[originally posted on www.foreststeward.com on Dec. 17, 2010]

Article reviewed: Forward-Looking Forest Restoration Under Climate Change—Are U.S. Nurseries Ready?

By T.L. Tepe and V.J. Meretsky. Published in Restoration Ecology 2010. Vol. 18 issue 6

The plot line: This is an opinion article, but the authors also did some social science work that provides some data that are presented. They called up state and private nurseries across the country and asked them if they are preparing for or even thinking about climate change with respect to changing the species of seedlings that they offer. Only 20% of the state nurseries said they were thinking about climate change, but most (87%) did offer some seedlings from a fairly broad range that extended beyond their state’s borders. The authors’ answer to their own question, “are U.S. nurseries ready?” seems to be for the most part, “no.” Nurseries are somewhat prepared simply because traditional demands have led them to have species from different climate zones (I would also add that there simply aren’t very many of them so they have to cover wide areas). But this preparedness doesn’t come from specifically planning for future climate scenarios. The authors conclude that in the future, managers will likely want to plant a much wider variety of species than they currently do, and nurseries should prepare for facilitating management responses to climate change by incorporating climate change into their planning.

Relevant quote: “Restoration practitioners considering forward-looking restoration should consider plantings that use a reasonably broad diversity of species to accommodate a range of likely future climates rather than limiting plantings to species suited only to a single predicted future climate.”

Relevance to landowners and stakeholders:

Nurseries are a vital part of the forest management infrastructure, regardless of whether forests are managed intensively for timber or less intensively for other conservation objectives. Seedlings are often planted (“artificial regeneration”) following a disturbance such as a harvest or wildfire in order to establish a cohort of new trees. This article reminds us that the consequences of tree planting are long-term and profound. Trees are long-lived creatures that potentially modify the environment for animals and plants for centuries. A newly established tree (if it survives) is likely to grow in a climatic environment that is different than the one it evolved in. If we take a proactive approach to managing forests to be resilient to climate change, then paying close attention to which species we plant is critical.

Nurseries store and raise the seedlings that are ultimately planted. Without nurseries, we would not have the option of reforesting disturbed areas. While in some cases reforestation may not be needed to meet objectives, in many cases it is the primary way of achieving the goal of quickly establishing a forest following a disturbance such as a severe wildfire. Unfortunately, there appears to be a downward trend in the number of state nurseries. While private nurseries may be able to compensate in terms of meeting short-term demands for seedlings, they are much less likely to be thinking about climate change.

My bottom-line interpretation of relevance for landowners and stakeholders is to support the continuation of state nurseries. We are going to need them. The need seems especially important in southwestern states, where there are apparently hardly any nurseries. When high intensity wildfires occur in dry ponderosa pine forests, burned areas often have no sign of becoming forests again. Planting could help meet the goal of re-establishing forests in these areas, but it can’t happen without the nursery infrastructure in place.

Relevance to managers:

I am not so sure that we can ever expect nurseries to be the driving force behind being better prepared for reforestation needs in the face of climate change. It is managers and regeneration foresters who ultimately drive the demand for seedlings. If they are willing to pay for being more ready for climate change, wouldn’t a nursery then provide them with the type of seedlings they want?

The challenge for managers, however, is dealing with the extreme uncertainty in which seedlings will actually be better adapted to a future climate. The authors make an understated point that it is not just a changing climate but a changing disturbance regime that will shift where tree species will grow in the future.

The authors suggest a hedge-betting approach to dealing with uncertainty. There could be a wide range of species that will be adapted to the future climate. Rather than pick the one species that appears to be the most likely to survive, they suggest using a number of different possibilities based on the likely range of possible future conditions. This is essentially a form of active adaptive management, which I have discussed previously. It also brings up the significant risk of planting species outside of their ranges, which I have discussed previously. Finally, it also brings up how adaptable species might be to climate change just by staying put, which I have also discussed previously.

The bottom line relevance for managers is to take a good look at the seed zone map that is currently used and consider its relevance given the reality of climate change. Here is one for northern California. It was last revised in 1969. Surely this and other seed zone maps are out of date and they more relevance every year that goes by. In the forest that I manage, I have begun small trials where I have planted seedlings from different climatic zones. I have not planted species other than what are locally native, but I have tried to get seedlings from different zones that might be closer to the climate that will occur in my forest in the future. Seedling survival and growth will then be tracked over time. I’ll let you know the results in a couple of decades. Ideally, this will be done on much bigger scales and across large regions (akin to common garden experiments).

A number of websites were given for those interested in learning how climate might change locally. The Nature Conservancy's Climate Wizard looked to be the most interesting, although it doesn't capture the great uncertainty involved with projections.

Critique and/or limitations (there’s always something, no matter how good the article is) for the pedants:

The authors could have done more to recognize the importance of acting with caution when it comes to planting species outside their current zones. Rather than just discuss the planting of new species, they could have also discussed the planting of the same species from different climatic zones. Tree species often cover diverse climates and have high genetic diversity across their entire range.

Using state boundaries as a way to judge if nurseries have broad zones from which they get seeds is not very meaningful because the size and shape of states varies so widely. It would have been more meaningful to actually draw seed source zones around nurseries and see how well these zones overlapped with forest cover across the United States. But this would have obviously been a lot more work… perhaps it can be a future study.

[originally posted on www.foreststeward.com on Dec. 10, 2010]

Article reviewed: Long-term vegetation responses to reintroduction and repeated use of fire in mixed-conifer forests of the Sierra Nevada

By K.M. Webster and C.B. Halpern. Published in Ecosphere, Vol. 1(5): 1-17. Available for full download here (in this new and OPEN ACCESS journal).

The plot line: Sequoia and Kings Canyon National Parks have the longest history of using prescribed fire in Sierra Nevada forests. The authors of this article analyzed data that were collected in the parks over time from sites that were either burned once, burned twice, or not burned at all. They looked for differences in how the treatments influenced understory species composition during the 10 to 20 years that followed burns. The relatively long-term nature of the monitoring allowed them to detect delayed effects of the burning that otherwise may not have been detected. The long-tenured burning program in the parks also allowed them to characterize effects of single versus follow-up second-entry burns on composition. Burning led to increases in the total number of species, especially beginning 5 years after the burns. Shrub species were especially responsive to the first-entry burns, and were then maintained with the second-entry burns. Ground cover made up of most types of plants tended to increase following burns, especially 10-20 years after burns. The authors suggest that prescribed burning programs can be very successful for reducing fuel while also achieving desired species compositions. The frequency of burns, their relative proximity to each other, and the severity of burns are discussed as critical management factors for burning programs.

Relevant quote: “If fire is to play an important role in restoration… it will need to be maintained as a frequent and spatially dynamic process on the landscape.”

Relevance to landowners and stakeholders:

Most people who have visited national or state parks in the Sierra Nevada have seen the signs and brochures that tout the important role that fire has had in shaping the forest. From an ecological perspective, the importance of fire is incontestable. It did indeed shape the forest. And now the forest has been forever altered because of fire suppression. We can never truly restore the forest conditions of the past, but using prescribed fire is one way that we can achieve modern goals of fuel reduction, species composition, and forest health.

Whether or not people who see the pro-fire signs in parks walk away as advocates for prescribed burning, however, depends a lot on their non-ecological perceptions of fire. One important factor is how sensitive their health is to smoke. In my neighborhood, I can talk to people endlessly about the benefits of fire, but all of those benefits are quickly forgotten when smoke from my prescribed fire creeps into their yard and starts to negatively impact their breathing. This is the great challenge for all of those pyro-foresters out there: How do you increase burning activity when the public's tolerance for smoke keeps declining?

This research suggests that increases in biodiversity following burning and then maintenance of diversity by repeat burns is one benefit that could be used to support fire (the more obvious one is the benefit of reducing high-severity fires that burn peoples’ houses down and put LOTS of smoke in the air, but that’s not really what this article was about). Biodiversity could even be put in the context of its importance for public health, as was demonstrated in last week’s post. Burning will likely remain a tough sell to anyone, however, who has asthma and who is already living in an area with high levels of air pollution (e.g. the Central Valley).

Relevance to managers:

• Burn when you can- many of us managers have far greater constraints than those within the parks. We work in the urban interface or have other logistical, legal, or risk-aversion challenges. While it is important to have objectives and clear plans about where/when to burn, often it is determined by weather and availability of personnel. So you end up burning when you can.

• Expect the unexpected- Fire is a blunt tool. In this study, a wide range of species composition responses resulted from patchiness in fire severity during burns. Other variable factors of species responses include the climate following the burn and availability of seed within soil banks or from nearby parent populations. Don’t expect to be able to predict exactly how the species composition will responds to fire. One thing that can be expected- continuing to suppress fire without doing anything else will decrease biodiversity until a high-severity fire occurs (which will, by the way, also increase biodiversity but not necessarily in a good way).
  

• The first burn is critical- It appeared from this study that the first burn after a long period of fire suppression was the critical one in influencing species diversity and cover over the next two decades. The second burn was important in maintaining composition, but did not appear to increase or decrease composition with anywhere near the same magnitude as the first burn. (the authors seemed to suggest that the second burns “enhanced” diversity, but I did not see that happening in the data or analysis that was given).

• The mechanical + burn option- This study did not include mechanical treatments that were followed by burns, but it makes me think of the mechanical+burn treatment as a potentially effective option for increasing biodiversity. A mechanical treatment that alters fuel structure in such a way that allows a hot yet manageable fire will likely see a distinct increase in richness and ground cover which can then perhaps be maintained by subsequent fires.

Critique and/or limitations (there’s always something, no matter how good the article is) for the pedants:

This study compares three basic treatment options: burning once, burning twice, and not burning at all. It is not a comparison of burning with mechanical treatments, so it should not be interpreted as a recommendation of burning over mechanical treatments. It is more a demonstration (a very interesting and important one) of the benefits of burning versus not burning at all.

It is also worth noting that the second-entry burns did not appear to have been applied in an experimental fashion (e.g. they were not selected randomly). It makes me wonder if they were selected for second entry burn because they burned in a particular way during the first burn. It does appear from the graphs (Fig. 1A) that the second-entry burns may have been selected for a second burn because the first burn was particularly hot. The pre-treatment tree density prior to second burns looks lower than the tree density 10 years after the first entry burns. This could be just due to chance or not important, but it does make me wonder about how these areas were selected for burning or not burning.

Their repeated measures analysis seems to give a lot of leverage to the early responses since there were fewer measurements available for later responses. Normally a repeated measures analysis will only include plots that have data that span the entire time range being considered. But they seemed to use a non-traditional type of analysis that let them use all of the plots even if they didn’t have data across the entire period. This is probably completely justifiable, but they didn’t explain why they chose this type of analysis, which I bet most other researchers have never used. Typically a non-standard approach has more discussion of why it was used.

Their management recommendation that fires be done “asynchronously” with white fir seed production in order to avoid a pulse of white fir establishing after fire does not seem feasible. Most fires are done in the fall, after seeds have already been dispersed (white fir dispersal is usually in August or September). So tree seedlings establishing after a prescribed fire will come from seeds produced after the fire. White fir cones mature in one year, so we can’t tell what the cone crop will be like following the fire. A slightly more feasible (but still challenging) option might be to time higher severity fires with bumper crops of pine species. Pine cones take 2 years to mature, so it is more feasible to time the treatment with next year’s seed crop. This wouldn’t decrease white fir establishment necessarily, but it might increase the relative amount of pine establishment compared to white fir.

[originally posted on www.foreststeward.com on Dec. 3, 2010]

Article reviewed: Impacts of biodiversity on the emergence and transmission of infectious diseases

By F. Keesing and many other authors. Published in Nature, Vol. 468, pp. 647-652.

The plot line: This article reviews declines in levels of biodiversity and concurrent increases in the spread of infectious diseases, many of which have infected humans (e.g. West Nile Virus, Haanta Virus, and Lyme’s Disease- carried by ticks on mice and opossums). They integrate several recent experimental studies along with observations of biodiversity-disease correlations to explain how decreases in biodiversity (as occurs when forests are cleared for agricultural use, for example) can lead to the spread of disease. While in some cases the loss of biodiversity could actually decrease the spread of certain diseases, they argue that most biodiversity losses are likely to increase the spread of diseases because of the kinds of species that are typically lost when biodiversity decreases.

Relevant quote: “Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases."

Relevance to landowners and stakeholders:

This article is relevant for anyone who doesn’t like getting an infectious disease that might kill them, which is most people, which is why it is in the widely-read journal Nature and covered by news outlets like NPR. The authors listed land use change as the most common driver of new infectious diseases in humans over the past 65 years. Loss of forests is an important part of land use change, especially considering that forests often house relatively high numbers of species.

Given the link between biodiversity and disease, there is obvious relevance for forest stakeholders. A clear benefit of keeping forests as forests (instead of say, a vineyard or a strip mall) has always been the protection of biodiversity, which is typically thought to be an inherently good thing. But why biodiversity is good is often not articulated by its advocates. This article helps give a specific reason related to human health for why biodiversity is, in general, good. When species are lost from ecosystems, they often are the ones that have resistance to disease. This removal of resistant plants can result in a relative or absolute increase in species that are not resistant to disease. These non-resistors become hosts to pathogens, which can spread rapidly and eventually end up “jumping” on to humans as hosts.

Relevance to managers:

The authors’ discussion of how diversity can be managed to reduce disease was disappointing. Although much of the review focused on natural ecosystems and how their diversity influences transmission of disease, the only recommendation they gave concerning ecosystem management was that conserving larger areas is better than conserving small areas. Forest managers realize, however, that how forests are managed within their boundaries is also just as important for biodiversity. You can have a very large forest with low diversity if management decisions alter the forest in such a way that drives down biodiversity across large landscapes. An example from California is the structural homogenization that has occurred across large forest tracts as a result of fire suppression. The management implications of this paper are best summarized by a colleague who is much smarter and more articulate than I once wrote:

“Diversity should be as much our practice as it is our purpose.”

In other words, managers can achieve biodiversity by striving for a diverse mix of management approaches for meeting objectives.

Critique and/or limitations (there’s always something, no matter how good the article is) for the pedants:

Like I said above, the management implications were disappointing and too simplistic. They also argue that weedy plant species, which are often the ones left behind when biodiversity decreases, can be more susceptible as hosts to disease. The implication being that increases in weedy species could increase disease transmission. But they do not offer any physiological explanation for why this would be the case, like they do with vertebrates. They do reference an article that may indeed explain the physiological reasoning, but they should have given the reasoning from the cited article.

[originally posted on www.foreststeward.com on Oct. 20, 2010]

-> This post graciously provided by the Battles lab at UC Berkeley <-

Article reviewed: Interactive effects of historical logging and fire exclusion on ponderosa pine forest structure in the northern Rockies

By C. Naficy, A. Sala, E. G. Keeling, J. Graham, and T. H. Deluca. Published in Ecological Applications, Vol. 20, No. 7, pp. 1851-1864. Full article available.

The plot line: This study evaluated the contribution of historical logging to the widespread increases in stand density and the abundance of fire-intolerant tree species that are often attributed solely to fire exclusion. The research was conducted in the ponderosa pine/Douglas-fir forests of the northern Rocky Mountains. The study paired 23 historically logged, fire-excluded sites with 23 unlogged, fire-excluded sites. In addition, the study compared stand structure and composition in unlogged, fire-excluded and logged, fire-excluded stands to contemporary unlogged, fire-maintained stands in order to provide a baseline to quantify management-induced changes in forest characteristics.

The authors conclude that historically logged, fire-excluded ponderosa pine forests of the northern Rocky Mountains have much higher average stand density, greater homogeneity of stand structure, more standing dead trees and increased abundance of fire-intolerant trees than similar unlogged, fire-excluded forests. Further, the study found that the interactive effect of fire exclusion and historical logging significantly exceeded the effects of fire exclusion alone. Based on these findings, the authors conclude that historically logged sites are more prone to severe wildfires and insect outbreaks than unlogged, fire-excluded forests and suggest that unique restoration approaches may be required to manage ponderosa pine forests with these distinct management histories.

Relevant quote: “To the extent that modern wildfires are driven by vegetation and fuel characteristics, historically logged stands are likely more prone to severe, stand-replacing wildfires than unlogged, fire-excluded stands.”

Relevance to landowners and stakeholders:

This article challenges the common assumption that fire suppression is the sole cause of the increased forest density that is associated with severe, contemporary wildfires and insect outbreaks in many fire-prone forests of the western United States. The article highlights the lack of data on the long-term effects of various modern silvicultural practices. The authors suggest that where allowance of natural fires is not feasible, the potential negative impacts of alternative fuels treatments requires more careful consideration as part of a longer term approach to fuels management.

Relevance to managers:

For managers attempting to reduce the risk of severe wildfires in ponderosa pine/Douglas fir forests in the northern Rocky Mountains, this study makes several suggestions:

• The current forest structure and composition in historically logged ponderosa pine forests suggests that these forests should be primary targets for fuels reduction efforts.

• While previously logged, fire-excluded forests may benefit from significant mechanical stand manipulations before fire can be safely introduced, unlogged, fire-excluded forests may require much less invasive treatments.

• The authors also conclude that the potential long-term risks associated with mechanical treatments, particularly in unlogged forests, should receive greater attention because the extent to which modern mechanical treatments could have similar long-term counterproductive effects remains largely unknown.

The authors note that the effects of the interaction between historical logging and fire exclusion are likely to vary across broad geographic regions and that long-term responses to timber harvest are likely sensitive to differences in the specific nature and intensity of past silvicultural treatments.

Critique and/or limitations (there’s always something, no matter how good the article is) for the pedants:

While we accepted the general conclusions of this article, we did have some methodological/analytical concerns. For instance, the article claims to be novel in its consideration of the interactive effects of historical logging and fire exclusion. However, this interaction was not actually tested with the statistical approach used in the study. The conclusions regarding the interaction of these disturbances actually examined the additive effects of these disturbances and simply implied the interaction. Many of the potential methodological problems in this study were difficult to avoid given the nature of the data. For instance, the lack of detailed historical data on logging history and the large variation in average fire return interval. We discussed the potential problems of the close proximity of the “paired” stands and the methodological problems with the treatment of the logged and unlogged sites as paired data. The statistical approach used (i.e., paired t-tests) was inappropriate given the selection strategy for the paired stands and was perhaps too simplistic of an approach to test some of the stated objectives, such as the interaction between historical logging and fire exclusion. Finally, one of the final conclusions of this paper was that historical logging had increased forest homogeneity. However, the impact on the homogenization of stand structure was never actually tested.