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(Arboricultural-styled) 'Fact of the Day'

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16/08/15. Fact #8.

 

A step back in time with this one courtesy of the very recently published A Dendrologist's Handbook.

 

During the Carboniferous Period some 345-280m years ago, the continent of Pangaea began to drift northwards from its southern hemisphere origins, and also began to pivot 30 degrees to the west. Giant insects developed, amphibians evolved further and reptiles became more land-based. Plants were reproducing in an alternating manner of asexual and sexual methods across different generations (spores and seed respectively). Equisetum plants (includes Horsetails) became huge, forming Calamites in damp, swampy areas, and forming Cordaites (that had pollen sacs and ovules at branch tips - later forming the first conifers, such as ginkgos, during the Permian Period 280-225m years ago) in drier areas. Clubmosses grew to 30-45m in height. All of this development was fueled by the equatorial climate induced by the drift northwards of Pangaea, particularly at the northern-most end of the super-continent.

 

Coal measures were thus formed very readily from such large plants in what now constitutes Northern Europe (given this segment of Pangaea was first to travel over the equator), once the sea began to engulf the swamps of massive clubmosses, semi-composting them and later compacting them down with silt and clay to form lignite, and eventually forming coal under continued compression events. It took 20m of rotted 'forest' biomass to produce a 1m-thick coal measure, so given many European coal measures are hundreds of metres thick, the length of time required to create such coal measures would have been hugely significant. This also adds significance to our eagerness to burn such stored coal, releasing carbon that has been locked away for hundreds of millions of years in mere decades.

 

The southern area of Pangaea (Africa, Australia) contained smaller plants and thus smaller coal measures, only beginning to lay down larger coal measures (that never amounted to the extent of the earlier coal measures, as the steamy swamps that produced the huge clubmosses and subsequent coal measures no longer existed due to climate change) much later once the southern segment of Pangaea did reach the equator (during the Cretaceous and Tertiary Periods) when plants had evolved to develop roots and reproduce sexually via seed. Evolutionary-speaking, the development of reproduction via seed was critical to the survival of plants long-term, as germination could be delayed until conditions were desirable.

 

Source: Davis, M. (2015) A Dendrologist's Handbook. UK: The Dendrologist.

Edited by Kveldssanger

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16/08/15. Fact #8.5.

 

Building on the above a little, though nonetheless as a tangent, Europe has so few tree species as tree populations could not retreat southwards as the ice sheets encroached into their territory, given the east-west running mountain ranges that are the Alps and Pyrenees, and the area that is now the Mediterranean Sea. Because of these blockading landscapes, tree diversity is rather low within Europe, when compared to the Americas and Asia.

 

The UK's plant diversity is even more impoverished as when the ice sheets last retreated 12,000 years ago, the subsequent rising of sea levels bridged the gap to mainland Europe. Thus, only species that had colonised during the 6,000 years after the ice caps began to retreat are found today - any others that may have potentially once again reached these shores (I suspect sweet chestnut, plane, holm oak, etc, though definitely Norway maple and larch) were barred from doing given the mass of water in the way.

 

Source: Davis, M. (2015) A Dendrologist's Handbook. UK: The Dendrologist.

 

Building on this, I read somewhere that the 'bog oaks' of the Channel area showed that the Channel was once heavily 'treed', and would therefore have facilitated succession into the UK from mainland Europe.

Edited by Kveldssanger

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Hah! It's literally rammed with information. Absolute wall of text in places, though paragraphed very well into digestible snippets. Few typos I noticed thus far and an incorrect Darwin quote, though as it's all from Davis' own notes it's darn impressive.

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Gary, pages 9-16 are incredible. Such a wonderful succinct history of botanists that introduced tree species to the UK, either by collecting seed through travels, or as gifts from connections such as gardeners for royalty in countries abroad (inside and outside Europe).

 

Reading this book has inspired me to buy John Evelyn's Sylva.

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Absurdly amusing how collecting plant seeds back in the 1700s and 1800s was seen as clandestine at times. Who ever would have thought horticulturalists would have, on expeditions to China, disguised themselves as Chinamen (complete with pigtail wigs!), given themselves fake Chinese names such as Sing Wah (Bright Flower), gone outside the zone permitted to foreigners and then gone exploring in a bid to smuggle back seeds and specimens for collections and for the nursery trade. Hilarious. The same happened in Japan with German surgeons working for the Dutch East India Company, who masqueraded as Dutchmen to get into Japan's Deshima Island (as only Dutch nationals were allowed entry to Japan for over 200 years until the mid 1800s), after claiming they were simply from the mountainous regions of Holland and their strong Bavarian accents were not because they were German nationals!

 

:lol:

Edited by Kveldssanger

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16/08/15. Fact #8.75.

 

A little fun fact for a pub quiz...

 

On average a 12m tree (40ft) can uptake as much as 225 litres of water (50 gallons) via its roots per day, can make 5kg (10lbs) of carbohydrates from its 1,800 square metres of leaf area, and during the synthesis of carbohydrates, release 1.7 cubic metres (60 cubic ft) of oxygen back into the atmosphere. Per year, the leaf area will utilise 50,000 cubic metres of air and directly filter-out one ton of particulate matter.

 

Cool, eh!

 

Source: Davis, M. (2015) A Dendrologist's Handbook. UK: The Dendrologist.

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17/08/15. Fact #9.

 

There are two main types of mycorrhizal fungi:

 

(1) Endomycorrhiza (arbuscular) - the fungus penetrates roots to form characteristic intracellular vesicles and arbuscles, occurring both in angiosperms and gymnosperms (approx. 80% of all higher-tier plants have such a relationship). Roots 'infected' with endomycorrhizae retain their root hairs, and the role of the fungus is essentially that of expanding soil 'availability'. Such species are not particularly diverse throughout a woodland area, though can sustain diverse plant populations. There is inter-specific and intra-specific competition between plant species for the establishment of symbiosis with such mycorrhizae.

 

(2) Ectomycorrhiza - the mycorrhizae do not penetrate living cells in the roots but, instead, only exist between them. Ectomycorrhiza are largely species-specific, and there is thus less competition for their resources when compared to endomycorrhiza as tree species can form a symbiosis with many ectomycorrhizal fungi species simultaneously without much competition.

 

N.B. Some mycorrhizal species are ectendomycorrhizal, which essentially means they possess the traits of both endo- and ecto- species. Research indicates suggests they may be important in the revegetation of disturbed sites and in the establishment of conifer seedlings in post-fire situations.

 

Sources:

 

Duhoux, E., Rinaudo, G., Diem, H., Auguy, F., Fernandez, D., Bogusz, D., Franche, C., Dommergues, Y., & Huguenin, B. (2001) Angiosperm Gymnostoma trees produce root nodules colonized by arbuscular mycorrhizal fungi related to Glomus. New Phytologist. 149 (1). p115-125.

 

Malloch, D., Pirozynski, K., & Raven, P. (1980) Ecological and evolutionary significance of mycorrhizal symbioses in vascular plants (a review). Proceedings of the National Academy of Sciences. 77 (4). p2113-2118.

 

Thomas, P. (2000) Trees: Their Natural History. UK: Cambridge University Press.

 

Trevor, E., Egger, K., & Peterson, L. (2001) Ectendomycorrhizal associations–characteristics and functions. Mycorrhiza. 11 (4). p167-177.

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19/08/15. Fact #10.

 

Cladoptosis is the process of natural branch senescence (or deterioration), which involves the re-allocation of resources to other parts of the tree's structure and is principally induced by a lack of light, which means retention of the to-be-shed branch is not efficient.

 

As the branch is 'shut down', conifers will deposit resins and broadleaves will deposit tyloses / gum, reducing the likelihood of pathogens entering the dying branch (such as specialised opportunists). At the protective zone, which typically exists around the area of the branch collar, wood becomes significantly lignified and is rich in extractives. The abscission zone, which resides on the outer side of the protection zone, eventually becomes the point of failure, and the protective zone then begins the process of wound occlusion as would naturally be expected. In stem junctions of juvenile oaks, the formation of regular xylem disables the abscission zone immediately after flushing of a branch, and in mature trees the frequency of active abscission zones increases with age and declining vigor.

 

Benefits of cladoptosis include that of trees not having an overly-busy crown (that increases wind sail area) and having a sustainable maintenance (maintenance respiration) requirement - lower branches are usually shed as light availability decreases - particularly when below 20%, as this is the usual cut-off for when branch retention operates at a 'loss'.

 

For species such as willow and poplar, the shedding of branches can even be a way of propagation. As willows and poplars are commonly found along water courses, one of their propagation techniques is to shed branches via cladoptosis, having these shed branches travel down stream and then potentially take root when washed-up.

 

Sources:

 

Bhat, K., Surendran, T., & Swarupanandan, K. (1986) Anatomy of branch abscission in Lagerstroemia microcarpa Wight. New Phytologist. 103 (1). p177-183.

 

Kozlowsky, T., Kramer, P., & Pallardy, S. (1991). The Physiological Ecology of Woody Plants. UK: Academic Press.

 

Rust, S. & Roloff, A. (2002) Reduced photosynthesis in old oak (Quercus robur): the impact of crown and hydraulic architecture. Tree Physiology. 22 (8). p597-601.

 

Thomas, P. (2000) Trees: Their Natural History. UK: Cambridge University Press.

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