Slim-Leaf Onion (Allium Amplectens) in Oak Haven Park

Slim-leaf Onion (Allium amplectens) in Oak Haven Park

Natasha d’Entremont April 1st, 2014 ER390 Independent Project Restoration of Natural Systems Diploma

Table of Contents

Abstract 2

Introduction 2

Oak Haven Park Site and Description 2

Site Value 5

Slim-leaf Onion (Allium amplectens) 6

Identification 6

Habitat 7

Reproduction and Dormancy 8

Methods 9

Site Inventory 9

Removal of Scotch broom (Cytisus scoparius) 9

Results 11

Discussion and Recommendations 13

Slim-leaf Onion Population monitoring 13

Trail removal and fencing 14

Scotch Broom (Cytisus scoparius) 16

Acknowledgments 16

Abstract

Oak Haven Park has been identified as an excellent example of a Garry Oak plant community with high conservation values. Slim-leaf onion (Allium amplectens) is a native species in Garry Oak ecosystems and is Blue listed in British Columbia as a vulnerable species to focus on for preventative conservation. The population of Slim-leaf Onion in Oak Haven Park was surveyed and found to be comparable in size with other populations in BC, and adds to the conservation value of the Park. Removal of broom (Cytisus scoparius) was undertaken in the vicinity of the Slim-leaf Onion population to preserve the habitat quality and open up more Garry Oak meadow for possible expansion of the Slim-leaf Onion Population. Recommendations for future health of the Population are the active discouragement of a walking pathway which tramples the plants, and continuing removal of Scotch Broom which will re-grow near the population site.

Introduction

Oak Haven Park Site location and description

Oak Haven Park in Central Saanich (Figure 1) is within the coastal Douglas-fir biogeoclimatic zone (CDFmm), which covers an area including the southwest coast of Vancouver Island, several gulf Islands, and a sliver of the sunshine coast on the mainland of BC (Meidinger and Pojar 1991). This area is characterized by wet winters and cool dry summers, with some of the mildest climates in Canada (Meidinger and Pojar 1991). Oak Haven Park was established in 1997 and has a conservation covenant on it to ensure protection of the conservation values of the park. The park is managed jointly by the District of Central Saanich and Habitat Acquisition Trust.

Figure 1. Oak Haven Park in its regional setting on the Saanich Peninsula.

Oak Haven Park is 10.2 ha of mostly forested hilltop, with a mix of Douglas fir forest in the lower elevation areas and scrub Garry oak in the mid to higher elevations. The higher elevations are a patchwork of open meadow, shrub vegetation, and oak forest. There are no permanent pools or streams in the park but there are seasonally wet areas during winter and spring. The park elevation ranges from 90-125 m above sea level, with a slope of 14-40% in its main northerly aspect, and a steeper slope of up to 80% on a southeast aspect from the highest point (Park Management Plan 1999) (Figure 2).

Figure 2. Topography and local setting of Oak Haven Park. Benvenuto Avenue is the road in yellow to the north.

Although Oak Haven is a small park, it can be passed through by many people as part of larger hikes. Oak Haven Park is part of a larger ecosystem associated with Tod creek and the Gowland Range, it has trails connecting to Gowland-Tod Provincial Park, and regional Saanich peninsula trails (Park Management Plan 1999).

Management of the park is focused mainly on conservation, with non-pedestrian use discouraged. In keeping with the conservation values, the best potential for human activities in the park has been identified as walking and nature appreciation, which have a low impact. Oak Haven Park provides walkers the potential to enjoy a relatively undisturbed Garry oak ecosystem. The housing lots surrounding the park have minimum lot areas, and the conservation covenant has restrictions on lot subdivision and removal of oak trees in an effort to reduce the impact of development on the park (Park Management Plan 1999).

The Oak Haven Park Management Plan has a detailed plant list for the park, including a list of invasive species. The species of focus for this project is the Slim-leaf onion (Allium amplectens), a locally rare vascular plant which is blue-listed in BC (Figure 3).

Figure 3. Location of Slim-leaf Onion (Allium amplectens) within Oak Haven Park. Benvenuto Avenue is the road in yellow to the north. GPS Coordinates UTM 10N, 467084 E, 5379142 N.

Site value

The scrub oak forest and Garry Oak Meadow ecosystem is considered a rare habitat in BC and Canada, as the habitat has been largely converted to urban and agricultural uses (Vellend et al. 2008). Conversion of natural habitat to urban and farming use and the suppression of fire has affected about 90% of the historic Garry oak landscape (Bjorkman and Vellend, 2010, MacDougall, 2004). The lack of regular fire in the landscape has facilitated the growth of Douglas-fir into previously open canopy areas, and invasive plants grow densely in many areas that do still have an open tree canopy. Garry oak meadows that do remain are often shallow soil sites where it is more difficult for Douglas-fir trees and invasive plants to grow densely, capitalizing on the drought tolerance of many Garry oak meadow species (MacDougall, 2004). Though historically oak savannah habitat was predominantly found in flat deep soil sites

(Vellend et al. 2008), the reduction in habitat has meant that rocky shallow soil sites are crucial refuges for Garry Oak meadow species, and Oak Haven Park has been evaluated as an excellent representation of a Garry oak plant community (Park Management Plan 1999).

The dominant invasive plants in Oak Haven Park are Daphne (Daphne laureola) in the Douglas- fir forested sections, and Scotch Broom (Cytisus scoparius) in the open mossy areas and scrub oak forest. Daphne is visible throughout the Douglas fir forest areas with low to medium density and a mix of young and mature plants. Scotch broom is present in all open canopy areas with medium to high density being the most common. Scotch broom is well established with mature plants as well as seedlings. Broom is identified as having significance in Garry oak ecosystems with high potential for damaging the habitat (GOERT 2002). Scotch broom is focused on for removal in this project due to it having the most potential impact on Slim-leaf Onion and the rare Garry Oak plant community.

Slim-leaf Onion (Allium amplectens)

Identification

Slim-leaf onion (Allium amplectens) is a spring flowering onion with perennial bulbs. It is rare in BC and is blue listed as a vulnerable species. The range of A. amplectens extends from Middlenatch Island in BC to southern California (BC conservation data 2014, Hawrynski 2002). All BC populations are found in the coastal Douglas-fir Biogeoclimatic zone, on dry rocky bluffs or in Garry oak meadows (GOERT 2011).

The flowers are on an umbellate, hemispheric inflorescence, and are a shade of white to pink (Figure 4) (Wheeler 2006, GOERT 2011). The light pink and white flowering populations have been found to be triploid, while the dark pink variant is tetraploid (Wheeler 2006). The population in Oak Haven Park was observed to flower very pale pink or white, and is of the more common triploid variety. The flowers have six tepals, six stamens, and one style (Wheeler

2006). ). Slim-Leaf Onion is very similar to Hookers onion (Allium acuminatum), but the tepals do not turn back at the tips as Hooker’s onion does (Pojar and Mackinnon 1994). Leaf senescence often occurs before the flowers are fully developed (Hawrynski & Allen 2011).

Figure 4. Slim-leaf onion flowers in Oak Haven Park, June 213.

Habitat

Slim-leaf onion is a locally abundant rare species, found in dense but small populations, in a specific habitat type over a large range (Hawrynski 2002). In BC Slim-leaf onion is at the northern end of its range and is restricted to the Garry oak ecosystem in southwest BC, which has high densities of human population (Hawrynski 2002). In a 1996 survey approximately 30 populations were found in Southwest BC (Hawrynski 2002). Previously known populations of Slim-leaf onion in BC, which were no longer extant when surveyed in 1996, were largely located

7 in the Victoria area on southern Vancouver Island, where there is a large human development density (Hawrynski 2002).

Slim-leaf onion can grow on a variety of substrates as long as there is reliable moisture in spring. Populations of Slim-leaf onion are usually found on southern or southwestern exposures, in full sunlight or light shade. There is often evidence of moisture from spring seepages on the site. The soil can range from very rocky shallow soil to deep rich soils (Hawrynski 2002, Hawrynski et al. 2011).

Reproduction & Dormancy

Slim-leaf onion reproduces by seed and vegetative offset (Wheeler 2006). Plants produce 1-3 seeds per flower, and in favorable conditions large bulbs can produce up to 8-12 offsets per year (Wheeler 2006). Most BC populations of slim-leaf onion are triploid which reduces sexual fertility (Comai 2005, Wheeler 2006). Vegetative propagation is likely the main mode of reproduction in most BC populations, with seed production minimal in relation to offsetting in the BC populations studied (Hawrynski 2002, Wheeler 2006). Clonal growth is likely much more important for a slim-leaf onion population growth rate than seedling recruitment due to this reduced fertility (Hawrynski 2002, Wheeler 2006).

Slim-leaf onion plants are often dormant for a prolonged period, with an average yearly dormancy in some populations of 38%. Plants are frequently dormant for multiple years (Hawrynski 2002, Hawrynski et al. 2011). This dormancy could be in response to environmental conditions being better or worse for the plants in different years, with the highest dormancy rates being found in the driest year’s springs (Hawrynski et al. 2011). Habitats which are dry or rocky tend to have a high proportion of flowering plants to vegetative plants. And habitats which have more moisture and deeper soil such as orchard grass habitats tend to have higher densities of non-flowering ramets (Hawrynski 2002).

Methods

Site Inventory

Current year slim-leaf onion flowers were counted to estimate the size of the onion population. The Meadow site of the population was divided into belt transects. Two ropes were laid down as transect lines 1 meter apart across the site. All flowers within the two ropes were then counted twice to get an accurate number. One rope would then be leapfrogged over the other to encompass the next 1 meter wide transect, and all the flowers in this next section counted. This process was repeated until all flowers in the population were counted.

The Meadow was located with GPS UTM coordinates. Slope was determined using a clinometer to measure the slope from highest point in the slim-leaf onion population to the lowest. Canopy cover was estimated from digital photographs. Aspect was determined with a compass.

Removal of Scotch Broom (Cytisus scoparius)

Scotch Broom (Cytisus scoparius) has been found to have a negative effect on The Garry Oak meadows it invades, with decreased Phosphorus available in the soil, and decreased native plant diversity (Shaben and Myers 2010).

Slim-leaf onion grows in spring and flowers in early summer, making March-June the highest risk months for removal of invasive species directly in and around the slim-leaf onion. When removing invasive species, there is less of a risk of damaging the slim-leaf onion when the onion is dormant, though soil disturbance could still have an effect. The areas beside the onion population have higher densities of broom, but removal should not directly damage any onion plants. Removal was done in late summer and in autumn, minimizing the risk of damage to the slim-leaf onion bulbs.

Scotch Broom was removed according to best practices recommended by the Garry Oak Ecosystems Recovery Team (GOERT 2002). The highest priority was to prevent further incursion of Scotch Broom into the location of the Slim-leaf onion (GOERT 2007). The slim-leaf onion patch was surrounded by low to medium density areas of Scotch Broom.

The second level of priority was to reduce the area of the meadow covered by broom where there was the most likelihood of possible expansion of the slim-leaf onion population. The uphill area from the population site was partially tree covered and heavily covered in native shrubs and a dense population of scotch broom. The downslope side consists largely of open meadow with an open canopy of Garry oak scrub trees, and a medium density of scotch broom. Removal of scotch broom on the downslope was determined to have the highest ecological impact as the broom was the main species detracting from the openness of the meadow (GOERT 2007). Much of the medium density broom consisted of dead plants producing no leaves or seeds. These plants pulled easily out of the ground with minimal disturbance of soil. A white fungus was observed growing on the dead underground portion of the stems.

Very small broom stems were pulled from the ground where there was little likelihood of disturbing the slim-leaf onion. Larger scotch broom stems were cut below ground level with pruning shears. The live scotch broom was removed from the site and placed in the Broom box provided by Saanich Parks at the access road into Oak Haven Park. There was a large proportion of dead scotch broom in the restoration area. These stems were dry and brittle and non- reproductive but still shading the ground in the meadow where they stood in dense stands. The stems were easily pulled out the ground with minimal soil disturbance as the roots seemed to have rotted away. The stems were broken and left scattered onsite to decompose as there was no risk of re-rooting.

Results

The slim-leaf onion population is in a small partially shaded meadow is bounded on 3 sides by Garry Oak and Douglas-fir trees (Figure 5). It is approximately 20 m in length and 10 metres wide. The aspect is northwest on a slope of 12 degrees. The canopy cover over the slim-leaf onion was 10% in winter and early spring, and 20% in late spring and summer once the Garry Oaks leafed out. This site has very moist soil in early spring. The GPS coordinates are UTM 10N, 467084 E, 5379142 N. There were no other sites of slim-leaf onion found in Oak Haven Park, though fools onion (Brodiaea hyacinthia) and hooker’s onion (Allium acuminatum) were widespread.

Figure 5. Meadow containing slim-leaf onion population in October 2013.

There were 913 flowering plants from the A. amplectens population at Oak Haven Park in June 2013 (Figure 6). Habitats which are dry or rocky tend to have a high proportion of flowering plants to vegetative plants. And habitats which have more moisture and deeper soil such as orchard grass habitats tend to have higher densities of non-flowering ramets (Hawrynski 2002).

Due to the moist grassy area of the Oak haven Park population it is likely that the count of flowering plants was an underestimate of the total population.

Figure 6. Slim-leaf Onion in bloom in Oak Haven Park, July 2013.

Broom was cleared from an area approximately 750 square meters to the northwest of the population. This area was downslope or at the same elevation as the Slim leaf onion, and comprised of open meadow and light shade. This area was determined to be the most valuable for the possible spread of the A. amplectens population based on the habitat requirements of existing populations (Hawrynski 2002).

Discussion & Recommendations

Slim-leaf onion population

Global warming models predict changes in temperature and rainfall for southern BC (Wang et al. 2012), which could cause stress on the slim-leaf onion populations located on dry rocky soils (Hawrynski 2002). For long term population viability the slim-leaf onion populations found in more sheltered and damp locations, such as in Oak Haven Park may be more likely to survive in the coming decades. This makes the Oak haven Park population likely to be important if A. amplectens becomes even rarer in southern BC. Since the Oak Haven Park population is already in a protected area, the main goals are to monitor the population to ensure it remains healthy, and be prepared for it to be of more significance in the future if the species is re-evaluated as red listed as habitat continues to be disrupted in BC.

Sites which have more moisture and deeper soil such as orchard grass habitats tend to have higher densities of non-flowering ramets of slim-leaf onion (Hawrynski 2002). Due to the moist grassy area of the Oak haven Park population it is likely that the count of flowering plants was an underestimate of the total population. Vegetative and flowering stages can exhibit dormancy for one or more season before returning to active growth (Hawrynski 2002). The six A. amplectens populations surveyed by Hawrynski (2002) had numbers of flowering plants ranging from 151 individuals to 1386, with an average over the years surveyed of 629 individual flowering plants per population. The 913 flowering plants counted at Oak Haven Park were in line with the numbers found in other BC populations (Hawrynski 2002), suggesting that the Oak Haven Park Slim-leaf onion population is at a healthy size.

A main concern of Habitat Acquisition Trust was the possibility of grasses on site supressing the growth of the slim-leaf onion through overtopping and shading, which would limit the onions growth and seed spread. Observations throughout the spring of 2013 (Figure 6) did not see this to be occurring.

I recommend continuing to do counts of flowering slim-leaf onion plants at the site on a yearly or bi-yearly basis. The method used for this project was quick and efficient to do, and would not take more than half an hour were two people to work together on it. Due to the tendency of A. amplectens to go dormant, short term data on the population size could be very misleading. A year of high dormancy could make the population seem much smaller than it really is. A longer term monitoring of plants would be needed to spot trends of population growth or decline.

Due to the tendency of A. amplectens to spread by bulb offsets, if there is interest in increasing the population of Oak Haven Park, it may require human intervention of moving bulbs. Translocations within a close area are often most successful if it utilizes stock or seed from already locally adapted plants (Hufford & Mazer, 2003). The movement of only a few bulbs may increase chance of survival, but would make the new location very genetically similar (Hufford & Mazer, 2003). Collecting the seeds that are made and transporting them within Oak Haven Park could encourage a satellite population to form.

Trail removal & fencing

Oak Haven Park currently has no clearly marked main trails, and visitors appear to choose their paths by following the trampled paths and areas where others have clearly gone before. There are only a few very deeply trampled trails through the park, and many intermediately trampled routes and lightly used routes. The need to manage undesired off-trail activities and close undesired trails is a common problem in day-use areas (Abbe and Manning 2007). The Slim-leaf onion population is found near the intersection of a well-used trail and an intermediate use trail, with a lightly used shortcut connecting the two which cuts directly through the population (Figure 7). People tend to choose to leave trails when there is evidence of another trail to follow (Coppes and Braunisch 2013), meaning that the current visible path through the slim-leaf onion population increases the likelihood of people continuing to use it. People also tend to leave clear trails when there is an easily accessible route they can see, such as through wide spaced trees and meadows (Coppes and Braunisch 2013), so the small meadow location of the

14 slim-leaf onion will likely draw walker’s paths again if the current path is removed. To discourage people from walking on the site, signage about the sensitive nature of the site could be posted, which has been found to reduce the number of people going off trail (Park et al. 2008). The most effective solution to the tendencies of people to go off trail is direct management, such as fencing off the sensitive area or trail (Park et al. 2008).

The small meadow containing the slim-leaf onion population is bordered by trees, with the trail passing through from the most open sides. I suggest the implementation of a split rail fence at the openings of the trail into the slim-leaf onion population. Particularly at the north end of the slim-leaf onion population, which is the widest opening into the area. Split-rail fencing is already used in some of the park areas to discourage visitor paths, and seems to have had some success as only one was observed to have a clear trampled area circumventing it.

Figure 7. Trampling of Slim-leaf Onion (Allium amplectens) in flower, June 2013.

Scotch broom (Cytisus scoparius)

Scotch broom can significantly affect the dynamic of a Garry oak plant community (GOERT 2002). Leaving the scotch broom on site will likely lead to even higher densities of broom (Parker 2000) which can crowd out wildflowers like the slim-leaf onion, and be detrimental to the conservation goals of the park. Removal of broom according to the best practices outlined by GOERT can improve the ecological functioning of Garry oak plant communities while minimizing further disturbance caused by the restoration efforts.

Broom removal seems to have some interest from the local population. During the time broom was being removed for this project, small amounts of additional broom were seen to have been placed in the broom box provided by Central Saanich, indicating some community interest in restoration efforts. Instructions of best practices for broom removal would be beneficial to maximize the impact of this initiative. These could be picture instructions on a sign, or a sign with a short list of tips for people. Broom removal would be an ongoing requirement in Oak Haven Park to maintain the ecological benefits of the recent removals. Saanich parks and Habitat Acquisition Trust have an interest in maintaining the park, but the best control would be by interested residents of the nearby area who could enjoy seeing the benefit of their efforts. If large-scale restoration is unfeasible, a focus on the area of the slim-leaf onion could be undertaken as an area of special restoration interest.

Acknowledgments

Wendy Tyrrell from Habitat Acquisition Trust for suggesting Oak Haven Park, showing me the location of the slim-leaf onion and arranging permission for me to work in the park. Alf Birch and William Batchelor for volunteering to assist me with fieldwork.

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