Monday, October 29, 2007

Water repulsion off montane forest leaves

A study published in the November issue of the journal Biotropica looks at the ability of trees in tropical montane forests to repel water from their leaves. Holder hypothesised that trees in montane forests should be better at repelling water than trees from drier environments - dry forests in Guatemala and a semiarid grassland-foothills ecotone in Colorado. However, he found montane forest trees were less able to repel water than dry forest or temperate grassland-foothill species. Holder suggested that the increased wettability of the montane forest species may be driven by their coating of epiphylls (plant and other organisms growing on the leaf surface), while increased ability to shed water may be selected for in dry environments because it may help channel water to the roots of the plants in arid environments.
  1. Holder, Curtis D. 2007. Leaf Water Repellency as an Adaptation to Tropical Montane Cloud Forest Environments. Biotropica 39 (6), 767-770. doi:10.1111/j.1744-7429.2007.00303.x
[Read the rest of my post Like water off the back of a duck]

Monday, October 22, 2007

Poor showing for fall colours

Warmer weather has been blamed for less than impressive Fall foliage in New England. According to Dave Gram, writing in the Buffalo News:

Forested hillsides usually riotous with reds, oranges and yellows have shown their colors only grudgingly in recent years, with many trees going straight from the dull green of late summer to the rust-brown of late fall with barely a stop at a brighter hue.

"It's nothing like it used to be," said University of Vermont plant biologist Tom Vogelmann, a Vermont native.

He says autumn has become too warm to elicit New England's richest colors.

While I'm no expert on this, the idea seems intuitively appealing. Brilliant Fall colours are a feature of the Great Lakes region - down here, leave tend to go from green to brown, often with only the slightest nod to yellows and reds. Unfortunately, "intuitively appealing" arguments can be misleading - after all, many people are attracted to creationism for just that reason.

It shouldn't be too difficult to answer the question of whether there is a correlation between Fall colours and climate change. The more interesting question is why there is such a correlation, why might drive such a change. The Gram article attempts to address this:

Warming climate affects trees in several ways.

Colors emerge on leaves in the fall, when the green chlorophyll that has dominated all spring and summer breaks down.

The process begins when shorter days signal leaves to form a layer at the base of their stems that cuts off the flow of water and nutrients. But in order to hasten the decline of chlorophyll, cold nights are needed.

In addition, warmer autumns and winters have been friendly to fungi that attack some trees, particularly the red and sugar maples that provide the most dazzling colors.

"The leaves fall off without ever becoming orange or yellow or red. They just go from green to brown," said Barry Rock, a forestry professor at the University of New Hampshire.

So where do the pigments come from? Why do the plants produce these pigments? While I didn't know the answer to that question, it didn't cross my mind that this was in any way a mystery. Turns out that it is a mystery. There are several hypotheses, including
  1. to attract fruit-dispersing birds (this only works for species with bird-disperse fruit and is, at best, an incomplete explanation; Hoch et al. 2001)
  2. anti-herbivore or anti-microbial defenses
  3. protection against drought or freezing tolerance
  4. protection against photoinhibition that might otherwise interfere with the recovery of nutrients from leaves (Holopainen and Peltonen 2002)
  5. as a means of signaling to aphids that a tree has invested heavily in chemical defenses (Hamilton and Brown 2001)
If Fall pigments play a protective role, it's reasonable to suggest that a shortened period of leaf senescence (triggered by a warmer Fall) might lead to reduced production of these compounds. It is, as I said before, an interesting story. Sadly, it seems like it's still just that - a story.
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  1. Hoch, W. A., Zeldin, E. L. and Mccown, B. H.. 2001. Physiological significance of anthocyanins during autumnal leaf senescence. –Tree Physiol. 21: 1–8.
  2. Holopainen, J. K. and Peltonen, P. 2002. Bright autumn colours of deciduous trees attract aphids: nutrient retranslocation hypothesis.Oikos 99 (1), 184–188.
  3. Hamilton, W. D. and Brown, S. P. 2001. Autumns tree colours as a handicap signal. –Proc. R. Soc. Lond. B Biol. Sci. 268: 1489–1493.

Friday, October 19, 2007

Human impacts on pre-Columbian tropical forests

Blogging on Peer-Reviewed Research

When European naturalists first visited the New World Tropics they saw vast forests that seemed untouched by humans. While indigenous people often lived in these forests, their populations were small. This led to a perception of tropical forests as primeval, “virgin” forests. In the last few decades, this perception has changed - large areas now covered by mature forests have a history of cultivation. In many cases, “primeval” forests are less than 500 years old.

La Selva biological station in Costa Rica is one of the premier research stations for Neotropical biology. Prior to archaeological study of the site, much of it was assumed to be free of human influence. However, the discovery of pre-Columbian artefacts led to the discovery that the site had been occupied at least 3000 years ago. Charcoal was more abundant in alluvial terraces (flatter areas with deeper, more fertile soil) and less abundant in the less fertile upland soils. A chronology, established by Sol (2000)*, divided the La Selva into four archaeological phases: La Cabaña 1000 – 1550 CE; La Selva 500 – 1000 CE; El Bosque 300 BCE– 500 CE; La Montaña 1500 –300 BCE.

To better understand the history of the site, Lisa Kennedy of Virginia Tech and Sally Horn of the University of Tennessee, Knoxville, undertook a study of sediment cores extracted from the Cantarra swamp*, a 0.5 ha wetland dominated by perennial herbs. They used pollen, charcoal and macrofossils to reconstruct the environmental history of the site. Wetlands are frequently used to reconstruct vegetation histories. As sediments accumulate in bodies of water, plant pollen, fern spores and charcoal fragments are trapped. Pollen coats are extremely tough, and decay takes place very slowly in waterlogged soils. If the vegetation surrounding the site changes, different types of pollen will be deposited into the site. Someone with the patience to sort through these cores can observe thousands of years of history in a few metres of sediment.

[Read the rest of the post]

  1. Sol, C., R. F. 2000. Asentamientos prehispánicos en la Reserva Biológica La Selva, Sarapiquí, Costa Rica: Sistemas de explotación de recursos naturales en un bosque tropical lluvioso. Licenciatura thesis, School of Anthropology and Sociology, University of Costa Rica.
  2. Lisa M. Kennedy, Sally P. Horn. A Late Holocene Pollen and Charcoal Record from La Selva Biological Station, Costa Rica. Biotropica (OnlineEarly Articles). doi:10.1111/j.1744-7429.2007.00334.x

Tuesday, October 09, 2007

Indian fruit genebank threatened

Jeremy at Agricultural Biodiversity Weblog reports that the government of Jharkand State in India plans to bulldoze the field genebanks of the Horticulture and Agro Forestry Research Programme in order to build housing for Members of Parliament and Members of the Legislative Assembly.

According to a story in the The Indian Express, the plan will take 288 acres of HARP's land, including 88 acres of Farm 2, and will destroy
5253 plants of different varieties of mango and litchi, 6,500 trees more than 30 years old, eight greenhouse nurseries, each with 4000-5000 plants of guava and jackfruit and a gene bank developed over 20 years to have a germplasm base of 239 varieties of mango and litchi.
As the story goes on to say, this goes beyond destroying decades of work - destruction of a gene bank will also hurt regional farmers
Not just that. “The gene bank of these valuable fruit-bearing tress will be destroyed for ever. It will seriously affect horticulture prospects of the farmers in this belt,” says HARP’s Principal Scientist Shivendra Kumar.
Not only is this a political decision, it's a decision being made by the state legislature to benefit state legislators. So it isn't too surprising that they are unmoved by external forces.
This also flies in the face of a letter from Union Agriculture Minister Sharad Pawar earlier this year asking Chief Minister Madhu Koda to shelve the plan and instead issue mutation certificate of this land whose title was transferred to the ICAR by the Ranchi Deputy Commissioner in 1976. In 1979, HARP was set up with 100 percent funding by the Union government.

Wednesday, October 03, 2007

Fighting to save Greene Prairie

The University of Wisconsin-Madison's Arboretum is famous for its restored prairies. The most famous is the Curtis Prairie, established in the 1930s and 40s. Less well known is the 50-acre Greene Prairie, which was restored almost single-handed by Henry Greene in the 1940s and 50s.

Greene Prairie is currently under threat from Reed Canary Grass (Phalaris arundinacea) a perennial grass native to Eurasia. In North America it is invasive in wet sites; the Wisconsin DNR estimates that it dominates 10% of the state's wetlands. The Greene Prairie initially lacked permanently flooded areas, but runoff from suburban have altered the site. Reed Canary Grass currently dominates 10 acres of the 50-acre site. (Reed Canary Grass at Greene Prairie from: Zedler, J.B. and J. Wilcox. 2005. Interconnected Restoration Challenges: Controlling invasives and reestablishing natives, Arboretum Leaflet 1).

So far, restoration efforts have had limited success. University of Wisconsin-Madison News reports on new efforts to incorporate students in the restoration project.

In the new plan, Arboretum staff will burn the experimental site and apply sethoxydim in the spring. Then, each fall, the ecology students will sow native seeds, survey plant diversity and abundance, and otherwise monitor the project's progress. In keeping with its experimental nature, researchers will review the data carefully each year and make adjustments to the approach as needed.

The team hopes not only to keep reed canary grass from spreading further, but also to push it back eventually toward the south. No matter what the final outcome, however, Herrick has no doubts about the benefits.

"At a time when resources are stretched, we could never, as Arboretum staff, pull off this experiment on our own. So, incorporating the students is a perfect way to do this," he says. "It's an education for them - first and foremost. But we also get to advance restoration ecology research and answer land care questions. It's a win, win, win, all the way around."