Download Number of crop species and number of plant families

Elissa Brown, Ben Sullender, Amy Teller
Assessing Biodiversity
It is essential that farms not only consistently produce the crops that we depend on but also
promote the vitality of the surrounding ecosystems. In order to assess the ecological impact of
farmer practices, we developed a scoring system to quantify one component of ecological
sustainability: biodiversity. Biodiversity is essential to any successfully functioning
agroecosystem. Biodiversity can be defined as “all species of plants, animals and
microorganisms existing and interacting within an ecosystem, and which play important
ecological functions such as pollination, organic matter decomposition, predation or parasitism
of undesirable organisms” (Nicholls and Altieri 2004), suggesting a complex relationship
between every organism involved. To get at this underlying complexity, it makes sense to take
on a multifaceted approach to most accurately quantify the sustainability of a particular
agroecosystem’s biodiversity (Benton, 2003).
For this assessment, our holon is the land contained within the farm boundary. To score
biodiversity within this holon, we consider factors which are grouped into two ecological
indicators, Crop Biodiversity and Associated Biodiversity. Crop Biodiversity takes into account
factors that influence the biodiversity of the productive, planned plant communities within the
farm, which are the crops that are planted deliberately in the farmer’s fields. These factors
include Number of crop species, Number of crop families, Evenness of crop species, Type of
rotation, and Type of cropping system. Associated Biodiversity is based on factors that influence
the biodiversity of all other organisms found within the farm borders, including non-crop plants
and wildlife. These factors include Impact of insecticides, Impact of herbicides, and Quality,
Extent, and Arrangement of non-cropped habitat. Based on our research, the factors involved in
determining Crop Biodiversity and Associated Biodiversity account for all types of biodiversity
found on a farm and all farmer choices that have a significant impact on farm biodiversity. The
scores for each factor are used to calculate the two ecological indicator scores, which are then
considered to evaluate each farm’s Total Biodiversity. For more information about how we chose
our factors and indicators as well as a detailed description of our scoring method, please see the
Appendix.
We visited 17 farms, 11 in China and 6 in southern Minnesota, where we spoke to the farmers,
made our own observations, and ultimately collected the data that we used in our biodiversity
assessment. The following table shows the scores each farm received for each factor, for both
indicators, and for its total biodiversity. The scores each farm received are discussed in more
detail after the table.
Chinese Farms
Duan Farm – 13.2 acres
Total Score: 6.2 (Crop Biodiversity: 7.7, Associated Biodiversity: 4.7)
Mr. Duan’s farm is a CSA that provides to 10 families and feeds 50 people from his own family.
He has 13.2 acres of land, of which 0.16 acres is in greenhouses. Duan receives a good score for
Crop Biodiversity, which was only hurt by his score of 5 for intercropping. His greenhouses
were intercropped, but much of his cropped land is in larger fields that were not intercropped.
He receives a lower score for Associated Biodiversity even though he doesn’t use pesticides
because he had very little non-cropped habitat. Overall, Duan’s farm is respectable in terms of
biodiversity, but improvements could be made, especially in the areas of habitat and
intercropping.
Ji Farm - 0.96 acres
Total Score: 6.5 (Crop Biodiversity: 9.1, Associated Biodiversity: 4.0)
Mr. Ji’s farm is also a CSA that provides to 150 families in Beijing and consists of 6 greenhouses
that are about 0.16 acres each. Ji receives a very admirable score for Crop Biodiversity because
of his extensive use of intercropping, his rotation practices and the 20 crops from 16 families that
he grows. He is hurt by his low Associated Biodiversity score, which he receives because he has
no non-cropped habitat at all. His land is contained within the greenhouses. Mr. Ji does not use
pesticides. An improvement in habitat is all Mr. Ji needs to get a great score for biodiversity, but
this may not be feasible on his land.
Ai Farm – 3.3 acres
Biodiversity Score: 2.8 (Crop Biodiversity: 1.2, Associated Biodiversity: 4.4)
Mr. Ai is a small farmer who grew only corn and barley on 3.3 acres up until 7 years ago. Since
the government required that much of his land be reforested, he now subsistence farms on 0.6
acres. He receives a low score for Crop Biodiversity because he only grows two crops, has no
rotation and corn is grown as a monoculture on 85% of his land. His Associated Biodiversity
score is also low because he has very little habitat, but he does not use pesticides. Mr. Ai
receives a low score for biodiversity overall which he may not have the capacity to improve.
Little Donkey Farm – 8.2 acres
Biodiversity Score: 7.1 (Crop Biodiversity: 8.6, Associated Biodiversity: 5.6)
Little Donkey Farm is a CSA owned by a village collective and operated by 5 managers, some
interns and students from Renmin University in Beijing. Little Donkey receives a very high
score for Crop Biodiversity because they grow 40 types of vegetables, have a rotation and
intercrop the vegetables. Little Donkey’s score for Associated Biodiversity is lower even though
they do not use pesticides. This is because Little Donkey has only a little bit of non-cropped
forested habitat on a few sections of the farm. Little Donkey earns a good score for biodiversity
and could improve mainly in the area of non-cropped habitat.
Liu Farm – 2 acres
Biodiversity Score: 5.1 (Crop Biodiversity: 5.1, Associated Biodiversity: 5.1)
Mr. Liu’s farm is one of the most “conventional” Chinese farms that we visited. He sells to
distributors, and people in Chengdu purchase his products. He receives a mediocre score for
Crop Biodiversity because he grows rice, corn and oranges on most of his land for most of the
year and grows vegetables only in the winter on some of the 0.5 acres that are in rice the rest of
the year. He intercrops and rotates only the vegetables, not the rest of his crops. Mr. Liu also
receives an average score for Associated Biodiversity. This is because he uses pesticides that are
toxic to non-target plants and insects, birds and some mammals. However, 0.7 acres of Mr.
Liu’s 2 acres are forested, non-cropped habitat due to the Chinese government’s reforestation
policy. This helps improve Mr. Liu’s score for associated biodiversity, although there is not
much variety in non-cropped habitat. This “conventional” Chinese farm receives a much better
biodiversity score than “conventional” American farms like Pahl’s.
Gao Farm – 1.8 acres
Total Score: 6.8 (Crop Biodiversity: 9.2, Associated Biodiversity: 4.4)
The Gaos are one of 7 families who cooperate in a CSA that supplies to urban residents of
Chengdu. Crop Biodiversity is good, as they grow a wide variety of crops, 20 species that are
from 12 crop families. Crops tend to be planted in small patches, providing the benefits of
intercropping, and a good rotation system is used. However, their score is hurt by their lack of
Associated Biodiversity, as very little non-cropped habitat exists within the extents of their farm
– only small field borders and plots rented by urbanites that go untended and become overgrown.
No pesticides or herbicides are used.
Wong Farm – 0.6 acres
Total Score: 5.7 (Crop Biodiversity: 7.1, Associated Biodiversity: 4.4)
The Wongs run their own CSA that provides vegetables to 15 Chengdu families. Their Crop
Biodiversity score is lower, as they grow a less diverse assortment of crops, 12 species from 5
crop families, and their rotation practices are not ideal since each year for four months mostly
rice is grown and no land is ever left fallow to rest. Many plots are intercropped though. Their
Associated Biodiversity score is low since the only non-cropped habitat within the farm is found
in small field borders, but no pesticides or herbicides are used.
Zhuyeqing Tea – 264 acres
Total Score: 4.2 (Crop Biodiversity: 1.9, Associated Biodiversity: 6.5)
Although five varieties of tea are grown on this giant tea farm, Crop Biodiversity suffers from
the lack of multiple families and the impossibility of rotation and rest. Their Associated
Biodiversity score is much higher. This is because the farm does also grow some fruit trees for
the purpose of increasing biodiversity though, and about 30% of the land, dispersed throughout
the hills, is forested. However, some low toxicity herbicides are used around the tea and sticky
flags are placed in the tea plants with the purpose of killing all insects that come into contact
with the flags.
Lei Farm – 1.7 acres
Total Score: 6.1 (Crop Biodiversity: 3.7, Associated Biodiversity: 8.5)
The Leis grow tea to sell to visitors on Emei Shan and a small amount of vegetables to feed
themselves. They get a low score on Crop Biodiversity because one variety of tea plant
dominates their farm – only 5% of their land is used to grow other vegetables. This system does
not allow for rotation or intercropping. Associated Biodiversity, however, is very good, as a large
portion of their land is habitat that is native to the mountain.
Lo Yu Farm– 8.2 acres
Total Score: 8.8 (Crop Biodiversity: 9.1, Associated Biodiversity: 8.5)
Lo Yu has a CSA that sells to residents and restaurants in Chengdu. His Crop Biodiversity is
good, as he grows 70 different vegetables with significant intercropping and good rotation
practices, leaving 20% of his land fallow each year. He also receives a good Associated
Biodiversity score because all land that doesn’t receive sufficient sunlight is growing native trees
and plants instead. 25% of his land is non-cropped habitat that is dispersed throughout the farm.
He does not use pesticides or herbicides.
Duofu Farm – 198 acres
Total Score: 5.9 (Crop Biodiversity: 7.2, Associated Biodiversity: 4.6)
Duofu Farm is a corporate organic farm that rents land from village farmers and employs them to
work for the corporation. Duofu receives a good score for Crop Biodiversity because they grow
a wide assortment of crops, 50 species. However, Duofu uses minimal intercropping and only
rotates the vegetable plots. Duofu does not receive a very good score for Associated Biodiversity
because there is little to no habitat preservation. The farm is planning to reduce their alreadydwindling wild acreage. No herbicides are used and BT pesticide is sprayed 3-5 times per
season.
American Farms
Gardens of Eagan – 100 acres
Total Score: 6.1 (Crop Biodiversity: 6.7, Associated Biodiversity: 5.5)
Gardens of Eagan is an organic farm that sells its produce to co-ops. They receive a good score
for Crop Biodiversity because they grow a diverse assortment of crops, 15 species, but they
devote a large portion of acreage to two main crops, corn and broccoli. A complex rotation
system is used, spanning the course of several years and using different types of cover crops.
However, very few acres are intercropped. Gardens of Eagan receives a mediocre score for
Associated Biodiversity because although they have a good amount of permanent habitat, it is
poorly arranged into large blocks and riparian barriers. Four main pesticides and herbicides are
applied as needed to specific areas of the farm.
Pahl’s – 1200 acres
Total Score: 4.3 (Crop Biodiversity: 6.5, Associated Biodiversity: 2.2)
Pahl’s, a large-scale corporate conventional farm, consists of many geographically separate
farms that grow different crops. For Crop Biodiversity, Pahl’s grows 16 crops, but the majority
of acreage is devoted to sweet corn. Different rotations are used depending on the crop, each
rotation system lasting several years and including cover crops. Pahl’s receives a very low score
for Associated Biodiversity because aside from insignificant windbreaks, there is no land kept in
permanent habitat. Many different types of pesticides and herbicides are used, each targeting a
separate crop.
Earthen Path – 14 acres
Total Score: 9.7 (Crop Biodiversity: 10.0, Associated Biodiversity: 9.5)
Earthen Path grows vegetables for its CSA members and to sell to co-ops in southeastern
Minnesota. This farm receives an excellent Crop Biodiversity score because a wide variety of
crops, 100 species from 20 crop families are grown, usually in long rows to take advantage of the
benefits of intercropping, and with a long rotation cycle. Associated Biodiversity is also
excellent, as 64% of the land is high-quality non-cropped habitat. However, even this score could
be improved if low toxicity pesticides were not used. According to our assessment, Earthen Path
is the highest scoring farm for Total Biodiversity and also for both indicators. The farmer
practices at Earthen Path could be considered aspirations for farmers who need to make
improvements in biodiversity.
Lutteke Organics – 1000 acres
Total Score: 6.3 (Crop Biodiversity: 4.7, Associated Biodiversity: 7.8)
The Lutteke farm is an organic farm that produces dairy products and eggs. They grow their
own feed for their dairy cows and we are assessing those fields. Lutteke Organics receives a
mediocre score for Crop Biodiversity. They grow only 4 crops, corn, alfalfa, oats, and soybeans,
but these crops are grown in relatively even distributions by area. Also, a 2-3 year rotation is
used, with land remaining as cropland for one year before being returned to pasture. Several
different types of cover crops are used, including red clover, winter rye, and oats. Lutteke
Organics receives a good score for Associated Biodiversity because they have non-cropped
habitat, arranged along the perimeter of fields, building sites, ditches, and the river. No
herbicides or pesticides are used.
Big Woods – 79 acres
Total Score: 8.3 (Crop Biodiversity: 9.2, Associated Biodiversity: 7.5)
Big Woods Farm is a CSA that grows a wide variety of crops, 20 species from 20 different
families, which are evenly distributed over the field acreage. A multiyear rotation using cover
crops is used. Some land is left in permanent pasture, and the majority of the acreage has some
intercropping. Therefore, Big Woods receives an excellent score for Crop Biodiversity. In terms
of Associated Biodiversity, 4 acres are left as permanent habitat, arranged so that they form
continuous riparian barriers. They are well dispersed and contain native plant species. This score
is hurt slightly by the practice of applying BT, pyganic, and Entrust to a small percentage of the
cropland once or twice a season.
Schrader Farms
Biodiversity Score: 2.9 (Crop biodiversity: 1.8, Associated biodiversity: 4.0)
Schrader Farms is a conventional corn and soybean farm. They receive a very low score for
Crop Biodiversity because they only grow two crops in monoculture and have a 2 years corn, 1
year soybeans rotation. The Schraders earn a better score for Associated Biodiversity because
they have 70 acres of wooded land with native species, continuous non-cropped areas and some
riparian barriers. However, they also use toxic pesticides on all of their land. The lack of crop
diversity is the biggest setback for biodiversity at Schrader Farm.
Conclusion
Our results demonstrate that farmers are in various stages of implementing practices that support
biodiversity. These farmers also seem to differ in their consciousness of how they are affecting
the environment. While our method of calculating farmer scores is by no means a fully accurate
and comprehensive evaluation, it is useful in illuminating the impacts of farmer choices on
biodiversity. Our scoring shows that farmer choices directly affect the sustainability of not only
their land, but also of the surrounding environment. If farmers are aware of their ecological
impacts and consider biodiversity when making farming choices, agroecosystems, surrounding
ecosystems and the farmers themselves will reap the benefits for years to come.
APPENDIX:
Background Information and Detailed Method
Crop Biodiversity
The number of different crop species and crop families involved in an agroecosystem are
essential determinants of biodiversity, as the strength of the agricultural community relies largely
on these two measures. According to Gliessman, the agroecologist “knows that a certain level of
complexity is desirable. By paying attention to the ecology of the crop community, it is possible
to create beneficial interactions and emergent qualities that not only reduce the need for external
inputs, but also increase yields” (Gliessman, p. 205). One fundamental measure of crop
biodiversity is the number of crops: the more crops, the higher the biodiversity. Having more
species in an ecosystem imparts a number of benefits on the land – higher biodiversity in natural
systems has been shown to reduce soil loss, improve water quality, increase biomass yield, as
well as provide wildlife habitat for pollinators and organisms essential for proper ecological
functioning (Adler et al., 2007). Another study demonstrates that a polyculture of three crops
increases the total yields of the combined three crops from the yields of the three crops grown in
monocultures (Amador 1980).
It is also important to take into consideration the Number of plant families growing within an
agricultural system. In much the same way that different species of plants create a more complex
(and therefore more productive and resilient) web of interactions, different plant families
contribute to the agricultural process mainly by balancing nutrient absorption. For instance, in
the corn-bean-squash combination, each plant makes different demands on the soil’s nutrients
(Gliessman, p. 222). If crops are all from the same family, they are more likely to exhaust the
soil of the same nutrients. To help improve the accuracy of these first two measurements,
Evenness of crop species should be considered as well. This factor expresses whether the
productive area is equally distributed among crops. Having many species and families of crops
does not represent strong biodiversity if all but a half-acre of farmland is devoted to just one crop
– this would be, in effect, a monoculture with a very small exception.
Although a physical measurement of the number of species in an agroecosystem is a good place
to begin classifying biodiversity, an accurate definition of biodiversity is much more complicated
than simply determining the number of crops and other organisms. A case study focusing on arid
ecosystems recommends that quantification of biodiversity needs to go beyond mere species
counting and move towards developing a “calculus of diversity” (Ayyad 2003). To help achieve
this more precise measure of biodiversity, the type of crop rotation can also be closely examined.
The USDA reports that having a crop rotation involving different types of crops often breaks
pest and disease cycles and prevents them from building to harmful levels (Padgitt and Bull
2006, p. 144). Additionally, planned crop rotations benefit yield, soil tilth, and help reduce
required fertilizer and pesticide inputs (Padgitt and Bull 2006, p. 143). Sample crop rotation
types include: growing the same crop every year with no rotation (no rotation), having a crop
rotation that completes a full cycle in a year (one year rotation), having a crop rotation that takes
several years to complete (multiyear rotation), and growing a crop to cover the topsoil after
harvest (growing a cover crop). Other types of rotation involve growing hay or allowing
cropland to go fallow/idle for at least one year.
It is important to look not only at agricultural diversity over time, influenced by crop rotation
practices, but also to consider the Type of cropping system a farmer uses, which influences
diversity in a given plot at a given time. Monoculture, the practice of planting a field with only
one crop species at a time, creates a simple ecosystem that is highly susceptible to disease and
pests. It fails to provide a sufficient habitat for natural enemies of pests and makes it easier for
certain pests to find food and reproduce (Nicholls, Altieri, 2004). Also, the single crop species
takes certain nutrients from the system and leaves one kind of organic material in the system, so
the system can easily become depleted of nutrients that cannot be biologically replaced by the
single crop species. Monoculture is thus not a sustainable agroecosystem. An intercropped
system is a more sustainable alternative, allowing multiple crops to fill different niches in the
agroecosystem, improving nutrient retention and recycling. In addition, intercropping makes a
farm less susceptible to pests. In a review paper on this topic, it was found that out of 198 total
herbivore species studied, 53% were found to be less abundant in a more diversely cropped
system (Risch et al., 1983). The benefits of even a simple three-crop polyculture are far greater
than a monoculture (Amador 1980).
Based on these findings, we have decided to include Number of crop species, Number of crop
families, Evenness of crop species, Type of rotation, and Type of cropping system as factors that
will contribute to the score for the Crop Biodiversity indicator.
To assess these factors, we ask the following questions. If answers aren’t received or there isn’t
time to ask, we make our own observations as we visit:
Number of crop species
How many crops are grown?
Number of plant families
How many families do the grown crops represent?
Evenness of crop area
How many acres are in crop production?
What is the acreage grown of each crop?
Type of rotation
How long is a typical rotation cycle?
Are cover crops used? If so, how often?
Is land ever left fallow or in pasture? If so, how often?
Type of cropping system
To what extent are fields planted in monoculture or intercropped?
(This could be asked or observed.)
Scores for all five Crop Biodiversity factors are based on scales from 0 to 10, with 10 being the
best for promoting biodiversity and 0 being the worst.
In Number of crop species, farms earn scores according to the following function:
Score = 20.13*(Number of crop species) / (Number of crop species + 10.5) – 1.7
# of crop species
This is because the greatest deterioration in ecosystem processes occurs as diversity declines
from moderate to low values. Ecosystem processes level off between moderate and high values
of biodiversity and then remain unaffected by further increases in diversity. Moderate is defined
as ~8 species, and high is defined as ~20 (McGrady-Steel et al., 1997), so we chose ~14 species
as the point at which additional species have no further positive effects on biodiversity services.
In Number of plant families, farms earn scores according to the same function as Number of crop
species. This is because all crops species should be from different families to maximize their
positive effect on biodiversity.
In Evenness of crop area, farms earn scores in the following way: Each crop makes up an actual
percentage of total crop area and also has an ideal percentage based on the total number of crops
(ideal percentage = # of crops / 100). We take the absolute value of the difference between the
absolute percentage and ideal percentage for each crop and average the results. The average
necessarily falls between 0 and 50. Since 50 is the worst possible value and 0 is the best, 50
corresponds to 0 on a 0-10 scale and 0 corresponds to 10. To find intermediate scores, we divide
by 5 and subtract from 10.
Example: A farm has three crops, so the each crop’s ideal percentage of total crop acreage is 33.
Actual percentages of the crops are 50, 25, and 25.
(|50-33| + |25-33| + |25-33|) / 3 = 11
10 – (11/5) = 7.8
In Type of rotation, farms earn scores according to the function depicted graphically below.
Since these values must be considered qualitatively, it is impossible to use a numerical function
to calculate scores this factor. It is useful, however, to see the scoring system on a continuum in
order to more accurately place farms that fall between broad categories.
No rotation
One-year
rotation with
fallow land and
no cover crop
One-year
rotation with
cover crop and
no fallow land
One-year
rotation with
cover crop and
fallow land
Multiyear
rotation with
fallow land and
no cover crop
Multiyear
rotation with
cover crop and
no fallow land
Multiyear
rotation with
fallow land and
cover crop
In Type of cropping system, farms earn scores according to the following function:
Score = (% intercropped area)/10
% intercropped area
Intercropping is better for diversity than growing crops in monocultures, so scores are be based
on an increasing linear relationship.
Associated Biodiversity
As farm machinery and chemicals have reduced the amount of labor required to manage land,
farmers have been enticed into putting as much land as possible into crop production (Benton et
al. 2003, Weibull et al. 2000). This has resulted in a decrease in the extent of non-cropped
habitats including field margins, hedgerows, and other boundary vegetation (Weibull et al.
2000). Consequently, the heterogeneity of many agricultural areas has drastically decreased.
Multiple studies have suggested that landscape heterogeneity or complexity and biodiversity are
directly related, and that non-cropped habitats are essential in sustaining the diversity and
abundance of insects, birds, and invertebrates on the farm (Benton et al. 2003, Boutin et al. 2008,
Hinsley et al. 2000, Holland and Fahrig 2000, Norton et al. 2009, Weibull et al. 2000).
Therefore, one of the most effective things farmers can do to encourage biodiversity is preserve,
create, and protect these habitats on a significant amount of their land.
The value of non-cropped habitat to wildlife depends not only on the Extent of habitat, but also
on the Quality of habitat. A good quality habitat can be defined as one that meets the needs of a
species. However, different species require different features. For example, many wildfowl
require dense vegetation to avoid detection by predators, but many other birds prefer sparse
vegetation to allow for easier foraging (Benton et al. 2003). This means that depending on what
species is being considered, habitats may vary in quality. Accordingly, the more diverse a habitat
is in its vegetation, the more animal species it is likely to support, and the more diverse its
supported community is likely to be (Benton et al. 2003, Norton et al. 2009). Farmers can thus
further encourage biodiversity on their farms by providing habitats that contain a variety of
plants, and also by providing a range of habitat systems such as wetlands, grasslands, wildflower
fields, and wooded areas, where appropriate. Preferably, these habitats should include native
plant species to support native fauna.
Along with extent and quality, the Arrangement of non-cropped habitat is important. Continuous
habitats, such as hedgerows, are preferable, as they can provide corridors for the movement of
plant, insect, bird, and invertebrate populations throughout the farm, allowing safer access to
resources and mates (Benton et al. 2003, Hinsley et al. 2000, Norton et al. 2009). It is also
preferable to have island habitats dispersed throughout the farm, as opposed to habitats
concentrated in one area, as they can then provide more accessible refuge for mobile birds and
insects (Benton et al. 2003, Weibull et al. 2000).
To reach their highest potential biodiversity, habitats must not be contaminated with harmful
chemicals. Insecticides and herbicides have the ability to kill associated biota or decrease the
capacity for these organisms to contribute to ecosystem processes (Nicholls, Altieri, 2004). Less
insecticide and herbicide use leads to a farm being more similar biologically to a natural system,
and therefore the farm is likely to be more ecologically sustainable. The three fundamental
aspects that determine the Impact of insecticides are exposure, the amount and rate applied, and
the toxicity of the pesticide(s) used (Bechini, 2009). It has also been found that when farmers do
not spray in field margins (strips of land between crops and the field boundary that extend for a
limited distance into the crop) more insects, birds, and flowering plants are found. This makes
whether or not a farmer sprays in field margins an important choice that impacts biodiversity
(Snoo, 1999).
Herbicides, agents used to kill unwanted plants, are not as toxic to animals as pesticides since
they are meant to target photosynthesis or other processes distinctive to plants. However, the
Impact of herbicides is still significant within an agroecosystem, as herbicides harm and kill
unintended plants as well. Plants have a huge role in ecosystem functioning, particularly nutrient
cycling (University of Florida IFAS Extension) and if these plants are harmed or killed, diversity
in the ecosystem will not be as well sustained. It has also been found that plant species richness
increases in field margins if herbicides are not sprayed there, including the growth of wild annual
and perennial species (Musters, 2008).
Based on these findings, we have decided to include Extent of non-cropped habitat, Quality of
non-cropped habitat, Arrangement of non-cropped habitat, Impact of Insecticides, and Impact of
Herbicides as factors that will contribute to the score for the Associated Biodiversity indicator.
To assess these factors, we ask the following questions. If answers aren’t received or there isn’t
time to ask, we make our own observations as we visit:
Extent of non-cropped habitat
How many acres is the total farm property?
How many acres are non-cropped habitats?
Quality of non-cropped habitat
How many different types of non-cropped area are on the property (e.g. grassy areas,
wetlands, wooded areas)?
Are native plant species growing in non-cropped areas?
Are there diverse ranges of plant species growing in each non-cropped area?
Arrangement of non-cropped habitat
Are non-cropped areas dispersed throughout the property?
Are there continuous non-cropped areas (e.g. field margins or hedgerows)?
Impact of Insecticides
Which insecticides do you use?
How often and how much do you apply?
Do you spray in field margins?
Impact of Herbicides
Which herbicides do you use?
How often and how much do you apply?
Do you spray in field margins?
Scores for all five Associated Biodiversity factors are based on scales from 0 to 10, with 10 being
the best for promoting biodiversity and 0 being the worst.
In Extent of non-cropped habitat, farms earn scores according to the following function: Score =
11.2 (% non-cropped area)/(% non-cropped area +12)
% non-cropped area
Although unrealistic for a functioning farm, 100% non-cropped habitat would be best for
biodiversity so it gets a score of 10. Since an increase in non-cropped habitat would have the
greatest positive effect on biodiversity services when there is less existing habitat, scores are
based on a curve that steeply increases at lower percentages.
In Quality of non-cropped habitat, farms earn scores according to the function depicted
graphically below. Since these values must be considered qualitatively, it is impossible to use a
numerical function to calculate scores this factor. It is useful, however, to see the scoring system
on a continuum in order to more accurately place farms that fall between broad categories.
Similar habitat types with
monocultures of nonnative species
More variation of
habitat types with
more diversity and
native species
Some variation of
habitat types with
some diversity and
native species
Great variation of
habitat types with
great diversity and
native species
In Arrangement of non-cropped habitat, farms earn scores according to the function depicted
graphically below. Since these values must be considered qualitatively, it is impossible to use a
numerical function to calculate scores this factor. It is useful, however, to see the scoring system
on a continuum in order to more accurately place farms that fall between broad categories.
Non-cropped areas
concentrated in one place
Some dispersal
throughout some of
the property
More dispersal
throughout more of
the property and
somewhat connected
Dispersed throughout
all of the property and
greatly connected
In both Impact of Insecticides and Impact of Herbicides, a farm’s score is determined by using
the following equation:
(0-10 score for toxicity) + 2*(1 – fraction of cropped land sprayed) = 0-10 score for pest or weed
control
Score for toxicity: Is the insecticide/herbicide harmful to soil organisms, rodents, larger
mammals, birds and/or non-targeted plants? If it is harmful to all 5 it is given a 0, 4 of 5 is given
a 2, 3 of 5 is given a 4, 2 of 5 is given a 6, 1 of 5 is given an 8, 0 of 5 is given a 10.
The information on toxicity is obtained from EXONET and other databases if necessary once we
learn which pesticides are used on each farm. If a farm uses more than one pesticide, the
toxicities of each of the pesticides are averaged and the fraction of cropped land sprayed is
added. The results are put into the equation to get a 0-10 score.
Methods of Calculation
Our Biodiversity Assessment involves categories on two levels: factors (e.g. Extent of noncropped habitat) and ecological indicators (e.g. Associated Biodiversity). The scores of factors
within each ecological indicator are be combined and weighted to determine that indicator’s
score, and the two indicator scores are be combined and weighted to determine a farm’s
BIODIVERSITY score.
While each factor is important to the overall quantification of its ecological indicator, the factors
affect the agroecosystem to different extents and are therefore given different weights within the
two indicators. Within Crop Biodiversity, Type of rotation and Type of cropping system have
more importance than simply the Number of crop species and Number of families. This is
because the type of rotation and type of cropping system that are used by the farmer have a
greater influence on ecosystem processes and soil nutrients than do the number of crop species
and families the farmer plants. Evenness of crop area is given the lowest weight since it is only
included as a mediating factor in the number of crop families and species.
Within Associated Biodiversity, the specific factors having to do with habitat are given a higher
combined weight than pest and weed control. This is because more habitat is better for
biodiversity than less, even if that habitat is polluted with chemicals; if diverse habitat is not
present on the farm, pesticides will not have a system with which to interfere. Within the factors
relating to habitat, Extent of non-cropped habitat is given more weight than both Arrangement
and Quality for the same reason: more habitat is better than less. Quality is given more weight
than Arrangement because it is more important to biodiversity for habitats to be well-suited to
many species than for habitats to be well-connected. Within the factors relating to chemicals,
Use of insecticides and Use of Herbicides are given equal weight because both plants and
animals are important to biodiversity.
In determining the final BIODIVERSITY score, Crop Biodiversity and Associated Biodiversity
are given equal weight. While crops cover a much greater area of most farms, non-cropped
habitats are much more valuable for supporting a broad spectrum of wildlife.
Crop Biodiversity Equation:
(Number of crop species score) x .2 + (Number of plant families score) x .2 + (Evenness of crop
area score) x .1 + (Type of rotation score) x .25 + (Type of cropping system score) x .25 = Crop
Biodiversity score (0-10)
Associated Biodiversity Equation:
(Extent of non-cropped habitat score) x .3 + (Quality of non-cropped habitat score) x .2 +
(Arrangement of non-cropped habitat score) x .1 + (Impact of insecticides score) x .2 + (Impact
of herbicides score) x .2 = Associated Biodiversity score (0-10)
BIODIVERSITY Equation:
(Crop Biodiversity score) x .5 + (Associated Biodiversity score) x .5 = BIODIVERSITY score
(0-10)
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