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Reports for 3/26
Up to Literature Search - Round 1
Hi everyone,
I hope the last couple of weeks have been good for you all, and featured at least a little chance to relax! Remember we're starting the chat a little later tomorrow (11:15 EST) to give Adina and Sergio a chance to get back from their class, and hopefully finishing up by about 12:45 EST. Looking forward to hearing everyone's thoughts!
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Now here's a little bit about LHs in eastern NA:
Basically, I didn't find a whole lot that explicitly addressed the role of LHs in a broader context or for providing very many ecosystem services. There were a fair number of studies on the connectivity benefits of linear corridors (see Zoho), but in general the idea seems understudied in the region. I did find a number of data sources that would be useful for comparing trends in successional habitat with agricultural productivity across the region, although the scale might be a little coarse (typically on counties/parishes), and we'd have to be a little inferential. It would be helpful to find more studies on the relationship of different successional habitats to active fields in the region (maybe I was just using the wrong searchwords...)
Talk with you all soon.
Just thought I'd post my short summary of what I have found from the west coast (mostly California). The good news is that there are tons of hedgerows (apparently) in the agricultural centers of California. And there are a bunch of organizations promoting them and boasting of all their ecosystem services (both on and off farm). I have found numerous technical reports and broshures describing what species to plant, how to plant and manage them, what the approximated costs will be, etc. etc. There is a whole group of folks at UCDavis (extension?) working on planing what they call 'insectary hedgerows', which are basically hedgerows that provide forage and nesting sites for beneficial insects (= predators and parasitoids that eat pest species). This is related to a general movement called Farmscaping, which involves the planting of hedgerows (amonth other things), to enhance on-farm biodiversity and reduce negative environmental impacts of agriculture. So there is a lot of prescriptive stuff and good data on which plant species attract the most 'beneficials' and which species you can plant to ensure year-round or season-long flowering (to provide forage fore bees & butterflies) and lots of discussion about how the use of native perennials (in the hedgerows or field borders) is cost effective, as they quickly become weed "resistent" once established (few years) and require less management and tend to bring in more benefials, etc.
The bad news is that I found very little in the way of actual studies or data to back up or re-affirm these recommendations (I'm still looking!).
What I did find:
One study looking at vegetative filter strips in pature lands to control runoff (Hay et al. 2006). Though they found that the filter strips did reduce the flow of nutrients and sediment, the effectiveness varied depending on the site-specific conditions. There was some information on strips of different widths.
One study documenting the use of riparian corridors by large mammals through vineyards and the importance of corridor width (Hilty & Merenlender 2004).
One study showing the benefits of a vegetative corridor running through a crop field in terms of housing pest predators and reducing the abundance of pests in the field. Unfortunately, they only examined two fields -- one with the corridor and one without. (Nicholls et al. 2001).
One grant report giving the results of a study where insects were monitored for two years in hedgerows and the ratio of beneficials to pests calculated (3:1).
I still have a couple of books that might have more actual data on the hedgerows that I will do my best to go through ASAP. At a glance, it would seem that most of the studies referenced are from teh 1960s!
Tangentially, I found one study on bees where they found more ground nesting bees in the weedy field borders than in the sunflower fields (and looked at the importance of nearby "natural habitats" vis GIS analysis) (Kim et al. 2006)
I did hear back from Claire Kremen and unfortunately, she has just started a field margin/hedgerow study, but they don't have any data yet.
There are a ton of websites that I still need to go through and some more people I hope to hear back from, so there may be more actual data/surveys from existing hedgerows.
Also, as we discussed in the chat, you can get data on pesticide use by county and crop in CA, which may be useful if we do a GIS analysis (relating pesticide application with % nearby natural habitat/scrub).
1) A study from Iowa comparing woody hedgerows with grassy field borders with respect to presence of ground beetles (predators). They found that early in the season, carabids were more active and species richness was higher in the corn fields bordered by woody hedges; this was not the case later in the season when corn was in full canopy; still, woddy borders may provide critical overwintering habitat for predatory beetles. Varchola & Dunn 2001. One exciting thing about this study is that there are some woody hedgerows left in Iowa! But can we get data on species composition???
2) Clarke & Reeder draft (I already e-mailed to everyone) -- this is a review of linear habitats in the USDA or CCRP conservation programs. Good ref list to check out. Also gives acreage and participation by state.
3) McIntyre, N.E. and T.R. Thompson 2003. This study compares four different CRP plantings with respect to arthropod prey for grassland birds with each other and with native shortgrass prairie; though CRP lands showed lover arthropod abundance than native prairie, the authors conclude that the plantings do provide a significant food resource for grassland birds.
4) Potentially useful books:
Altieri & Nicholls: Biodiversity and Pest Management in Agroecosystems (2004)
Pickett & Bugg: Enhancing Biological Control: Habitat management to promote natural enemies of agricultural pests (1998).
5) Winfree et al. 2007 -- this is the one I e-mailed everyone today. Interesting that they found more bees in agricultural/suburban/"disturbed" areas than extensive forest. Backs up the idea that mid-successional and/or otherwise disturved habitats may provide better source populations for pollinating insects.
6) Marino & Landis 1996 (uploaded to the new folder Jonathon created for us) -- Has data comparing parasitism rates in ag fields surrounded by hedgerows vs. not; species lists of hedgerows (veg). Study location is southern Michigan.
With the literature looking at the effects of linear habitats on wildlife (usually filter strips and grassed waterways) it is usually always the case that there is a greater diversity and number of wildlife species within the strips than in the crop field or pasture. There also seemed to be a common theme that wildlife benefits are better with strips that are wider, that have greater structural complexity, and that include forbs in addition to grasses. Studies that also looked at landscape scales generally all found that the complexity of the landscape is important as well.
I also found some articles that looked at insects, both beneficials and insects. However, not all of these were looking at a standard practice for strip habitat (i.e. filter strips) - they looked at a wide vairety of field edges, etc. Many of these studies also had really low sample sizes. One general conclusion is that there need to be more studies on the effects of these linear habitats on beneficial and pest insects. Since some farm bill programs now include beneficial insects as one of the purposes there is a need to now how to manage these programs for this purpose. For example, filter strips have 6 purposes, one of these is "restoring, creating, or enhancing herbaceous habitat for wildlife and beneficial insects." It is also imporant to study the potential pest problems caused by planting these habitats since farmers may be worried that putting in strips of habitat along the edges of their fields (or within fields) would cause problems as the habitat would harbor pests that would negativeley affect their crops. One study looked at various types of vegetated field edges and found that they did not cause an increase in outbreaks of the European corn borer, a major pest in corn (Stamps et al. 2007). In fact, fields with borders of warm season grasses had less outbreaks than field with no border or any other border type. In a study in Ottawa, Canada Holland and Fahrig (2000) found that the amount of woody field border in the landscape did not have an effect on the numbers of herbivorous insects in alfalfa fields.
Habitat and landscape complexity may not be as important for weed seed predators or carabid beetles as it is for wildlife (Menalled et al. 2000; Marino et al. 2000).
Some linear habitats can also help to increase carbon sequestration. In predominantly agricultural landscapes that focus on monocultures of annuals any addition of perennial habitat will increase the amount of carbon sequestered in the landscape. Uri (2001) calculated the potential carbon sequestration in various types of conservation programs used in US agriculture. Conservation buffer strips are specifically discussed in this paper.
Re: Reports for 3/26
Posted by
dtdalton
at
April 01. 2007
My efforts so far have focused on management of linear
habitats to accomplish biodiversity conservation goals. Foundations and extension offices of many US universities (Pennsylvania
State, University
of Minnesota, University of Northern Iowa)
reflect recent trends addressing roadside vegetation management. Native prairie species plantings along the
roadsides of the Midwest may serve as
important corridors for insects and birds.
However, some studies have shown that habitat-sensitive and
disturbance-tolerant butterfly species may benefit differentially to roadside
management regimes. Bee diversity also is
affected by species composition of the roadside vegetation community. An adaptive management approach should be
maintained to accomplish pre-defined objectives along roadsides, where a diversity
of strategies should be used on a landscape scale.
I believe that lots of research has probably been done
addressing management strategies, but we have hardly scraped the surface of
what needs to be compiled. Integrated
Roadside Vegetation Management (IRVM) may add to other ROW data from industry
sources (in which regions have we found ROW data to extract???). To accompany live fence data from Central America, certain state programs exist to increase
the use of living snow fences, if only we can extract the raw data. So far I have had limited success in
contacting representatives for agencies which deal with linear habitats for
roadside management. The US Forest
Service published in 2000 a nice guide to various roadside management techniques
using vegetation to stabilize weak or exposed slopes. In addition, the NRCS has published two short
papers detailing silvopastoral systems and methods by which agroforestry
practices can be integrated with other management techniques.
To summarize, it seems that there are data to address the impact
linear habitats have on management goals, but the question is more an issue as
to where to focus the research. Management
of roadside habitats appears to be critical for endangered ecosystems (native
prairie, for example), but a broader search of university extension programs
would undoubtedly be helpful. I still
hope to receive feedback from people I have tried to contact.