Posts Tagged: Lake Tahoe
Hawks v. humans: Making anxious circles in the sky
Article reviewed: Restoring forest raptors: Influence on human disturbance and forest condition on Northern Goshawks
By M. Morrison, R. Young, J. Romsos, and R. Golightly. Published in Restoration Ecology, Vol. 19 No. 2 pp. 273-279, accessible here.
The plot line: Suspecting that human interactions with goshawks are causing their decline (like has been observed in Europe), the researchers measured human activity (hiking) and development (roads and houses) differences between areas that are occupied frequently versus infrequently to see if there was a difference. Human activity was higher in areas not used as much by goshawks, but the difference was not detectable with statistical tests and two particularly popular hiking spots appeared to be the reason for the difference (although the authors don’t mention this). Road density did appear to be greater in areas that were not used as much by goshawks, but there were also differences in forest structure and elevation between frequently and infrequently occupied sites. Despite largely inconclusive results, management recommendations are made.
Relevant quote: “There is little reason… to restore structural conditions for the goshawk if human disturbance will negate any positive benefits.”
Relevance to landowners and stakeholders:
As I have observed when listening to landowners who manage their forest for wildlife, they often do so because they enjoy seeing wildlife (who doesn’t?). Seeing wildlife on land managed for wildlife is tremendously gratifying. There is a paradox, however, if the human love for wildlife is unrequited. Such may be the case with goshawks. Although this study did not find evidence to support that human interaction is correlated with goshawk frequency, it would not be surprising if there was such a relationship because of possible adverse physiological responses to human presence (especially if the humans are directly harassing them). So the primary relevance is… don’t harass goshawks when you are hiking!
Relevance to managers:
The relevance with respect to managing forests is limited because of the experimental design, low statistical power, and habitat differences between study sites. The study did suggest what seems to be an efficient design for monitoring goshawks. They found that an “occupancy index” (# of observations over time / # of surveys; frequency, in other words) was related to reproductive success. One could therefore measure occupancy index and assume that it is pretty well correlated with reproductive success. They also point out that it is important to survey multiple years because of wide year-to-year variability in breeding success.
Critique and/or limitation (there's always something, no matter how good the article is):
In the abstract and many times in the results and discussion, they state that human interaction was much higher in areas that were infrequently occupied by goshawks. Technically, this was true. But they also relied on a statistical test to inform them on whether or not they would get the same result consistently if they were to do the experiment again (i.e to tell them if the difference was “real”). The difference was far from what most people (even wildlife biologists who tend to have higher p value thresholds) would consider significant in a statistical sense (p=0.322). P-value thresholds (which they never defined) are subjective and in many cases useless, but if you use hypothesis testing, you can’t just dismiss non-significant results in some cases and accept them in others. The authors even make very broad management recommendations based on this non-significant result.
I wouldn’t critique this inference if the data actually did suggest that there was a real difference, but it doesn’t. Eight sites were used in the pool of frequently occupied territories and 13 in the pool of infrequently occupied territories. The reason they found a large difference in human activity (and the reason why the difference was not significant) was that two of the infrequently occupied sites were exceptionally popular hiking areas. This pushed the variance (and the p value) way up. We don’t know if these are true outliers or not because the sample size was small. But if you take these two sites out, there is virtually no difference in human activity between frequently and infrequently occupied territories. To make broad management recommendations from what appear to be inconclusive results seems far from appropriate.
Here are their data, with human interaction regressed against occupancy:
See those two points way up at the top? Those were exceptionally popular hiking areas with a lot of human interaction. When you take those out there is no relationship at all. Actually, when you leave them in there is still no relationship if your p-threshold (alpha) is 0.05 or even 0.10. And if you do accept it as a real relationship, the adjusted r2 value is a miniscule 0.07. Is that a close enough relationship to base a management recommendation on?
The counter-argument could be that when you consider all of the results, in sum, they add up to being enough to make a management recommendation. But when considering all the results, it just makes me think that there is even less reason for making management recommendations. The infrequently and frequently occupied sites had differences in forest structure. How do we know these differences are not the reason for the differences in occupancy frequency? They were not big differences in forest structure, but neither were the differences in human activity.
I do grant that there was a solid difference in road density between frequently and infrequently occupied areas. But there is no “weight of evidence” from many different results that suggests human activity in general has caused a decline in goshawk occupancy.
In the methods, they say that occupancy is not used as a continuous variable because of gap in the data, but then it is indeed used as a continuous variable to correlate occupancy with human activity, local road extent, and road+trail extent. How come the gap is not an issue with those variables? (you can kind of see the gap in the graph above between 0.5 and 0.8 on the x-axis).
They lead off the restoration implications with this: “Our results suggest that goshawk protection within the Basin has been insufficient and that some of the territories require actions to restore vegetation to pre-settlement conditions.” This is problematic: 1) They did not evaluate the sufficiency of protection measures. No overall measure of goshawk trend or status is made. The protection measures between occupied and unoccupied territories (their primary variable of interest) were the same. 2) They did not study how vegetation change since settlement has impacted goshawks. This is the first mention of pre-settlement conditions in the whole article.
Article reviewed: Restoring forest raptors: Influence on human disturbance and forest condition on Northern Goshawks
By M. Morrison, R. Young, J. Romsos, and R. Golightly. Published in Restoration Ecology, Vol. 19 No. 2 pp. 273-279
The plot line: Suspecting that human interactions with goshawks are causing their decline (like has been observed in Europe), the researchers measured human activity (hiking) and development (roads and houses) differences between areas that are occupied frequently versus infrequently to see if there was a difference. Human activity was higher in areas not used as much by goshawks, but the difference was not detectable with a statistical test and two particularly popular hiking spots appeared to be the reason for the difference (although the authors don’t mention this). Road density did appear to be greater in areas that were not used as much by goshawks, but there were also differences in forest structure and elevation between frequently and infrequently occupied sites. Despite largely inconclusive results, management recommendations are made.
Relevant quote: “There is little reason… to restore structural conditions for the goshawk if human disturbance will negate any positive benefits.”
Relevance to landowners and stakeholders:
As I have observed when listening to landowners who manage their forest for wildlife, they often do so because they enjoy seeing wildlife (who doesn’t?). Seeing wildlife on land managed for wildlife is tremendously gratifying. There is a paradox, however, if the human love for wildlife is unrequited. Such may be the case with goshawks. Although this study did not find evidence to support that human interaction is correlated with goshawk frequency, it would not be surprising if there was such a relationship because of possible adverse physiological responses to human presence (especially if the humans are directly harassing them). So the primary relevance is… don’t harass goshawks when you are hiking!
Relevance to managers:
The relevance with respect to managing forests is limited because of the experimental design, low statistical power, and habitat differences between study sites. The study did suggest what seems to be an efficient design for monitoring goshawks. They found that an “occupancy index” (# of observations over time / # of surveys; frequency, in other words) was related to reproductive success. One could therefore measure occupancy index and assume that it is pretty well correlated with reproductive success. They also point out that it is important to survey multiple years because of wide year-to-year variability in breeding success.
Critique and/or limitation (there's always something, no matter how good the article is):
In the abstract and many times in the results and discussion, they state that human interaction was much higher in areas that were infrequently occupied by goshawks. Technically, this was true. But they also relied on a statistical test to inform them on whether or not they would get the same result consistently if they were to do the experiment again (i.e to tell them if the difference was “real”). The difference was far from what most people (even wildlife biologists who tend to have higher p value thresholds) would consider significant in a statistical sense (p=0.322). P-value thresholds (which they never defined) are subjective and in many cases useless, but if you use hypothesis testing, you can’t just dismiss non-significant results in some cases and accept them in others. The authors even make very broad management recommendations based on this non-significant result.
I wouldn’t critique this inference if the data actually did suggest that there was a real difference, but it doesn’t. Eight sites were used in the pool of frequently occupied territories and 13 in the pool of infrequently occupied territories. The reason they found a large difference in human activity (and the reason why the difference was not significant) was that two of the infrequently occupied sites were exceptionally popular hiking areas. This pushed the variance (and the p value) way up. We don’t know if these are true outliers or not because the sample size was small. But if you take these two sites out, there is virtually no difference in human activity between frequently and infrequently occupied territories. To make broad management recommendations from what appear to be inconclusive results seems far from appropriate.
Here are their data, with human interaction regressed against occupancy:
See those two points way up at the top? Those were exceptionally popular hiking areas with a lot of human interaction. When you take those out there is no relationship at all. Actually, when you leave them in there is still no relationship if your p-threshold (alpha) is 0.05 or even 0.10. And if you do accept it as a real relationship, the adjusted r2 value is a miniscule 0.07. Is that a close enough relationship to base a management recommendation on?
The counter-argument could be that when you consider all of the results, in sum, they add up to being enough to make a management recommendation. But when considering all the results, it just makes me think that there is even less reason for making management recommendations. The infrequently and frequently occupied sites had differences in forest structure. How do we know these differences are not the reason for the differences in occupancy frequency? They were not big differences in forest structure, but neither were the differences in human activity.
I do grant that there was a solid difference in road density between frequently and infrequently occupied areas. But there is no “weight of evidence” from many different results that suggests human activity in general has caused a decline in goshawk occupancy.
In the methods, they say that occupancy is not used as a continuous variable because of gap in the data, but then it is indeed used as a continuous variable to correlate occupancy with human activity, local road extent, and road+trail extent. How come the gap is not an issue with those variables? (you can kind of see the gap in the graph above between 0.5 and 0.8 on the x-axis).
They lead off the restoration implications with this: “Our results suggest that goshawk protection within the Basin has been insufficient and that some of the territories require actions to restore vegetation to pre-settlement conditions.” This is problematic: 1) They did not evaluate protection measures. The protection measures between occupied and unoccupied territories (their primary variable of interest) were the same. 2) They did not study how vegetation change since settlement has impacted goshawks. This is the first mention of pre-settlement conditions in the whole article.
Lake Tahoe clarity not impaired by Angora Fire
The clarity of the Sierra Nevada's largest alpine lake - Lake Tahoe - was not significantly impaired in the aftermath of the 2007 Angora Fire, according to a story in the Reno Gazette-Journal.
Proactive steps taken by the U.S. Forest Service to reseed the land charred by the fire, which burned 254 homes and blackened 3,000 acres, were credited for helping stave off erosion that could have clouded the lake.
The story was prompted by the release in August of the results of an annual survey of Lake Tahoe clarity by the UC Davis Tahoe Environmental Research Center. TERC reported that the lake was clear to an average depth of 68.1 feet in 2009, holding steady for the ninth year in a row. However, the lake is considerably less clear than it was when researchers first began tracking its clarity in 1968, when it was clear to an average depth of 102.4 feet.
"There was concern that erosion from the (Angora) burn area would get into the lake and cause problems," TERC director Geoff Schladow told the Reno paper. "But we found that the impact from the fire was negligible, which was a great relief for us. All we can say is we may have dodged a bullet on that one."
The newspaper also presented other findings from the 2009 TERC report:
- Invasive quagga mussels were found on 10 boats inspected by Tahoe management agencies as they headed for the lake.
- More precipitation fell as rain and less as snow.
- Algae attached to rocks and docks increased along the northeast shoreline.
- The amount of water-clouding particles and nutrients reaching the lake by west-side streams increased as precipitation rose from previous years.
Lake Tahoe clarity holding steady. (Photo by Roy Tennant, freelargephotos.com)
Dutch Dragon Chipper at South Lake Tahoe
The video below shows a unique Dutch Dragon mobile in-woods chipper operating on California Tahoe Conservancy urban lots in South Lake Tahoe in early July. The equipment was purchased by David Mercer of Cross Check Services LLC in order to better process woody biomass from fuels reduction projects in the Tahoe basin. This is the only Dutch Dragon chipper in the USA.The nature of fuels reduction work in the wildland urban interface (WUI) is expensive due to the small scale operations and high equipment move-in and move-out costs. David looked at many options including a regular chipper or one on tracks. However, he decided that a truly mobile option would be one that was mounted on a forwarder base. There are a number of manufacturers of this type of equipment, mostly based in Europe. Manufacturers include Dutch Dragon, BRUKS, Valmet, Silvatech.
The company decided that the Dutch Dragon EC 10075 drum chipper & bin was the best for their needs and opted to mount the package on a Valmet 890 forwarder. This is the largest chipper and bin combination offered by Dutch Dragon. The chip box is 28 cu yd and can be raised to over 14ft high in order to dump the chips into a chip van. The roller feed input can handle material up to 3.3ft x 2.5ft. The Valmet forwarder was sourced in Scotland and shipped to Holland for the chipper and chip box to be integrated prior to shipping to the US. The process from order to delivery was less than 8 weeks. The forwarder and chipper use standard (available in the US) components.
The video shows two different approaches to operation.The chipper can either operate in the woods where the onboard chip box is filled, and then unloaded at roadside, or for material at the landing or roadside it can chip directly into a chip van. The company believes that this equipment is a good alternative to purchasing a stand-alone chipper that would not be self-propelled and would need a loader to feed it.
This particular work area is located south of Pioneer Trail on 42 acres of California Tahoe Conservancy urban lots. The work is paid for with federal funds via the Nevada Fire Safe Council and administered through the Lake Valley Fire Protection District. It is part of a 200 acre, 600 parcel project. The chips were trucked to the power plant at Loyalton (which has recently been closed).
It is great to see a contractor investing in alternative approaches to woody biomass handling. The challenge in is ensuring a continual supply of work and also identifying further markets for the chipped biomass.
Northern Nevada Correctional Center
Last week, on the way to Mammoth Lakes for Sierra Solutions, I visited the biomass fueled cogeneration plant at the Northern Nevada Correctional Center, at Carson City, with Dave Atkins (Fuels for Schools) and Marcus Kauffman (Resource Innovations). The facility is in the red/brown building in the middle right of the above picture. We met with Jason Perock from the Nevada Division of Forestry and Ken Lyngar the plant manager. The facility is designed to produce 1 MW of electricity and to heat over 400,000 square foot of space. It can produce up to 30 MMBTU/hr heat.
The $8.5m plant opened in 2007 but has been plagued by operating problems and issues with sourcing fuel. However, it appears that the team has finally overcome these barriers and the system has run without problem for a couple of months producing 650 kW of electricity and heating most of the prison complex. Ken estimated that they are currently saving over $3500 per day compared to using the original natural gas system.
Inside the firebox of the Hurst Boiler
The system uses approximately 32 BDT of woody biomass every 24 hours (approximately 12,000 BDT/yr. Previously there was a reliance on construction and demolition (C & D) wood that was often being hauled long distances. Recently they have managed to develop local supplies from forestry contractors based in the Lake Tahoe area. The use of forestry chips results in a lower ash content compared to the C & D material – this is because there is less dirt and other contaminants in the material sourced from the forest. The forestry chip also handles better in the augers, conveyors and on the grate itself, whereas the C & D material was prone to bridging (or bird nesting) due to the fact that it is generally processed in grinders which give it a stringy structure. They intend to stockpile logs which they will chip throughout the winter season.
Forest sourced chips (L) vs ground C & D material (R)
The experiences associated with this project are invaluable and point to some key elements to consider before installing a biomass fueled system:
Technology – take care selecting the right technology for your energy need and appropriate to the available fuel supply. It may be better to buy a turnkey system rather than buying different components from different suppliers.
Fuel supply – consider where it will come from, at what price and in what form (chips, logs etc).
Involve the operators and maintenance people who will run the facility on a daily basis in the planning process – their insight and experience are invaluable.
Community and political support – consider issues such as air quality, truck movements, the impacts of forest management in addition to the potential costs savings.
Experience - An end user (heat or electricity customer) does not typically have biomass handling or logging experience; they just want to be able to flick a switch. You need to consider the supply chain in addition to the changed operations and maintenance routine. An Energy Savings Performance Contract with an Energy Services Company (ESCO) removes some of this responsibility but still offers cost savings. Ensure that performance contracts are appropriate and enforceable.
First cost consciousness is a big barrier in the public sector especially in today’s funding environment. You need to build a strong case to demonstrate the savings and societal benefits in switching to a biomass based fuel source.
It is great to see the project start to yield some of its potential. If they keep running with no problems they could have paid back the initial investment in 7 years or less with the additional benefit of providing a market for thousands of tons of woody biomass from fuels reduction projects on National Forest System lands in the Lake Tahoe Basin.
The steam turbine (generator is to the left)
Dave, Marcus and Jason discussing fuel specification