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Archive for the ‘Forests’ Category
Sunday, January 8th, 2012
Although I’ve been working on new ideas since leaving Michigan and returning to London about a year ago, there’s still lots to do to examining alternative forest management strategies.
Several years ago we set out to develop a simulation model that could be used to investigate the effects of interactions between timber harvest and deer browse disturbances on economic productivity and wildlife habitat. We’ve already published several papers on this work, but just before Christmas we submitted a manuscript to Ecological Modelling entitled ‘Modelling for forest management synergies and trade-offs: Tree regeneration, timber and wildlife’. In the manuscript we report error analyses of the full simulation model (which uses the USFS Forest Vegeation Simulator) and use the model to investigate scenarios of different timber and deer management actions. Our results indicate that greater harvest of commercially low-value ironwood and lower deer densities significantly increase sugar maple regeneration success over the long term.
I expect we’ll also report some of these results at the Fourth Forest Vegetation Simulator (FVS) Conference to be held in April this year in Fort Collins, CO. Our abstract, entitled ‘Investigating combined long-term effects of variable tree regeneration and timber management on forest wildlife and timber production using FVS’, has been accepted for oral presentation. It would be great to be there myself to present the paper and discuss things with other FVS experts, but I’m not sure if that will be possible. If it’s not, Megan Matonis will present as, handily, she’s currently doing her PhD in that neck of the woods at Colorado State University.
In the meantime, Megan and I are in the process of finishing off a different manuscript describing the mesic conifer planting experiment we did in Michigan. In that experiment we planted seedlings of white pine (Pinus strobus), hemlock (Tsuga canadensis), and white spruce (Picea glauca) in northern hardwood stands with variable deer densities and then monitored browse on the seedlings over two years. We found that damage to pine and hemlock seedlings was inversely related to increasing snow depth, and our data suggest a positive relationship between hemlock browse and deer density. These results suggest that hemlock restoration efforts will not be successful without protection from deer. Hopefully we’ll submit the manuscript, possibly to the Northern Journal of Applied Forestry, in the next month or so.
All of this work has been pursued with management in mind, so it was nice this week to receive a call from Bob Doepker, a manager at the Michigan Department of Natural Resources with whom we worked to co-ordinate data collection and establish key research questions. Bob had some questions about the details and implications of our previous findings for deer habitat, tree regeneration and how they should be managed. It was good to catch up, and no doubt our ongoing work will continue to contribute to contemporary management understanding and planning.
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Forests, MichiganUP, Modelling, Publications | Comments Off
Wednesday, September 28th, 2011
I’ve not been in the office much over the last month or so, but that’s all about to change now that the new academic term has arrived!
Since I last posted, I attended and presented work at the Royal Geographical Society Annual Conference, one presentation on our managed forest landscape modelling in Michigan and one on the narrative properties of simulation modelling. Both presentations were in the environmental modelling and decision making session, but despite being the graveyard session (last of the conference!) we had some interesting questions and discussion. I tried out Prezi for my narratives presentation (brought to my attention by Tom Smith). It certainly requires a different approach than the linear style PowerPoint enforces. Whether Prezi is a more useful tool probably depends on the message you’re trying to communicate – if your story isn’t particularly linear then Prezi might be useful.
These last few days I’ve been up in Edinburgh visiting folks at the Forestry Commission’s Northern Research Station to discuss the socio-ecological modelling of potential woodland creation I’ve been working on recently. I also got to talk with Derek Robinson at the University of Edinburgh about some of these issues. Everyone seemed interested in what I’ve been doing, particularly with the ideas I’ve been bouncing around relating to the work Burton and Wilson have been doing on post-productivist farmer self-identities, how these self-identities might change, how they might influence adoption of woodland planting and how we might model that. For example, I think an agent-based simulation approach might be particularly useful for exploring what Burton and Wilson term the ‘‘temporal discordance’ in the transition towards a post-productivist agricultural regime”. And I also think there’s potential to tie it in with work like my former CSIS colleague Xiaodong Chen has been doing using agent-based approaches to model the effects of social norms on enrollment in payments for ecosystem services (such as woodland creation).
I was away on holiday for a couple of weeks after the RGS. On returning, I’ve been preparing for King’s Geography tutorials with the incoming first year undergraduates. The small groups we’ll be working will allow us to discuss and explore critical thinking and techniques about issues and questions in physical geography. Looking forward a busy autumn term!
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Forests, Geographic, Modelling, Social | Comments Off
Thursday, July 7th, 2011
Since I last posted, THREE of the papers I’ve mentioned here previously have become available online! Here are their details, abstracts are below. Email me if you can’t get hold of them yourself.
Millington, J.D.A., Walters, M.B., Matonis, M.S., Laurent, E.J., Hall, K.R. and Liu, J. (2011) Combined long-term effects of variable tree regeneration and timber management on forest songbirds and timber production Forest Ecology and Management 262 718-729 doi: 10.1016/j.foreco.2011.05.002
Millington, J.D.A. and Perry, G.L.W. (2011) Multi-model inference in biogeography Geography Compass 5(7) 448-530 doi: 10.1111/j.1749-8198.2011.00433.x
Millington, J.D.A., Demeritt, D. and Romero-Calcerrada, R. (2011) Participatory evaluation of agent-based land use models Journal of Land Use Science 6(2-3) 195-210 doi:10.1080/1747423X.2011.558595
Millington, J.D.A. et al. (2011) Combined long-term effects of variable tree regeneration and timber management on forest songbirds and timber production Forest Ecology and Management 262 718-729
Abstract
The structure of forest stands is an important determinant of habitat use by songbirds, including species of conservation concern. In this paper, we investigate the combined long-term impacts of variable tree regeneration and timber management on stand structure, songbird occupancy probabilities, and timber production in northern hardwood forests. We develop species-specific relationships between bird species occupancy and forest stand structure for canopy-dependent black-throated green warbler (Dendroica virens), eastern wood-pewee (Contopus virens), least flycatcher (Empidonax minimus) and rose-breasted grosbeak (Pheucticus ludovicianus) from field data collected in northern hardwood forests of Michigan’s Upper Peninsula. We integrate these bird-forest structure relationships with a forest simulation model that couples a forest-gap tree regeneration submodel developed from our field data with the US Forest Service Forest Vegetation Simulator (Ontario variant). Our bird occupancy models are better than null models for all species, and indicate species-specific responses to management-related forest structure variables. When simulated over a century, higher overall tree regeneration densities and greater proportions of commercially high value, deer browse-preferred, canopy tree Acer saccharum (sugar maple) than low-value, browse-avoided subcanopy tree Ostrya virginiana (ironwood) ensure conditions allowing larger harvests of merchantable timber and had greater impacts on bird occupancy probability change. Compared to full regeneration, no regeneration over 100 years reduces merchantable timber volumes by up to 25% and drives differences in bird occupancy probability change of up to 30%. We also find that harvest prescriptions can be tailored to affect both timber removal volumes and bird occupancy probability simultaneously, but only when regeneration is adequate. When regeneration is poor (e.g., 25% or less of trees succeed in regenerating), timber harvest prescriptions have a greater relative influence on bird species occupancy probabilities than on the volume of merchantable timber harvested. However, regeneration density and composition, particularly the density of Acer saccharum regenerating, have the greatest long-term effects on canopy bird occupancy probability. Our results imply that forest and wildlife managers need to work together to ensure tree regeneration density and composition are adequate for both timber production and the maintenance of habitat for avian species over the long-term. Where tree regeneration is currently poor (e.g., due to deer herbivory), forest and wildlife managers should pay particularly close attention to the long-term impacts of timber harvest prescriptions on bird species.
Millington, J.D.A. and Perry, G.L.W. (2011) Multi-model inference in biogeography Geography Compass 5(7) 448-530
Abstract
Multi-model inference (MMI) aims to contribute to the production of scientific knowledge by simultaneously comparing the evidence data provide for multiple hypotheses, each represented as a model. With roots in the method of ‘multiple working hypotheses’, MMI techniques have been advocated as an alternative to null-hypothesis significance testing. In this paper, we review two complementary MMI techniques – model selection and model averaging – and highlight examples of their use by biogeographers. Model selection provides a means to simultaneously compare multiple models to evaluate how well each is supported by data, and potentially to identify the best supported model(s). When model selection indicates no clear ‘best’ model, model averaging is useful to account for parameter uncertainty. Both techniques can be implemented in information-theoretic and Bayesian frameworks and we outline the debate about interpretations of the different approaches. We summarise recommendations for avoiding philosophical and methodological pitfalls, and suggest when each technique is best used. We advocate a pragmatic approach to MMI, one that emphasises the ‘thoughtful, science-based, a priori’ modelling that others have argued is vital to ensure valid scientific inference.
Millington et al. (2011) Participatory evaluation of agent-based land use models Journal of Land Use Science 6(2-3) 195-210
Abstract
A key issue facing contemporary agent-based land-use models (ABLUMs) is model evaluation. In this article, we outline some of the epistemological problems facing the evaluation of ABLUMs, including the definition of boundaries for modelling open systems. In light of these issues and given the characteristics of ABLUMs, participatory model evaluation by local stakeholders may be a preferable avenue to pursue. We present a case study of participatory model evaluation for an agent-based model designed to examine the impacts of land-use/cover change on wildfire regimes for a region of Spain. Although model output was endorsed by interviewees as credible, several alterations to model structure were suggested. Of broader interest, we found that some interviewees conflated model structure with scenario boundary conditions. If an interactive participatory modelling approach is not possible, an emphasis on ensuring that stakeholders understand the distinction between model structure and scenario boundary conditions will be particularly important.
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Academic, Ecological, Forests, Geographic, Landscapes, MichiganUP, Modelling, Publications, Statistical | Comments Off
Sunday, May 15th, 2011
Earlier this week I was in Leipzig, Germany, to meet the Ecological Modelling research group at the Helmholz Centre for Environmental Research (UFZ) and one of my PhD supervisors, Dr. George Perry. While there I was lucky to meet and talk with some renowned ecological modellers: Thorsten Wiegand, who’s work includes spatial point process modelling (although some of his discussion with George about that was a bit technical for me!); Volker Grimm, proponent the ‘Pattern-Oriented Modelling’ approach (look out for a new review of this in Phil Trans. of the Royal Society in the near future), and Andreas Huth, notable forest dynamics modeller.
At UFZ I gave a presentation I entitled “Future Forests: Managing and Creating Forests for Biodiversity, Recreation, Timber and Carbon” in which I talked about some of the work I did in Michigan and the new project I’m working on now in the UK. The talk seemed to go down well and the research group had some very good questions, both about technical aspects of the modelling and the issues it is applied to (i.e. forest ecosystem management and woodland creation, including the Woodland Carbon Code). Thanks to Juergen Groeneveld for organising this (and his hospitality at UFZ).
Much of the data I presented regarding the Michigan work was collected by Megan Matonis. Her analyses of that data, on which I helped and supervised, are now available to read in a paper that is currently in press with Forest Ecology and Management (email me if you can’t access the online version).
Another interesting activity at UFZ was hearing Roger Pielke Jr. talk about the need to ‘change the climate change narrative’. In his talk he suggested that understanding all carbon policy can be boiled down to a single sentence;
‘people engage in economic activity that uses energy from carbon emitting generation’.
He emphasised that he thinks the “Targets and Timetables” approach to reducing anthropogenic carbon emissions is flawed. As an example, he used the case of the UK and the Climate Change Act of 2008 which set the aim of an 80% cut in the country’s carbon emissions by 2050 compared to 1990 levels, with an intermediate target of 34% by 2020. However, Pielke argues that given the ‘iron’ law of climate policy (that we cannot mitigate emissions by reducing GDP, both because people will pay only so much to mitigation now, and because increasing GDP is seen as a virtue by way of its effects on povety reduction) we cannot hit these types of targets.
Previous decarbonisation of the UK economy has been achieved by replacing the contribution to GDP from high-emitting manufacturing with low-emitting financial services. He wonders how long can this go and presented his estimate that for the UK to actually hit its 2020 target it will have to build more than 40 nuclear power stations in the next 10 years. In this context, he suggested that the building of a third runway at Heathrow was an insignificant concern (in terms of the new emissions it would generate) when there are still 1.5 billion people globally who do not have access to electricity. His argument is that we do not know how to achieve the targets and the timetables we have set ourselves.
Pielke argues that we must change the climate change narrative from
“We need to use less energy and fossil fuels are cheap“
to
“We need more energy and fossil fuels are too expensive“.
This would allow these 1.5 billion people to access the electricity they aspire to whilst driving the growth of alternative, cleaner, sources of energy. I like this argument – and his one about making small steps towards these change to reach bigger changes – but it seems to run counter to his point about the insignificance of another runway at Heathrow (which by increasing capacity for flights would continue the narrative of cheap fossil-fuelled energy). Opening a third runway but only allowing non-fossil-fuelled aeroplanes to use it is ultimately most consistent with the change in narrative he argues for.
And of course, while at UFZ, George Perry and I took the opportunity to discuss past, current and ongoing work over beers and dinner. Mainly we discussed the idea surrounding the narrative properties of generative simulation models and on which I plan to submit a manuscript to a journal for publication soon. But we also thought about other areas of research including land use modelling (continuing our work in Spain) and landscape disturbance-succession modeling (including the use of the LFSM I’ve developed with paleo-estimates of wildfire regimes).
All-in-all a very interesting and productive trip!
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Academic, Forests, MichiganUP, Modelling | Comments Off
Tuesday, January 18th, 2011
Not surprisingly, during my time at Michigan State University many of my posts on this blog focused on the work I was doing there on forest ecosystem management. I’ll continue to write papers and use and develop the simulation model I initiated at MSU, but now I’m back in London I’m sure the emphasis on this blog will switch to the primary work I’ll be doing here. Before it does, here’s a post on the work I’ve done recently related to the Michigan study and which I’m about to submit for review.
I’ve written here previously about how I’ve been working on modelling the long-term impacts of poor tree regeneration on forest structure and estimating bird presence in forests given their structural characteristics. In my last few months in Michigan, I integrated these two issues as part of the development of the integrated ecological-economic simulation model. The aim was to assess trade-offs between between protecting bird species of conservation concern and ensuring the productivity of industrial forests given the variable tree regeneration densities we have seen across our study area and given the timber harvest options available. I was particularly interested in how the variations in tree regeneration we have seen across our study area [we have a paper on these currently under review - more details soon] might influence long-term forest sustainability. Simulation modelling is an excellent way to look at these types of issues over long time periods.
To examine the trade-offs I integrated bird occupancy models I had developed for four bird species (black-throated green warbler, eastern wood pewee, least flycatcher and rose-breasted grosbeak) with our our model of forest gap regeneration and FVS. I then used the model to simulate various scenarios of regeneration and timber harvest prescriptions. For example, I simulated different densities of trees regenerating in the forest gaps created by timber harvest and different proportions of these trees as either sugar maple or ironwood. These are the sorts of variables that Megan Matonis found to vary across our study area and that are most likely driven by white-tailed deer herbivory. With the simulation model we could then look at how these different scenarios influence forest structure and, in turn, bird occupancy probability. We also looked at how different timber harvest prescriptions interact with these different densities and compositions of regenerating trees.
Using our model for a simulated century we found that the four bird species we examined responded uniquely to changes in forest structure (in turn due to the variation in regeneration composition and density and timber harvest prescriptions). We also found that 100-year average timber volume removals, which varied with harvest prescriptions and regeneration, were related to bird occupancy for three of the four species, positively for two and negatively for one. These results suggest that timber harvest prescriptions can be tailored to influence both timber removal volumes and bird occupancy probability, but only when regeneration is adequate. This is illustrated by the figure below for one of the bird species.
Mean annual timber removed is plotted on the horizontal axis and mean bird occupancy probability on the vertical axis. The different colours of points are the different densities of regeneration (darker is higher) and the different shapes are the different timber harvest prescriptions. When regeneration is poorer (lighter colours), differences in the volume of timber removed are smaller between prescriptions (horizontal axis) than differences in bird occupancy probability (vertical axis, relative to the uncertainty bars).
These results imply that management actions that promote high tree regeneration rates (for example, by reducing deer herbivory) will benefit both bird populations and timber production in the long-term. Consequently, we suggest that where tree regeneration is currently poor, forest managers should pay closer attention to the long-term impacts of timber harvest prescriptions on bird species.
As I highlighted above, this work is very near being submitted for publication. I’ll post here as the review and publication process progresses (and maybe try to use fewer hyphens in the title).
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Ecological, Forests, MichiganUP, Modelling | Comments Off
Wednesday, August 11th, 2010
It’s been a while since I posted here about the forest modelling I’ve been working on here at MSU. Over the last couple of months I’ve been working on finalizing the regeneration modelling component, refining the timber harvest rules, linking simulations to the bird occupancy modelling I started this spring, and writing it all up for manuscripts.
Across our study area we’ve found that regeneration of juvenile trees following timber harvest varies greatly. For example, from our empirical data we find that sugar maple saplings were present in over 70% of northern forest gaps but were completely absent from 96% of gaps in southern areas. Megan Matonis suggested in her thesis that this variation is related to snow depth, deer density and soil nutrient conditions. To examine the potential long-term effects of these differences in regeneration on forest structure I’ve been running our simulation model with pre-set levels of regeneration that reflect our observations, ranging from the maximum possible (given the space available in a post-harvest gap) to a complete absence of regenerating juvenile trees.
These ‘gaps’ I’m talking about are created in northern hardwood forests when individual or small groups of trees are removed in an uneven-aged timber management approach. The removal of these trees creates openings (‘gaps’) in the forest canopy allowing light into lower levels for younger trees [gaps may also be created naturally but we're focusing on those created by human activity which is the dominant driver in our study area]. When harvesting trees in this approach foresters aim to produce a forest structure with a ‘reverse-J’ distribution of tree sizes; high densities of small, young trees and low densities of larger, older trees (approximating a gamma-distribution like I found in our data previously). The idea is that through time an abundant supply of competing smaller trees will replace larger trees trees that are removed.
Representing this approach in our model (using FVS keywords [.pdf]) requires quite a bit of code, but working through the example provided by Don Vandendriesche [.pdf] helped. This approach requires the model user to specify a residual basal area (the area occupied by trees) and the ratio between the number of trees in successive size classes (the q-factor).
To examine my initial results (and to help debugging during the whole modelling process) I used R to plot size-class distributions for tree densities and basal area. As is the norm I used size-classes defined by the diameter-at-breast-height of the trees (5 cm or about 2 inches). Then I combined plots for simulated years into animated .gif files to see how the distributions changed through time for different regeneration levels. Here are a couple of examples (click for larger versions):
By the end of these 200-year simulations the same stand has a very different forest structure. In the top example regeneration is sufficient to replace trees removed during harvest, growing into larger size-classes as more resources (light and space) become available. But in the bottom example we see the consequences of when no new trees grow to replace the the removed trees – by the mid-21st century there are no trees in the smaller size-classes and timber harvesting has to become less frequent to meet timber removal goals (and remain viable).
I’m continuing to analyse the model output in a more quantitative manner and assessing the impacts of these potential changes in forest structure on bird habitat (specifically the probability that different species will be present in a forest stand). All together this should make a nice manuscript and provide some interesting information for the foresters working in these northern hardwood forests.
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Forests, MichiganUP, Modelling | 2 Comments »
Sunday, July 11th, 2010
Around the time I wrote this blog about the National Assessment of UK Forestry and Climate Change Steering Group report I was thinking about writing a proposal to the Leverhulme Trust for an Early Career Fellowship. I found out recently that my proposal was successful and so from January 2011 I will be back at King’s College, London!
The Leverhulme Trust makes awards in support of research and education with special emphasis on original and significant research that aims to remove barriers between traditional disciplines. Their Early Career Fellowships are awarded across all disciplines and in 2010 approximately 70 were expected to be awarded to individuals to hold at universities in the UK. Given the emphasis on original, significant and cross-disciplinary research made by the Trust I looked for something that matched my research skills in coupled human and natural systems modelling but that pushed work in that area in a new direction. I thought back to the ideas about model narratives I have previously explored with David O’Sullivan and George Perry (but have not worked on since then) and Bill Cronon’s plenary address at the Royal Geographical Society in 2006 on the need for ‘sustainable narratives’. With that in mind, and given the UK Forestry and Climate change report I had been reading, I decided to make a pitch for a project that would explore how narratives from the use of models could help individuals identify how local actions transcend scales to mitigate global climate change in the context of the anticipated woodland planting that will be ongoing in the UK in future years. It proved to be a successful pitch!
I’m sure I will blog plenty more about the project in the future, so for now I will just leave you with the proposal rationale (below). I’m looking forward to getting to work on this when I get back to London, but before that there’s plenty more things to get done on the Michigan forest landscape ecological-economic modelling.
Model narratives for climate change mitigation
The abstract, vast, and systemic narratives that dominate the issue of global climate change do little to illustrate to individuals and groups how their actions might contribute to mitigate the effects of what is often framed as a global problem (Cronon 2006). Ways to improve the ability of individuals and groups to identify how their local actions transcend scales to mitigate global climate change are needed. In this research I will explore how narratives produced from computer simulation models that represent individuals’ actions can provide people with insights into how their behaviour affects system properties at a larger scale. Although the narrative properties of simulation models have been highlighted (O’Sullivan 2004), the use of models to develop localised narratives of climate change which emphasise individual agency has yet to be explored. Confronting individuals with these narratives will also help researchers reveal important underlying, and possibly implicitly held, assumptions that influence choices and behaviour.
This research will address the following general questions:
- How can computer simulation models be better used to reveal to individuals how their local actions can contribute to global environmental issues such as Climate Change Mitigation (CCM)?
- What are the narrative properties of simulation models and how can they be exploited to help individuals find meaning about their actions as they relate to global climate change?
- By using simulation tools to spur reflection what can we learn about the factors influencing individuals’ choices and behaviour with regards CCM options?
Answering these questions will require a uniquely interdisciplinary research approach that spans the physical sciences, social sciences and humanities. Such ground-breaking, boundary-crossing work is necessary if we are to re-connect the physical sciences with the publics they intend to benefit and find solutions to large-scale and pressing environmental problems. For example, one of the key findings from a recent report by the National Assessment of UK Forestry and Climate Change Steering Group (Read et al. 2009) was that “[t]he extent to which the potential for additional [greenhouse gas] emissions abatement through tree planting is realized … will be determined in large part by economic forces and society’s attitudes rather than by scientific and technical issues alone” (p.xvii). The report also argued the need “to better understand and consider the role of different influences affecting choices and behaviour. Without the appropriate emotional, cultural or psychological disposition, information will make no difference.” (p.210). Narratives based on scientific understanding which portray how individuals can make a difference to large-scale, diffuse environmental issues will be important for fostering such a disposition. Simulation models – quantitative representations of reality which provide a means to logically examine how high-level and large-scale patterns are generated by lower-level and smaller-scale processes and events – have the potential to contribute to the construction of these narratives.
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Academic, CHANS, Environmental, Forests, Modelling, Social, Sustainability | 1 Comment »
Tuesday, March 2nd, 2010
Birds have been given short shrift in my posts blog posts about the Michigan UP ecological-economic modelling project. It’s not that we have forgotten about them, it’s just that before we got to incoporating them into our modelling there were other things to deal with first. Now that we’ve made progress on modelling deer distribution it’s time to turn our attention to how we can represent the potential impacts of forest management on bird habitat so that we might better understand the tradeoffs that will need to be negotiated to achieve both economic and ecological sustainability.
 Ovenbird (Seiurus aurocapillus) One of the things we want to do is link our bird-vegetation modelling with Laila Racevskis‘ assessment of the economic value of bird species she did during her PhD research. Laila assessed local residents’ willingess-to-pay for ensuring the conservation of several bird species of concern in our study area. If we can use our model to examine the effects of different timber management plans (each yielding different timber volumes) on the number of bird species present in an area we can use Laila’s data to examine the economic tradeoffs between different management approaches. The first thing we need to do to achieve this is be able to estimate how many bird species would be present in a given forest stand.
Right now the plan is to estimate the presence of songbird species of concern in forest stands by using the data Ed Laurent collected during his PhD research at MSU. To this end I’ve been doing some reading on the latest occupancy modelling approaches and reviewing the literature on its application to birds in managed forests. Probably the most popular current approach was developed recently by Darryl Mackenzie and colleagues – it allows the the estimation of whether a site is occupied by a given species or not when we know that our detection is imperfect (i.e. when we know we have false negative observations in our bird presence data). The publication of some nice overviews of this approach (e.g. Mackenzie 2006) plus the development of software to perform the analyses are likely to be at the root of this popularity.
The basic idea of the approach is that if we are able to make multiple observations at a site (and if we assume that bird populations and habitat do not change between these observations) we can use the probability of each bird observation history at a site across all the sites to form a model likelihood. This likelihood can then be used to estimate the parameters using any likelihood-based estimation procedure. Covariates can be used to model both the probability of observation and detection (i.e. we can account for factors that may have hindered bird observation such a wind strength or the time of day). I won’t go into further detail here because there’s an excellent online book that will lead you through the modelling process, and you can download the software and try it yourself.
Two recent papers have used this approach to investigate bird species presence given different forest conditions. DeWan et al. 2009 used Mackenzie’s occupancy modelling approach to examine impacts of urbanization on forest birds in New York State (they do a good job of explaining how they apply Mackenzie’s approach to their data and study area). DeWan considered landscape variables such as perimeter-area ratios of habitat patches and proximity to urban area to create occupancy models for 9 birds species at ~100 sites. They found that accounting for imperfect bird detection was important and that habitat patch “perimeter-area ratio had the most consistent influence on both detection probability and occupancy” (p989).
In a slightly different approach Smith et al. 2008 estimated site occupancy of the black-throated blue warbler (Dendroica caerulescens) and ovenbird (Seiurus aurocapillus) in 20 northern hardwood-conifer forest stands in Vermont. At each bird observation site they had also collected stand structure variables including basal area, understory density and tree diameters (in contrast to DeWan et al who only considered landscape-level variables). Smith et al. write their results “demonstrate that stand-level forest structure can be used to predict the occurrence of forest songbirds in northern hardwood-conifer forests” (p43) and “suggest that the role of stand-level vegetation may have been underestimated in the past” (p36).
Our approach will take the best aspects from both these studies; the large sample size of DeWan et al. with the consideration of stand-level variables like Smith et al. More on this again soon I expect.
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Ecological, Forests, MichiganUP, Modelling, Statistical | 2 Comments »
Saturday, December 19th, 2009
Update January 2010: This paper is now online with doi 10.1016/j.foreco.2009.12.020.
I received some good news this morning as I prepared to head back to the UK for the holidays. The paper I started writing back in January examining the white-tailed deer distribution in our managed forest landscape (the analysis for which inspired posts on Bayesian and ensemble modelling) has been accepted for publication and is ‘In Press’! I’ve copied the abstract below.
Another piece of publications news I received a while back is that the paper I co-authored with Raul Romero-Calcerrada and others modelling socioeconomic data to understand patterns of human-caused wildfire ignition risk has now officially been published in Ecological Modelling.
Happy Holidays everyone!
Effects of local and regional landscape characteristics on wildlife distribution across managed forests (In Press) Millington, Walters, Matonis, and Liu Forest Ecology and Management
Abstract
Understanding impacts of local and regional landscape characteristics on spatial distributions of wildlife species is vital for achieving ecological and economic sustainability of forested landscapes. This understanding is important because wildlife species such as white-tailed deer (Odocoileus virginianus) have the potential to affect forest dynamics differently across space. Here, we quantify the effects of local and regional landscape characteristics on the spatial distribution of white-tailed deer, produce maps of estimated deer density using these quantified relationships, provide measures of uncertainty for these maps to aid interpretation, and show how this information can be used to guide co-management of deer and forests. Specifically, we use ordinary least squares and Bayesian regression methods to model the spatial distribution of white-tailed deer in northern hardwood stands during the winter in the managed hardwood-conifer forests of the central Upper Peninsula of Michigan, USA. Our results show that deer density is higher nearer lowland conifer stands and in areas where northern hardwood trees have small mean diameter-at-breast-height. Other factors related with deer density include mean northern hardwood basal area (negative relationship), proportion of lowland conifer forest cover (positive relationship), and mean daily snow depth (negative relationship).The modeling methods we present provide a means to identify locations in forest landscapes where wildlife and forest managers may most effectively co-ordinate their actions.
Keywords: wildlife distribution; landscape characteristics; managed forest; ungulate herbivory; northern hardwood; lowland conifer; white-tailed deer
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Forests, MichiganUP, Modelling, Publications, Wildfire | Comments Off
Saturday, December 12th, 2009
In the climate change debate there’s been a lot of talk about current Amazonian rainforest deforestation, but I’ve heard much less about the role of the UK’s forests for carbon sequestration. Given the relative size of the UK to the Amazonian rainforest that’s not so surprising – The Nature Conservancy suggests the area of rainforest cut down each year (20 million hectares) is the same as the combined area of England, Scotland and Wales. The estimated 5000 years it took [.pdf] to go from 75% of the UK covered by forests and woodlands to the current 12% just doesn’t compare.
Recently, however, the case been made for increasing UK forest and woodland cover as a form of climate change mitigation. This summer the UK Low Carbon Transition Plan identified woodland creation as a cost-effective way of mitigating climate change and recognised the importance of supporting tree-planting initiatives. More recently, the National Assessment of UK Forestry and Climate Change Steering Group has provided its response to the IPCC Fourth Assessment Report and argues there is a clear need for more woodlands.
One of the main findings of this initial assessment was that an increase in woodland area of 23,000 ha per year over the next 40 years could abate 10% of UK 2050 greenhouse gas emissions. With echos of the recommendation from the Stern Review on the Economics of Climate Change to ‘Act now or pay later’, the key message from this assessment is ‘Plant now and use sustainably’. The long maturation times of forest systems means that it may take take 50–100 years for actions to pay off.
Being such a long-standing investment it’s vital that the benefits of planted woodlands and forests are not outweighed by negative impacts on biodiversity, food security, landscape and water supply. From this stand-point there is much to be done and the assessment recommends that “further scientific and socio-economic analysis is required to enable the UK to achieve the full [climate] adaptation and mitigation potential of forestry” and that “clear, robust, research programmes will be needed to underpin the changes of forestry policy and practice which are required to meet the new and challenging circumstances”.
A question that immediately springs to my mind is where these woodlands should be placed to maximise their carbon sequestration payoff while minimising negative impacts on other aspects of the landscape. For example, if arable agricultural land is to be converted, how will biodiversity be affected by the removal of hedgerows? What would this conversion of agricultural land mean for local economies? Which species will benefit in terms of habitat connectivity and which will lose out? Addressing questions like these will be important as forest policy moves toward returning UK forest cover area near levels seen elsewhere in Europe.
This work by James D.A. Millington is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
Posted in Ecological, Forests, Landscapes, Sustainability | Comments Off
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