Appendix Table 5AL continued

Perturbations

Unmanaged (Arable Tilled)1

Invasive Species: Root Parasites2

Climate Change: Drought

Land-Use Change: To Forest

Goods

Service

Net

Net

Net

and Services

Rank

Biotic

Abiotic

Vulnerability Impact

Vulnerability Impact

Vulnerability Impact

Nutrient cycling

3

** microbial activities including mycorrhizae micro-food web control

* climate, soil properties

P-cycling

0-1 [dependent - / + on whether biotic factors, e.g., microbial activities, micro-food web slowed]

2 [biological — activity decreased21; possible further reduction in NPP through salinization]

0 [change to 0 nutrient conserving mechanisms]

Biodiversity

-3

* roots, biogenic structures

** climate, soil resource quality microhabitats

0-1 [dependent - / + on impact on rhizosphere biota]

0 [dependent on -22 abiotic drivers, resource quality, microhabitats, roots]

0 [dependent on + forest type, litter quality and quantity, increased biotic processes and invertebrate engineers]

1 Other arable systems—for example, no-till, ridge-till—are not considered, but subject to similar vulnerability; magnitude may vary

2 Considers general case of root parasite invasion, for example, root knot nematode {Meloidogyne spp.)«

3 Drought is defined as 20 percent decrease in summer precipitation, based on an average for a 10-year period. This is in contrast to episodic drought, for example, in semi-dry African savanna.

4 Drought can have a significant economic impact on agriculture. For example, the cumulative damage from the four drought years (1996, 1998, 1999, and 2000) to the agricultural industry in Texas is US$5.515 billion since 1996. (Myers 2002; see also http://www.txwin.net/dpc/dpc%20biennial%20report.pdf)

^ Plant varieties are bred for resistance to drought, but success is variable. See (http://www.hort.purdue.edu/newcrop/proceedingsl999/v4-060.html).

7 Bingham 2001.

8 Refers to runoff to streams.

9 There are many levels of drought and types of managed arable soils, thus vulnerability and net impact is highly context dependent. For example, in the prairies under drought conditions, farmers allow fields to go fallow to store water. However, soil is left bare, and if drought continues, soil erosion by wind and the loose stability of the soil surface are negative consequences.

10 Response by farmers to drought can include switching the crop planted.

11 Refers to biological control of diseases and pests of crop plants.

12 Refers to genetically modified crops.

13 Can have change in types of pests under extensive drought. For example, grasshopper and locust populations can be extensive, some nematodes can thrive, but generally caterpillar populations are reduced. Furthermore, there may be a possible exacerbation of plant-pest interaction with drought: for example, plants previously weakened by drought may be more susceptible to pests.

14 Service of recreational land use is very culturally dependent and dependent on type of forest planted: for example, landscape with a monoculture of tree species may not be an improvement on a landscape of crop monocultures.

^ There is a gradient in microbial activity, decomposition, and organic matter buildup along a drought gradient. Whether a drought starts in a moist situation or in a dry situation will influence services such as carbon sequestration (www.ornl.gov/carbon_sequestration/).

16 Service of carbon sequestration is very dependent on forest type; for example, although pine forests have the same aboveground productivity as deciduous forests, they have lower carbon sequestration.

17 Habitat provision for high visibility and/or threatened species.

18 Habitat provisioning may not increase significantly if land-use change is from annual monoculture to perennial monoculture.

19 Effects of drought on soil formation and structure are very soil texture dependent. For example, drought has a major effect in sandy soils, but effects are less dramatic in clay soils.

20 Service of soil formation is very dependent on forest type: for example, soil formation under pine can lead to development of podsol.

21 Buljovic & Engels 2001.

22 With severe drought, earthworms will be lost from soil, but numbers of termites and ants may increase. In general, biodiversity in cultivated soil is only marginally affected by drought, as most species under arable conditions are resistant and resilient.

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