General comments on the book chapter

I really enjoyed the Perfecto and Vandermeer article - a great mix of theory and case study, a rich bibliography, and on one of my favorite topics - sustainable agriculture. 

This question I have is on a detail in the section on "Extinctions in Fragments and Migrations Through the Matrix" (page 5789 column 2) that left me questioning one of the conclusions. If I had the authors around to ask, I would, but perhaps another (ecologist) reader can help respond to this question.

In short, I'm wondering if fragmenting a continuous habitat would have an effect on the "natural enemies" of a given species population, as well as having an effect on that species' migration ability. The authors point out that fragmenting ecosystems can reduce a species' resistance to regional extinction by reducing the migration options, but it seems to me that there may be some parallel effect of a fragmented ecosystem on the predators.

Anyway, this is a curiosity I ran into, and not central to the paper - but if anyone has researched this area I'd be interested to learn more.
 - Christina

I enjoyed the Perfecto and Vandermeer article but I'm left with some questions that I'm not sure how to grapple with.  How can we incorporate the larger climatic effects of the culmination of many small spatial scale decisions?  The aggregate influence of many small spatial scale changes to the landscape have the potential to modify climate - in the tropics this primarily means precipitation - which can then feed back on and influence the small spatial scale.  

In particular regarding this idea of a matrix for tropical agriculture we need to consider how the small spatial scale agriculture impacts climate in tropical systems:

Albedo - trees are darker than crops (in general).  The effect scales with total area converted to agriculture and thus doesn't have much distinction between the two agricultural options.

Surface Roughness - forests are rougher than agricultural fields, but the edges of forests are particularly important.  At the forest/crop (or pasture) boundary the contrast in roughness can set up atmospheric convection which causes it to rain more over the field but less over the forest.  This local shift in precipitation can lead to stress within the forest and possible decline which can then lead to larger drops in overall precipitation. The total "forest edge length" is thus the driving variable and is potentially much larger in a matrix system of agriculture compared to commercial ag (if the areas are similar).   How could this be included in the optimizations of the Perfecto and Vandermeer paper?

Evapo-trapsiration - is a function of plant type and local water availability, i.e. precipitation.  ET acts as a feedback in this system but is not driving the change.

The Perfecto and Vandermeer article offered an extensive and cogent argument on how agriculture can be linked to conservation goals. I appreciated how the authors established assumptions in the literature (e.g. “intensive agriculture is more productive than small-landholder agriculture”) and systematically overturned these ideas with evidence. Overall, the article built to a logical conclusion with its importance clearly outlined and clarified my own thinking on these issues; it is a great piece.

Still, I have three critiques for the article, which I will try to tie to the issue of convergent vs. divergent models more broadly. Perhaps today’s lecture will do this, but it would be helpful to have more information on what the book authors mean when they use these terms, as the article itself does not explicitly references “divergent vs. convergent development models.”

1) Agroecological vs. Industrial models for food production:
While the argument that “on average organic and agroecological systems produce as much, if not more, than conventional systems,” is well argued with evidence from a review article, the limits to this argument are not traced. Are there differences in the amount of total land that could be used in agroecological/organic vs. industrial agricultural systems? Would agroecological/organic systems, at full scale, provide adequate food? What would the labour/cost differences be? How would these differences affect development trajectories (costs of food, benefits from increased employment)? While I think the beginnings of these questions and arguments are included in the article, these kinds of questions would be valuable to expand on in a subsequent book chapter. If these arguments are made strongly, then the case for agricultural systems that benefit people and ecosystem resilience (convergent model) will be that much stronger.

2) Limits to the matrix model (Agriculture + ecosystems):
Again, the matrix model is an intriguing argument, since if the argument is correct and was implemented, it would create significant benefits for both development and biodiversity (convergent model in line with sustainable development goals). However, the article, or subsequent book chapter, could more adequately explore limits to the matrix model by explaining some of the potential differences between agricultural land and forest (or other) ecosystems. While the matrix is well explained as an issue of habitat fragmentation, local extinctions and migration through adjacent habitat there may be important differences between an agricultural plot’s ability to support migrations and a traditional ecosystem’s ability. These differences could affect extinction rates, and thereby, the amount of agricultural land that can be substituted for intact ecosystems. This could affect development models, decreasing the amount of land that could be used for smallholder agriculture if the substitutability is significantly limited. Overall, this could affect the meta-argument, since limits to smallholder agriculture could potentially provide inadequate scale for necessary food production and inadequate land for conservation goals. These may be difficult questions, not yet worked out in empirical research; nevertheless, the limits to the matrix model, or other convergent models, could be more adequately acknowledged in order to strengthen their appeal.

3) Beliefs amongst development/environment practitioners:
Finally, I disagree with the decision to quote Angelsen & Kaimowitz’s 2001 paper, “Tradeoffs or Synergies? Agricultural Intensification, Economic Development and the Environment,” stating: “the belief that technological progress in agriculture reduces pressure on forests by allowing farmers to produce the same amount of food in a smaller area has become almost an article of faith in development and environmental circles.” While this may be “an article of faith” in some circles, I think development and environmental communities are quite critical of this premise, particularly in 2010. There is significant literature on the environmental and health impacts of intensification as well as the economic impacts of overproduction on rural livelihoods. Indeed, this paper argues these points during the latter half. Choosing this quote puts the discussion back a decade and does not acknowledge changes or current thinking (as the authors do themselves in the rest of the piece!). For the book chapter, it may be useful to place such statements in historical context rather that using divisive language, when possible.

The authors make a strong case that we must consider metapopulation dynamics in order to conserve biodiversity within the agricultural landscape. This ties into broader goals of having landscapes that provide multiple ecosystem services. However, the discussion of the FT model seemed (to me) to be a bit of a straw man. It seems odd to expect that any local agricultural intensification would necessarily lead to local conservation of land. Rather, I think we must think about the global land demand and how changes in production can affect the global marketplace and market signals (I'm thinking about the ILUC debate for biofuels).

The article makes two interesting suggestions: 1) productivity doesn't really matter (i.e. "The search for more productivity ... is not necessarily a rational project" pg 5790) and 2) even if it did, we could simply use agro-ecological techniques to achieve the same productivity. Since food demand is expected to double in the next 50 years (due to increased population + meat demand), I think it's clear that productivity matters! Unless agricultural yields increase on existing ag lands, we will need to clear most of the world's remaining tropical ecosystems for agriculture. Even if we keep a good matrix in these cleared lands, I'm not sure this is desirable for carbon emissions, biodiversity, etc (!?). (For example, Burney et al 2010 estimate in PNAS that we would have required additional cropland area the size of Russia to feed today's population if no ag intensification had occurred between 1960 and today.) If we can use agro-ecological methods to achieve increased yields, that would certainly be great ... although the paper doesn't provide a roadmap for how this would occur given labor requirements, price premiums, etc.

I found that the article made a compelling point for the use of the matrix-model as a means to develop an agroecological system that sustains biodiversity.  However, I thought the article overstated the potential its potential to serve as a large-scale alternative to agricultural intensification. My primary issue with this article was the stance it took on agricultural productivity.  The paper hinges on the idea that small-scale agriculture can be productive enough to support our growing population.

I was skeptical of this claim until I dug a little into the data myself.  The papers cited were old (Carnia, 1985; Sen,1962), but I was surprised to see newer papers reiterate this claim, generally pointing to higher marginal cost of inputs/supervision, greater land use intensity on smaller farmers, etc.

However, I’m still un-convinced that a complete cost-benefit analysis would indicate small-scale farming is more efficient.  Does anyone know of more complete examination of the cost of agricultural productivity at different scales?  A quick scan of the literature demonstrated to me that this is a controversial area, and perhaps worth examining deeper in any forthcoming book chapter.  For example, a study by Assunção  and Ghatak show that when incorporate the heterogeneity of the workers skill into models of farm size vs. productivity, the traditional inverse relationship disappears. This was attributed in part to the fact that better farmers tend to have smaller farms (somewhat counter-intuitive).  The paper reports: They report: “An interesting policy implication of this model is that any type of land reform that takes land from the rich and gives it to the poor is not going to improve productivity.”   Other research I found (Levine and Helfland) suggest that productivity may fall at first, but later rises with much larger farms.

In any case, I’m still in the process of looking for more data on determinants of agricultural productivity (mechanization/technological inputs, quality of underlying land) as I realize most of my knowledge in this area is anecdotal (from working for an agricultural non-profit before coming here).

I am also concerned about the other costs associated with agricultural production – disseminating materials and information, vulnerability to weather conditions, transportation costs to cities, quality control, etc.   For example, would we still be able to get enough food to the cities?  How would we continue to ensure food safety and quality? 

In any case, Perfecto did convince me that if we look at all the ecological benefits of matrix-based models, this model would be much more attractive to those working in development. I am also convinced that it could be part of a long-term sustainable food plan, but hopefully our discussion will help me to think about this further.

A couple references (though I found dozens more with a single google search of "farm size and productivity" and similar language).

Assunção, Juliano  and Maitreesh Ghatak. "Can unobserved heterogeneity in farmer ability explain the inverse relationship between farm size and productivity."  Economics Letters 80 (2003) 189–194.

Levine, Edward and S. Helfland. "Farm Size and the determinants of productive efficiency in the Brazilian Center-West."  Agricultural Economics 31 (2004) 241–249.

The article and discussion of convergent agricultural systems reminded me of some work a friend of mine was doing in Costa Rica related to the Mesoamerican biological corridor. One of the goals of the project was to link the Pacific coast dry forest through a series of protected land masses to facilitate the movement of biodiversity in the region.  The coordinating nations at that time were Mexico and the Central American nations, but they were hoping to create a truly pan-American corridor in the future, reaching north to Alaska and south to Argentina. 

Basically, her job was to use satellite images to determine gaps in the corridor and then visit agricultural lands to establish conservation easements with the property owners.  The easement provided government based financial incentives to maintain the land “undeveloped.”  Although some farms were larger, many of the farmlands were small, family owned farms that could fit into the convergent model we spoke of.  Though not mentioned explicitly yesterday, it is important that we keep these corridors in mind when working within the convergent matrix so that species can more easily move with the fragmented habitats.

Interestingly, my friend came to the US to work on conservation easements in New England.  Her biggest surprise was that while in Central America, she was working with farmers to have them leave there lands “wild,” in the US, most of the easements she worked on were to hold back urban sprawl in order to preserve the rural landscape, not for any particular biological conservation benefit.  As we did discuss, social and political pressures also play a role in the matrix.

Attached are two reviews of the Mesoamerican biological corridor.  It is still a work in progress, but seems to be contributing not only to facilitate flow of biodiversity, but also regional cooperation and partnerships.

Are there similar projects being developed transnationally in other parts of the world?  What type of success are they having? 

a short review of the project review of the project can be found here: http://www.tbpa.net/docs/pdfs/Meso_American_Biological_Corridor.pdf

A longer one here:

http://www.unep.org/dewa/eccreports/ECPI_Latin_America_Assessment_Final_Report_Feb21.pdf

I think the question you rose concerning the effect of fragmentation on predators really depends on the species system you are looking to. Even though I didn't research on the effects of fragmentation, some of my colleagues did it and their results were that it really depends on the specific predator and its mobility. I know that a lot of that research is going on in the different BIOTA projects, a cooperation between German and African researchers: www.biota-africa.org. 

In short, I'm wondering if fragmenting a continuous habitat would have an effect on the "natural enemies" of a given species population, as well as having an effect on that species' migration ability. The authors point out that fragmenting ecosystems can reduce a species' resistance to regional extinction by reducing the migration options, but it seems to me that there may be some parallel effect of a fragmented ecosystem on the predators.