When you step into your garden during the Spring or Summer months, you might be aware of the scent of honeysuckle, lavender or indeed an old fashioned rose.  Similarly, in a woodland the scent of pine or other conifers may permeate the air.  These various scents often involve a group of compounds known as the terpenes.  The resin that exudes from pine bark is rich in terpenes. Terpenes are used in the building of many complex organic molecules and contribute to the make-up of volatile, organic compounds [VOCs] - produced by many plants.  The scents released from nectaries or other parts of flowering plants are often associated with attracting pollinating insects, but they can serve other functions.  For example, some VOCs released by a plant may warn surrounding plants of attack by insects. However, as you walk down the street, the air is rarely filled with these pleasant, natural scents. Instead the fumes of traffic, factories and industry assail us.  They are the exhaust emissions from cars, lorries, buses etc, plus the various bits and pieces [particulates] that are released from the ‘rubber’ of car tyres, brake pads etc.  The damaging effects of particulates are now well documented.  The effects include lung disease such as chronic obstructive pulmonary disease (COPD) and reduced lung function.   Particulates help create the concoction of substances that we inhale; sadly our air is often polluted with many different compounds. Scientists from Oxford University and Kew recently investigated air quality in different locations around Oxford.  The locations varied from the centre of the town, where the Botanic Garden is found, out to the University’s Wytham Woods.  Wytham is one of the most intensively studied woodland areas in the world.  The wood ‘holds’ 500 plus plant species and 800 or more butterfly and moth species. Records of bird populations go back some sixty or more years (largely due to the work of David Lack and others).   The air samples that the scientists collected were subjected to detailed chemical analysis using the technique of gas chromatography-mass spectrometry. Some 245 different compounds were identified in the various air samples, with each of the six different sites haveing their own signature collection of chemicals.  Sites near to busy roads contained high levels of benzene and toluene, which are traffic-related chemicals.  The tree rich areas naturally showed a greater presence of plant chemicals (VOCs).  Unsurprisingly, when they sampled the air in the Botanic Garden (over the course of a year), they found the highest levels of these plant compounds.  Warmer weather increased the levels of these VOCs / plant derived chemicals, which have been associated with improved mood and stress reduction. Full details of the Oxford study here : https://nph.onlinelibrary.wiley.com/doi/10.1002/ppp3.70191

Certain woodland plants are found in the understory.  Plants like wood anemones, woodruff and lungwort bloom early in the year. These plants make use of a ‘window of opportunity’ when the light levels are good as the tree canopy has not developed, the leaves have not yet expanded. They use this ‘window of light ‘ to flower.   However, climate change is affecting many ecosystems - including woodlands.  With warmer temperatures, leaf buds tend to open earlier and the leaves begin to expand.  If the window for growth is reduced, how can the wood anemones and others cope ? [caption id="attachment_38093" align="aligncenter" width="700"] wood anemone[/caption] To investigate this question, scientists based the Universities of Tübingen and Frankfurt examined thousands of preserved herbarium specimens of early flowering plants, dating back over a hundred years.  The sheets not only hold specimens collected when they were flowering but also have  information on ‘when and where collected’.  Each sheet is a a moment in time from over a century ago.  Collectively, the 6000+ sheets allowed the scientists to establish historic flowering times of woodland plants over large areas of Europe. [caption id="attachment_38094" align="aligncenter" width="700"] Woodruff[/caption] The information extracted from the herbarium records revealed that plants like wild garlic and wood sorrel now bloom some six days early than at the beginning of the twentieth century.  For each 1oc rise in (Spring) temperature, their lowering has advanced by more than 3 days.  This means that they have gained time in the light - in an open canopy.  Whilst they may have gained time,  these early flowering plants are at greater risk of frosts.  It may also be that their pollinating agents may not be around - unless they too have brought forward their development / life cycle. There is some evidence that such changes are taking place.  Recent work at Wytham Wood (outside Oxford) has shown that blue tits have moved forward their egg laying to 'match' the development of the oak canopy, and the appearance of caterpillars (on which the young are fed).  Essentially, the timing of the food chain has changed..  Hopefully, such changes will occur in different ecosystems across the country.

When in Oxford, it is always a pleasure to visit the Oxford Botanic garden but until now I have never made it out to its ‘satellite’ – the Harcourt Arboretum.  The arboretum is only some six miles away, near the village of Nuneham Courtenay (on the A4074). The ‘core’ of the arboretum is the Pinetum (associated with William Gilpin 1762-1843), where mature monkey puzzle trees and giant redwoods can be seen.   The grounds are extensive including native woodland areas and a  considerable area of meadow (together, these would have originally formed an impressive entrance to Nuneham House).  Read more...

There are over 2,200 botanic gardens in 153 countries around the world and the UK's oldest is Oxford's.  It is fairly small considering how many plants it contains, covering about 4.5 acres, and it feels very like the Chelsea Physic Garden in London.  This may not be too surprising as they were both founded to support the practice and teaching of medicine.  The Oxford Botanic Gardens were founded in 1621 as the Physic Garden and after only a few years the yew tree (see photo below) was planted which is still in the garden today.  Read more...