Too Much Water And Fertilizer Bad For Plant Diversity
Too much of multiple good things - water or nutrients, for example - may decrease the diversity of plant life in an ecosystem while increasing the productivity of a few species, a UC Irvine scientist has discovered.
This finding provides a new explanation for why grasslands, lakes and rivers polluted with nitrogen and phosphorus, usually from agriculture, contain a limited number of plant species. For example, where the Mississippi River empties into the Gulf of Mexico, the water contains low levels of oxygen and high levels of nitrogen and phosphorus used in fertilizers resulting in reduced plant diversity.
"Our results show nutrient pollution can cause loss of plant species from a habitat that can persist for more than 100 years," said W. Stanley Harpole, postdoctoral researcher in ecology and evolutionary biology at UCI and first author of the study. "This means human actions that simplify habitats can lead to long-term loss of biodiversity. "
This study appeared March 25 in the online edition of the journal Nature.
The findings are based on experiments conducted at the University of California's Sedgwick Reserve in the Santa Ynez Valley. Researchers applied combinations of water and nutrients - including nitrogen, phosphorus and cations - to plots of grassland and found that areas treated with all of the resources had the fewest number of species but the highest productivity of a select few plant types.
When the many resources that plants compete for become overly abundant, the environment simplifies, and an emphasis is placed on a single environmental factor such as space or sunlight. Only a few species best adapted to the new environmental conditions will thrive, Harpole said.
The experiment, combined with an analysis of a similar 150-year-old study, supports the scientists' theory that plant diversity is directly related to the number of limiting factors such as levels of nitrogen, phosphorus, potassium and water.
The 4th Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) has a finely calibrated lexicon of certainty. "Virtually certain", it blares when it assigns a 99% probability to hot days
getting hotter and more frequent. "Very likely", or more than 90% probable, are heavier rains. And so on down the list including the wishy-washy "more likely than not" when assigning a greater than 50%
probability, such as the chance that human activities are affecting the intensity of hurricanes.
Such care is crucial in a field that is still, in some areas, shot through with uncertainty. The IPCC has gone far in tightening up some key scientific unknowns about climate change (see `From words to action'), but many still remain. Some conclusions such as the effect on particular regions of the world, or exactly how much sea level will rise remain more uncertain than others. This means that there's plenty of work left for the climate scientists on whom the IPCC process depends.
Perhaps most critically, researchers know relatively little about feedback effects that might enhance or weaken the pace and effects of climate change. The complex flow of carbon between soils, plants, the oceans and the atmosphere is still being pinned down by large-scale climate experiments. Some experts predict that, in a warmer world, ecosystems that are currently sinks for carbon, such as the Arctic tundra, may turn into carbon sources. But no one can yet accurately predict how this might pan out, and feedbacks among land
and air could end up putting far more carbon dioxide into the atmosphere than currently forecast.
Other big unknowns are the effects of the take-up of carbon dioxide by the oceans, which removes the gas from the atmosphere and locks it away in the calcium carbonate of the shells and skeletons of marine organisms. Higher levels of atmospheric carbon dioxide are expected to make the seas more acidic and slow down the rate of calcification, ultimately reducing the ocean's ability to absorb more carbon dioxide. But precisely how the biology of marine creatures would play into that effect is unknown. Nor is it known how changes in plankton composition and coral reefs, for example, might affect carbon dioxide concentrations.
Pinning down biological feedbacks will be critical for future reports, says Richard Bellerby, a chemical oceanographer at the Bjerknes Center for Climate Research in Bergen, Norway. "We're going blindly into the
future," he says.
Another major source of uncertainty and of debate at the Paris meeting where the IPCC report was finalized is the rise in sea level. In 2001, the IPCC predicted a rise of between 9 and 88 centimetres by 2100, as a result of melting ice caps and the thermal expansion of the ocean. This time around, the group has narrowed that range to between 19 and 58 centimetres. But some scientists say that this is an underestimate.
Stefan Rahmstorf, an oceanographer at the Potsdam Institute of Climate Impact Research in Germany, believes, for instance, that global sea level could rise by much more than that. In a paper published online
the day before the IPCC report's release, Rahmstorf and his colleagues argue that sea-level rises will be close to the worst-case predictions of climate models (S. Rahmstorf et al. Science doi:10.1126/ science.1136843; 2007). "If anything, the IPCC has been conservative, " he says.
Key sticking points include the inability of global climate models to produce the amount of sea-level rise observed over the past couple of decades and whether ice flow at the bases of glaciers is accelerating
or not. How volatile Antarctic and Greenland glaciers might become in a warmer world is therefore pretty much guesswork. For the first time, the IPCC report predicts how changing climate might affect particular regions of the world. But these forecasts are only in their infancy, modellers warn. For some areas, models predict specific and well understood effects, such as hotter summers in Spain and smaller snowpacks (the accumulation of snow each season) in the Rocky Mountains in the United States. But improved analyses that
incorporate clouds, snow and ice into the models must be developed if regional predictions are to become more accurate, says Rasmus Benestad, a climate modeller at the Norwegian Meteorological Institute
in Oslo.
Extreme weather is another example of the remaining uncertainties. Climate researchers believe that storms and heavy rainfall will become more frequent as the planet warms. But pinning down where and when
that might happen is not so simple. In the tropics, rising sea-surface temperatures can be linked in a
relatively straightforward manner to storm formation, and the case for more intense storms seems more or less settled. But in the mid-latitudes, where atmospheric processes are more complex, some climate models predict more storms whereas others do not.
Improving the models, experts say, requires better data. Gaps and errors in observations are attributable to many causes: snowfall gauges that ice up, oceanographic floats that get lost, and changeovers in satellites that throw off carefully calibrated trends, to name but a few. Cloud and storm records urgently need to be
reprocessed using uniform techniques, says Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, and coordinating lead author of the report's chapter on
surface and atmospheric change.
"The IPCC report is a consensus report, and one that develops over nearly three years," he says. "This means that it is not the leading or bleeding edge of the science."
Here are the steps I recommend you follow to build and level your soil-beds:
1) Start with a very straight 8 to 10'-long 2" X 2" board (2 X 4's will also work, but they're very heavy for the ladies to use). Paint or stain it, to minimize warping.
2) Attach a string level to the center of the board with plenty of good glue.
3) After determining what direction you want to place your beds, with the high end nearest the watering source, and the beds as level as possible (do NOT worry about the location of the sun or the shape of your yard, but DO consider SHADE and avoid it!), measure and stake your beds, and tie nylon strings tight - 6" above the surface - along both sides.
4) dig or till the entire length of the beds 18"-wide to a depth of AT LEAST 8". DO NOT apply any Pre-Plant or Weekly Feed to the soil-bed until AFTER it has been leveled, or most of your fertilizers will end up in only half of the bed.
5) Dig or till the aisle space SHALLOWLY - just a couple of inches deep.
6) Pull 2" of soil from the center of the aisle to the string, the entire length and on both sides of the bed.
7) Smooth and level the top of the soil-bed while breaking up any clods, and make the soil-bed the same width,immediately under the strings, all along its length.
5) Starting at the high end, check the level of the entire length of your bed BEFORE beginning to move dirt.
6) Supposing you had measurements at the end of your 10'-long level showing a difference of 2", 1", and 3", it would indicate the high end of the bed is 6" higher than the low end of the 30'-long soil-bed.
7) With a shovel, throw dirt from the top half of the soil-bed onto the bottom half, with more dirt coming from the first 10' and going to the last 10'.
Your goal is to lower the high end of the bed by 3" and raise the low end 3" while keeping the bed flat and even throughout its length. This takes some practice, but it becomes easier after doing a few, and the beds are EASIER to do the second time, after they've once been leveled!
9) Only AFTER leveling the bed as described above do you apply and till or dig in the Weekly Feed ( 16 ounces for 30', or 1/2 ounce per running foot) and Pre-Plant mixes (32 ounces for 30', or 1 ounce per running foot).
10) After the fertilizers have been applied and mixed with the soil, re-check your level, smooth the top of the soil-bed, making the width equal throughout the entire length, and then begin making the ridges.
11. Pull 2 to 3" of soil from the center of the bed to create a 4"-high ridge on both sides and ends of the bed with the top immediately under the strings.
12) When the ridges are complete drag a rake down the center of the bed to smooth and level the planting area. This should be about 12"-wide, and about 1" higher than the aisles. DO NOT make your beds
with the planting area more than 2" higher than the aisles! This will lead to watering problems, and your beds will dry out too quickly.
13) Re-check the level of your bed throughout its length, and move dirt to assure that it is level. You should have no more than 1" of fall in a 30'-long soil-bed
First, the bucket handle *will* break off and drop your tomato. It did this on every bucket I did. Try imbedding the handle in the actual bucket at least two inches from the top (not the edges or lip where most connect) or taking it off completely and running heavy cable through with holes at about the same point.
Two, extra holes in the bottom for drainage. I put the extra holes and then covered the bottom with landscape material before planting. The extra holes helped prevent the water runoff from goint solely down the plant stem.
Third, preferably use a determinate growth tomato. A semi-determinate is ok but may get too heavy. A indeterminate will get way to heavy unless you make sure to clip the tips of each runner when they reach a certain length, but you will have to stay on top of this.
Fourth, make sure your hanging spot will get at least 6 hours of sunlight. Most spots I found to hang in did not get enough sunlight for the tomatoes, and they are really, really heavy to move once they are planted, not to
mention awkward (once you lift it, you cannot set the bucket down).
Fifth, use potting soil, not garden dirt. Garden dirt compacts down real heavily in these and will prevent the root growth that you want. And lastly, make sure that during the dry season they get enough water. A
lid on top will probably help with this since it will help prevent evaporation, but you must also water these very frequently.
Organic Gardening and Composting Classes April 2007
Saturday, April 7th - Sustainable Landscape
Installation at Alemany Farm
Join Garden for the Environment and Alemany Farm for a work day in sustainable landscape installation atAlemany Farm. Dig-in at Alemanys four-acre farm site with a brief introduction to sustainable landscaping
principles and a hands-on site installation. This is the culminating class of our Resource Efficient Gardening and Landscaping (RELE) Program but prior attendance in RELE classes is not required. Please pre-register by calling (415) 731-5627. This workshop will be held at Alemany Farm, located on Alemany Blvd. at Ellsworth St. 10 am 1 pm. For directions to and more information about Alemany Farm, visit www.alemanyfarm. org or call (415) 568-1296. FREE!
Sunday, April 15th - Community Library (Tea and Readings too)
A one-day public library created by artists, gardeners and friends of the Garden for the Environment. Invited, one and all, to bring a selection from your private library to the garden for a one-day only public library. By sharing a selection of your favorite books we will temporarily create a collective dream library. Please bring no more than ten books on the following themes: Urban gardening, art and nature, food history, art/policy/farming, sustainability, future of food, social history of food/gardens. Books can be children's books, non-fiction, how-to guides, scientific/botanica l illustrations, recipe books and fiction. Come prepared to read, sip tea and share selections from your favorite books. The Community Library will be held at The Garden for the Environment, located on 7th Ave. at Lawton Streets, from 12 noon until 4:30 pm. (with readings at 2pm)
Please call 731-5627 for more information. This event was conceived of by Amy Franceschini, Artist-in-Residence at Garden for the Environment.
Sunday, April 15th - Spring Composting at Double Rock Community Garden
Jump-start your spring garden with some home-made compost! Aside from giving veggies and flowers a
healthy start, composting encourages beneficial organisms in the soil and can help break the life cycle of plant pests and disease. This fun, hands-on class teaches methods for backyard and worm composting for home and community gardens. Come learn what you can do to improve your garden and prevent organic waste from ending up in the landfill! Class is FREE and open to all San Francisco residents. Sunday, April 15th, 11 am - 1 pm. Work party and potluck to follow-come lend a hand to this beautiful community garden in Bayview Hunter's Point! DOUBLE ROCK COMMUNITY GARDEN, Griffith & Fitzgerald.
Your goal is to lower the high end of the bed by 3" and raise the low end 3" while keeping the bed flat and even throughout its length. This takes some practice, but it becomes easier after doing a few, and the beds are EASIER to do the second time, after they've once been leveled!
