Influence of Climate

Large-scale patterns in terrestrial primary productivity have been explained by climatic variables. In above-ground vegetation, nutrient storage generally increases in the order: boreal < temperate < tropical forests (Table 21.2). In contrast, forest floor nutrient content and residence time increase from tropical to boreal forests, as a result of slower decomposition in the cold conditions of higher latitudes.

In subarctic woodland soils and Alaskan taiga forests, nutrient cycling rates are low because of extreme environmental conditions.121 Arctic and subarctic forest ecosystems have lower rates of nutrient turnover and primary production because of low soil temperature, a short growing season, low net AET and the occurrence of permafrost. Low temperature reduces microbial activity, litter decomposition rates, and nutrient availability and increases C accumulation in soil.

In contrast with high latitudes, conditions in a tropical forest favor microbial activity throughout the year, which generally results in faster decomposition except in situations with periodic flooding, soil dessication, and low litter quality.131 Rates of plant material decay are an order of magnitude higher in tropical soils than in subarctic woodland soils. The low storage of C and high amount of litter production in highly productive tropical forests contrasts with the high C storage and low litter production in boreal forests (Table 21.2).

TABLE 21.2 Nutrient Distribution in Different Forest Ecosystems

Vegetation (Mg ha_1)

Forest Floor (Mg ha ')

Soil (Mg ha1)

Residence Time (year)

Carbon

Boreal coniferous

78-93

37-113

41-207

800

Temperate deciduous

103-367

42-105

185-223

200

Tropical rain forest

332-359

7-72

2-188

120

Nitrogen

Boreal coniferous

0.3-0.5

0.6-1.1

0.7-2.87

200

Temperate deciduous

0.1—1.2

0.2-1.0

2.0-9.45

6

Tropical rain forest

1.0-4.0

0.03-0.05

5.0-19.2

0.6

Phosphorus

Boreal coniferous

0.033-0.060

0.075-0.15

0.04-1.06

300

Temperate deciduous

0.06-0.08

0.20-0.10

0.91-1.68

6

Tropical rain forest

0.2-0.3

0.001-0.005

0.06-7.2

0.6

Potassium

Boreal coniferous

0.15-0.35

0.3-0.75

0.07-0.8

100

Temperate deciduous

0.3-0.6

0.050-0.15

0.01-38

1

Tropical rain forest

2.0-3.5

0.020-0.040

0.05-7.1

0.2

 
Source
< Prev   CONTENTS   Source   Next >