Temperate Rain Forests of British Columbia

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We visited the Stanley Park and Capilano Park during our visit to British Columbia (BC), mainly to see the temperate rain forests. 

How is the temperate rain forests different from its tropical cousin?

The term ‘rainforest’ implies forests in high rainfall area, making them very dense and green.  Tropical rainforests lie closer to the equator while temperate rainforests are found at latitudes between the two Tropics and Polar Circles.  This causes temperate rainforests to be cooler, have less precipitation, contain less biodiversity and slower decomposition than their tropical counterparts.  Canada’s rainforest falls between the Arctic Circle and the Tropic of Cancer, forming a narrow band along the coast of the Pacific Ocean from Alaska to Northern California. Other countries that have temperate rainforests are Chile, New Zealand and Norway.

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In the morning we visited the Capilano Suspension Bridge Park.  The park offers visitors a unique mix of adventure, history and culture.  The park showcases a totem pole park, North America’s largest private collection of First Nations totem poles, period decor and costumes.

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Totem pole is a monument created by Northwest Coast Aboriginal people to serve as a signboard, genealogical record and memorial.  Carved of large red cedar and painted in vibrant colours, they are usually erected to reflect the history of that lineage.  Theses poles are also erected as memorial poles, grave figures, house posts, house front poles, welcoming poles and mortuary poles.

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The entrance to the park as the name suggests is by way of a suspension bridge.  The bridge was originally built in 1889 of hemp ropes with cedar plank deck.  It was replaced with a wire cable bridge in 1903.  The bridge was completely rebuilt in 1956.  We enjoyed the thrill of crossing the 450-foot long swaying bridge, suspended 230 feet above Capilano River. The bridge offered a splendid view of the river and the forest below.

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An eco-guided tour is conducted by the Park every hour, which was very informative, covering various ecological aspects of the forest in the Park.  The guide educated us about the rainforest, trees. trout ponds and the undergrowth.

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The first stop was at a banana slug.  The guide explained that there are no earthworms in these forests and these slugs contribute to the decomposition of organic matter into humus. These slugs are covered with a special slimy coating that numbs the mouth of any predator.  Racoons roll the slugs in mud to coat them and then eat them.

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We stopped next at a nurse log.  Fallen logs are called nurse logs as they help new seedling growth by creating an elevated and moist habitat.  Decomposition being comparatively slower when compared to tropical forests, results in a deep layer of decaying organic matter that forms the top layer of the forest floor.  This gives a cushioning effect while walking on it. 

Canada’s temperate rainforest is dominated by a relatively small number of tree species because the seeds need to regenerate in the low light levels on the forest floor caused the thick canopy.  Most of the trees found in this forest are coniferous trees like the Western Hemlock, Yellow Cedar, Western Red Cedar, Douglas-fir, and Spruce.  The coniferous trees are well adapted to the temperatures and shorter daylight hours of the winter as they remain green and keep their foliage in winter which helps then to photosynthesise throughout the year.

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The thick and uneven tree canopies that cover the coastal rainforest allow little sunlight to reach the forest floor, so undergrowth must adapt accordingly.  Indeed, the ground is mostly covered by plants that do not need much sunlight, like ferns. Small trees also grow under the shade of the taller ones. In order to get sunlight, some plants grow on bark and branches of trees, where there is more sunlight than on the forest floor.

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Along lakes and rivers and gaps left by fallen trees, which lets in more sunlight in, few deciduous tree species like Bigleaf Maple, Red Alder and Black Cottonwood thrive.  

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The guide escorted us to the ‘Grandma of Capilano’ – the tallest tree in the forest.  It is a Douglas Fir, aged over 1300 years, standing tall at 76 M. 

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After the guided tour, we ascended a foot bridge for Treetops Adventure Tour – a self guided tour.  This leg consisted of seven footbridges suspended between magnificent 250-year-old Douglas Fir trees, forming a walkway up to 30 M above the forest floor.  The elevated walkway offered a woodpecker’s eye view of the forest.

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The walkway has been created without harming the trees, with no nails or bolts drilled into them.  Metallic collars hold the ends of the walkway on to trees and are moved every eight years to facilitate the tree to grow. 

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On our way back to the parking lot was the Cliffwalk.  This heart-pounding cliff-side journey took us  through rainforest vegetation on a series of suspended walkways jutting out from the granite cliff face above Capilano River.  The Cliffwalk is high and narrow and in some sections, very strong glass is all that separated us from the canyon below. The narrow walkway has fixed handrails supported by steel beams cantilevered from 16 anchor points in the granite rock face of the canyon.  Various information boards along the walkway explained the interaction between water, granite, salmon, flora and fauna.

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We then drove to Stanley Park on the beaches of the Pacific Ocean, a green oasis in the midst of the heavily built urban landscape of Vancouver.  The 400-hectare natural West Coast rainforest offered us rare scenic views of the ocean with ships anchored, mountains, sky, and majestic trees along Stanley Park’s famous Seawall.  We walked around the park on the walking track which ran all along the beach, adjacent to a separate cycling track.

Our visit to the temperate rain forest parks were both educative and recreational.  Hermann Hesse, a German-born Swiss poet once said “Trees are sanctuaries. Whoever knows how to speak to them, whoever knows how to listen to them, can learn the truth. They do not preach learning and precepts, they preach, undeterred by particulars, the ancient law of life.”

 

Why Do Soldiers Break Step On A Suspension Bridge?

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Our son Nikhil and I had a discussion about the phenomenon of resonance about which he had a class that day. My mind wandered back to Mr PT Cherian’s high school physics classes. Mr Cherian had a knack of explaining basic principles of physics by citing real life examples which were simple and easy to assimilate. For more about Mr Cherian, please refer my blog https://rejinces.net/2014/07/15/guru-dakshina/.

Mr Cherian explained resonance by using a simple experiment.

He had three pendulums of different lengths and two of the same length (B & D) tied to a rubber hose. He swung one of the two pendulums of equal lengths and after a few minutes, all the other pendulums begun to swing with the other pendulum of equal length swinging as much as the other. This he explained was as a result of resonance and the frequency of the two pendulums with equal lengths were same and hence they resonated.

Bridges and buildings have a natural frequency of vibration within them. A force applied to an object at the same frequency as the object’s natural frequency will amplify the vibration of the object due to mechanical resonance. Mr Cherian explained that while on a swing, one can go higher with a jerk of a bend knee or a swing of the legs and a car wobbles at a particular speed; are all examples mechanical resonance. The shattering of glass by singers with their voice is also by the same principle.

Mr Cherian then narrated an incidence which took place in 1831 when a brigade of soldiers marched in step across England’s Broughton Suspension Bridge. The marching steps of the soldiers happened to resonate with the natural frequency and the bridge broke apart, throwing dozens of men into the water. After this, the British Army issued orders that soldiers while crossing a suspension bridge must ‘break step‘ and not march in unison.

If soldiers march in unison across a,suspension bridge, they apply a force at the frequency of their step. If their frequency is closely matched to the bridge’s frequency, soldiers’ rhythmic marching will amplify the natural frequency of the bridge. If the mechanical resonance is strong enough, the bridge can vibrate until it collapses due to the movement.

A similar tragedy was averted in June 2000 when a large crowd assembled at the opening of London’s Millennium Bridge. As crowds packed the bridge, their footfalls made the bridge vibrate slightly. Many in the crowd fell spontaneously into step with the bridge’s vibrations, inadvertently amplifying them. The police swung into action to clear the crowd off the bridge. Though engineers insist the Millennium Bridge was never in danger of collapse, the bridge was closed for about a year while construction crews installed energy-dissipating dampers to minimise the vibration caused by pedestrians.

Another example of mechanical resonance was the destruction of Tacoma Narrows Bridge in Washington in 1940. Even though the bridge was designed to withstand winds of up to 200 kmph, on that fateful day the wind speed recorded was mere 60 kmph. A mechanical resonance resulted due to the wind at that particular speed hitting the bridge perpendicularly.   Continued winds increased the vibrations until the waves grew so large and violent that they broke the bridge apart.

In May 1999, two girls were drowned and 15 others injured when a suspension bridge across a river collapsed in Panathur, Kasargod in Kerala State of India. The incident occurred when a group of people taking part in a funeral procession entered the suspension bridge  The bridge tilted and collapsed, again due to mechanical resonance.

In a similar incident in February 2014, eight people died and more than 30 injured when a suspension bridge collapsed over a dry stream in the North-Western province of Lai Chau in Vietnam. The accident happened as a group of local residents walked across the bridge to bring the coffin of a local official to a graveyard. The group had walked 15 meters on the bridge when it suddenly collapsed.

What could have triggered off the mechanical resonance in the above two cases? The villagers participating in the two funerals were surely never drilled down by any Sergeant Majors.

It is felt that anyone while on a funeral procession walks slowly and is often accompanied by the drums or hymns being sung at a melancholic pace. The funeral participants tend to bunch together, mainly due to their sadness. These factors could have forced the funeral participants to march in step, without their knowledge. Another reason of marching in step could be that one does not want to step on another’s foot and the best way to avoid is to walk in step with the person in the front. In both the cases, the coffin was carried by the coffin bearers with their hands. This needed the coffin bearers to walk in unison.

In all probability, the frequency of walking of the mourners in the funeral procession could have resonated with the natural frequency of the bridge, causing the bridge to swing violently. The pandemonium that could have set out must have caused panic, resulting in the mourners rushing to get off the bridge causing a stampede.

Hence in future the rule must be that not only the soldiers need to break steps on a suspension bridge, but also a funeral procession.