Category: botany

The strawberry timebomb: how basic plant biology can help you store your produce

Posted on by andy.winfield
Two days ago I purchased an alarmingly large number of strawberries. I couldn’t help myself. Grown in Cheddar, these sweet little ripe morsels are a welcome break from the onslaught of last year’s apples and a plethora of citrus. When you try to eat seasonally and with reduced transportation miles, you appreciate the appearance of new season fruit that much more.
Non-climacteric fruit, such as strawberries, do not continue to ripen once picked
Strawberries have to be picked at their peak of ripeness as
they don’t ripen any further once they’re separated from the
plant – known as non-climacteric fruit.
Photo credit: Nicola Temple

The moment I placed the box on my kitchen counter, however, I felt as though a timer began counting down on a bomb. But rather than finishing off with an explosion, it would be more of a moldy, decayed mess of fruit wasting away. In response, I did as my mother before me did, and I issued relentless alarm calls to my family, “Eat strawberries…strawberries would go well with that…why are you eating that pear? EAT strawberries!” Luckily the troops rallied and I’m happy to report that there was no waste.

This strawberry time bomb is more technically that stage between when a fruit has reached its peak ripeness and when it first starts to deteriorate. Strawberries, unlike some other fruits, do not continue to ripen when picked and so they have to be picked when they are perfectly ripe otherwise they will taste somewhat inferior. The rotting timer starts the minute the strawberry is picked and is running down from field (or poly tunnel) to consumer. So why is it that strawberries don’t ripen further after they’re picked, but fruits like tomatoes do?

Ethylene and rapid respiration: qualities of the climacteric fruit

The answer lies in some basic plant physiology. Some fruits produce a lot of ethylene and undergo rapid respiration during ripening, which means the fruits continue to ripen even once they are separated from the plant. These are known as climacteric fruits. As one would expect, non-climacteric fruits produce very little ethylene, do not undergo periods of rapid respiration and do not ripen any further once picked from the plant.
Ethylene plays a major role in the regulation of the ripening process and affects the rate at which the fruit ripens. Producers use this to their advantage. Bananas, for example, are picked hard and green and stored mature but unripe. When a retailer places an order, the bananas are placed in a room and ethylene is pumped in to ripen the fruit up for sale.
Ethylene is even used by industry as a de-greening agent for non-climacteric fruits, such as citrus. It is used to break down the green chlorophyll pigment in the peel of many citrus fruits, like orange and lemon, which essentially makes a somewhat unripe fruit appear ripe to the consumer.
The genetic regulation behind the climacteric characteristics of plants is very complex and not yet completely understood. For example, different melon varieties can be climacteric or non-climacteric. If a climacteric melon is crossed with a non-climacteric melon, the fruit is generally climacteric, suggesting it might be a genetically dominant character trait. Yet, other experiments that have crossed two non-climacteric melons have generated climacteric melons. This implies that the trait is more complex than a dominantly inherited trait.

Examples of climacteric versus non-climacteric fruits

There may be a few items on these lists that make you take a second look as we don’t commonly think of them as fruits, but rather as vegetables. However, aubergines, courgettes and cucumbers are indeed fruits.
Climacteric Fruits
Non-climacteric fruits
Apple
Aubergine
Apricot
Bell peppers
Avocado
Cherries
Banana
Citrus fruits
Cantaloupe
Courgettes
Fig
Cucumber
Kiwi
Grapes
Mango
Lychee
Passion fruit
Most berries
Peach
Pomegranate
Pear
Strawberries
Plum
Pineapples
Tomato
Watermelon

How to store climacteric fruits and non-climacteric fruits

Tomatoes are a climacteric fruit - they continue to ripen after picking.
Different varieties of tomatoes, a climacteric fruit, on
display at a French market. Photo credit: Shelby Temple.

Knowing the difference between your climacteric and non-climacteric fruits can help you store them appropriately.

Climacteric fruits are best stored at room temperature. They are picked before they are ripe and refrigeration can slow the ripening process. Since these fruits will continue to ripen after picking, they generally have a shorter shelf-life, but refrigerating them once they have fully ripened could extend the shelf life somewhat. 
Non-climacteric fruits, on the other hand, are picked when fully ripe and are best stored in the refrigerator to slow their deterioration. They generally have a longer shelf-life as they don’t continue to ripen (though I don’t consider this to be true of berries).
Don’t store climacteric fruits with non-climacteric fruits as the ethylene produced by fruits such as bananas can speed up the rotting process of an already ripe fruit. However, this natural ethylene production can also work to your advantage. Avocados, for example, are often sold hard as rocks and if you wish to speed up the ripening process, you can store them with bananas in a paper bag on the counter.

The climacteric character of fruit is an active area of research due to the direct applications for the way we pick, transport and store our food. As much as I am an advocate for scientific solutions, I hope overindulging on the sweet delicious fruit of local strawberries during this precious time of year is never resolved – it is simply a matter of tradition.

The science of nectar

Posted on by andy.winfield
Nectar is that sweet reward that flowering plants provide animals in exchange for their services as pollinators. It sounds incredibly simple on one level – much like rewarding a dog with a treat after it obeys a command. However, dig a little deeper and you realise that the reproductive success of the plant is dependent on very subtle yet complex characteristics of this substance – including when it’s produced and how much is produced, as well as its very composition.
Flowering plants will optimise the characteristics of their nectar in order to influence the foraging behaviours of pollinators and ultimately improve their reproductive fitness. The characteristics of the nectar not only determine which pollinators are attracted and when they come, but how frequently they visit and how long they stay. Suddenly one realises that there is an extremely complex system of regulatory mechanisms behind nectar secretion, which have not only influenced the evolution of flowering plants, but of the pollinators themselves.
Red admiral butterfly close up
Red Admiral butterfly (Vanessa atalanta) drinking nectar. 
Photo credit: Shelby Temple.

Nectar isn’t just about sugar

But before we get into the evolution, let’s first consider what nectar is, because as it turns out it’s not just about sugar – there are a number of things in nectar that are important for pollinators.
There is no denying, however, that carbohydrates – sugars such as glucose, sucrose and fructose – are usually the main constituent of nectar. Nectar will be anywhere between 7 to 70 % carbohydrates per water weight [1]. Other sugars might also be present in small amounts as well as sugar alcohols, such as sorbitol. It is these sugars that are the primary energy source for nectar consumers.
Amino acids and proteins are the next most abundant solute in nectar after the sugars. There are essential and non-essential amino acids, which are the building blocks for proteins and there are some non-protein amino acids that are constituents of enzymes and preservatives. It is thought that the amino acid and protein content of nectar may play a role in the taste preferences of insects [1], presumably related to their nutritional needs.
The water content of nectar may also be an important reward for pollinators, particularly in dry habitats.
Nectar also contains important ions, such as potassium, as well as antioxidants, trace amounts of lipids and some secondary compounds that seem to be associated with resistance to herbivory. 
Macro photography bee
A bee gathering its nectar reward in the Botanic Garden.
Photo credit: Shelby Temple.
Many species have also been shown to have antimicrobial compounds in their nectar, which prevents microbes from growing in the nectar as well as inhibiting florally transmitted diseases [2].
Terpinoids, which are the volatile organic compounds that give flowers their scent, also accumulate in the nectar.
The composition and consistency of nectar is extremely variable as it is tuned to the needs of the nectarivores (it’s a word…really). Flowers frequented by hummingbirds, for example, generally produce nectar in small amounts with high sugar content, while those frequented by more generalist passerine birds produce dilute nectar in large quantities. There has been some evidence that honeybees have a preference for warmer nectar that’s less viscous, regardless of the sugar concentration [3]. Bats also seem to prefer less viscous nectar, though will preferentially select more dilute nectar as the water content is extremely important for their rehydration.

Not all nectar is produced in the flower

Nectar is produced in glands known as nectaries. The glands are commonly found at the base of flowers, where they produce nectar as a reward for pollinators. However, there are also extrafloral nectaries located elsewhere on the plant, often on the leaves or petiole – the stalk that attaches the leaf blade to the stem. These nectaries provide a reward for mutualistic animals, almost exclusively ants, which benefit the plant. The ants help protect certain plant species by getting rid of the eggs of herbivorous insects deposited on the foliage and in return they feast on the nutrient rich nectar secreted by the extrafloral nectaries.
Extrafloral nectaries might be particularly critical at certain times in the plant’s lifecycle. For example, there are often nectaries located on the pedicelthat secrete nectar when the flowers are in bud. This attracts ants, which help protect the vulnerable flower buds from herbivorous insects and improves the reproductive success of the plant [4].
Unlike nectar produced in the flower, nectar produced in the extrafloral nectaries is far less variable as it is attracting mostly ants.

Darwin’s orchid: a classic example of the coevolution of flowering plants and their pollinators

Producing nectar may use up to 37% of a plant’s available energy [5]. This means that producing it comes with some cost to the plant, but these costs are clearly outweighed by the benefits of attracting pollinators that are far more efficient than relying on wind or water.
The evolution of flowering plants and their pollinators is the most frequently used example of coevolution – the physical characteristics of both flower and animal evolving to become more specialised. It was around 120 million years ago that honeybees developed longer tongues than their short-tongued ancestors in order to access the nectar reward flowers had started to produce. Their social structure became more complex and they became fuzzier and developed pollen baskets in order to carry protein-rich pollen, but also facilitating their role as pollinators.
Darwin’s orchid in bloom at the Botanic
Garden last year. Photo credit: Andy Winfield.
The flowers also changed shape in response to the preferences of their pollinators. The most classic of these examples is Darwin’s orchid (Angraecum sesquipedale) with a flower depth of 20 to 35 centimetres. The Madagascar orchid was named after Darwin because he proposed, based on its shape alone, that it had to be pollinated by an insect with a proboscis of lengths unheard of at the time. Forty years later, Morgan’s sphinx moth (Xanthopan morganii), was discovered with an unusually large proboscis…and it was indeed the pollinator of this orchid.
It is also thought that nectar chemistry itself has evolved in response to pollinators. As mentioned earlier, bats prefer nectar with low sugar concentrations and as a result bat pollinated plants from very diverse and distantly related taxonomic groups have evolved nectar with low sugar concentrations.

Deceit and robbing

Not all flowers use nectar – some have non-rewarding flowers. Around 30-40% of species within the orchid family do not produce rewarding nectar in their flowers [6] and instead use different methods to attract pollinators. Orchid flowers may look like another species that provides nectar or they may mimic shelters or brood-sites or even pollinators themselves in order to draw the attentions of individuals looking for a place to shelter or for a potential mate (such as in bumble-bee orchids).
Just as plants have found ways to get pollinated without producing nectar, some animals have found ways to get nectar yet avoid being pollinators. Some flower visitors – known as nectar robbers – will avoid the normal route to the nectar, usually avoiding the floral opening all together and pierce or bite the flower elsewhere to extract the nectar directly without coming into contact with any of the reproductive parts.
For many years it was thought that nectar robbers had a negative or neutral effect on the plants, but over the last couple of decades, research has shown they can also have a positive effect on the plant. Firstly, some nectar robbers do ultimately end up pollinating the plants. Secondly, their presence can modify the behaviours of the pollinators. For example, if flowers have less nectar (because the robbers have extracted some) then pollinators will visit more flowers, increase their foraging range, travel further distances and spend less time at each flower – all of which could improve cross pollination and increase genetic diversity. Maloof et al [7] provide a good review on this topic.  
There has been extensive research done on the characteristics of nectar and its relationship with pollinators. More recent research, however, is starting to unravel the mechanisms by which plants produce nectar – identifying some of the pathways sugars are transported within the plant and concentrated in their nectar [8]. There is still lots to learn.

Sources:

[1] Pacini E, Nicolson SW (2007). Chapter 1: Introduction, In: Nicolson SW, Nepi M, Pacini E (Eds.) Nectaries and Nectar. Springer: The Netherlands. ISBN: 978-1-4020-5936-0. (pages 8-10).
[2] Sasu MA, Wall KL, Stephenson AG (2010). Antimicrobial nectar inhibits a florally transmitted pathogen of a wild Cucurbita pepo (Cucurbitaceae). American Journal of Botany 97 (6): 1025-1030. (link)
[3] Nicolson SW, de Veer L, Köhler A, Pirk CWW. Honeybees prefer warmer nectar and less viscous nectar, regardless of sugar concentration (link).
[4] Bentley BL (1977). The protective function of ants visiting the extrafloral nectaries of Bixa orellana (Bixaceae). J. Ecol. 65 (1): 27.38.
[5] Pyke GH (1991). What does it cost a plant to produce floral nectar? Nature 350: 58-59. doi: 10.1038/350058a0
[6] Johnson SD, Hobbhahn N, Bytebier B (2013). Ancestral deceit and labile evolution of nectar production in the African orchid genus Disa. Biol. Lett. 9 (5): 20130500. doi: 10.1098/rsbl.2013.0500.
[8] Lin IW et al.(2014). Nectar secretion requires sucrose phosphate synthases and the sugar transporter SWEET9. Nature 508: 546-549. doi: 10.1038/nature13082

The Native Bluebell: Britain’s favourite flower in trouble

Posted on by andy.winfield

by Helen Roberts


It is a beautiful spring morning in May and I am taking my children for a walk. We are venturing to some local woods on the edge of the Mendip Hills, a stone’s throw away from our house.

The woods are secreted away in a limestone gorge. The stubby cliffs of limestone are clothed in ivy and gradually open up into a steep sided valley. A tiny stream channels through the gorge; tributaries often disappearing down sink holes. We trek across a ploughed field to the gate that lets us into the wood.

As we pass through the kissing gate, there is an overwhelming smell – it’s the heady perfume of the native bluebell, Hyacinthoides non-scripta. The woods are carpeted in vibrant blue (the colour almost glows it is so vivid), dotted with ferns and intermingled with wood anemones (Anemone nemorosa), Lady’s smock (Cardamine pratensis), wild garlic (Allium ursinum), greater stitchwort (Stellaria holostea) and yellow archangel (Lamiastrum galeobdolon). It is one of my favourite places for a walk in the spring and it is made special because of the sight and smell of bluebells.

Bluebell woods in Britain are under threat

British woodland with bluebells in bloom

Bluebells blanket the ground in British woodlands
this time of year. Photo credit: Shelby Temple

Bluebell woods are an iconic part of our natural heritage and are one of the most beautiful sights to encounter in the British countryside. They were voted Britain’s favourite flower in Plantlife’s ‘CountyFlowers’ project in 2002 and we have 50% of the entire world population in our country.
Sadly, the indigenous bluebell, Hyacinthoides non-scripta, is in danger because it cross breeds with the commonly planted Spanish bluebell (Hyacinthoideshispanica) and with the resulting fertile hybrid (Hyacinthoides x massartiana). Molecular studies have shown that the Spanish bluebell and the native bluebell have a shared ancestor [1], but Hyacinthoides non-scripta has developed in isolation over the last 8,000 years, its range to the north of the Spanish bluebell [2].

Polluting bluebell genetics

The Spanish bluebell has been grown as a garden plant in Britain since 1683 [3] and it and its hybrid have now ‘gone over the garden wall’ and are encroaching on our native bluebell woods. Its leap over the ‘wall’ has most likely been facilitated by bulbs being thrown out or dumped near native woodlands. The Spanish bluebell looks a thug of a plant next to our native one – being a much bigger plant – and is reported far more vigorous. 
Hyacinthoides non-scripta
Native bluebells are low to the ground and
deep blue to violet in colour. The flower spike
distinctly nods to one side. Photo credit: Glyn Baker
[CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)],
via Wikimedia Commons
In its native range, the Spanish bluebell has a wider ecological tolerance to that of the native bluebell. It copes better with drier and more exposed conditions and can therefore grow in more open sites, such as roadside verges and waste ground. The Spanish bluebell is a garden favourite because it’s so much larger and can establish itself and grow quickly. Both the Spanish bluebell and its hybrid, however, have the ability to take over leading to the loss of genetic integrity of the native bluebell.
The native and bluebell hybrid are really difficult to tell apart even by expert botanists and sometimes the only way to distinguish between them is to apply DNA analysis. Many gardeners are sold the hybrid mislabeled as ‘English Bluebell’ and have planted them in good faith thinking these were the native bluebell.

The hybrids were first recorded in the wild in 1963, though they were likely there long before then as the Spanish bluebell was first recorded in the wild in 1909. The Natural History Museum gives good guidance on how to identify your bluebells with a supporting video given by botanist Fred Rumsey here.

Nation-wide bluebell surveys show extent of Spanish bluebell invasion

A survey performed by Plantlife International in 2003 found that one in six broadleaved woodlands surveyed were found to contain the hybrid or Spanish bluebell. The survey drew attention to the threat posed to our native bluebell as well as the need for more research in order to better understand species distribution, gene transfer across species and appropriate horticultural management of bluebell species.
Thankfully, it has been illegal (without a license) for anyone to collect and sell native bluebells from the wild since 1998 as they are protected under the Countryside and Wildlife Act (1981). Current legislation allows for the issuing of a special license to collect wild seed for commercial sale. These safeguards ensure that collection is done sustainably and protects wild bluebell populations.
The native bluebell is a priority species under the UK BiodiversityAction Plan (BAP). Plantlife International states that it’s vital that the horticultural industry stop the deceiving sale of the Spanish and hybrid bluebell as native bluebell. Plantlife has also worked with Flora Locale to set up an industry code of practice. Flora Locale helps people get in touch with suppliers in their area who sell seeds of local provenance. Another initiative between Landlife and the Mersey Forest produces a legitimate source of bulbs grown from seed with a long term programme running to plant them in new woodlands. Plantlife International also gives advice about making sure that gardeners check suppliers of bluebells and how to remove Spanish or hybrid bluebells from your land – read more here.
The Natural History Museum launched a bluebell survey in 2006 (of which you can take part) to look at the extent to which non-native bluebells have spread into the British countryside. Results from the last eight years show that most bluebells in urban areas are now hybrids, but fortunately there are still large areas of countryside containing our native species.
Since 2010, the survey has concentrated on comparing the flowering times of native and non-native bluebells to understand how they will each respond to climate change. By comparing recent surveys with past data, it is possible to find out whether the flowering season is changing. These data need to be collected over many years in order to tease out any real effects of climate change from the natural fluctuations inherent in any population.

Sources:

[1] Grundmann, M. et al. (2010). Phylogeny and taxonomy of the bluebell genus Hyacinthoides, Asparagaceae [Hyacinthaceae]. Taxon, 59 (1): 68-82.
[2] Natural History Museum [website] Hyacinthoides non-scripta (British bluebell). http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/endangered-species/hyacinthoides-non-scripta/
[3] Pilgrim, E. and N. Hutchinson. Bluebells for Britain: A report on the 2003 Bluebells for Britain survey.  Plantlife International. <http://www.plantlife.org.uk/uploads/documents/Blubells-for-Britain-report.pdf>

More sources of information on bluebells:

Preston C.D. et al. (2002). New Atlas of the British and Irish Flora: An Atlas of the Vascular Plants of Britain, Ireland, The Isle of Man and the Channel Islands. ISBN: 9780198510673. [Provides information on each taxon]

Tines T.D.. et al. (2012). The Wild Things Guide to the Changing Plants of the British Isles. ISBN: 9781905026999. [Provides information on the spread of non-native bluebells]

Forests may be more vulnerable to pests and disease in the future

Posted on by andy.winfield
As I sit in my home office watching the autumn rains and winds strip the last remaining colourful leaves off the trees outside, I find myself in awe of the tree. There’s a primary school across the street from my house and there are several huge beautiful chestnuts in its grounds where I watched the children shelter from the sun on hot days. There’s also the spindliest little apple tree that one could imagine, which despite its size produced at least a dozen enormous apples this year!
Trees affect every aspect of our lives – they provide food, timber, pulp and fibre, but beyond this they have important ecosystem functions in the natural landscape. Trees help to regulate our climate, they store and sequester carbon (about 30% of global CO2 emissions are absorbed by forests), they store water helping to prevent floods, they purify water and they provide habitat.
However, widespread pests and diseases have taken their toll on natural forests over the past century with outbreaks seemingly becoming more frequent and widespread in recent years. There has been considerable focus on the devastating effects of these outbreaks on trees with large economic value – orchards and timber plantations for example – but what are the consequences of the widespread death of our forests in terms of ecosystem services?
Oak in its autumn colours.
A review published recently in the journal Science considers this exact issue. UK researchers from the Universities of St. Andrews, Cambridge and Oxford reviewed the consequences of tree pests and diseases on ecosystem services around the globe.  The authors concluded that our current approaches to pest and disease management do not take into account the ecosystem services or the beneficiaries of these services provided by forests and that new approaches are needed, particularly as the likelihood of pest and disease outbreaks increases as a result of global climate change and globalisation.

Who’s attacking our forests?

Trees are attacked by any number of pests and diseases, including bacteria, viruses, invertebrates, water molds and fungi. The effects of these pathogens may be compounded as well; trees that have been defoliated by insects may be more vulnerable to disease.
Millions of years of co-evolution have generally allowed trees to build up natural defenses to the pathogens they encounter in their native environments.  However, the introduction of species or the movement of species outside their historical ranges has opened up a whole new world of pathogens that have been the cause of the most devastating attacks on our global forests in the last 200 years.
The American chestnut (Castanea dentata) was devastated by chestnut blight – a fungus accidentally introduced to eastern North American forests around 1900. In the early 20thcentury, over a quarter of the trees across approximately 200 million acres of eastern hardwood forests were American chestnuts, but by 1993 its frequency had declined to 0.5%. Today the tree is effectively extinct as very few mature trees are producing nuts.
Dutch elm disease – another fungal pathogen, which is transmitted by bark beetles – is familiar both in North America and Europe as it has eliminated mature elms (Ulmus spp.) from much of the landscape. Now there is concern that ash (Fraxinus excelsior) could suffer the same fate due to another fungal pathogen (Chalara fraxinea), which has been killing trees in Poland since the 1990s. Scientists are monitoring its spread to the rest of Europe.
The devastation wreaked on a Canadian forest by the
mountain pine beetle. Credit: D. Huber, Simon Fraser University
Public Affairs and Media Relations (Flickr CC).
As a Canadian I would be remiss if I didn’t also mention the devastating effects of the mountain pine beetle (Dendroctonus ponderosae). It has already killed several million hectares of pine species in Canada and the US and they expect over 37 million hectares of forest to be affected in British Columbia alone before 2020.
Of course, with globalisation and the widespread movement of plants and plant products around the world, the frequency and spread of pests and disease is only likely to increase. Climate change will also improve conditions for pests and disease as milder conditions in some areas may let some pathogens increase their natural range, or may permit pest populations to explode in numbers.

Attack of the Frankenfungus


When pathogens move around the globe they are not only introduced to new hosts and plant prey, they can also escape the natural predators and diseases that keep their populations under control.
This global movement also exposes pathogens to new genes that can make them even more virulent. For example, when the fungus that causes Dutch elm disease, Ophiostoma novo-ulmi, spread across the northern hemisphere, it hybridised with a native fungus species (O. ulmi) and acquired some new genes that decreased the elm’s ability to resist infection.   

What does the loss of dominant tree species mean for our forests?

Widespread loss of a dominant tree species can have devastating effects far beyond any economic value they may have had. A wide range of ecosystem services will initially be harmed, such as retention and purification of water, wildlife habitat and carbon storage. Large stands of dead trees also become fuel for wildfires, which are far less specific about their victims and further alter the ecosystem.
However, inevitably the lost trees are replaced by new species and as this natural succession occurs some of the ecosystem services will be restored – carbon storage and water purification, for example. Unfortunately, other ecosystem services may never be restored. New tree species will create different habitats altering the biodiversity. 
Some ecosystems are particularly vulnerable as they are dominated by a species that plays a critical role in maintaining the structure of that ecological community – known as a keystone species. Boreal forest (or taiga) is an excellent example of this. The conifers that dominate the northern latitudes of boreal regions are adapted to short growing seasons, recurring disturbance from storms, fire and floods, and growing in peatlands. Loss of any species in these regions would have a significant impact on the ecosystem structure.

Climate change packs a one-two punch for forests

Not only does climate change have the potential to increase the numbers and range of pests and disease, it can also make forests more susceptible to these infestations. Though the future is uncertain, predicted increases in extreme weather events – droughts, floods, cyclones, and extreme temperature fluctuations – are likely to put our forests under severe stress, increasing their vulnerability. 
Of course, some pests may also be hindered by climate change. For instance, species that rely on an insulating blanket of snow to overwinter may be more vulnerable if snow cover is reduced in a milder climate scenario.

What is the future of our forests?

Nobody knows the answer to this question. However, the UK authors of the Science paper bring to light the need to do more fundamental research in understanding how pathogens affect natural forest communities. To date, most research has focussed on economically important species, yet the ecological role of forests and the ecosystem services they provide have considerable value also.
The long life span of trees has been a barrier to understanding some aspects of the infection and spread of some pathogens; the time it takes for some trees to reach a reproductive stage could outlive the careers of some scientists. However, new methods in molecular biology are overcoming these barriers these days. Understanding the process behind these pathogens will help in the prediction of their spread as well as how they may respond to climate change.
The authors also call for better management approaches that identify different classes of threat, which are defined by (i) the type of disease-causing agent (e.g. fungus, bacteria, insect), (ii) how it moves (e.g. wind, water, animal, wood imports) and (iii) the type of ecosystem service threatened (e.g. keystone species, timber value).
Management practices can also help build resilience in our forests. For example, practices that help preserve the genetic diversity of species and avoid monoculture will provide the genetic foundation that will help species resist disease. Steps to mitigate climate change may help reduce the abiotic stress on forests and reduce the expansion of pest populations.

Though there remain many unknowns and the future is uncertain, the critical role forests play globally is clear. So, if you are able, get out into a local wood or forest today and appreciate it. Those trees are cleaning the air we breathe and the water we drink. They grew that apple you brought along for a snack! They’re doing a lot as they stand there, so appreciate it…dare I even say…hug a tree?!  Who knows, you might start a trend?!
The original paper is: Boyd IL, Freer-Smith PH, Gilligan CA, Godfray HCJ. (2013) The consequence of tree pests and disease for ecosystem services. Science, 342 (6160): doi 10.1126/science.1235773
The AAAS press release associated with the paper can be found here.

The benefits of flowering early

Posted on by andy.winfield

Bristol was a swirl of snowflakes and blossoms earlier this week. Monday on my walk the cutting wind was relentless. Yet, despite my frozen nose and numb fingertips, I stopped to admire the many splashes of colour along my route – a street lined with blossom-laden plum trees, front gardens lined with daffodils, heather and crocuses, splashes of primulas and even some snow drops in the local woods. As my teeth chattered despite my thick down coat, I did marvel at these early spring bloomers that have clearly found it to their advantage to flower despite cold temperatures, relatively short days, and a paucity of pollinators. So, what exactly arethe advantages of being the first blossoms of spring?
A robin and crocuses, both soaking up some sunshine
on Thursday at the Botanic Garden.

Early woodland blossoms have access to more light

The first and perhaps most obvious advantage is that these early blossoms appear before the deciduous trees come into leaf, which gives them more access to light. Many of these early blossoms are naturally woodland flowers and so as soon as conditions become tolerable, these flowers put all of their energy into producing foliage and flowers before the forest canopy has formed. If successfully pollinated, the plant will produce a seed for dispersal. Then, as the forest floor becomes shaded by the trees above, the flower and foliage die back and any unused nutrients are returned into the roots or bulb. There will be no sign of these plants above ground for the rest of the year.
Though this may sound very much like a ‘get-up-and-go’ approach to flowering, the timing of when each species, and indeed each plant, flowers is incredibly complex and scientists have yet to figure out all the intricacies. It is affected by physical factors, such as soil nutrients, water, sunlight, day length and temperature, but it is also affected by biological factors, such as abundance of pollinators, herbivorous predators, seed dispersers and competition from other plants.  All of these factors may ultimately affect the reproductive success of the plant; flower too early and there may not be sufficient to set seed, but flower too late and the bird species that normally disperse the seed may have already migrated to over-wintering grounds.

There is less competition for pollinators

Though there are fewer pollinators about in early spring, there are also fewer blossoms to compete for their attentions. Insects that emerge in early spring or that forage throughout the winter, such as some bumblebee species, do not have a plethora of blossoms to choose from, so this increases the likelihood that the flowers that are out will get a visit.

There is more time for seed maturation

For some early season blossoms, such as fruit trees, there is an enormous investment in seed production, which takes time. The benefit in the end, of course, is a rather extravagant and often delicious means of dispersing seed great distances.

Early blossoms favour out-crossing  (Munguía-Rosas et al., 2011)

Fewer blossoms in early spring also mean that pollinators will travel greater distances between flowers. As a result, a flower may receive pollen from a more distant flower, which may be less similar genetically. It’s the floral equivalent of “bringing in new blood”, also known as out-crossing.  Perhaps the genetic material carried in that pollen encodes some increased resistance to frost or disease…or perhaps not. Most importantly, it is adding diversity to the population, which is the foundation for adaptation.
The crocuses in my front garden are in full bloom.

The evolution of early bloomers

There are not only differences in the time that plants flower between species, but also between populations of the same species and between plants of the same population. For example, the crocuses at the front of my garden, which have been exposed to more direct sunlight, are much further along than those in my back garden, which are shaded by a cedar hedge. This is a clear example of differences in the resources available in these two different growing environments.
However, consider a woodland covered with bluebells, what drives those first few bluebells to burst out before the others? It might be slight differences in their growing environments, but it is also in part a result of their genetic makeup. A sort of bluebell “aptitude” if you will that predisposes them to go to flower quickly – two separate bluebells, under the same growing conditions, may still flower at different times. Of course, it is therefore inevitable that those bluebells that are first to bloom will be pollinated by others that are in blossom, giving rise to new generations of early bloomers.
It might also be that environmental conditions are such that early bloomers are for some reason more successful in reproducing, perhaps because pollinators favour early bloomers (Munguia-Rosas et al., 2011). This will eventually drive the flowering time of entire populations earlier each season and over time this will become fixed within the genetic makeup of that population, in as few as three generations for some species (Galloway and Burgess, 2012).

Temperate plants tend to be more flexible with their flowering times

In temperate climates, there are much bigger differences in variables such as frost, temperature and day length across the landscape, between the seasons and between years. As a result, flowering plants in these regions exhibit tremendous variability in their flowering time – it is an adaptive flexibility that enables them to take advantage of the best growing conditions possible regardless of when they might happen (within reason of course).

If you’re going to be a risk-taker, be sure and have a plan B

Of course, many of these early spring blossoms have what could be considered a back-up plan. Snowdrops, crocuses, and daffodils are all capable of both sexual and asexual reproduction. So, if there is a prolonged heavy frost after these flowers have emerged or they are not successfully pollinated for any other reason during the season, then the bulbs will still form new small bulbs that are genetically identical to the parental bulbs. However, it is sexual production that brings genetic diversity to a population and this is what will allow a population to adapt to changing environmental conditions and resist disease.
There is a lovely clip herefrom the BBC’s Private Life of Plantson their website showing the progression of early blossoms as a British woodland bursts to life in the spring.
Well, I hope you are getting the opportunity to enjoy these early spring blossoms! Also, be sure to come out to the Botanic Garden over the Easter weekend to enjoy the Easter Sculpture Exhibition – amazing art, refreshments, and garden tours sounds like an ideal way to spend a weekend to me, I’m definitely going to be there!
Here are the references used above:
Galloway LF and Burgess KS. 2012. Artificial selection on flowering time: influence on reproductive phenology across natural light environments. Journal of Ecology 100: 852-861. http://www.cfbiodiv.org/userfiles/1111.pdf

Munguía-Rosas MA, Ollerton J, Parra-Tabla V, De-Nova JA. 2011. Meta-analysis of phenotypic selection on flowering phenology suggests that early flowering plants are favoured. Ecology Letters 14 (5):511-521.