Forests make heatwaves ‘initially warmer’


During heatwaves forests reduce their evaporation, causing the atmosphere to warm up even more, say researchers.

During extremely long periods of heat, however, this reduction enables the forests to continue their evaporation for longer, so the net effect is ultimately one of cooling in relation to the surroundings, explained a team of scientists led by Ryan Teuling from Wageningen University in the Netherlands.

Writing in the journal Nature Geoscience, Dr Teuling worked on the investigation in collaboration with climate researchers from a number of European countries.

The study was prompted by recent heatwaves in Europe, which had raised interest in questions about the influence of land use on temperatures and climate.

Up to now, scientists had assumed that a lack of precipitation during heatwaves automatically led to a reduction in evaporation.

That reduction was thought to be less for forests, because trees, with their deeper root systems, have more water available to them. Examination of the precise role of land use, however, has been largely neglected up to now.

The study found large differences in evaporation strategies during heat waves. Grasslands evaporate more at higher temperatures and stop only when no more water is available.

Forests, in contrast, respond to higher temperatures by evaporating less, which leaves more water at their disposal.

During brief heatwaves, therefore, the greatest warming is found above forests, but during prolonged heat waves the increased evaporation of grasslands ends up causing a shortage of water.

This can lead to exceptionally high temperatures, such as those measured in France in the summer of 2003.

This mechanism might also offer an explanation for the unusually high temperatures near Moscow this summer, the researchers suggest.

In these types of extreme situations, forests in fact have a cooling effect on the climate.

The research was done on the basis of observations made above forests and grasslands in Europe by an extensive network of flux towers. For areas without towers, satellite data were used.

Source: Wageningen University press release

Date: 06/09/2010

Twiglet: Trees and roots


  • First thing to emerge from a seed is the embryonic root – the radicle.
  • In most plants, this primary root will develop secondary or lateral roots that grow out away from the main root as the plant grows.
  • The growth of any root is dependent on a small ball of dividing cells just behind the root tip. This collection of cells is called a meristem; it generates new cells to extend the root and form new root tissue (such as the xylem and phloem – the conducting tissues).
  • A long tap root may develop in suitable soils, whilst, in sandy ot peaty soils, the lateral roots may dominate.
  • Studies indicate the dominance of the young tap root is often lost quite early in development in many tree species.
  • The deepest root systems are probably found on desert plants.
  • Tree roots do not generally occur too deep in the soil, with the majority of roots found in the top one to two metres.
  • Trees tend to have shallow but extensive root systems.
  • The spread of the lateral roots can be as great as the spread of the canopy or crown, even further in some cases.
  • One study showed that the root spread of poplars was three times the crown radius. This type of root system is sometimes referred to as an extensive system.
  • An intensive root system is one that is confined to a smaller volume of soil, relying on shorter lateral that have numerous fine endings. This system is seen in beech (Fagus sylvatica), which was one of the species that suffered more than most in the drought of 1976.
  • The survey of trees blown over in the October 1987 Great Storm showed that only 2-3% had distinct tap roots.
  • Oak, pine and silver fir are among the species with persistent tap roots.
  • Other species have what are known as “heart root systems”, where larger and smaller roots penetrate the soil diagonally from the main trunk. Trees such as larch, lime and birch can fall into this category.
  • A surface root system is one where the roots tend to run horizontally just below the soil surface, with a few roots going deeper and vertically. Ash, aspen and Norway spruce are examples of trees with these kinds of roots.
  • The root system depends upon the local geology, soil type, climate, drainage… so, if a local area is water logged, this will limit the gas exchange which in turn will affect the amount of oxygen the roots can get for respiration (which generates the energy needed for growth and the absorption of minerals).
  • When oxygen levels in the soil falls, root growth is reduced or stops completely — the availability of oxygen can also be reduced by the compaction of the soil.

Source: Woodland Trust

Indonesia favours palm oil over peatlands


The Indonesian government will allow developers to convert millions of hectares of land for oil palm plantations, reports Mongabay.com.

The decision threatens to undermine Indonesia’s efforts to reduce greenhouse gas emissions from land use and fashion itself as a leader on the environment among tropical countries.

Gatot Irianto, head of research and development for the Agriculture Ministry, said the department is drafting a decree that would allow the drainage and conversion of peatland areas into oil palm estates.

“We still need land for oil palm plantations,” he told the Jakarta Post during a conference organised by the National Commission on Climate Change.

“We’ve discussed the draft with stakeholders, including hard-line activists, to convince them that converting peatland is safe,” he added.

“We promise to promote eco-friendly management to ward off complaints from overseas buyers and international communities.”

Degradation and destruction of peatlands in Indonesia results in hundreds of millions of tonnes of greenhouse gas emissions each year.

Generally, developers dig a canal to drain the land, extract valuable timber, before clearing the vegetation using fire.

In dry years these fires can burn for months, contributing to the “haze” that plagues south-east Asian with increasing frequency.

Fires in peatlands are especially persistent, since they can continue to smolder underground for years even after surface fires are extinguished by monsoon rains.

While burning releases enormous amounts of carbon dioxide, merely draining peatlands also contributes to global warming. Once exposed to air, the peat oxidises, leading to decomposition and the relsease of carbon dioxide.

A study led by UK researcher Dr Susan Page from the University of Leicester found that producing one tonne of palm oil on peatland resulted in the release of up to 70 tonnes over 25 years as a result of forest conversion, peat loss and emissions from slash-and-burn fires.

Source: Mongabay.com

Date: 15/02/2009

Drought threatens Jordan’s olive trees


Persistent drought in southern Jordan could lead to the decimation of thousands of olive trees in the city of Karak, 120km south of Amman, reports the UN’s IRIN news service.

“We witness in summer a dramatic increase in temperatures and in winter a lack of rain,” said Ahmed Koufahi, executive director of the Jordan Environment Society.

“Our problem will worsen in the future and drought could strike all around the kingdom,” Koufahi told IRIN.

Olive trees could end up dying in the town ahead of the coming winter season, said Abdullah Fadel, a farmer from Iraq town, 20km south of Karak.

“Last year we had little rain during winter. This resulted in a small output of olives compared with previous years, but now we fear that all trees will die because we have not been able to water them for a while now,” said Fadel.

Farmers said at least 30,000 olive trees were on the brink of dying after freshwater springs in the area dried up.

Many farmers resorted to purchasing water from tanks in the city, but the high cost prevented them from splashing out continuously.

“We are still far from the winter season. I don’t know what will happen until the first drop of rain comes, but it looks like all the trees in the town could die,” said Fadel.

At least 20 springs have provided the olive groves with water over the past decades, helping residents turn their town into a small green oasis.

But successive declines in levels of rain water have dried up almost 15 springs, said environmentalists.

Local residents use the springs for washing and cooking as the authorities often ration water to households in cities and towns across the kingdom because of chronic shortages.

In addition, the government has adopted a policy against digging underground water springs in an attempt to preserve water.

According to Aktham Mdanat, head of the Karak agriculture department, the drought is expected to lead to a 50% fall in this year’s olive harvest.

Residents of the town, which has a population of 7,000 people, have called for the construction of dams to help collect as much rainwater as possible during the winter season.

Jordan is one of the 10 most water-impoverished countries in the world.

The desert kingdom has no river capable of providing the country with enough water as the Jordan River has turned into a small stream after its tributaries were diverted by Israel for agricultural purposes, according to Salameh Hiari, a professor at the University of Jordan.

Jordan does not have natural lakes either. It’s population of 5.6m depends solely on rainfall for its water supply.

Source: IRIN News

Date: 17/09/2008

Thai queen urges nation to save forests


The Queen of Thailand has urged the nation to conserve its forests and water supplies, the Bangkok Post reports.

She used her birthday address on Tuesday to voice her concerns about the country’s dwindling water resources.

“I have read foreign publications and learned that in the next 15 years fresh water will be scarce,” she told a gathering of government ministers, dignitaries and members of the public.

“I am worried that our country lacks large fresh water resources – there are only forests,” the Thai royal added.

“Forests are where water is collected uderground; forests will soak up rainwater which will otherwise flow to the seas – they are a good source of water.”

The queen acknowledged that future water needs could be met by desalination plants, but warned that Thailand was unlikely to to be able to afford the technology on a scale to meet all of the nation’s water needed.

Source: The Bangkok Post

Date: 13/08/2008

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