Every tree matters: Even a little deforestation alters climate

by Bill Laurence

Thinking about knocking down a few trees in the backyard?  Think again.  Felling even a handful of trees can change the local climate, according to a new study.

Think twice before cutting...

Think twice before cutting…

It’s been known for some time that clearing forests can have regional-scale impacts on climate by reducing evapotranspiration (the emission of water vapor by plants, which cools the land) and changing albedo (how much solar radiation gets reflected away from the ground surface).

But now it appears these effects happen at surprisingly small scales.  Especially in warmer parts of the world, clearing even a football field-sized area is enough to provoke significant heating of the immediate area.

That’s an important insight.  Folks living in tropical and subtropical areas often complain that deforested lands are unpleasantly warm, less productive for farming, and more prone to harboring diseases.

So, spread the word: Cutting down trees doesn’t just have a global impact, by increasing carbon emissions; or a regional impact, by changing evapotranspiration and albedo.

Killing trees also has a sizable local impact, meaning it directly affects the quality of life of those living nearby.

Source: http://alert-conservation.org/issues-research-highlights/2014/4/16/every-tree-matters-even-a-little-deforestation-alters-climate

Tree growth never slows

Idea debunked that young trees have the edge on their older siblings in carbon accumulation. by Jeff Tollefson


Native forest in Ancares Mountains, NW of Iberian Peninsula. Rubén Portas Copyright.

Many foresters have long assumed that trees gradually lose their vigour as they mature, but a new analysis suggests that the larger a tree gets, the more kilos of carbon it puts on each year.

“The trees that are adding the most mass are the biggest ones, and that holds pretty much everywhere on Earth that we looked,” says Nathan Stephenson, an ecologist at the US Geological Survey in Three Rivers, California, and the first author of the study, which appears today inNature1. “Trees have the equivalent of an adolescent growth spurt, but it just keeps going.”

The scientific literature is chock-full of studies that focus on forests’ initial growth and their gradual move towards a plateau in the amount of carbon they store as they reach maturity2. Researchers have also documented a reduction in growth at the level of individual leaves in older trees3.

In their study, Stephenson and his colleagues analysed reams of data on 673,046 trees from 403 species in monitored forest plots, in both tropical and temperate areas around the world. They found that the largest trees gained the most mass each year in 97% of the species, capitalizing on their additional leaves and adding ever more girth high in the sky.

Although they relied mostly on existing data, the team calculated growth rates at the level of the individual trees, whereas earlier studies had typically looked at the overall carbon stored in a plot.

Estimating absolute growth for any tree remains problematic, in part because researchers typically take measurements at a person’s height and have to extrapolate the growth rate higher up. But the researchers’ calculations consistently showed that larger trees added the most mass. In one old-growth forest plot in the western United States, for instance, trees larger than 100 centimetres in diameter comprised just 6% of trees, but accounted for 33% of the growth.

The findings build on a detailed case study published in 2010, which showed similar growth trends for two of the world’s tallest trees — the coast redwood (Sequoia sempervirens) and the eucalyptus (Eucalyptus regnans)4, both of which can grow well past 100 metres in height. In that study, researchers climbed, and took detailed measurements of, branches and limbs throughout the canopy to calculate overall tree growth. Stephen Sillett, a botanist at Humboldt State University in Arcata, California, who led the 2010 study, says that the latest analysis confirms that his group’s basic findings apply to almost all trees.

The results are consistent with the known reduction in growth at the leaf level as trees age. Although individual leaves may be less efficient, older trees have more of them. And in older forests, fewer large trees dominate growth trends until they are eventually brought down by a combination of fungi, fires, wind and gravity; the rate of carbon accumulation depends on how fast old forests turn over.

“It’s the geometric reality of tree growth: bigger trees have more leaves, and they have more surface across which wood is deposited,” Sillett says. “The idea that older forests are decadent — it’s really just a myth.”

The findings help to resolve some of these contradictions, says Maurizio Mencuccini, a forest ecologist at the University of Edinburgh, UK. The younger trees may grow faster on a relative scale, he says, meaning that they take less time to, say, double in size. ”But on an absolute scale, the old trees keep growing far more.”

The study has broad implications for forest management, whether in maximizing the yield of timber harvests or providing old-growth habitat and increasing carbon stocks. More broadly, the research could help scientists to develop better models of how forests function and their role in regulating the climate.

Nature: doi:10.1038/nature.2014.14536
Source: http://www.nature.com/news/tree-growth-never-slows-1.14536? 


Big trees, like the old-growth forests they inhabit, are declining globally

Rhett Butler, mongabay.com 

Already on the decline, demise of giant trees may be hastened by global warming.

Already on the decline worldwide, big trees face a dire future due to habitat fragmentation, selective harvesting by loggers, exotic invaders, and the effects of climate change, warns an article published this week in New Scientist magazine. 
Reviewing research from forests around the world, William F. Laurance, an ecologist at James Cook University in Cairns, Australia, provides evidence of decline among the world’s “biggest and most magnificent” trees and details the range of threats they face. He says their demise will have substantial impacts on biodiversity and forest ecology, while worsening climate change.

“To persist, big trees need a safe place to live and long periods of stability,” he told mongabay.com via email. “But time and stability are becoming very rare commodities in our modern world.”

Giant trees offer critical habitat and forage for wildlife, while transpiring massive amounts of water through their leaves, contributing to local rainfall. Old trees also lock up massive amounts of carbon — in some forests they can account for up to a quarter of living biomass.

Dipterocarp in Borneo
Dipterocarps are commonly targeted by loggers in Southeast Asia. This Dipterocarp was photographed in Borneo by Rhett A. Butler.

But their ability to sequester carbon and render other ecosystem services is threatened by human activities. Some of the world’s largest trees are particularly targeted by loggers. The oldest trees are among the most valuable and therefore the first to be cut in “virgin” forest areas.

Big trees are also sensitive to fragmentation, which exposes them to stronger winds and drier conditions. Laurance’s own work in the Amazon has shown substantial die-off of canopy giants in small forest fragments. Their susceptibility seems counter-intuitive given big trees’ life histories, which invariably include periods of drought and other stress.

“All around the tropics, big canopy and emergent trees are succumbing to strong droughts,” Laurance said. “That’s been a surprise to me and many other ecologists, because big, ancient trees would have had to survive many droughts in the past.”

Forest giants may suffer disproportionately from climate change, writes Laurance in New Scientist, highlighting research in La Selva, Costa Rica by David and Deborah Clark.

      “Trees are probably getting a double-whammy when the thermometer rises,’ says David Clark. “During the day, their photosynthesis shuts down when it gets too warm, and at night they consume more energy because their metabolic rate increases, much as a reptile’s would do when it gets warmer.” With less energy being produced in warmer years and more being consumed just to survive, there is less energy available for growth.
    The Clarks’ hypothesis, if correct, means tropical forests could shrink over time. The largest, oldest trees would progressively die off and tend not to be replaced. Alarmingly, this might trigger a positive feedback that could destabilize the climate: as older trees die, forests would release some of their stored carbon into the atmosphere, prompting a vicious circle of further warming, forest shrinkage and carbon emissions.
Giant Kapok tree in the Brazilian Amazon
Giant Kapok tree in the Brazilian Amazon. Photo by Rhett A. Butler.

Laurance notes climate change is having less direct impacts on forests, including creating conditions for exotic pathogens to thrive. For example, pathogens such as Dutch Elm Disease, introduced by trade or circumstance, can devastate native forests.

All told, the outlook for big trees is not good, according to Laurance.

“The decline of big trees foretells a different world where ancient behemoths are replaced by short-lived pioneers and generalists that can grow anywhere, where forests store less carbon and sustain fewer dependent animals, where giant cathedral-like crowns become a thing of the past.”

Source: http://news.mongabay.com/2012/0126-big_trees.html

Forest ‘management’ does far more harm than good

By George Wuerthner

There’s an old cliche that one can’t see the forest for the trees.It is used to describe people who are so focused on some detail that they fail to see the big picture.Nowhere is this failure to see the forest for the trees more evident than the presumed need to thin forests to reduce so-called dangers and/or damage from wildfire and beetle outbreaks.

Contrary to popular opinion, we probably do not have enough dead trees in our forest ecosystems.
And this deficit is a serious problem because dead trees are critical to the long term productivity of forests, and perhaps more important to forest ecosystems than live trees.

Dead trees are not a “wasted” resource. It is questionable whether we can we remove substantial quantities of live or dead wood from the forest without serious long-term biological impoverishment to forest ecosystems.

An abundance of dead trees — rather than a sign of forest sickness, as commonly portrayed — demonstrates that the forest ecosystem is functioning well.Wildfires and beetles are the major ecological processes that recruit dead wood that is the foundation for healthy forest ecosystems.

Recent research points out the multiple ways that dead trees and downed wood are critical to the forest as well as wildlife.Approximately 45 percent of all bird species and two-thirds of all wildlife (mammals, amphibians, etc.) depend on dead trees and downed wood at some point in their lives.
Dead trees are very important for functioning aquatic ecosystems as well. At least half of the aquatic habitat in small- to medium-size streams comes from dead wood. In general, the more wood you have in the stream, the more fish, insects and other aquatic life.

Once a tree falls to the ground and gradually molders back into the soil, it provides home to many small insects and invertebrates that are the lifeblood of the forest. For instance, hundreds of species of ground-nesting bees make their homes in downed trees.These bees are major pollinators of flowers and flowering shrubs in the forest.

And it’s not just wildlife that depends on dead trees. A recent review of 1,200 lichen species found that 10 percent were only found on dead trees and many others prefer dead trees as their prime habitat.
Lichens, among other things, are important converters of atmospheric nitrogen into fixed nitrogen, important for plant growth.

Contrary to the popular opinion that beetles “destroy the forest” and fires “sterilize” the soils or create biological deserts, several recent studies have concluded that both beetle-killed forests and the burned forests that remain after stand-replacement wildfires have among the highest biodiversity of any habitat type.

Logging, thinning, biomass removal and other forest management creates unhealthy forest ecosystems by removal of dead wood and thwarting the natural agents that recruit dead wood into the ecosystem.
Beyond impoverishing the forest ecosystem, logging also degrades forest ecosystems by spreading weeds, compacting soil, altering waterflow, disturbing wildlife, creating new ORV trails, and increasing sedimentation, among other impacts.

In short, current efforts to thwart and limit beetle outbreaks and wildfires create “unhealthy forests.”
In fact, nearly everything that foresters do — from thinning forests to suppressing fires — degrades and impoverishes the forest ecosystem. Forest “management” is so focused on trees and wood products that it represents a critical failure to see the forest for the trees.

Source: http://www.bendbulletin.com/archive/2013/04/16/forest_management_does_far_more_harm_than_good.html