7. Biodiversity Patterns in Relation to Climate
121
species richness occurs in the warm temperate zone where the flora
of interior climates intergrades with the rainforest flora and broadleaf
evergreens reach their northern limit of distribution. There is relatively
little published information available on community structure and its
relation to microclimate and soils in the most diverse rainforest regions
(Hawk , 1977; Waring & Major, 1964; Whittaker, 1960).
. A major exception to this general trend of species diversity declines
with latitude appears to be the bryophytes. High levels of species diversity
exist in high-latitude rainforest regions , with no obvious decline with
latitude (Jarman, Kantrilas, & Brown, 1991; Worley, 1970). It appears
that northern areas provide a greater array of recently deglaciated and
poorly drained sites, which offer minimal competition from vascular plant
species. The cool, persistently wet climate provides optimal conditions for
bryophyte growth . Bryophytes are better able to grow under extremely
low light conditions , which prevail at high latitudes (e.g., Alaback, 1982).
Much more detailed information is needed on these poorly understood
taxa, especially upper-canopy epiphytes, which are the most poorly
collected.
Landscape-Level Diversity Patterns
Biodiversity patterns at the landscape scale have important implications
to wildlife habitat and to the development of conservation strategies
in temperate rainforest regions. Just as habitat generalists appear to
dominate the high-latitude regions of temperate rainforest, habitat
generalists also appear to dominate poor growing sites in the region, as
discussed earlier. Soils differences are critical in the temperate rainforest
region, because of the limited importance of moisture stress as a physiological constraint and the strong tendency toward rapid podzolization and
paludification (Ugolini & Mann, 1979). Highly podzolized or paludified
soils in this region have thick organic layers, are highly acidified, and
although they contain significant nutrient pools , they usually have low
nutrient availability for vascular plants. Most plants depend on soil
mycorrhizae to extract nutrients from these organic soils. In peatlands,
soils also provide poor rooting substrates and quickly dry out during
rainless days during the summer. As a consequence, drought-tolerant,
thick-leafed circumpolar evergreen shrubs dominate these habitats
(Neiland, 1971).
Across a gradient of soil moisture and nutrient regime in the perhumid
and subpolar zone , a distinct pattern in biodiversity develops. The highest
diversity occurs in meadows along the ocean, lakes, and recent glacial
areas . This is also the zone most likely to be affected by human disturbance. In terms of absolute number of species, forests, peatlands, and
alpine meadows have the greatest richness. If species richness per unit
121
species richness occurs in the warm temperate zone where the flora
of interior climates intergrades with the rainforest flora and broadleaf
evergreens reach their northern limit of distribution. There is relatively
little published information available on community structure and its
relation to microclimate and soils in the most diverse rainforest regions
(Hawk , 1977; Waring & Major, 1964; Whittaker, 1960).
. A major exception to this general trend of species diversity declines
with latitude appears to be the bryophytes. High levels of species diversity
exist in high-latitude rainforest regions , with no obvious decline with
latitude (Jarman, Kantrilas, & Brown, 1991; Worley, 1970). It appears
that northern areas provide a greater array of recently deglaciated and
poorly drained sites, which offer minimal competition from vascular plant
species. The cool, persistently wet climate provides optimal conditions for
bryophyte growth . Bryophytes are better able to grow under extremely
low light conditions , which prevail at high latitudes (e.g., Alaback, 1982).
Much more detailed information is needed on these poorly understood
taxa, especially upper-canopy epiphytes, which are the most poorly
collected.
Landscape-Level Diversity Patterns
Biodiversity patterns at the landscape scale have important implications
to wildlife habitat and to the development of conservation strategies
in temperate rainforest regions. Just as habitat generalists appear to
dominate the high-latitude regions of temperate rainforest, habitat
generalists also appear to dominate poor growing sites in the region, as
discussed earlier. Soils differences are critical in the temperate rainforest
region, because of the limited importance of moisture stress as a physiological constraint and the strong tendency toward rapid podzolization and
paludification (Ugolini & Mann, 1979). Highly podzolized or paludified
soils in this region have thick organic layers, are highly acidified, and
although they contain significant nutrient pools , they usually have low
nutrient availability for vascular plants. Most plants depend on soil
mycorrhizae to extract nutrients from these organic soils. In peatlands,
soils also provide poor rooting substrates and quickly dry out during
rainless days during the summer. As a consequence, drought-tolerant,
thick-leafed circumpolar evergreen shrubs dominate these habitats
(Neiland, 1971).
Across a gradient of soil moisture and nutrient regime in the perhumid
and subpolar zone , a distinct pattern in biodiversity develops. The highest
diversity occurs in meadows along the ocean, lakes, and recent glacial
areas . This is also the zone most likely to be affected by human disturbance. In terms of absolute number of species, forests, peatlands, and
alpine meadows have the greatest richness. If species richness per unit