Joshua Creek Challenges

The patchwork of influences covering the lands of Joshua Creek mean it is beset with a huge array of challenges. To the trained naturalist’s eye, there are many competing influences in modern-day Joshua Creek, and three stand out like a sore thumb in Joshua’s nature sanctuaries: 1) the inundation of the forest with non-native (foreign) invasive trees & shrubs, 2) the Ash tree declines due to Emerald Ash Borer, and 3) encroachment/elimination of natural spaces and buffers.

 Non-native invasive trees and shrubs:

Non-native plant species are plants that originate from another part of the planet that were introduced to our region by humans, often in the horticulture trade. Non-native invasive plants are the worst of these – these foreign species flourish in our nature sanctuaries, so much so that they can invade and conquer our native plant communities and push out native plants and animals, changing ecosystems drastically.

Spring is an exceptional time to spot non-native Asian Honeysuckles. Species like Tartarian Honeysuckle (Lonicera tatarica), Morrow Honeysuckle (Lonicera morrowii) and their hybrids are easy to spot in spring in Joshua Creek because they leaf out fairly early, forming a “haze” of green leaves in the layer of the forest they occupy densely – the ~0.5m-2m height range. These species are tricky to differentiate, but they are all invasive, and eventually their arching stems fill in to cover large tracts of forest, pushing out native shrubs and changing light conditions for saplings spring flowers.

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Asian honeysuckle species like Tartarian Honeysuckle can easily invade meadows, woodlands and forests. Once established, they are difficult to get rid of, and can drastically alter the ecology of the forest understory. In spring, they show up as a “haze” of fresh green sprouts in the under-story of many of Joshua Creek’s natural areas.
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Common Buckthorn can quickly create one-species thickets in disturbed areas, such as beside this trail (above). Buckthorn is also very comfortable in forests, and slowly invades even shady natural areas. Chemicals released from the roots deter the growth of many other plant species, but favour other buckthorns, including new seedlings.

In other areas, the European Common Buckthorn (Rhamnus cathartica) forms dense stands where the the land has been deforested, disturbed, and left to regrow. Common Buckthorn grows taller than the Asian Honeysuckles, but is just as invasive, easily dominating open spaces and spreading into forested areas. What’s worse, Common Buckthorn releases chemicals from its roots into the soils – chemicals that buckthorns love, but other plants dislike. Their seeds also sprout up readily from underneath their own kind – something other plants have difficulty doing underneath other buckthorns. These things make Common Buckthorn a very destructive invasive plant.

Going forward, it will be important in areas like this to keep an eye on these species and remove them when possible. Otherwise, they may be slowly changing – and sterilizing – the habitats we have left.

Emerald Ash Borer:

Our Ash trees were a robust, common and versatile group prior to the arrival of the small green Asian beetle known as the Emerald Ash Borer (Agrilus planipennis). White Ash (Fraxinus americana) prefers the dry uplands, Green Ash (Fraxinus pennsylvanica) flourishes in lowlands and swamps, while Black Ash (F. nigra), Pumpkin Ash (F. profunda) and Blue Ash (F. quadrangulata) are mainly swamp species. In Joshua Creek, the creek’s floodplain lowlands and swamps are still home to some Black Ash as well as countless Green Ash, and these Ash forest and swamp ecosystems are on their way out in a big, big way.

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Ash trees and Ash-dominated habitat types are found in many areas of Joshua Creek, including swamps (a,c), lowland forests (d), and drier forests. In swamps, both Black Ash (Fraxinus nigra, b: tree on left) and Green Ash (F. pennsylvanica, b: tree on right) can be found growing side-by-side, but Green Ash is by far the most abundant species.

Discovered in 2002, having likely arrived a decade earlier, the Emerald Ash Borer has cut a devastating path across Ontario, starting in Windsor and heading north and east. While tiny individually, Emerald Ash Borer larvae infest ash trees under the bark in large numbers, blocking the trees’ circulatory system, slowly killing the tree over a period of several years. The beetles emerge as adults in early summer to mate and disperse, flying far and wide to new Ash trees.

Emerald Ash Borer damage shows up in a number of ways – weakened trees show canopy die-off, and lose progressively larger branches. They often grow “epicormic” sprouts on their stems, where the tree is trying to re-grow underneath its damaged vascular system. But one of the most eye-catching signs are the strips of bark chipped off by foraging birds like woodpeckers, which dapple the trunks with light markings. As the trees decline, they also become dangerous, and prone to breaking or falling. As a final blow, dying trees open up the forest, knocking the nature sanctuaries into a younger stage of habitat development. For a creek like Joshua that has already experienced a lot of deforestation, this is a tough blow. Removal of tree cover also allows invasive species to flourish, and un-shades the creek causing the water to warm too much. Big changes are ahead – and it is unclear what the final outcome to all this will be.

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All of our native Ash species are susceptible to Emerald Ash Borer (EAB). Infestations eventually show signs such as epicormic growths (i.e. trunk sprouts, a), bark stripping by woodpeckers such as the Hairy Woodpecker (b), and crown (canopy) die-back and death of fine branches (c). Infested trees become increasingly dead, brittle and hazardous, and must be cut down before they cause harm (d). Occasionally, green prism traps (e) and purple prism traps (not shown) are still observed, which have a scent lure in the centre to attract EAB nearby and are coated with sticky glue. These are the standard research tool to survey for EAB to figure out how far the infestation has spread, and to monitor numbers of beetles in an area. Invasive shrubs like Tartarian Honeysuckle stand ready in the understory of several of Joshua Creek’s Ash forests (f), awaiting the day when the canopy will open up and they can flourish. Invasion of habitats by invasive species could be a major hurdle following Ash die-off in these areas.
Removal of protective natural buffers and habitats:

Perhaps the oldest challenge facing Joshua Creek has been the clearing and fragmenting of its natural lands. Since European settlers began to farm this region hundreds of years ago, places like Joshua Creek have continued to lose habitat. Swamps and wetlands were commonly drained when possible, and along with the fertile uplands were tilled and farmed. For a creek, this meant not only big losses of vital habitats and plant communities in its watershed, but big losses in water quality and stability.

Forests and swamps shade small creek tributaries, keeping the waters crisp and cool. Contrary to intuition, colder water actually holds more vital oxygen than warm water – so while warm water is great for humans to swim in, it is deadly for many sensitive fish and insects, which may suffocate. By opening up treed and shrubby habitats, the creek waters warmed, lowering the quality of many tributaries, and eventually main Joshua Creek creek itself.

Forests, swamps, marshes, and other native plant communities are also crucial for water stability and flood prevention. Barren, open, and concrete-filled landscapes shed water quickly, meaning powerful storm surges overflow streams during rain events and dry up during dry periods. In contrast, a watershed filled with natural plant communities pulls in rainwater like a sponge, greatly reducing storm surges during rains, and providing slow-release water supplies in between rain events, so that things do not simply dry up. Wetlands are especially good at this, and have the bonus function of filtering rainwater, leading to cleaner streams with few contaminants. Removal of natural space impaired water stability in Joshua Creek, which suffers from problems due to storm surge flood events. 

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Large-scale creek and watershed modifications have plagued Joshua Creek since European settlers began to clear the landscape for farming. The clearing of land and the engineering of channelized, straight, artificial creek beds (a,b,c) appeal to human sensibilities, but are extreme-ly unnatural compared to the forested landscape and meandering creek that once were stand-ard (d). Cleared, modified landscapes are more prone to erosion, storm surges, problems with water stability, and leave the creek itself open to the warming sun, making it inhospitable to aquatic organisms that need cold water. Artificial waterways also include culverts (e) and underground stormwater drains which “efficiently” pass water into Joshua Creek, but are suboptimal for habitat value.

Much of Joshua’s headwaters are still in largely-exposed farmland, and around 2/3 of the creek’s watershed is heavily developed with urban and suburban infrastructure. Some sections of creek have even been artificially straightened, with manicured grassy portions close to the water. But not all is bad news – there are a few regions where land appears to be regenerating natural habitat cover, and big stretches of the headwaters are still undeveloped.

Going forward, we will be able to improve on Joshua Creek’s habitat coverage, and any improvements made will not only benefit the creek, but increase our green spaces, improve our water, and raise our quality of life. Creeks like Joshua need your support! Be sure to keep an eye out for them, and make your opinion known when planning decisions are being made for your region!

Read more about Discover Your Creek Adventure at Joshua Creek

All photos and text provided by David d’Entremont.