion of open water and provide enhanced habitat for marsh birds, ducks and muskrat. The enhancements added over 6 acres of open water to the 50 acre emergent marsh. Excavated organic spoils were removed from the wetland to the greatest extent practicable, but in some cases, spoils were side-cast in shallow depths within the wetland, near each excavation. Depths of these spoils were held to no greater than 10 inches to allow the soil to remain saturated, keep the soil drainage classification as ‘very poorly drained’, and meet our objective of revegetating the spoil areas with native hydrophytic plants.
Prior to restoration, most areas within this marsh were dominated by cattails as a monoculture, growing densely as a perched or dry marsh. Open water was lacking, and the hydrology was basically apparent only as it kept this perched substrate moist from below, or during high water events.
The water levels in the marsh are tied to the water levels in Cayuga Lake which fluctuate throughout the year, but are somewhat stable during the growing season. Lake levels are manipulated by the NYS Canal Corporation through a series of locks. Levels are set to accommodate boat traffic during the summer at about 383.5 ft. above sea level, and prevent ice damage in the winter at below 382 feet. Lake water levels during construction (3/30/07 to 4/7/07 ) increased through a range of 384.0 to 384.5 feet above sea level.
Restoration work included level ditching and potholing. Some spoil areas were seeded and planted to provide a diversity of plants known to be beneficial to wildlife, and reduce growth of non-native plants; others were left alone to observe the characteristics of natural growth of vegetation.
Surveys were made to assess the growth of plants in the disturbed areas and to monitor wildlife use of the enhanced marsh. Simple vegetation assessment surveys were conducted post construction, in September 2008. Secretive marsh bird playback surveys were performed in 2007 and 2008.
Methods
Vegetation surveys:
Ten random points were surveyed for vegetation within 1 x 1 meter quadrants. Five of these points were located in undisturbed areas within the marsh, and five were located in areas where organic spoils were side cast. Plant species were also identified throughout the marsh and between quadrants whenever they were encountered. Future surveys are planned for 3, 5, and 10 years post restoration (2009, 2011 and 2016).
Wildlife surveys:
In addition to vegetation surveys, secretive marsh bird surveys were performed at Canoga Marsh in 2008. A tape player with marsh bird calls was used to solicit bird response. The National Marsh Bird Monitoring Program Protocol developed by Courtney J. Conway was used. On two separate occasions Canoga Marsh was surveyed using an eleven minute call broadcast sequence broken down into two sections: first, a five minute passive period (silence), immediately followed by a six minute call sequence in which thirty seconds of calls for each bird (6 species) is followed by thirty seconds of silence. For this series of surveys we used least bittern, sora rail, Virginia rail, king rail, American bittern, and pied-billed grebe calls.
Results and Discussion
Vegetation:
Disturbed areas remained dominated by cattail (Typha sp.), but were overtopped with jewelweed (Impatiens capensis) and other species, making most of this area matted down and structurally different from undisturbed areas. Although cattail densities were 40-70 stems per square meter (spsm), in both disturbed and undisturbed areas, the disturbed areas contained a density of 3-5 spsm of jewelweed which typically represented nearly 80-90% cover.
Undisturbed areas are still representative of the marsh before restoration work. Although a few additional species were noted in survey plots, these undisturbed areas typically had the same form; a dominant monoculture of cattail growing high and erect.
It is interesting to note that none of the species planted (Figure 1 and Appendix C) in the spoil areas after completion of the excavation work were found in any plot. Outside of the plots, it was noted that many of the bareroot plantings (buttonbush, Canada
Figure 1. List of species planted in Canoga Marsh wetland enhancement project, 2007.
Number or Pounds
|
Common Name
|
Scientific Name
|
Notes
| |
40 pounds
|
Barnyard Grass
|
Echinochloa muricata
| ||
40 pounds
|
Fowl
|
Poa palustris
| ||
5 pounds
|
Wetland Meadow mix
|
Ernst Seed # 122
| ||
300 pounds
|
Japanese Millet
|
Echinochloa crusgalli
| ||
40 pounds
|
Annual Ryegrass
|
Secale cereale
| ||
125 pounds
|
Custom Dike mix
|
Merritt Seed Co.
| ||
1 pound
|
Rattlesnake Grass
|
Glyceria Canadensis
| ||
240
|
Hightide Switchgrass
| |||
300
|
Calamagrostis Canadensis
| |||
40
|
Buttonbush
|
Cephalanthus occidentalis
| ||
400
|
Prairie Cordgrass
|
Spartina pectinata
|
A focus of the plant surveys was to detect the presence of invasive species, especially purple loosestrife (Lythrum salicaria) and Phragmites (Phragmites australis). Only one of the 5 survey points in the disturbed areas contained an invasive that was not present in undisturbed plots. The invasive plant in this case, was purple loosestrife. General observations suggest loosestrife is a concern in several disturbed areas, particularly those near water. Phragmites was not detected in any plot, but the small stands that were present before the enhancement are still present.
Plant species diversity in the disturbed areas was greater than undisturbed (8 vs 3 species) (Fig. 2). Some of these plants (smartweed, vervain, tear thumb) are considered beneficial for wildlife, primarily for seed or soft mast production. But, several of these plants can be of concern as invasive plants. Bittersweet nightshade (Solanum dulcamara) is an invasive exotic, listed as invasive in the lower 48 states and known to be poisonous to livestock. Hedge bindweed (Convolvulus sepium) is a native vine and member of the morning glory family. It is commonly associated with gardens and corn fields and can become dominant. We recommend continued monitoring of the disturbed areas for the spread of these two species, but immediate action is not recommended as these species are not expected to dominate in wet sites. Immediate action is recommended for control of purple loosestrife. In fact, loosestrife leaf-feeding beetles were released here in the summer of 2007 and should provide control, but continued monitoring is recommended.
Wetland plants colonized the disturbed spoil at a similar rate to what was found throughout the marsh. Six of the 8 species (75%) found in plots in the disturbed areas have a wetland indicator status of FAC or wetter (Fig. 2). Under NY’s freshwater wetlands laws, species that are FAC or wetter (OBL, FACW+, FACW-, FAC+), are considered in qualifying a site as a wetland. Two of the 3 species (67%) found in plots in undisturbed areas have a wetland indicator status of FAC or wetter. Fourteen of nineteen species (74%) found throughout the marsh are FAC or wetter (Fig. 3).
At the time of the surveys, the ditched and potholed areas in most cases, particularly where they were connected to the lake, held water deep enough (greater than 3 feet deep) to suppress cattail growth. Those that were not connected held water, but cattail was growing through the water in many of these areas. Cayuga Lake water levels were around 383 feet during September 2008, when vegetation surveys were made (Canal Corp).
The potholes were designed to have irregular bottoms with a 4-foot maximum depth and varying side slopes from the shallowest at 6 to 1 to the steepest at 3 to 1 (horizontal to vertical). Approximately 2/3rds of the excavated areas were cut 4 to 5 feet below the water level at the time of excavation. Cayuga Lake records suggest that water levels were 384.5 feet above sea level during excavation, resulting in pothole bottoms varying slightly around a 380 foot elevation. We know that the projected summer water level in Cayuga Lake is about 383.5, so the deepest water levels in the potholes should be about 3.5 feet. Levels have historically fluctuated within 0.5 feet of this mark during the growing season and times when waterfowl would be expected to use the area for brood rearing.
Approximately 6.7 acres of open water were added to this 50 acre section of emergent marsh through the construction of potholes and ditches. We expect these areas will diminish over time as cattail spreads into the shallow water along the sloped excavated areas.
Water depths of 3 feet are suggested to prevent growth of cattail, however these depths must be held throughout the year. Once cattail is established there seems to be great site variability in how water depths can be used to control density, and the muskrat population will play an important part in this process, as well. It will be important to monitor how cattails and muskrats colonize the varying elevations of excavated and disturbed areas in this marsh.
Future vegetation surveys could include submergent species within the excavated potholes or ditches.
Figure 2. Plants, and their wetland indicator status, found (9/2008) within the disturbed and undisturbed, one square meter quadrants on the Canoga marsh enhancement project.
Species
|
Common Name
|
disturbed quadrants (#)
|
undisturbed quadrants (#)
|
Wetland Indicator Status
|
Typha sp.
|
Cattail
|
5
|
5
|
OBL
|
Impatiens capensis
|
Spotted Touch-
Me-Not
|
5
|
1
|
FACW
|
Solanum dulcamara
|
Bittersweet Nightshade
|
2
|
2
|
FAC-
|
Convolvulus sepium
|
Hedge Bindweed
|
2
|
0
|
FAC-
|
Polygonum hydropiper
|
Common Smartweed
|
1
|
0
|
OBL
|
Verbena hestate
|
Blue Vervain
|
1
|
0
|
FACW+
|
Polygonum sagittatum
|
Arrow-leaved Tearthumb
|
1
|
0
|
OBL
|
Lythrum salicaria
|
Purple Loosestr
ife
|
1
|
0
|
FACW+
|
Figure 3 Wetland Indicator Status for plants found in organic spoils and through
out Canoga Marsh, 2008.
No comments:
Post a Comment