Exotic & Invasive plant species on Lawsons Brook

A  mid-summer 2023 Survey 

Flowering Multiflora Rose on July 7, 2023 just below the dam on Williams Lake.
Click on images for larger versions

On July 7, 2023 I noted a large clump of Rosa multiflora on Lawsons Brook – the stream that drains Williams Lake – just below the Dam. It’s easily spotted during it’s peak flowering period (latter part of June into early July).

I was somewhat surprised as in the spring of  2021, I had observed small plants at that location, as well as close to the Parking Lot and the culvert where Lawson’s Brook flows under Purcell’s Cove Road.  Williams Lake Conservation Company member  Melanie Dobson cut the clump on the south side back in 2022.

I have observed elsewhere that  multiflora plants cut back  take 2 years to recover sufficiently to begin to flower again; what surprised me in this case was the vigour of the regrowth of the Lawson Brook plants in 2023. It’s a very wet, probably quite fertile site, and relatively open which would probably accounts for it. There is a lot Canada Holly in the area; it’s  likely that that where R. multiflora is abundant within this area, it has displaced/outcompeted Canada Holly.

Publicly available Map of SWP. Inset shows Lawsons Brook. Map from post on WLCC website Sep 23, 2017; inset added.

The R. multiflora sighting led to some discussion as to whether these R. multiflora plants are actually  located within the SWP (Shaw Wilderness Park) or are on private property as they appeared to be mostly on the north side of Lawsons Brook;  publicly available maps (e.g., as at left) were too coarse to  see exactly where the SWP boundary lay in relation to Lawsons Brook. The issue was clarified when an  NCC official showed us their map of the SWP property: the north side of Lawson’s Brook lies entirely within the SWP; over most of the  length of Lawsons Brook, there is a minimum of 10 meters beyond the northern side of the Brook that lies within the SWP;  in a couple of spots only about 5 m.

To get a better sense of the state of Rosa multiflora and other invasive species on Lawsons Brook,  on July 20, I walked the south side of the  Brook from Purcell’s Cove Road to Williams Lake and noted and photographed every separate occurrence of any exotic (non-native) plant species lying within a minimum of 10 m from the Brook on the south side; and any occurrence close to the bank on the north side. (Because water was running fast and furious – after a lot of rain in June and July – I couldn’t cross the brook). The photos were taken with an Olympus Tough TG4 camera and are GPS-tagged.

Japanese Knotweed spanning Lawsons Brook. View iNaturalist Record

Each occurrence was entered as a record in iNaturalist and given the tag  InvExoSurvey20Jy2023LawsonBk. I added a few more from observations on July 21 and Aug 2, 2023. Currently (Aug 4, 2023) there are 27 observations/7 species listed under that tag. Of those 7 species, two are exotic but are not considered invasive* (European Ash and Bittersweet Nightshade). One – Japanese Spirea –  (I am a little uncertain about this ID) is recorded as invasive in parts of the U.S.; it occurs  in the wild in southern Canada but is not considered  invasive here, and the specimen I observed was a small plant.

The Invasive Species were

Japanese Barberry – 10 observations
Multiflora Rose – 7 0bservations
Japanese Knotweed – 5 observations
Border Pivet – 2 observations

*For a general description of exotic and invasive species in NS, see Weedy immigrants adorn N.S. Also view Hill, N.M., and Blaney, C.S. 2009. Exotic and invasive vascular plants of the Atlantic Maritime Ecozone. In Assessment of Species Diversity in the Atlantic Maritime Ecozone. Edited by D.F. McAlpine and I.M. Smith. NRC Research Press, Ottawa, Canada. Pages 1–18; The floral Elements of Nova Scotia by NM Hill in Nova Scotia Plants, pp vii-xv.; Atlantic Conservation Data Centre;

The panel below shows the locations of discrete plants or colonies for the invasive species:

Occurrence of discrete individual plants or colonies of invasive plant species on Lawsons Brook in mid-summer, 2023. The symbols with a purple-o inside are occurrences reported at other times by myself or others within the prescribed area. Click on image for a larger version.

Of note:
Multiflora rose was restricted to wetter areas of the  upper reaches of Lawson’s Brook and its floodplain. There are 2 points on the map near Purcell’s Cove Road from earlier observations; these plants were removed by Melanie Dobson. This species occurred in wetter areas.
Conversely, Japanese Knotweed, also found in wetter areas,  was restricted to the lower reaches of Lawson’s Brook.
Overall, Japanese Barberry was the most widespread invasive species on Lawson’s Brook. Typically it occurred as thickets on banks by the Brook.
There were two separate, large Border Pivet plants in the upper reaches of the brook at the edge of the Brook.
There was one smallish Japanese Spirea close to Williams lake, well away from the brook.
Overall, invasive species were most common toward the upper and lower reaches of the Brook.

Clump of Japanese Barberry, approx 3 x 1.5 m oriented along the Brook. View iNaturalist Record

Japanese Barberry: A new invasive species for NS?
The commonness of Japanese Barberry was a surprise.  Where it develops into thickets, I suspect it could effectively suppress recruitment of new trees and shrubs such as Yellow Birch, Red Maple, Red Oak, Striped Maple, Witch Hazel and Hobble Bush as well as ground hers such as Wild Sasparilla  (Aralia nudicaulis) and Canada Mayflower (Maianthemum canadense).Currently there are 3 records on iNaturalists of Japanese Barberry in other areas of the Backlands, but it’s pretty likely there are more. It is clearly a species we should be on the lookout for more broadly within the Backlands  and probably elsewhere.

Japanese Barberry is not currently Aug 7, 2023) listed as an Invasive Species for NS by the  Nova Scotia Invasive Species Council, nor is it listed in their Invasive Species Guide as an invasive species that occurs elsewhere in N.A. and that we should look out for in NS. **UPDATE Aug 18, 2023: The NS Invasive Species Council has recently released their new Grow Me Instead guidebook in which Japanese Barberry and Common Barberry are cited as potential invasives in NS & NB; they suggest alternative native species to grow in their stead in our gardens.

Japanese Barberry is known as an Invasive Species in other area of NA – e.g. in my bookshelf reference: Invasive Plants: a Guide to Identification, Impacts and Control of Common North American Species by SR Kaufman and W. Kaufman, Stackpole Books, 2007. (There is 3rd Ed. – 2023). They note that “Japanese Barberry prefers partial sunlight but also does well in shade, especially in younger forests.”

Under “WHAT IT DOES IN THE ECOSYSYTEM” the Kaufmans write Birds…eat barberries and spread seeds far and wide… [It] can also grow from root creepers or from branches rooting on contact with the ground. This enables a single branch to form a thicket. Japanese Barberry at high densities lowers plant diversity, and the leaf litter causes changes in soil chemistry.”

Under MANAGEMENT in Kaufman and Kaufman (2007): “When numbers are limited, shallow but tough roots allow this shrub to be hand pulled using a hoe or mattock to dig up root systems. Spring is the best time for manual or mechanical control. Controlled burns in fire-resistant plant communities will also kill barberry. Herbicides labelled for brush control can be sprayed or painted on stumps after cutting.”

 Privets (Ligustrum sp) Up and Coming Invasives?

Privet on Lawsons Brook. View iNaturalist records 175918623 and 176357645

I sighted 2 large privet plants on wet ground by the water in the upper reaches of Lawson’s Brook, likely either Border privet (Ligusticum obtsifolium, of eastern Asian origin, or Common Privet (Ligustrum vulgare) native to central and southern Europe, north Africa and southwestern Asia. Privets as a group are described by Kaufman and Kaufman (2007) as invasive; Common Privet has the widest range, including NS. The privets “grow along woodland edges, in floodplains, old fields, riparian forests, and upland forests. Tolerant of shade and occasional drought.”The Kaufmans note under WHAT IT DOESIN THE ECOSYSTEM: “Privets form dense stands that out compete native plants for space, light and water. few insects feed on it because chemicals in the leaves inhibit digestion. Deer, however, will feed on privet. Birds eat the fruits and disperse the seeds to forest gaps and into fields.”

Under MANAGEMENT: ” Young plants can be hand-pulled or pulled with the aid of an uprooting tool like a weed wrench or mattock. Shrubs can also be cut multiple times until they die. For large stands, plants can be spreayed with a system herbicide in late autumn or early spring when most other plants are dormant. Herbicide can also be painted on cut stumps or applied to the bark”.

Japanese Spirea (tentative ID) View iNaturalist record 175919167

JAPANESE SPIREA: One small plant (circa 50 cm height), tentatively identified as Spirea japonica, was sighted on drier but seasonally flooded ground in the upper reaches of Lawsons brook. This species is of east Asian origin; it is cited by Kaufman and Kaufman (2009) as “reported as invasive from Pennsylvania south to North Carolina and west into Kentucky and Tennessee  but grows from southern Canada south to Georgia and west to Illinois”. So probably we do not have to concerned about this species, for now at least. It is an “exotic” but is not an “invasive exotic”.

Currently, Japanese Barberry, Privets and Japanese Spirea are NOT listed by the Nova Scotia Invasive Species Council as invasive in NS or amongst the 35 species they list that are invasive elsewhere in N.A. and that we should keep an eye out for in NS.* UPDATE Aug 18, 2023: The NS Invasive Species Council has recently released their new Grow Me Instead guidebook in which Japanese Barberry and Privets are cited as invasives in our region.

Quite what to do, if anything, about the invasive species on Lawson’s Brook bears  discussion. I especially look to  Melanie Dobson for comment about the practical challenges of controlling them – and thank her for ongoing efforts!  It’s quite possible that without her efforts, there would be a lot more than there are now.

Melanie Dobson cuts back Japanese Knotweed in lower Lawsons Brook, July 20, 2023

In our 2013 survey of the Williams Lake Backlands*, lower Lawsons Brook was the only area where we observed any exotic species and we noted that “The two exotic species (Japanese Knotweed and Japanese Barberry) were found only close to Purcell’s Cove Road”.
*Ecological Assessment of the Plant Communities of the Williams Lake Backlands, by Nick Hill and David Patriquin. 2013. Report to Williams lake Conservation Company. Available on Dalspace.

We did not look in detail at Lawsons brook at the time, but we walked the route on the south side many times as we accessed the Williams Lake Backlands. So I think it can be stated that there has been an overall increase in exotics in the Lawson’s Brook area since 2013.

Some factors that could make Lawson’s Brook particularly susceptible to invasives:
– it’s proximity to Purcells Cove Road and to a popular swimming spot on Williams Lakel
– disturbance associated with construction of the wide, gravelled SWP trail to the lake;
– natural disturbance associated with periods of heavy water flow/ice in Lawson’s Brook;
– historical (settler times) disturbances associated with the adjacent “ice road” and a mill near the mouth of the brook.

Interestingly, exotic species are hard to find over most of the SWP currently. Routinely I am on the lookout for exotic and invasive plant species when I walk along the single track trail that leads from top of the all-access trail at Williams Lake through to the Jack Pine barrens; I have never observed any exotics except in a couple of spots off-trail in the barrens area where there are remnants of old habitations. Lack of exotic plants species is considered to be an indicator of high ‘Ecological Integrity’ (LaPaix et al., 2009).

On July 7, 2023, I walked the Shaw Wilderness Park single track trail that goes from Williams Lake along a major watercourse and up into the barrens with Nick Hill and we sighted no exotic species (invasive or not), except by an old foundation near the end of the trail. On July 31 I walked the same routed except diverged towards the end continued along the watercourse to the ‘Great Fen’,  looking carefully for any exotic species, and saw none.

I doubt that will last. But if we are vigilant and remove new occurrences quickly, we can keep them out with relatively little effort. As well, we should view such occurrences as indicators of new disturbance or higher levels of human disturbance and take action to reduce such disturbances as possible and appropriate.

– David P, Aug 4, 2023.

Section Positions on Lawson’s Brook. The locations were determined with a Garmin Map 62S GPS unit, accuracy circa +/-3 m. Locations of most plant records identified in iNaturalist are based on locations given by Olympus Tough TG4 camera and could be up to 10 m or more off; however, the sections  in whihc they occurred (eg L2-L3) are identified in the iNaturalist records.


iNaturalist Project for Lawson’s Brook. Click on image to go to the Project Page

Lawsons Brook “Place Map”

View looking upstream in a section of Lawsons Brook free of invasive plants. Aug 2, 2023.

This page is posted as a subpage under www.backlandscoalition.ca/natural history/Exotic & Invasive Plants