15 4Nature, food, and water
London
*
Berlin+Rome+Bucharest+Stockholm+Barcelona+Nantes
Chicago+San Diego/Tijuana+Philadelphia+Ottawa
Edmonton
Por
tland
Atlanta
- Mexico City
*
Santiago
*
Brasilia+Tegucigalpa
Iquitos
- Cairo
*
Nairobi
*
Bamako+East London
Abeche
Beijing
*
Moscow
*
Seoul
*
Te h r a n
*
Sapporo+Ulaanbaatar
Erzurum
Kagoshima
Bangkok
*
Kuala Lumpur+Cuttack
Samarinda
Canberra
Rahimyar Khan
Europe North
America
Latin
America
Africa West-East
Asia
South Asia-
Australia
Avera
ge
Average size of patches within cropland
landscapes (km
2 )
Geographic area, with cities from large to small population
20
10
5 4 3 2 1 0
= Wooded patches
= Crop fields
Figure 6.10Average size of woods and fields within agricultural landscapes relative
to geography and city size. Average sizes of woods and fields are estimated in all
agricultural landscapes 1 km^2 = 247 acres. Within each geographic area, cities are
in decreasing order of population (Table5.1).See Figure 6.2 caption for city
information.
is to maintain at least two major market-gardening areas in proximity to the
metropolitan area.
Woods and field sizes in cropland landscapes
[F8]In most regions, average field size and woods size are about the same within
acropland landscape no matter the type of cropland(Figure6.10).
Some woods grew up from former fields, and some fields are likely to become
woods over time. The farmer has flexibility, and is also likely to change the
crops over time, as markets and owners and interests evolve. Dispersing small
woods evenly across the cropland landscape may spread predators over the area
sufficient to reduce crop pest populations, thus increasing crop production.
Aregular grid on the land is normally considered ecologically undesirable,
in part because it favors only a subset of the natural species complement for