Palynology Contemporary pollen distribution in ...

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Contemporary pollen distribution in coastal California and Oregon Linda E. Heusser

a

a

Lamont‐Doherty Geological Observatory , Columbia University , Palisades , New York , 10964 Published online: 24 Aug 2010.

To cite this article: Linda E. Heusser (1983) Contemporary pollen distribution in coastal California and Oregon, Palynology, 7:1, 19-42, DOI: 10.1080/01916122.1983.9989251 To link to this article: http://dx.doi.org/10.1080/01916122.1983.9989251

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CONTEMPORARY POLLEN DISTRIBUTION IN COASTAL CALIFORNIA AND OREGON

Downloaded by [Columbia University] at 08:01 01 January 2015

LINDA E. HEUSSER Lamont-Doherty Geological Observatory of Columbia University Palisades, New York 10964

Abstract Modern pollen data (394 samples from 98 sites) from north coastal California and eastern Oregon show differences in pollen percentages among the major vegetation regions sampled. Isopoll (contours of pollen percentages) maps for 12 pollen types show the influence of vegetational and non-vegetational factors in patterns of pollen distribution. Regional patterns correlate between Sequoia sempervirens pollen and coastal redwood forest, Quercus pollen and oak woodlands, Tsuga heterophylla and western hemlock forests, and Picea sitchensis pollen and Sitka spruce forests. Factor analysis of the pollen data synthesizes the pollen rain in the major units of the natural vegetation, and produces distinctive pollen signatures (groups of covarying pollen types) for regional vegetational units, ranging from lowlying coastal redwood forests and oak woodlands through mixed evergreen forests, montane forests and alpine environments of the Coast Range and Cascade Mountains.

INTRODUCTION

In science as in many other fields of human endeavor present conditions are used to interpret past events. In palynology, our understanding of the relation between present pollen assemblages and their environment limits our use of fossil pollen spectra to interpret past environmental changes. Data sets that relate North America pollen assemblages and vegetation are available for diverse regions of varying size (e.g., Davis, 1963; Davis and Webb, 1975; Lichti-Federovich and Ritchie, 1965; Webb and McAndrews, 1976). Modern pollen data sets quantitatively related to climatic variables are more limited in distribution and size (Short et al., 1981; Webb and Bryson, 1972). Most of these pollen data are concentrated in the eastern half of the continent. Studies of pollen rain from coastal vegetation zones of western North America (southeast Alaska, Washington, and Oregon) have been published by Palynology, 7: 19-42 (1983)

Hansen (1949), Heusser (1964; 1969; 1973; 1978a,b,c), and others (e.g., Florer, 1972). Regression equations derived from modern pollen deposition data at 180 sites from the northwest Pacific coast were used to generate estimates of precipitation and temperature (Heusser et al., 1980; Mathewes and Heusser, 1981). Modern pollen data sets from coastal California are scarce. This study summarizes results from the first stage in a long-range program to document the pollen rain of the major vegetation areas of north coastal California and coastal Oregon to aid in interpreting Quaternary and Tertiary pollen spectra in continental and marine sediments of the region. Previously, G. J. West (written commun., 1981) described pollen assemblages from selected plant communities in and around the Sacramento-San Joaquin Delta, California.

DATA SOURCES

Sample sites lie between 35°N and 45°N, and between 121° 30'W, and 114° 30'W, a region famous for its exceptional flora (Waring and Franklin, 1979; Raven and Axelrod, 1978). The distinctive mosaic vegetation of north coastal California and south coastal Oregon (Text-Figure 1), a mixture of northern temperate and southern xeric elements, contains unique, diverse plant communities. These include low-land coastal forests with Picea sitchensis, Tsuga heterophylla, and Abies grandis; mixed evergreen forests with Pseudotsuga menziesii, Quercus chrysolepis, Q. agrifolia, and Q. kelloggii; oak woodlands; closed-cone pine and cypress forests with Pinus muricata, Pinus radiata or Cupressus pygmaea; coastal redwood forests (Sequoia semper-

20

PALYNOLOGY, VOLUME 7 — 1983

94-100 92.93/ | 5 .88-91 44°-

85

Major Vegetation Areas

*«87 # 84


Sitka spruce Grand fir Western hemlock Garry oak 42° -\ Montane forests Grand fir Douglas fir Ponderosa pine 40° -J

c o

CD O

o a o o

Q_

Mixed evergreen Redwood

[g£j Oak Coast cypress and pine Chaparral

124°

122°

120°

Text-Figure 1. Major vegetation areas and site locations. Left. Vegetation zones are generalized modifications of the potential natural vegetation formations of California (Barbour and Major, 1977), and phytosociological groupings of vegetation areas of Oregon (Franklin and Dyrness, 1973). Right. Site locations of modern pollen rain samples used in this study. Site descriptions are given in Table 1.


Pollen distribution in California and Oregon

virens); and chaparral with Adenostoma, Arctostaphylos, and Ceanothus (Barbour and Major, 1977; Franklin and Dyrness, 1973). See Table 5 for a list of common names of these and other species. Montane forests which grow above low-level coniferous forests in north coastal California are recognized by the occurrence of Abies concolor. The Coast Range montane and Klamath montane forests also include A. magnified shastensis, Tsuga mertensiana, Pinus ponderosa, Pseudotsuga menziesii, and Pinus lambertiana (Sawyer and Thornburgh, 1977). Montane forests in Oregon include Abies amabilis, A. lasiocarpa, A. magnified shastensis, and Tsuga mertensiana zones. Below these subalpine forests Franklin and Dyrness (1973), distinguish the Abies grandis, Pseudotsuga menziesii, and Pinus ponderosa zones. The vegetation displays latitudinal, longitudinal, and altitudinal zonation related to the distribution of moisture and temperature (Text-Figure 2) in the summer-dry, winter-wet Mediterranean climate, a maritime climate primarily controlled by zonal circulation over the Pacific Ocean and by the northwest trending Coast Ranges. Most precipitation is the result of winter low-pressure systems approaching from the Pacific Ocean. Maritime air masses are blocked by the coastal mountains, and precipitation decreases to a minimum within the interior valleys. There is a general south-north and east-west decrease in temperature, the latter related to the moderating effect of the Pacific Ocean on coastal temperatures (Text-Figure 2). In the Pacific Coastal Forest, Tsuga heterophylla, Picea sitchensis, Abies grandis, and Sequoia sempervirens are associated with mesic, temperate environments with mild winters and warm, dryer summers, except for directly on the Pacific coast where fog is common and summers are relatively cool and moist. Diurnal and seasonal temperature fluctuations are low near the Pacific Ocean (on the order of 6-10°C) and the amplitude of mean monthly temperatures may be very close (about 0.5°C) to the amplitude over the open ocean (Barbour and Major, 1977). Quercus, chaparral, and Pinus ponderosa are restricted to warm, relatively xeric environments with large temperature ranges. In California oak woodlands, for example, mean temperature varies about 20°C between the warmest and coldest months (Wolfe, 1979). The climate regimes of the mixed evergreen forest are as diverse as the composition of the forest, ranging from dry to wet, with seasonal temperature fluctuations ranging from 6°C to 30°C. Ecological requirements of the dominant species of

21

California montane forests are poorly known, but the general altitudinal increase in precipitation and decrease in temperature are undoubtedly determining factors in the distribution of the forest communities (Sawyer and Thornburgh, 1977). On the seaward slope of the Coast Range precipitation increases at 125mm/100m, and the mean annual temperature lapse rate is about -0.46°C (Major, 1977). The cold month mean of montane forests appears to coincide with the - 2 ° isotherm (Wolfe, 1979). In Oregon, temperature is regarded as the major environmental constraint on the distribution of montane forests. The Tsuga mertensiana zone is characterized by cool, wet conditions (average annual temperature = 3.8°C; annual precipitation = 1600-2800mm) (Franklin and Dyrness, 1973). The complexity of the vegetation patterns and the diversity of the forest communities have been attributed to the varied environments (topographic, edaphic, microclimatic) of the northwest Pacific Coast. The disjunct nature of the closed-cone pine and cypress forests is related to fragmentation of formerly continuous communities during climatic fluctuations of the past 20,000 years (Raven and Axlerod, 1978), as well as to edaphic endemism (McMillan, 1956; Westman, 1975). Continued biotic and abiotic disturbances, such as fire, landslides, floods, and earthquakes, also influence the distribution of vegetation. Periodic fires and flooding are significant factors in the perpetuation of redwood forests, and the chaparral of California is a classic example of adaptation to fire. METHODS

Site Selection

Sample sites were selected with the intent of determining the nature of the pollen rain of the major vegetational units of northwest California and adjacent parts of Oregon (Table 1). For broad-scale pollen rain studies, lakes are usually regarded as prime sampling sites. Pollen from lake sediments yields regional data, as compared with the more localized data derived from bogs, moss-polsters, or duff samples. In areas disturbed by logging or grazing, subsurface lacustrine sediments provide the opportunity to obtain pollen data from presettlement vegetation, vegetation undisturbed by logging or grazing (Berglund, 1979; Webb et al., 1978). Lakes are not abundant in north coastal California. Six Rivers National Forest, for example, contains an average of one lake per 18,000 hectares (Marcot,

22


TEMPERATURE January, mean minimum July, mean maximum (degrees C) (degrees C)

PRECIPITATION mean annual (mm)


22°-

441000

42 -

1000 40 -

2000'

1000-

26'

1500* 38 -

5.0° •

124

123

Text-Figure 2. Precipitation and temperatures in coastal California and Oregon. (Adapted from Franklin and Dyrness, 1973; and Sternes, 1974.-

23


TABLE 1 BRIEF DESCRIPTION OF SAMPLE SITES


SAMPLE

SITE NAME

ELEVATION (M)

VEGETATION ZONE

SAMPLE TYPE

1.

McCrary's Marsh

100

Coast pine-cypress

duff

2.

Cowell State Park

120

Redwood

duff

3.

10km N Cowell St. Park

120

Mixed hardwood/oak

duff

4.

Armstrong Redwoods

150

Redwood

moss

5.

Kruse Rhododendron Reserve

200

Redwood/Douglas fir + tan oak

duff

6.

Ridge Skm S Gualala

180

Redwood/Douglas fir + pine

duff

7.

Slope Skm S Gualala

160

Redwood/Douglas fir + oak

duff

8.

Maillard Redwoods

280

Redwood, + tan oak

moss

9.

20km S Ukiah

640

Oak/mixed hardwood + Rhus, Castanopsis, Q. lobata, Arbutus

duff

10.

E side of summit SW Ukiah on Rt. 253

500

Oak/mixed hardwood + Q. chrysolepis, Q. lobata, Rhus, Lithocarpus

duff

11.

Mendocino Nat. Forest 20km N Upper Lake

400

Blue oak/digger pine mixed evergreen + Q. lobata P. ponderosa

duff

12.

Mendocino Nat. Forest 15km N Upper Lake

400

Oak (blue oak/digger pine), Rhus

moss

13.

Clear Lake

400

Oak

moss

14.

Walker Ridge, E Clear Lake

600

Blue oak/digger pine

duff

15.

Walker Ridge, E Clear Lake

300

Oak + Rhus, Pinus

duff

16.

Walker Ridge, 25km W Williams

150

Oak + Arctostaphylos

moss

17.

Jackson State Forest, 25km W Williams

600

Redwood/mixed evergreen Q. lobata, Rhus, P. menziesii

18.

Jackson State Forest

100

Redwood + Douglas fir Lithocarpus, Rhus

19.

Jackson State Forest

200

Redwood + Abies grandis, Rhododendron

20.

near Caspar

100

Coast pine & cypress P. muricata, P. contorta, Cupressus pygmaea

21.

Keller Lake, Mendocino National Forest

1800

Montane + A. concolor, P. lambertiana

moss

moss

duff


24

Butte Creek, Mendocino National Forest

1354

23.

Snow Basin, Mendocino National Forest

2000

24.

near Black Butte, Mendocino Nat. Forest

2000

near Black Butte,

1900

22.

25.

Black Butte Transect


Big Spur, Mendocino National Forest

Montane + A. concolor, A. magnified, Libocedrus

duff

Montane + A.

duff

concolor,

Montane + P. jeffreyi

duff

Arctostaphylos 1700

Montane + P. jeffreyi, A. concolor, Pseudotsuga

duff

1700

Montane + Pseudotsuga P' jeffreyi, P. lambertiana

duff

Mendocino Nat. Forest 27.

duff

Libocedrus, Pinus sp.

Mendocino Nat. Forest 26.

Montane + P. jeffreyi, Arbutus, Quercus sp.

A. concolor,

Libocedrus

28.

Black Butte Transect Mendocino Nat. Forest

1200

Mixed evergreen + Pseudotsuga, P. jeffreyi, Q. kelloggii

duff

29.


1100

Mixed evergreen + P. jeffreyi, P. lambertiana, Q. kelloggii, Castanopsis

duff

30.

Black Butte Transect

Chaparral +

duff

900

Arctostaphylos,

Ceanothus

Mendocino Nat. Forest

duff


600


500

33.

Lowery Lake

900

Mixed evergreen + Quercus, Rhus, Corylus

lake

34.

Dry Lake

1100

Mixed evergreen + Pseudotsuga, Quercus, Libocedrus

lake

35.

Rice Lake

1200

Mixed evergreen + Quercus, Pseudotsuga

lake

36.

Rice Lake

1200

Mixed evergreen + Quercus, Pseudotsuga

lake

37.

Rice Lake

1200

Mixed evergreen + Abies, Quercus, Pseudotsuga

lake

38.

Rice Lake

1200

Mixed evergreen + Quercus

lake

39.

Lost Lake

1100

Mixed evergreen + Pseudotsuga

lake

40.

Lake Mountain

1200

Oak/mixed evergreen + Pinus, Pseudotsuga

moss

41.

Humboldt State Forest

140

Redwood

moss

42.


140

Redwood + Corylus

43.


50

31.

32.

Chaparral + P. sabiniana duff Blue oak/digger pine

Redwood

Lithocarpus,

moss

moss

25



44.

Grizzly Bear Redwoods State Forest

150

Redwood + Acer Lithocarpus, Corylus

45.

Schelling's Bog

900

Mixed evergreen + Q. kelloggi, Pseudotsuga, Alnus, Lithocarpus

moss

46.

Snow Mountain

300

Redwood (60yr stand) Pseudotsuga

moss

47.

Greater Twin Pond Six Rivers Nat. Forest

800

Mixed evergreen + Q. chrysolepsis, Pseudotsuga, Chrysolepsis

lake

48.

Lesser Twin Pond Six Rivers Nat. Forest

800

Mixed evergreen + Pseudotsuga

lake

49.

Big Lake Six Rivers Nat. Forest

900

Mixed evergreen

lake

Pseudotsuga

50.

Lake Anna Trinity Alps

2200

Alpine + Carex Gramineae, Juncus

duff

51.

Trinity Alps

2200

Alpine meadow + Aster Lupinus, Polygonum

duff

52.

Gibson Peak

2500

Alpine

duff

2200

Upper montane T. mertensiana

duff

Trinity Alps 53.


54.

Gibson Peak Trinity Alps

2500

Alpine

duff

55.

Lake Anna

2300

Alpine Gramineae, Cyperaceae

duff

Trinity Alps 56.


2300

Alpine

duff

57.


2300

Upper montane + T. mertensiana, Lupinus

duff

58.


2300

Upper montane +

duff

A. magnifica, Lupinus, Polygonum

59.


2300

Upper montane + T. mertensiana

duff

60.

Waterdog Lake Six Rivers Nat. Forest

1800

Montane + A. magnifica A. concolor, Libocedrus

lake

61.

Waterdog Lake Six Rivers Nat. Forest

1800

Montane

lake

62.

Onion Lake

1400

Mixed evergreen A. concolor, P. Jeffreyi, P. contorta, Pseudotsuga

lake

Sitka spruce-grand fir

moss

Redwood + Lithocarpus, T. heterophylla, Pseudotsuga, Alnus

moss

Six Rivers Nat. Forest

63.

Big Lagoon Bog

64.

Lady Bird Johnson Grove Redwood Nat. Park

10 430


26


65.

Prairie Creek Redwoods Redwood Nat. Park

100

Redwood + T. heterophylla, Acer circinnatum

66.

Prairie Creek Redwoods Redwood Nat. Park

60

Redwood/Sitka spruce + T. heterophylla, P. menziesii

moss

67.

Jedidiah Smith Redwoods

90

Redwood + T. heterophylla, Lithocarpus

moss

68.

Jedidiah Smith Redwoods

190

Redwood + T. heterophylla, Rhododendron

69.

Young's Meadow Siskyou Mts.

1300

Montane + A. concolor Libocedrus, Pinus, Quercus, Pseudotsuga, Alnus

70.

Whiskey Lake Siskyou Mts.

1500

Montane + P. ponderosa P. lambertiana, Libocedrus, A. concolor, P. breweriana

71.

Whiskey Lake Siskyou Mts.

1500

Montane

lake

72.

Preston Peak Siskyou Mts.

1400

Montane + P. breweriana, A. concolor, Pinus

moss

73.

Preston Peak Siskyou Mts.

1300

Montane (serpentine) P. attenuata, P. monticola, Q. vaccinifolia

duff

74.

Chetko River

150

Redwood + P. menziesii Lithocarpus, Alnus, Acer

moss

75.

Lake of the Woods Winema Nat. Forest

1500

Montane + A. concolor

lake

76.

J Spur Pond Winema Nat. Forest

1700

Montane + A. concolor T. mertensiana, Arctostaphylos

lake

77.

Sky Lakes Boundary Winema Nat. Forest

1800

Montane + A. concolor T. mertensiana

moss

78.

Sky Lakes Boundary Winema Nat. Forest

1800

Montane + A. concolor T. mertensiana

79.

Penn Prairie Winema Nat. Forest

1500

Montane + A. magnifica P. ponderosa, Picea engelmannii

80.

Penn Prairie Winema Nat. Forest

1500

Montane

81.

Nannee Creek Winema Nat. Forest

1800

Montane + T. mertensiana, P. contorta, P. monticola

moss

82.

F.S. Rd 3414 Winema Nat. Forest

1900

Montane + A. magnifica T. mertensiana

moss

83.

Crater Lake Nat. Pk.

2000

Montane + A. magnifica T. mertensiana

moss

84.

Gold Lake Natural Research Area

1500

Montane + T. mertensiana, P. contorta, P. menziesii

moss

85.

Andrews Research Forest Stand 2

500

Western hemlock + P. menziesii, Rhododendron

moss

duff

moss



27

86.


490

Western hemlock + Rhododendron, P. menziesii

87.


510

Western hemlock + P. menziesii

88.


1400

Oregon montane + A. amabilis, A. procera, T. heterophylla, P. menziesii

moss

89.


1000

Montane + T. heterophylla, T. plicata, A. amabilis, P. menziesii

moss

90.


1500

Montane + A. amabilis, A. procera, P. menziesii

moss

91.


1600

Montane + A. amabilis, A. procera, T. mertensiana

moss

92.

Deschutes Nat. Forest*

1200

Oregon montane + A. grandis, P. lambertiana

duff

93.

Lost Lake, Deschutes Nat. Forest*

1350

Oregon montane + A. grandis, P. menziesii

duff

94.


1300

Oregon montane + A. grandis, P. menziesii

duff

95.


1000

Oregon montane

duff

96.

Sisters, Deschutes Nat. Forest*

1000

P. ponderosa, P. contorta

duff

97.


1000

P. ponderosa zone

duff

98.

Cascade Head Experimental Forest

Sitka spruce zone + T. heterophylla

moss

300

•Indicates data previously published (Heusser, 1978c).

1978). Slumpponds are more numerous than lakes but are generally small, young, and associated with early successional vegetation. Due to the relative absence of lakes and the vast area of land disturbed by logging, grazing, and farming. I sampled pollen from sites in relatively mature communities — preferably in natural research areas, wilderness areas, and state and national forests. To broaden the data base in Oregon, data from six sites previously published by Heusser (1978c) are included. (Brief site descriptions are given in Table 1.) Pollen sampling procedures varied with the nature of the material present. Short cores were taken from lakes and/or ponds with a modified Livingston or a Davis sampler. Bogs were cored either with a Davis or Hiller sampler, or by sampling a small pit dug in the upper half meter of peat. These short cores and

sections were sampled at 5 cm intervals. From sites which lacked lakes, ponds, or bogs, surface samples of duff or humus and moss-polsters were collected in multiple sets of five (Adam and Mehringer, 1975). About 84 percent of the samples were moss or duff. Vegetation analyses and/or plant lists were made at all pollen collecting sites, except in Andrews Research Forest where pollen was collected from reference stands for which detailed vegetation data was published (Hawks et al., 1978). Sample preparation

Sample preparation of measured amounts of sediments (an average of 5 cc lake or bog sediment, and 100 cc of surface duff or moss) included use of microscreens and standard chemical techniques such


28


as KOH, HF, and acetolysis. The final residue was mounted in glycerin gelatin. Percentages of six samples from Deschutes National Forest, Oregon, are based on sums of at least 500 grains (Heusser, 1978c). For all other samples, the pollen sum is based on 300 pollen grains, excluding obligate aquatics. Multiple surface samples (duff and moss polsters) were processed and counted individually; therefore, the pollen sum from these sites is the average of 1500 pollen grains. All samples from short cores were processed and analyzed, and the youngest horizon dominated by pollen from undisturbed, upland vegetation is included in this data set.

RESULTS

The dominant pollen types identified are placed in fourteen categories: (1) Pinus, which includes about 14 species of pine; (2) Picea, consisting of P. sitchensis on the coast and P. engelmanii and P. breweriana in montane forests; (3) Tsuga heterophylla; (4) Tsuga mertensiana; (5) Pseudotsuga menziesii; (6) Abies, consisting of five species; (7) Sequoia sempervirens; (8) Quercus, which represents about 16 species in the region sampled; (9) Lithocarpus densiflora, which may also include the relatively indistinguishable, small pollen grains of Castanopsis chrysophylla; (10) Alnus, consisting of five species; (11) Cupressus type, including the families Taxodiaceae, Cupressaceae, and Taxaceae; (12) the Rosaceae, Rhamnaceae, and Anacardiaceae families, including

Adenostoma,

Ceanothus, and Rhus; (13)

Gramineae; and (14) Compositae. Table 2 summarizes the general statistics for the raw data (the data are available from the author on request). Pinus has the highest average value at 32%, followed by Sequoia sempervirens, and Quercus, with average values of 14% and 13%, respectively. Tsuga heterophylla, Tsuga mertensiana, and the Rosaceae-Rhamnaceae-Anacardiaceae group each have a maximum value of more than 50%; and Picea and Pseudotsuga menziesii, a maximum value of more than 40%. Percentage data of selected pollen types are presented visually in two ways: (1) contour maps of pollen percentages show the geographic distribution of pollen isopolls (Text-Figures 3-6); and (2) composite transects across California and Oregon show variations with topographic and geographic change (Text-Figures 7 and 8). Isopoll maps were not produced for vegetation groups, such as the Gramineae and Compositae, in which regional patterns were not

apparent. Concentration or influx data are not presented, because the large differences between sediment types sampled in this study make the use of statistics based on sedimentation rates questionable. Pinus (Text-Figure 3a). Pinus is the most widely distributed pollen group, and forms at least 10% of the pollen sum in 80% of the samples. Large amounts of Pinus pollen are found in the high elevation interior forests: the P. ponderosa zone of the east side of the Cascade Range (67-70%); the Abies concolor and Tsuga mertensiana zones of the High Cascades (58-82%); Klamath montane forest with Pinus ponderosa (66-71%); the Pinus albicaulis zone of the Trinity Alps (52-77%); the Abies concolor zone and Pinus jeffreyi woodlands of the southern part of the Coast Range (up to 83%), the disjunct closed-cone pine and cypress forests along the Pacific Coast (>50%). Minimum amounts of Pinus (0-10%) are recorded from sites in the coastal conifer forests of Picea sitchensis, Abies grandis, Tsuga heterophylla, and Sequoia sempervirens, and in mixed hardwood forests. Quercus (Text-Figure 3b). Large amounts of Quercus pollen are restricted to samples taken in the lee of the Coast Range south of 41 °N. Peak values occur in blue oak-digger pine forests (up to 82%), mixed hardwood forests, and in the southern part of the mixed evergreen forests (55%-60%). Quercus pollen is essentially absent from needle-leaved evergreen forest formations, although one sample from Maillard Redwoods, a small (98 ha) stand surrounded by mixed hardwoods, contains 18% Quercus pollen. Sequoia sempervirens (Text-Figure 3c). Pollen identified as S. sempervirens is narrowly confined to samples from coastal redwood forests in which it completely dominates the pollen rain (ranging from 40-90% of the total pollen sum). Small amounts of S. sempervirens pollen are recorded from two coastal sites adjacent to redwood forests: from one open site occupied by Pinus radiata (Text-Figure 1, site 1, in which Sequoia sempervirens pollen = 6%), and from Big Lagoon Bog which is immediately surrounded by Picea sitchensis (Text-Figure 1, site 63, in which Sequoia sempervirens pollen = 2%). Otherwise, S. sempervirens pollen is not present. Picea (Text-Figure 4a). Maximum values of Picea pollen (42-63%) are in samples from coastal grand fir-Sitka spruce forests. A few grains of Picea (P. sitchensis) are found in spectra from the northernmost redwood forests close to the ocean. Small quantities (io° | u

Q

ii i ii ^

-

^40% 124*

rM

I

122°

120°

n ="50 124° 124"

122°

120°

124°

122°

Text-Figure 3. Isopoll maps of Pinus, Quercus, and Sequoia sempervirens.

tion, i.e., sites in Klamath montane forests with P. breweriana, and sites in the P. engelmannii zone in the eastern Cascades. Picea pollen was not identified south of 41 °N. Tsuga heterophylla (Text-Figure 4b). T. heterophylla pollen is significant only in samples from the northern part of this study area, and appears in quantity only in samples from western hemlock associations (Text-Figure 1). Highest percentages are recorded from sites in the T. heterophylla and Abies amabilis zones on the west slope of the Cascades (Site 23 = 53%). The maximum amount comes from a stand dominated by mature, old-growth T. heterophylla and Pseudotsuga menziesii with the understory trees dominated by Tsuga (Hawks et al., 1978). In the sample from the coastal Sitka spruce and western hemlock zones of Oregon, T. heterophylla pollen accounts for 40% of the pollen sum.

Trace amounts of T. heterophylla pollen are contained in samples from coastal redwood (sample 2, 6, 19, 65-67) and mixed evergreen forests of California (sample 45 and 46), and in samples from montane forests of Oregon (sample 82-84, 92-96). Alnus (Text-Figure 4c). Alnus pollen (Alnus incana, A. rhombifolia, A. rubra, A. sinuata, A. tenuifolia) is widespread; from northern Oregon through central California, and from forests at sea level on the edge of the Pacific Ocean to alpine meadows in the Trinity Mountains, California. Only four samples have no Alnus, three from the chaparral and one from a site in mature coastal redwoods. Highest values range from 10-25% in this data set which consists of samples containing less than 50% Alnus pollen. These high alder percentages occur in relatively young stands. For example, in a cutover, 60-year stand of Sequoia sempervirens on Snow

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