THIRD ANNUAL SANTA CRUZ TARPLANT POPULATION …afisher/post/drywell/PapersReports... · Objectives...

THIRD ANNUAL SANTA CRUZ TARPLANT POPULATION ASSESSMENT FOR THE

291-ACRE WATSONVILLE MUNICIPAL AIRPORT

STUDY AREA CITY OF WATSONVILLE, SANTA CRUZ COUNTY, CALIFORNIA

Prepared for: CITY OF WATSONVILLE,

WATSONVILLE MUNICIPAL AIRPORT 100 Aviation Way

Watsonville, CA. 95076

Prepared by:

12240 Herdal Drive, Ste. 14 Auburn, California 95603

(530) 888‐0130

AUGUST 2014

TABLE OF CONTENTS

INTRODUCTION .......................................................................................................................................... 1

Project Location.................................................................................................................................... 1 Setting .................................................................................................................................................... 1 Status of Santa Cruz Tarplant ............................................................................................................ 1 History and Findings of Past Santa Cruz Tarplant Assessments ................................................. 4 Objectives of the Assessment ............................................................................................................. 5

METHODOLOGY .......................................................................................................................................... 5

Survey Approach and Methodology ................................................................................................ 5 Field Methodology ........................................................................................................................ 6 Mapping of SCT Sub-populations .............................................................................................. 7 Santa Cruz Tarplant Seed Count Estimation ............................................................................ 7

SURVEY RESULTS ........................................................................................................................................ 9

Descriptions of Representative Sub-populations .......................................................................... 12 SCT Seeds per Plant Estimate .......................................................................................................... 15

CONCLUSIONS ........................................................................................................................................... 16

FIGURES

Figure 1. Site & Vicinity Map .................................................................................................................. 2 Figure 2. Aerial Photograph .................................................................................................................... 3 Figure 3. Santa Cruz Tarplant Population Densities ............................................................................ 8 Figure 4. Site Photos (Oblique Aerial) .................................................................................................. 18 Figure 5. Site Photos (Oblique Aerial) .................................................................................................. 19 Figure 6. Site Photo (Oblique Aerial) ................................................................................................... 20 Figure 7. Site Photos (Oblique Aerial) .................................................................................................. 21 Figure 8. Site Photos (Oblique Aerial) .................................................................................................. 22 Figure 9. Site Photos (Oblique Aerial) .................................................................................................. 23 Figure 10. Site Photos (Ground) ............................................................................................................ 24 Figure 11. Site Photos (Ground) ............................................................................................................. 25 Figure 12. Site Photos (Ground .............................................................................................................. 26 Figure 13. Site Photos (Ground) ............................................................................................................. 27

TABLES

Table 1. Monthly Rainfall Near Watsonville Municipal Airport – Tarplant Survey Years ............ 6 Table 2. Density Rating for Santa Cruz Tarplant at Watsonville Municipal Airport ...................... 7 Table 3. Estimated Santa Cruz Tarplant Population by Location ...................................................... 9

Watsonville Municipal Airport Study Area Salix Consulting, Inc. Third Annual Tarplant Population Assessment 1 August 2014

THIRD ANNUAL SANTA CRUZ TARPLANT POPULATION ASSESSMENT

FOR THE 291-ACRE WATSONVILLE MUNICIPAL AIRPORT STUDY

AREA

INTRODUCTION

Project Location

Salix Consulting, Inc. conducted a third year Santa Cruz tarplant (SCT) population assessment for an approximately 291-acre study area at the Watsonville Municipal Airport in Watsonville, Santa Cruz County, California. The Watsonville Municipal Airport (Airport) study area is located north of Highway 1, approximately 1.5 miles west of downtown Watsonville. The airport is located along the central coast, approximately 2.5 miles northeast of the Pacific Ocean. The airport is situated within the Los Corralitos and San Andres land grants, Township 11 and 12 South, and Range 1 and 2 East on the 7.5 minute Watsonville West USGS quadrangle. Approximate latitude and longitude for the center of the site is 36 56’ 05” North and 121 47’ 27” West (Figure 1).

Setting

Site elevations range between 60 feet in the southern portion of the airport property and 140 feet in the northern portion. The study area is primarily a maintained grassland and paved surfaces and buildings associated with airport operations. In addition to normal airport operations, the Watsonville Municipal Airport also contains a shooting range west of runway 2-20 (Figure 2).

Adjacent land uses include commercial, industrial, and residential. Higher density residential and commercial land uses occur further to the east; while rural residential, agricultural, and undeveloped land uses occur further to the west. Highway 1 bisects the southern portion of the airport property. A tributary to Harkins Slough runs south along the western boundary. Wetland swales, streams, and Harkins Slough continue offsite to the south and east.

Status of Santa Cruz Tarplant

Santa Cruz Tarplant (Holocarpha macradenia) is listed by the federal government as threatened and by the State of California as endangered. Final ruling on critical habitat for Santa Cruz tarplant was established by the USFWS on October 16, 2002. One of the California critical habitat units, Unit I – Watsonville Unit covers most of the airport property (approximately 222 acres) northeast of Highway 1. It includes the unpaved areas around the airport runways and taxiways.

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Study Area

Watsonville Airport

Watsonville, CAJuly 21, 2014

2012 Aerial Photo


History and Findings of Past Santa Cruz Tarplant Assessments

As addressed in the Biological Supplement for the Watsonville Municipal Airport Proposed Reconstruction of Taxiway C and Phase I of the General Aviation Apron (North Fork Associates and Wallace Environmental Consulting 2011), habitat for Santa Cruz tarplant historically consisted of grasslands and prairies found on coastal terraces below 330 feet in elevation from Monterey County to Marin County. As of 2011, Santa Cruz tarplant was known to exist at up to 15 native populations in the Monterey Bay area and eight transplant populations in Contra Costa County. Additionally, three areas have been planted as experimental populations as part of ongoing research. All native San Francisco Bay area populations have been extirpated.

The Watsonville Municipal Airport supports the largest extant population of Santa Cruz tarplant. The numbers of Santa Cruz tarplant individuals far surpass the total of all other populations combined. This is likely due to the airport’s favorable consistent, annual management practices.

According to the Mitigation Plan for Santa Cruz Tarplant and Coastal Terrace Prairie at the Watsonville Airport, prepared by John Gilchrist & Associates (draft, 2004), Santa Cruz tarplant population was first formally documented at the airport in 1993 by Randall Morgan. The total number of tarplant was estimated at approximately 459,000 plants occupying 36.05 acres. In 1993, the airport altered its mowing regime to promote the spread of tarplant by adjusting blade height and timing of maintenance mowing to avoid impacts to the tarplant. In fall 1995, Airport staff began a program to establish tarplant in areas of the airport where it did not occur. The purpose of the program was to determine the feasibility of relocating tarplant and maintaining relocation populations over time, with the goal of mitigating for potential loss of tarplant due to airport expansion. As a result of these maintenance practices, the number of tarplant individuals and acreage coverage increased.

Gilchrist notes that additional population censuses were performed in 1994, 1998, 1999, 2000, 2001, and 2003. The number of individual plants and acreage coverage varied over these years. The highest numbers were recorded in 1998 when John Gilchrist & Associates performed a detailed census, finding just under 28 million tarplant individuals occupying 44.11 acres. According to Gilchrist, the abundance and extensive distribution of the 1998 population was likely due to the heavy El Niño rainfall of the 1997-98 winter, during which 46.72 inches of rainfall (217% of normal) was recorded. (Average rainfall for Watsonville is approximately 21.53 inches per year.)

The 1999 survey estimated approximately 8,208,785 tarplant individuals on 28.95 acres. Rainfall during this year had been much less than the previous El Niño year (21.13 inches), and some habitat “may have been disturbed by disking the previous winter.”

In 2001, 17.36 inches of rainfall was recorded, and the survey estimated 2,496,709 tarplant individuals on 33.78 acres. In 2003, a visual inspection was conducted, and tarplant “was found in areas and in densities similar to previous years, but appeared to be less abundant overall.” Rainfall for 2002-03 was 20.24 inches.


Gilchrist states that a comparison of annual tarplant census data to annual rainfall data “suggests that rainfall has a definite effect on tarplant abundance but is not the sole controlling factor.” Other factors may include grassland management, fire events, and relocation efforts that began after the initial 1993 survey. The Mitigation Plan for Santa Cruz Tarplant and Coastal Terrace Prairie at the Watsonville Airport includes a table displaying annual rainfall by month during the tarplant census years described in the report (page 5a).

In 2012 and 2013, Salix Consulting conducted a tarplant population assessment to map the distribution of Santa Cruz tarplant at the Airport, assess population densities within each sub-population, and estimate (not count) the number of plants within each sub-population. Survey results from 2012 (conducted on July 23 and July 24) estimated approximately 512,000 individuals of SCT inhabiting 18.1 acres of the study area. The majority of the species observed were diminutive, and a high distribution of them occurred on scraped areas with hard packed soil. The 2013 survey was conducted on June 27-29. Results indicated a 35% increase in SCT observed (approximately 692,000 individuals) and almost 26% more land (22.8 acres) mapped for SCT than in 2012. As with the 2012 survey however, most of the observed SCT occurred over scraped areas and plants were diminutive.

Objectives of the Assessment

As with the previous two surveys, the primary objective of this survey was to map the distribution of the Santa Cruz Tarplant population on the airport property.

The secondary objective was to determine the approximate number and density of plants that occur within this population. Because it was necessary to take time constraints and cost into consideration, formal sampling protocols were not utilized. Instead, visual estimation was utilized, which can provide a good approximation of distribution and density but not necessarily an accurate count, which would result from using a formal sampling protocol.

METHODOLOGY

Survey Approach and Methodology

The 2014 Survey was conducted July 2-4, 2014 by Jeff Glazner, assisted by Matthew Shaffer, and was timed to coincide with the peak blooming period (late June through late July) of Santa Cruz Tarplant. Rainfall to-date for 2013-2014 had totaled 9.49 inches (Table 1), the smallest amount in recent years. The previous year, 2012-2013, had also been dryer than average totaling 12.83 inches. Most of the rainfall in 2012-2013 occurred in November and December. In 2013-2014, most rainfall took place between February and April (during which 8.55 inches of the season’s 9.49 inches of rain fell), with the heaviest precipitation occurring in February.


Table 1.

Monthly Rainfall Near Watsonville Municipal Airport – Tarplant Survey Years

Field Methodology

All non-paved areas of the 291-acre airport property (Figure 1 and 2) were evaluated for SCT. The site was walked along meandering transects that would allow location of SCT if it were present. Transects were closer together in areas where there was a higher likelihood of locating SCT. For example, the agricultural field at the southern end of the airport and areas with deeper or tilled soils were less likely to support SCT, so transects were spaced further apart in those areas.

When SCT was located, the area was evaluated for the limits of the sub-population. Once this evaluation was complete, a Trimble GeoXT 6000 GPS (sub-meter accuracy) was used to map a polygon around the outliers of the sub-population. The data were compiled using ArcGIS 10.2 to create the Santa Cruz Tarplant Occurrence map.

When the limits of a sub-population were determined and mapped and the population observed, a visual estimation of the number of plants within each sub-population was made. This was done by simple independent visual observation between the two people conducting the survey. Small areas of the population were counted and visually extrapolated to the remainder of the population. Formal sampling protocols were not

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Annual

1992-93

0.86 0.01 7.01 10.47 5.71 2.87 0.73 1.21 0.37 0.00 0.00 0.01 29.25

1997-98

1.09 6.18 3.63 10.23 15.99 3.84 3.01 2.46 0.14 0.00 0.00 0.15 46.72

1998-99

0.61 2.95 0.91 4.98 7.10 2.90 1.68 0.00 0.00 0.00 0.00 0.00 21.13

1999-2000

0.22 3.30 0.29 7.39 10.14 2.59 0.98 0.76 0.09 0.00 0.16 0.09 26.01

2000-01

3.10 0.49 0.76 3.44 6.28 1.98 1.12 0.00 0.00 0.00 0.02 .017 17.36

2001-02

0.34 4.30 7.89 1.48 0.70 1.51 0.24 0.29 0.00 0.00 0.07 0.00 16.82

2002-03

0.00 3.40 8.88 1.27 1.71 1.22 2.52 1.16 0.02 0.02 0.02 0.02 20.24

2011-12

1.96 2.19 .05 2.70 .61 5.09 3.01 0.04 0.21 0.05 0.01 0.00 15.92

2012-13

0.35 4.42 6.09 0.68 0.44 0.48 0.32 0.00 0.04 0.01 - - 12.83

2013-14

0.05 0.46 0.33 0.05 4.74 2.54 1.27 0.05 0.00 - - - 9.49


followed due to time constraints and because the emphasis of the study was on mapping and not actual plant counts.

A density rating (low, medium, high) was assigned for each sub-population based on the number of plants estimated to be present over a given area. The density thresholds were created to provide a visual representation of the relative densities of each sub-population of SCT. Table 2 describes the rating for each density category assigned to each subpopulation.

Table 2.

Density Rating for Santa Cruz Tarplant at Watsonville Municipal Airport

Density Rating Description of Density Low Very sparse; SCT not a

dominant plant in the area (up to 8000 plants per acre)

Medium Clusters of SCT sparsely scattered; may be a dominant or co-dominant plant in some areas (8001 to 20000 plants per

acre High Very dense population; SCT

one of the dominant plants in the area (20001 to 67000 plants

per acre)

Density judgments were made based on visual observations during the field assessment. Assignments are qualitative and generally represent the number of plants over the sub-population area.

Mapping of SCT Sub-populations

Areas where SCT were located were assessed for their population size. Once the boundary of the sub-population was mapped, the number of plants in the sub-population were estimated (Santa Cruz Tarplant Occurrence map, Figure 3.

Santa Cruz Tarplant Seed Count Estimation

In addition to the SCT population estimate, twenty flowerheads from several different plant forms were analyzed in an effort to ascertain the approximate number of seeds in a typical flowerhead. With this information and an estimate of the number of plants and flowerheads present, an approximation of the number of seeds in the population could be made. Examination of flowerheads was made with a 20X lens and seed counts were tallied. The results of this effort are discussed in the Conclusions section at the end of this document.

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SANTA CRUZ TARPLANTAREAS JULY 2014

Figure 3

Watsonville, CA

Notes:Tarplant census dates July 2-4, 2014Aerial Photo - 2014Study Area 291 acres

Study Area

Total 23.1 ac

Santa Cruz Tarplant Population Densities#* Individual or Small Clusters

Low (10 to 8000 plants/ac) 1.0 ac

Medium (8001 to 20000 plants/ac) 9.5 ac

High ( 20001 to 67000 plants/ac) 12.6 ac


SURVEY RESULTS

As shown in Figure 3, Santa Cruz tarplant sub-populations were identified and mapped in areas around Runway 9-27, Taxiway C, Runway 2-20, Taxiway A, and the general aviation apron. In addition, commonly-associated species within the vicinity of SCT areas were identified and include Acmispon americanus, Aira caryophyllea, Briza minor, Danthonia californica, Erodium botrys, Festuca perennis, Hordeum murinum, Lactuca serriola, Leontodon saxatilis, Plantago lanceolata, Plantage major, Trifolium angustifolium, and coast tarweed (Madia sativa).

The sub-populations are identified by density (color-coded) and numbered on Figure 3. Table 3 provides a summary of the locations of sub-populations and the estimated numbers of plants in each sub-population, which is followed by descriptions of representative sub-populations. Site photos are provided at the end of the document; Figures 4 through 9 are aerial oblique photos of the airport, Figure 10 shows comparative robust and diminutive forms of SCT, and Figures 11 through 13 are ground photos of representative areas where SCT was found.

Table 3.

2014 Estimated Santa Cruz Tarplant Sub-Population by Location

Number Location of

Sub-population Density Rating Estimated

Plant Count Acreage (±)

1 Runway 2 end, near

shooting range Medium 800 0.04

2 Runway 2 end, near

shooting range High 14,000 0.47

3 Runway 2 end Medium 1,400 0.11

4 Runway 2 end

along Taxiway A Medium 20 0.001

5

Runway 2 end in infield between

runway and Taxiway A at

number

High 32,000 0.64

5a


runway and Taxiway A

Medium 1,200 0.07

6 Runway 2-20,

midway on west side

High 120,000 1.81

7

Runway 2-20, in infield midway, between runway and Taxiway A

High 22,000 0.69

8 Runway 2-20 in

infield near Taxiway C,

High 32,000 0.73


Number Location of Sub-population

Density Rating Estimated Plant Count

Acreage (±)

between runway and Taxiway A

near G.A. Apron

8a Runway 2-20

between Taxiway A and G.A. Apron

Low 70 0.05

9

At intersection of Runways 2-20 and 9-27, infield near

Taxiway C

Medium 2,500 0.25

10

Runway 9-27 in infield, midway between runway and Taxiway C

Low 2,000 0.26

11

Runway 9-27 in infield, midway between runway and Taxiway C

Medium 3,000 0.19

12

Runway 27 in infield between

runway and Taxiway C

High 140,000 2.53

14

Near Runway 27 on south side of

Taxiway C near hangar

Medium 4,000 0.28

15 Runway 27 near

numbers and along Taxiway C

High 4,500 0.22

17 Along northeastern side of Runway 27

Low 500 0.53

18 North of Runway 9-27 and east of

Runway 20 Medium 160,000 8.18

19 North end of Runway 2-20

Medium 3,000 0.31

20 West side of

northern end of Runway 2-20

Medium 800 0.08

21 North side of

western portion of Runway 9-27

High 125,000 4.09

24



High 7,500 0.36

27 Runway 9 end in infield between

High 20,000 0.86


Number Location of Sub-population

Density Rating Estimated Plant Count

Acreage (±)


29 Southern boundary of western portion

of Taxiway C High 2,000 0.09

31 Runway 2 infield between runway and Taxiway A

High 3,500 0.06

32 East of Taxiway A and south of G.A.

Apron Low 50 0.009


Apron Medium 200 0.01

34 West side of


Low 300 0.05

36 Runway 2 end on

west side, near shooting range

High 500 0.01

38 Southern boundary of Taxiway C west

of windsock Low 10 0.007

39



High 750 0.03


Apron Low 40 0.01

44 East of Taxiway A, near G.A. Apron

Low 200 0.03

45 East end of Runway 27

Low 25 0.004

46 East end of Runway 27

Low 500 0.07

47 West side of


Medium 20 0.001

48 West of Runway 2-

20, midway Medium 200 0.02

49 Taxiway C near

west side of Runway 9-27

Low 20 0.01

TOTALS ±705,000 ±23.16


Descriptions of Representative Sub-populations

Locations #1 and #2

Two areas occur just west of the southern end of Runway 2-20 in a highly-disturbed area, adjacent to the road leading to the shooting range. There are two distinct areas of SCT in large numbers with moderate vegetation cover, mostly small plants with minimal branching (Figure 4).

Location #3

Between 2013 and 2014 locations 3, 3a, 3b, and 3c combined into one area, location 3, which features a moderate scattering of plants located between the gravel entry road to the shooting range and the corner of Runway 2. This area is highly disturbed beyond regular mowing and has mostly low growth with few branching stems (Figure 4).

Location #4

Approximately twenty individuals of SCT are located just off the pavement of Taxiway A near its intersection with the end of Runway 2. This is a highly-disturbed location beyond regular mowing that is influenced by adjacent hayfield disturbance (Figure 4).

Locations #5 and #5a

A very dense area of SCT is located in the infield near the numbers on Runway 2. Additional medium-density clusters of plants are found in the northern section of the same infield (location 5a) (Figure 4).

Location #6

High-density population of SCT is located in scraped area at the bottom of a drainage area west of and midway along Runway 2-20. Soils are very thin due to scraping. Plants are thriving in scraped area, with robust growth and good stem branching (Figures 5.1 and 11).

Location #7

Dense population is located near midfield of Runway 2-20, between the runway and Taxiway A. Highest density of plants are gathered at the base of a shallow swale with robust growth (Figures 5.1 and 11).

Locations #8 and #8a

A dense population is located in same infield area as location 7. At location 8a between Taxiway A and the G.A. Apron, plants occur in small, low-density clusters (Figures 5.1, 5.2, and 6).

Location #9

A highly-disturbed area of medium-density population is located in the small infield area bound by two taxiways and two runways. The majority of SCT is small and is found along a shallow depression near the edge of the infield area (Figure 6).


Locations #10 and #11

Both populations are located in the infield bound by Taxiways A and C and Runway 9-27. Location 10 is low-density, and location 11 is medium-density. Plants are low to the ground (Figure 7.1).

Location #12

This population occupies most of the infield between the eastern end of Runway 27 and Taxiway C. It is heavily populated, with high-density robust plant growth at the edge of the pavement, along a shallow depression (Figure 7.1 and 7.2).

Location #14

Locations 13 and 14 have combined since 2013, forming one area, Location 14. It is a medium-density population of robust plant growth along Taxiway C and by a hangar, near the end of Runway 27 (Figure 7.2).

Location #15

Population is located near the numbers at Runway 27, along Taxiway C. High-density population is on the east side of the taxiway in a partially-disturbed area. Most plants are small, but there is some robust growth (Figures 7.2 and 12).

Location #17

A low-density linear population of small SCT parallel to and just north of Runway 27 in a disturbed area. An additional arm of the population runs along the slope of a drainage ditch (Figure 7.2).

Location #18

The largest area of all sub-populations on airport, this area contains the largest population of SCT. It occurs over a scraped area north of Runway 9-27 and east of Runway 2-20. Density varies greatly throughout population, with mostly small plants with minimal branching (Figures 7.1, 8.1, and 13).

Location #19

A medium-density population is located in a scraped, hard-packed area immediately off of the end of Runway 20. Plants are clearly located in a particular pattern based on grading (Figures 8.1, 8.2, and 13).

Location #20

This small, medium-density area is located well away from other populations, just west of the displaced threshold of Runway 20. Plants are mainly low to the ground (Figures 6, 8.2, and 12).

Location #21

This dense and highly variable population is located parallel to Runway 9 in a formerly scraped area. Locations 23 and 35 appear to have been annexed to this location since


2013. Additional scarce plant growth occurs off the west end of Runway 9, mostly small plant growth with robust and dense growth along the base of the scraped area (Figures 9.2 and 12).

Location #24

A high-density population is located at the west end of the infield near the intersection of Runway 9 and Taxiway C. Location 24 includes location 41 from the 2013 survey (Figures 9.1 and 9.2).

Location #27

Location 27 now includes location 40 from the 2013 survey. It is a high-density population along the infield area between Runway 9 and Taxiway C, on hard-packed soil with very small plants with minimal branching (Figures 9.1, 9.2, and 13).

Location #29

A small, dense population is located south of Taxiway C at the western end; mostly low growth (Figure 9.1).

Location #31

A small population of densely-packed SCT occurs in the infield area along Taxiway A and Runway 2. Robust growth and good branching are evident (Figures 4, 5.1, and 11).

Locations #32 and #33

Small clusters of medium-density, low-level growth occur at location 33, near Taxiway A and south of G.A. Apron. Low-density robust growth occurs at location 32, east of Taxiway A and south of G.A. Apron. The robust growth may be due to runoff from a nearby workshop (Figure 5.2).

Location #34

Located west of the end of Runway 20 is a small, low-density population of fairly robust growth and branching stems that occurs in tight clusters along the base of a swale (Figures 8.1 and 8.2).

Location #36

Located west of Runway 2, northeast of the shooting range, is a high-density clusters of branching plants throughout a shallow ditch with hard-packed ground (Figure 4).

Location #38

A sparse cluster of small plants occurs south of Taxiway C and west of the windsock (Figure 9.1).

Location #39

A high-density population of medium-sized growth occurs infield, between Runway 9 and Taxiway C (Figure 9.1 and 9.2).


Location #43

Low-density scattered growth occurs east of Taxiway A and south of the G.A. Apron, mostly low growth with little branching. This location is new since 2013 (Figure 5.2).

Location #44

New location with low-density growth occurring in small clusters of low-lying plants with branching stems, located east of Taxiway A, near the G.A. Apron (Figure 5.2).

Location #45

A small, low-density cluster of robust SCT growth with healthy branching occurs northeast of the end of Runway 27. This is mediocre habitat, with heavy vegetation cover and loose soil. This location is new since 2013 (Figure 7.2).

Location #46

This new site is located east of Runway 27 in mediocre habitat similar to location #45. Sparse clusters of plants ranging from small to medium sized, with branching present (Figure 7.2).

Location #47

A small population of medium-density, robust SCT with good branching occurs in another new location on the west side of the northern end of Runway 2-20, near the edge of the property (Figure 8.2).

Location #48

A thin strip of mostly-robust, medium density SCT growth occurs along hard-packed soil, bordering soft-soiled land and a creek, located west of Runway 2-20, midway along and near the edge of the property. SCT has not been previously found in this area (Figures 5.1 and 9.2).

Location #49

A new location near Taxiway C on the west end of Runway 9-27, with scattered plant growth, low to the ground (Figure 9.1).

SCT Seeds per Plant Estimate

Seed counts were estimated on a small sample size (20 plants) with a 20x scope. On average, each flowerhead contained 53 disk flowers and 10 ray flowers for a total of 63 seeds per flowerhead.

It is estimated that, on average, approximately three flowerheads per plant were produced on plants with little or no branching (diminutive form). For plants exhibiting medium to extensive branching (robust form), it is estimated that on average, there were approximately 15 flowerheads per plant.


Given the estimated distribution of robust and diminutive SCT (80% diminutive, 20% robust), it was calculated that there are approximately 200,000,000 potential disk flower seeds and 40,000,000 potential ray flower seeds in the study area. Viability was not measured.

CONCLUSIONS

This Santa Cruz Tarplant (SCT) assessment at the Watsonville Municipal Airport was conducted during the peak blooming period, on July 2-4, 2014. All unpaved areas of the airport upper surfaces were walked and visually observed for the presence or absence of SCT. When located, the boundaries of the sub-population were determined, mapped with a sub-meter GPS, and the number of plants in the sub-population were estimated. SCT was identified on approximately 23.1 acres of the study area. It is estimated that there are approximately 705,000 individual plants within these areas.

Previous surveys of this population have identified between 28.95 acres in 1999 and 44.11 acres of SCT area in 1998, and between 459,000 plants in 1993 and just under 28,000,000 plants following the heavy El Niño rainfall of the 1997-98 winter. The area identified in this assessment is about half of the area identified in previous years, and the current estimate of the number of individuals present may be in the low range, although these estimates are slightly higher than in 2013 and moderately higher than in 2012.

The reasons for the smaller footprint and number of plants could include several factors including the third consecutive low-rainfall year, the timing of regular mowing in relation to plant phenology, or sparse outliers that were crowded with adjacent non-SCT species and thus, difficult to locate. The extended period of low rainfall is a likely cause for the majority of the plants being diminutive (only a few inches tall) and flowering over a shorter period of time.

A distinct pattern of plant distribution was observed, based on surface soil characteristics: areas that have been scraped in the past and have a hard-packed and clayey surface are the areas that support most of the plants on the airport. Areas where the surface soils are deeper and less hard-packed (and typically less clayey) typically support a more weedy flora are not likely to support SCT. Over a third of the plants occur in the infields between the runways and the taxiways. These are the historically scraped areas referred to above. Other large sub-populations occur in scraped areas adjacent to the runways and taxiways.

The population density and area of SCT fluctuated minimally from 2013. Compared to 2013, there has been a 1.9% increase in the overall estimated population of SCT and a 1.8% increase in the overall acreage where SCT was found. There have been minor shifts in the local distribution of most populations, although most of the SCT locations remain similar between 2013 and 2014. Additionally, some previously separate populations of SCT appear to have merged between 2013 and 2014, for example, locations 21, 23, and 35 (now just location 21). Additional small populations of SCT were located and mapped where they were not previously recorded (locations 43 through 49).


Most of the species observed in 2014were only a few inches tall, as opposed to the more robust plants which over a foot tall. A reasonable approximation for the diminutive form is 80%, the reciprocal 20% being robust.

PhotoRDate:RJulyR3,R2014

Watsonville,RCAWatsonville Airport

Figure 4

SANTA CRUZTARPLANT AREAS

FigureR4R-ROverRRunwayR2-20RfacingRnortheast.

3136

4

1 5a

5

3

2

Photo-Date:-July-3,-2014

Watsonville,-CAWatsonville Airport

Figure 5


31

48 7

8

6

32

3343

44 8a

8

Figure-5.1---Facing-northwest-over-Runway-2-20.

Figure-5.2---Facing-northwest-over-Airport.

PhotoODate:OJulyO3,O2014

Watsonville,OCAWatsonville Airport

Figure 6


FigureO6O-OOverORunwayO2-20OfacingOsouthwest.

9

20

8

76



Figure 7


Figure-7.1---Facing-northwest-over-airport-hangars.

Figure-7.2---Facing-southwest-over-Runway-9-27.

10

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12

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15

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45



Figure 8



Figure-8.2---Over-Runway-2-20-facing-southwest.

19

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18

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Figure 9



Figure-9.2---Facing-southeast-over-airport.

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49

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24

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39

21 24

4827

39

Robust:SCT:growth:on:hard-packed:terrain.:

Diminutive:form.

Santa:Cruz:Tarplant.

Photo:Date::July:4,:2014

SITE PHOTOS

Figure 10

Watsonville,:CA

Watsonville Airport

LocationW6WfacingWsoutheast.W

LocationW7WfacingWnorthwest.

LocationW31WfacingWsouthwest.

PhotoWDate:WJulyW2,W2014

SITE PHOTOS

Figure 11

Watsonville,WCA

Watsonville Airport

Locationv20vfacingvnortheast.v

Locationv21vfacingvwest.

Locationv15vfacingvsouthwest.

PhotovDate:vJulyv3,v2014

SITE PHOTOS

Figure 12

Watsonville,vCA

Watsonville Airport

Locationv27vfacingvsoutheast.v

Locationv18vfacingvwest.

Locationv19vfacingvsouthwest.

PhotovDate:vJulyv4,v2014

SITE PHOTOS

Figure 13

Watsonville,vCA

Watsonville Airport

THIRD ANNUAL SANTA CRUZ TARPLANT POPULATION …afisher/post/drywell/PapersReports... · Objectives...

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