Evergreen Coniferous Forests of the Pacific Northwest

Reprint Series 29 June 1979, Volume 204, pp. 1380-1386 IE

R. H. Waring and J. F. Franklin

Copyright © 1979 by the American Association for the Advancement of Science maintaining the conifer gene pool in the Pacific Northwest (2). Environmental features have also been proposed as major factors in conifer dominance. Chaney et al. (3) suggest Evergreen Coniferous Forests that arid periods caused hardwood losses. Daubenmire (4) identifies cool sum- of the Pacific Northwest mers, coupled with the inability of deciduous hardwoods to utilize frequent warm days in spring and fall. Regal (5) pro- Massive long-lived conifers dominating these forests posed that gymnosperms survive as are adapted to a winter-wet, summer-dry environment. dominants only in environments that are, in some way, harsh or rigorous; however, he concedes uncertainty as to how R. H. Waring and J. F. Franklin the coniferous forests of the Pacific Northwest conform to this hypothesis. The steep mountainous topography of coastal northwestern America might sug- Along the Pacific Coast of north- ocarpus), chinquapin (Castanopsis), gest youthful, thin soils as a factor, but western America, the dominant vegeta- maple (Acer), oak (Quercus), and alder regional soils are, in fact, at least as deep tion consists of dense forests of ever- (Alms)-which can achieve some local and as fertile as those of other temperate green conifers, which clothe the land- importance. However, conifer-hard- forest regions. Hence, while harsh cli- scapes from northern California to the wood roles in the Pacific Northwest mates, thin soils, and periodic wildfires panhandle of Alaska (Fig. 1). The forests largely are the reverse of those in eastern are probably factors in the development are unrivaled both in the size and longev- North America. For example, north- of the conifer forests of intermountain ity of individual trees and in the accumu- western hardwoods often play pioneer western North America in the rain shad- ow of the coastal mountains, these factors fail to explain conifer dominance in Summary. The massive, evergreen coniferous forests in the Pacific Northwest are the coastal region. unique among temperate forest regions of the world. The region’s forests escaped Knowledge of the structure and func- decimation during Pleistocene glaciation; they are now dominated by a few broadly tion of the northwestern coniferous for- distributed and well-adapted conifers that grow to large size and great age. Large est has been greatly extended by studies trees with evergreen needle- or scale-like leaves have distinct advantages under the conducted as part of the International Bi- current climatic regime. Photosynthesis and nutrient uptake and storage are possible ological Program. In this article, we ap- during the relatively warm, wet fall and winter months. High evaporative demand dur- ply these data to examine the relative ing the warm, dry summer reduces photosynthesis. Deciduous hardwoods are re- merit of evergreen conifer and deciduous peatedly at a disadvantage in competing with conifers in the regional climate. Their hardwood habitats under existing climat- photosynthesis is predominantly limited to the growing season when evaporative de- ic conditions. Because regional climatic mand is high and water is often limiting. Most nutrients needed are also less available regimes have been similar for several at this time. The large size attained by conifers provides a buffer against environmen- epochs, we propose that the advantages tal stress (especially for nutrients and moisture). The long duration between destruc- enjoyed by evergreen conifers in such tive fires and storms permits conifers to outgrow hardwoods with more limited stature environments have been key factors in and life spans. competitively eliminating much of the original hardwood flora. In addition, we document the large biomass and produc- lations of biomass of individual stands. roles [such as red alder (Alnus rubra)] or tivity values of the forests and suggest Furthermore, the massive evergreen occupy habitats whose environmental how massiveness is advantageous. canopies of these forests contrast with features significantly differ from the re- the deciduous hardwood or mixed hard- gional norm [for example, Oregon white wood-conifer stands typical of the North oak (Quercus garryana) on droughty Paleobotanical Record Temperate Zone. habitats]. The degree of conifer dominance is im- What factors favored the evolution of During the early and middle Miocene pressive. In the Cascade Mountains and these massive, conifer-dominated forests 18 to 28 million years ago, more than 40 Coast Range of the Pacific Northwest, in contrast to the deciduous hardwood genera of woody dicotyledons extended the biomass of conifers is 1000 times that forests in other temperate regions? Sci- from Oregon north through Alaska and of the hardwoods. Of the 25 coniferous entists since Von Humboldt in the mid- Siberia to Japan (6, 7). A pure coniferous species in these forests many represent 1800’s have speculated on this topic. Al- forest existed only in the uplands, above the largest, and often the longest-lived, though some have suggested that cold 500 meters in Japan and above 700 me- of their genera (Table 1). Still represent- temperatures during glacial epochs elimi- ters in Oregon. Thus, the areas domi- ed are arboreal evergreen and deciduous nated many hardwood genera (1), this is nated by conifers-mostly fir, spruce, taxa-such as species of tan oak (Lith- clearly not the case. Most hardwood ex- and hemlock-were highly disjunct dur- tinction actually occurred during the ing the early and middle Miocene in Dr. Waring is professor of forest ecology in the Pliocene, much earlier than the Pleisto- School of Forestry, Oregon State University, Cor- northwestern North America and north- vallis 97331. Dr. Franklin is chief plant ecologist at cene when relatively mild environments eastern Asia (7, 8). the Forestry Sciences Laboratory, U.S. Department of Agriculture Forest Service, Corvallis, Oregon and good north-south routes for propaga- By the late Miocene 12 to 18 million 9733 1. tion may have been major factors in years ago, coniferous forests began to 1380 0036-8075/79/0629-1380$01.75/0 Copyright © 1979 AAAS SCIENCE, VOL. 204, 29 JUNE 1979 occupy large areas in the uplands. Floras today. Major components of the original (Fig. 2A). In other temperate forest re- at intermediate elevations throughout widespread deciduous hardwood forest gions, summers are typically hotter and the western United States contained still persist in Japan, China, Europe, and more humid, and the winters are much moderate to large amounts of fir, spruce, parts of the eastern United States. Their colder. During the growing season in the and hemlock (6). For the first time, a extinction from the Pacific Northwest Pacific Northwest, night temperatures coniferous forest extended continuously probably was related to changes in cli- usually remain below 120C, often drop- from the uplands of Oregon northward mate that favor the conifers present ping to 10°C near the coast or along cold through British Columbia and into today. air drainages in the mountain valleys. Alaska (7). Dew may form on cool nights, but clear During the late Miocene or early Plio- warm days cause the water to evaporate cene some 10 to 12 million years ago, a Present Climate quickly, resulting in evaporative de- rich boreal forest of spruce, pine, and mands much higher than those experi- hemlock-with smaller quantities of Climatically the region experiences enced at similar temperatures in other larch, fir, beech, oak, and elm-was es- wet mild winters and warm dry sum- temperate forest regions. Past regional tablished in northeastern Siberia (9). A mers. The dormant season, when shoot comparisons have underestimated evap- similar trend was occurring in Alaska. growth is inactive, is characterized by orative differences by using a simple However, in Oregon, the early Pliocene heavy precipitation with daytime tem- estimate of potential evaporation (11) floras west of the Cascade Mountains peratures usually above freezing. Away that does not consider differences in hu- contained an impoverished deciduous from the coast, the growing season is midity (12). This method for assessing flora with hickory, elm, and sycamore characterized by warm temperatures, evaporation in the Pacific Northwest still represented (3). Thus, more hard- clear days, and little precipitation. Water leads to values 25 to 60 percent too low wood species became extinct during the storage in snowpack, soils, and vegeta- for July and August. late Pliocene than during any period tion-as well as pulses of fog, clouds, or Another significant climatic difference since. cool maritime air which reduce evapo- from other temperate forest regions may By the early Pleistocene, some 1.5 mil- transpiration-obviously are more im- be the absence of typhoons and hurri- lion years ago, and before major glacia- portant during a summer drought. canes that frequent eastern Asia and tion, the flora of the Pacific Northwest The climate varies considerably as a eastern North America. Frequent de- was essentially established as it appears consequence of the interplay between structive storms presumably would in- maritime and continental air masses and hibit evolution toward massiveness, re- mountain ranges. Along the coast where gardless of other potential benefits (13, the maritime influence is strongest, mild 14). temperatures are associated with pro- longed cloudiness and narrow diurnal and seasonal fluctuations (60 to IO0C) in temperature. Winters are extremely wet, and freezing temperatures are rare. Sum- mers are cool and relatively dry, but extended periods of cloudiness and fog often greatly reduce evaporation. Valleys in the lee of the Coast Range are drier, subject to greater temperature extremes and evaporative demand as are the lower elevation sites in the Cascades. On the western slopes of the Cascade Moun- tains, precipitation increases, and temperature regimes moderate until subalpine environments, with their cooler temperatures and deep winter snow-

packs, are encountered. This pattern is 01 similar throughout the region although areas to the south are warmer and drier than those to the north. Immediately to 0 """"'~' J FMAMJJASOND the east of the mountain crest begins an- Month other region with a more arid and conti- Fig. 2. Monthly distribution of precipitation nental climate, as well as sparser and for selected stations: (A) In the Pacific North- shorter forests (10). west: Eureka, California, 410N, 1240W, 101 The climate contrasts strikingly with cm annual precipitation; Seattle, Washington, that of other temperate forest regions. 480N, 1220W, 85 cm annual precipitation; Major forest regions in the eastern Portland, Oregon, 450N, 1230W, 106 cm annual precipitation; Roseburg, Oregon, 430N, United States, eastern Asia. and Europe 1230W, 82 cm annual precipitation. (B) In oth- have more evenly distributed precipi- er north temperate climates: Eskdalemuir, Fig. 1. The Pacific Northwest region, domi- tation throughout the year with no reduc- Scotland, 550N, 30W, 159 cm annual pre- 0 nated by massive coniferous forests, extends tion during the growing season (Fig. 2B). ciptation; New Haven, Connecticut, 41 N. from northwestern California to the south- 300W, 104 cm annual precipitation; Sapporo, Throughout most of the Pacific North- 0 0 western coast of Alaska. The crest of the Japan, 43 N, 141 E, 104 cm annual precipi- Coast Range or Cascade Mountains forms the west, less than 10 percent of the total tation; Frankfurt, Germany, 500N, 80E, 61 cm eastern boundary of the region. precipitation falls during the summer annual precipitation. [Adapted from (63)]. 29 JUNE 1979 1381 Forest Structure rather than occur as isolated individuals. stem biomass of 3200 ton/ha reported for Fujimori's (15) nondestructive analysis three redwood stands on alluvial flats The huge accumulations of biomass of a coast redwood forest in Humboldt (17). which typify the forests of the Pacific State Park in California revealed a basal Analyses of superlative stands are not Northwest amaze everyone encounter- area of 343 square meters per hectare confined to redwood nor to very old for- ing them. In natural forests, numerous and a stem biomass of 3461 tons per hec- ests (Table 2). Maximum values for individual trees 100 to 200 centimeters in tare. Addition of branch, leaf, and partic- Douglas fir and noble fir forests appear to diameter at breast height (1.37 m) extend ularly root biomass would increase the be about half those for redwood, but their crowns 60 to 80 m into the air. Such estimate of standing crop to well in ex- they still greatly exceed accepted norms stands are rivaled only by a few of the cess of 4000 ton/ha-very close to Fuji- for other temperate forests (18). eucalyptus forests of Australia. Biomass mori’s (16) earlier estimate of 4525 ton/ Continued data collection increasingly accumulates to record levels because ha for a coast redwood grove. These fig- shows that large biomass accumulations these large, long-lived species dominate ures are larger but consistent with the are the rule rather than the exception. Aboveground biomass in 11 forests dominated by Douglas fir, western hem- Table 1. Typical and maximum ages and dimensions attained by selected species of forest trees on better sites in the Pacific Northwest. Typical values mainly from Franklin and Dyrness (10); lock, and noble fir situated along mois- maximum diameters from American Forestry Association (61); maximum ages from Fowells ture and temperature gradients in the Or- (62); or our own observations. egon Cascade Range (19) averaged 1070 Typical Maximum ton/ha and ranged from 734 to 1773 ton/ ha (20).The most detailed analysis avail- Species Age Diameter Height Age Diameter able is for a 450-year-old Douglas fir for- (years) (cm) (m) (years) (cm) est on a 10-ha watershed in the Cascade Silver fir >400 90 to 110 44 to 55 590 2 06 Mountains of western Oregon (21) (Table (Abies amabilis) 3). The amount of biomass in living trees Noble fir >400 100 to 150 45 to 70 >500 270 is quite remarkable given the apparent (Abies procera) decadence of the stand as evidenced by Port-Orford-cedar >500 120 to 180 60 359 (Chamaecyparis lawsoniana) the large weight of dead trees and logs. Alaska- yellow-cedar > 1000 100 to 150 30 to 40 3500 297 These biomass values are in sharp (Chamaecyparis nootkatenis) contrast to those in other forest re- Western larch >700 140 50 915 233 gions-boreal, temperate, or tropical. (Larix occidentalis) Incense-cedar >500 90 to 120 45 > 542 368 Art and Marks (22) tabulated maximum (Libocedrus decurrens) aboveground biomass values of 422,575, Engelman spruce >400 > 100 45 to 50 >500 23 1 and 415 ton/ha for temperate deciduous, (Picea engelmannii) temperate evergreen hardwood, and Sitka spruce >500 180 to 230 70 to 75 >750 525 (Picea sitchensis) tropical forests. Biomass of cool temper- Sugar pine >400 100 to 125 45 to 55 306 ate hemlock forests in Japan and the (Pinus lambertiania) northeastern United States reportedly Western white pine >400 110 60 615 197 exceeds 600 ton/ha, a value still below (Pinus monticola) biomass accumulations in the Pacific Ponderosa pine >600 75 to 125 30 to 50 726 267 (Pinus ponderosa) Northwest. Douglas fir >750 150 to 220 70 to 80 1200 434 One biomass component worthy of (Pseudotsuga menziesii) special note is foliage. Leaf biomass and Coast redwood > 1250 150 to 380 75 to 100 2200 50 1 surface area in the Pacific Northwest de- (Sequoia sempervirens) Western redcedar > 1000 150 to 300 >60 > 1200 63 1 velop slowly, taking 50 years or more to (Thuja plicata) reach a maximum (23); in the eastern Westem hemlock >400 90 to 120 50 to 65 >500 260 United States, development occasionally ( Tsug a h et erophylla) peaks in as little as 4 years after germina- Mountain hemlock >400 75 to 100 >35 >800 22 1 tion (24). Projected canopy surface areas (Tsuga mertensiana) in the Pacific Northwest usually reach a

Table 2. Biomass and productivity values for some young- and old-growth coniferous forest stands in the Pacific Northwest. Net Basal Stem produc- Dominant species, area volume Biomass tivity age, and location Source (m2/ha) (m3/ha) (ton/ha) (ton/ha/ per year) Western hemlock and Sitka spruce; 110 years; Oregon Coast (18) 98 1,987 87 1 10.3 Douglas fir and western hemlock; 100 years; Oregon Cascades (18) 63 1,406 66 1 12.7 Noble fir and Douglas fir; 115 years; Oregon Cascades (18) 98 1,989 880 13.0 Coast redwood; > 1000 years; northern California Coast (15) 338 10,817 3,461* Coast redwood; “old-growth”; alluvial flats, California Coast (17) 247 9,500 3,200 14.3 Douglas fir and western hemlock; >400 years; Oregon Cascades (18) 127 3,600 1,590* Noble fir; 400 years; Washington Cascades (18) 147 4,106 1,562*

*Stems only

1382 SCIENCE, VOL. 204 leaf area index of 10 m2 of leaf surface Table 3. Biomass for a 450-year-old Douglas at 150 ton/ha per year; estimates for a area per square meter of ground surface fir forest in the Cascade Mountains (26). mixed oak and pine forest in New York (m2/m2) and often exceed 15 (17, 25). Biomass and a tulip poplar forest in Tennessee Item Leaf area index in the series of 11 refer- (ton/ha) were 15.2 and 15.9 tonlha per year (31). ence stands mentioned earlier averaged The net effect of the high levels of au- 2 2 Foliage 12.4 15, ranging from 10 to 20 m /m . These Aboveground in living plants 718.0 totrophic respiration is to make the con- leaf areas are much greater than those in Total in living plants 870.0 trast in gross productivity between most temperate hardwood forests which In logs and standing dead trees 215.0 northwestern conifer and eastern hard- Total ecosystem organic matter 1249.0 rarely exceed 6 m2/m2(26, 27). They also wood forests much greater than the con- far exceed leaf areas reached by red al- trast in net primary productivity. der in the Pacific Northwest (28) that, To conclude this section, the coastal converted from biomass figures, repre- regions of the Pacific Northwest are sent less than 10 m2/m2.If the density of in diameter growth at 25 years and in dominated by evergreen coniferous for- aboveground biomass is limited (27),the height growth at 30 years. Wood produc- ests with biomass accumulations far ex- heights of northwestern conifers may be tion from a single (100-year) crop rota- ceeding those of forests in other north a factor in the high values for leaf bio- tion of Douglas fir is about 22 percent temperate regions. This mainly results mass and area. greater than from two 50-year rotations from sustained growth of tree species of pine. Recent studies of height growth with long life spans, rather than from patterns for higher-elevation Douglas fir, greatly superior annual net productiv- Productivity nobie fir, and hemlock have further ities. documented that substantial height Productivity of the Pacific Northwest growth of these species may be sus- temperate forests generally is com- tained into their second and third cen- Adaptations to Temperature parable to forest stands in other temper- tunes (30). ate regions. Biomass in young stands Gross productivity rates (per unit of All these structural characteristics- probably accumulates at 15 to 25 tordha leaf area) are probably greater in many massiveness, evergreenness, large leaf annually in fully stocked stands on bet- tropical rain forests and warm-temper- areas, and even the needle-shaped leaf- ter-than-average sites. Mature or old- ature evergreen-broadleaf forests, but are functionally advantageous under the growth stands have lower net productiv- the lesser respiration rates in the Pacific moisture, temperature, and nutrient re- ities (Table 2); net productivity was 10.8 Northwest often show up in superior net gimes of the Pacific Northwest. Mild tonlha in an old-growth stand dominated productivity (13). However, total respi- winter temperatures permit substantial by Douglas fir (21). ration for the massive northwestern con- winter photosynthesis, and cool summer Annual net productivity can be very iferous forests is much higher than in nights make large leaf and other biomass great on the best sites. Fujimori (13) re- temperate deciduous forests. Grier and components less costly to maintain than ported annual net production of 36.2 ton/ Logan (21) estimated autotrophic respi- in other temperate forest regions. ha in a 26-year-old coastal stand of west- ration by a 450-year-old Douglas fir stand Conifers can assimilate over a broad ern hemlock. Young forests of coast redwood also have high early productivities Month on good sites (15, 17). Maximum values Ian Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec reported are substantially lower for tem- 100 perate deciduous forest (24.1 tonlha per year for tulip poplar), temperate evergreen hardwood forests (28.0 tonlha per year), and conifer plantations (29.1 ton/ -I ha per year for Cryptomeria) (22). Fig. 3. Simulated photosyn- Ix 50 In early years, however, annual pro- thetic rates for 1- to 2-m tall n I ductivity in many other mesic temperate Pseudotsuga menziesii grow- E ing in a coastal Sitka spruce U forests typically equals or exceeds that r* forest (upper) and a drier 0 in the Pacific Northwest. The key to the 0 Douglas fir forest in the west- M larger biomass accumulations in the Pa- ern Cascade Mountains of Or- -E cific Northwest is clearly in the sustained egon (20). Thin line shows po- 2 0 tential photosynthesis without height growth and longevity of the domi- 100 constraints due to moisture c nants, coupled with their ability to accu- c stress, frost, or low soil tem- x mulate and maintain a large amount of 0w Douglas fir perature; thick line incorpo- c foliage. These tree species continue to rates these constraints. A high c0 a grow substantially in diameter and proportion of yearly photosyn- height, and stands accumulate biomass thesis occurs outside the “growing season” on all of long after those in other temperate re- these sites. gions have reached equilibrium. This is cn well illustrated by comparing growth of loblolly pine in the Southeast and Doug- Growing season las fir in the Pacific Northwest (29). Ini- tially, the pine grows faster than Douglas fir, being 100 percent taller at 10 years; 0 100 200 300 however, Douglas fir overtakes the pine Year day 29 JUNE 1979 1383 temperature range. Considerable carbon uous hardwoods. The winter advantage site in a coastal zone with Sitka spruce uptake is possible below freezing (32), of the evergreen conifers is further en- and western hemlock where the moisture even by coastal species such as Sitka hanced by their long, conical crowns that regime is most favorable with a hot dry spruce (33).Significant winter accumula- intercept greater amounts of diffuse light zone where Douglas fir dominates the tions of dry matter by conifers have been common during the winter when the sun western slopes of the Cascade Moun- recorded in maritime climates (34).Sitka angles are low (38). tains. spruce seedlings in Scotland actually During the growing season, stomatal doubled their dry weight between late closure is induced by both soil drought September and mid-April (35). Adaptations to the Moisture Regime and high evaporative demand (39-41). During the dormant season for trees in Seasonal reductions in available soil wa- the Pacific Northwest, substantial net Photosynthesis is constrained by unfa- ter cause plant water deficits in some lo- photosynthesis occurs over a wide range vorable moisture regimes during the cations and limit the degree and duration of environments. Winter temperatures summer months-the “growing season” to which stomata open (41). Likewise, are mild and subfreezing day temper- upon which deciduous plants are so de- increasing evaporative demand, as mea- atures are uncommon, even in montane pendent. The dry summers cause stoma- sured by the water vapor deficit of the environments (36).Model simulations in- ta on leaf surfaces to close, reducing wa- atmosphere, can by itself bring about dicate that as much as half of the annual ter loss and subsequent carbon dioxide stomatal closure by both conifers and net carbon assimilation by Douglas fir uptake. Effects of summer drought are hardwoods (40, 42-44). From hundreds occurs between October and May (37) particularly apparent on dry sites where of field measurements on diverse plants (Fig. 3). This long period of favorable nearly 70 percent of the annual net pho- native to the Pacific Northwest, we temperature (and moisture conditions, as tosynthesis occurs outside the growing found none able to maintain open stoma- seen below) is mostly lost to the decid- season. For example, Fig. 3 contrasts a ta at high evaporative demands, regard- less of the availability of soil water (Fig. 4). Ei g. 4. Maximum stoma- Evergreen conifers tend to have signif- 10 tal conductances recorded icant advantages over deciduous hard- 09 at different evaporative woods during periods of moisture defi- demands (vapor pressure ciency even though photosynthesis is ad- deficits) for a variety of - versely affected in both groups. The -? 0.7 native species growing un der conditions with ade- needle-shaped conifer leaves remain quate soil water. Conifers: closer to ambient temperatures than 1, Douglas fir (N = 312); broad leaves (45) because heat exchange 2, western hemlock (N = is less inhibited. As a result, respiration 40 4); deciduous trees: 3, dogwood (N = 402); 4, and transpiration are likely to be higher big ; leaf maple (N = 68); for broadleaf species than for conifers. evergreen broadleaf tree: Because evaporative demand usually ex- 5, chinquapin (N = 159); ceeds critical limits throughout much of deciduous shrub: 6, vine mz ple; evergreen broad- the area during the growing season, the 0‘ I I I I I environment is obviously less than opti- 10 20 30 40 50 leatf shrubs: 7, rhododen- = Vapor pressure deficit (mb) dron (N 451); 8, salal mum for plants that depend on this sea- (N = 435) [data from (44)]. son for their major carbon assimilation. The large volume of sapwood, a structural feature of conifer forests, dampens the effect of dry summer months. Both hardwoods and conifers utilize some wa- m I I ter from conducting tissues to help meet Fig. 5. Evaporative daily transpiration requirements (46). demand (A) in rela- tion to seasonal varia- However, the conifers have cells that ap- tion in sapwood water parently are easier to refill and that, be- storage of old-growth cause the trees grow larger, store more Douglas fir (B). De- water (Fig. 5). A single SO-in Douglas fir pletion begins in April may store 4000 liters of water (41). A for- well before the “growing season” and est stand can have water available ex- declines to minimum ceeding 250 m3/ha which may supply up 200 levels during the to half the daily water budget (42). -- warm, dry summer Hence, sapwood represents a significant k months. Occasional r buffer against extremes of negative water 150 summer rains provide > potential in foliage and stem. Although 0 for partial recharge, r“ but complete re- full hydration usually occurs during the m charge occurs during winter, conifers may partially recharge 100 p the fall and is com- 0 sapwood after- summer rain showers. 1 v) pleted in midwinter (42 ) . Hardwoods, particularly ring porous species, have no mechanism for ef- JJASONDJFMAM fectively refilling vessels in large trees. Month In summary, the conifers have ex- 1384 SCIENCE, VOL. 204 cellent control of water loss without in- lower requirements of conifers. Nitrogen pend on the litter rather than on the soil creasing their leaf temperatures. More- in foliage of 450-year-old Douglar fir for nutrients. For example, a 20-year-old over, they can develop water storage to a rarely exceeds 0.8 percent (dry weight forest of Douglas fir obtains 55 percent of greater extent than hardwoods and uti- basis), less than half that of most hard- its nitrogen from the litter while a 100- lize these adaptations during severe con- woods (53, 54), yet needles appear year-old forest may, on some sites, take ditions common during the growing sea- healthy (51). Although Pacific Northwest essentially all of its nitrogen from this son. conifers hold greater foliage biomass source (56). Yet the quality of the litter than hardwood forests, less than 20 per- declines and litter decay rates slow, cent is replaced each year so that the to- making dependence upon this nutrient Adaptations to Nutrient Regimes tal requirement is usually less than that source disadvantageous (60). for the more demanding hardwoods. Co- The temperate coniferous forests of niferous forests require half the calcium References and Notes the Pacific Northwest are evolutionary of hardwood forests grown on similar 1. A. Gray and J. D. Hooker, ”The vegetation of the Rocky Mountain region and a comparison responses not only to moisture and tem- soils for 100 years (54), in part because with that of other parts of the world,” U.S. conifer wood has only about 20 percent Geol. Surv. Geogr. Surv. Bull. 6, (1882), pp.1- perature conditions, but also to distinc- 77: A. W. Kiichler, Ann. Assoc. Am. Geogr. tive nutrient regimes. Many features of of the calcium content of deciduous 36, 122 (1946). 2. R. R. Silen, J. For. 60, 407 (1962). these regimes contrast with those of hardwoods (53). Conifers are also be- 3. R. W. Chaney, C. Condit, D. I. Axelrod, Car- more typical, temperate hardwood re- lieved to more efficiently extract nitro- negie Inst. Washington, Publ. 553 (1944), p. 407. 4. R. Daubenmire, J. Biogeogr. 2, 1 (1976); in Pro- gions in the north, partially because of gen and phosphorus from various ceedings of the Symposium on Terrestrial and the winter-wet, summer-dry climate. sources (55). Aquatic Studies of the Northwest, R. D. An- drews III etal., Eds. (Eastern Washington State For example, most decomposition and Northwestern conifers meet increas- College Press, Cheney, 1976), p. 159. ing proportions of their total nutrient re- 5. P. J. Regal, Science 196, 622 (1977). subsequent nutrient release from organic 6. R. W. Chaney and D. I. Axelrod, Carnegie litter occurs during the cool, wet ”dor- quirements by redistribution from older Inst. Washington Publ. 617 (1959), p. 237. 7. J. A. Wolfe and E. B. Leopold, in The Bering mant” season and may essentially cease tissue, especially senescent needles. For Land Bridge, D. M. Hopkins, Ed. (Stanford during the dry summer. Slow summer example, half the nitrogen required by a Univ. Press, Stanford, Calif., 1967), p. 193. 8. R. W. Chaney, Carnegie Inst. Washington Publ. decomposition has been reported from 100-year-old stand of Douglas fir is met 476 (1938), p. 323. such diverse sites as Douglas fir and by redistribution from older foliage (56). 9. 0. M. Petrov, “The stratigraphy of the Quater- nary deposits of the southern parts of the western hemlock forests at low and At 100 years, the annual nitrogen re- Chukotsk Peninsula,” Moscow Academy of Sci- middle elevations (47) and subalpine fir quirement drops from a peak demand of ences Commission for the Study of the Quater- nary, Bull. 28 (1963), p. 135 (translated by M. C. forests in the Cascade Range (48). In .about 50 kilograms per hectare to around Blake, U.S. Geological Survey, Menlo Park, Calif.). Montana forests of Douglas fir. more 30 kilograms per hectare. Other north- 10. J. F. Franklin and C. T. Dymess, “Natural veg- than 90 percent of the weight loss by lit- western conifers behave similarly and etation of Oregon and Washington,” U.S.. For. Serv. Gen. Tech. Rep. PNW-8 (1973). ter takes place- under winter snow de- may be even more conservative (57). 11. C. W. Thornthwaite, Geogr. Rev. 38,55 (1948). spite subzero air temperatures In Deciduous hardwoods also generally 12. J. R. Eagleman, Visualization of Climate (En- (49). vironmental Publications, Lawrence, Kan., western Oregon, almost no measurable redistribute substantial nutrients from 1973). 13. T. Fujimori, “Primary productivity of a young decomposition occurs in July and August foliage before leaf fall, but their total re- Tsuga heterophylla stand and some speculations (47). quirements are higher. The nitrogen re- about biomass of forest communities on the Ore- gon Coast,” U.S. For. Serv. Res. Pap. PNW- The massiveness of the forests also quirement of mature hardwoods in the 123 (1971), pp. 1-11. contributes to the uniqueness of the nu- eastern United States is reportedly 70 kg/ 14. This is difficult to document but is relevant in the sense that for trees to grow to large sizes and trient regimes by binding large amounts ha each year for the canopy to develop, old ages the genetic potential for so doing must of nutrients into standing crops. Without and less than one-third of this can be met exist, and the environment must allow the species to express this potential. In one way or an- frequent ground fires, organic matter- by redistribution from storage sites with- other, the environment of the Pacific Northwest in the trees (58).This should apply equal- is apparently more suitable for the development particularly large logs and branches-ac- of tall trees and extended life spans. Less fre- cumulates on the forest floor. Both the ly to hardwoods in the Pacific North- quent occurrence of strong winds, such as typhoons and humcanes, that disturb or weaken climate and forest combine to create west. forest communities in other temperate regions is conditions where large episodic losses of Hence, most hardwoods that compete one hypothesis; less favorable environmental of p conditions for development .Iathogens is an nitrogen (50) and other nutrients result with conifers in the Pacific Northwest ei- alternative. from infrequent wildfires and subsequent ther having nitrogen-fixing abilities (for 15. T. Fujimori, J. Jpn. For. Soc. 59, 435 (1977). 16. ~. ibid. 54, 230 (1972). leaching. example, alder) or are at a disadvantage 17. W. E.Westman and R. H. Whittaker, J. Ecol. The peculiarities of these nutrient re- on most sites. Their total nutrient re- 63, 493 (1975). 18. T. Fujimori, S. Kawanabe, H. Saito, C. C. gimes combine to favor plants that have quirement is higher than for associated Grier, T. Shidei, J. Jpn. For. Soc. 58, 360 (1976). low nutrient requirements, that con- conifers and must be met largely by up- 19. D. B. Zobel. W. A. McKee, G. M. Hawk, Ecol. servatively use acquired nutrients, and take from the soil and litter. Yet decom- Monogr. 46, 135 (1976). 20. W. H. Emmingham, unpublished data. that can accumulate nutrients during the position and nutrient release are at low 21. C. C. Grier and R. S. Logan, Ecol. Monogr. 47, wet dormant season when decomposi- levels during the summer months when 373._j (1977) 22. H. W. Art and P. L. Marks, Maine Life Sci. tion is most active. In these ways, ever- hardwood nutrient demand is high. The Agric. Exp. Stn. Misc. Publ. 132 (1971), p. 2. green conifers appear to have distinct ad- large pulses nutrients leached dur- 23. J. N. Long and J. Turner, J. Appl. Ecol. 12, 179 of (1975). vantages over deciduous hardwoods. ing the wet fall and winter season are 24. P. L. Marks and F. H. Bormann, Science 176, 914 (1972). Conifers generally require fewer nutri- more available to conifers than to 25. H. L. Gholz, F. K. Fitz, R. H. Waring, Can. J. ents and use them more efficiently than deciduous trees that have shed their For. Res. 6, 49 (1976). 26. D. E. Reichle, Analysis of Temperate Forest most hardwoods do. Foliage retention leaves (59). Ecosystems, Ecological Studies (Springer-Ver- for several years, reducing annual nutri- The binding of nutrients into biomass lag, New York, 1969), vol. 1. 27. Y. Tadaki, in Primary)Productivity of Japanese ent requirements (51, 52) , is obviously during succession again stresses decid- Forests, T. Shidei and T. Kira, Eds. (Univ. of advantageous. The low levels of nutri- uous hardwoods more than conifers. As Tokyo Press, Tokyo, 1977), p. 39. 28. J. Zavitkovski and R. D. Stevens, Ecology 53, ents in foliage also give evidence of the they age, forest trees increasingly de- 235 (1972). 29 JUNE 1979 1385 29. N. Worthington. Pulp Pap. 28, 34 (1954). 1525 (1974): D. R. Thompson and T. M. Hinck- cent of the total in mature northwestern conifer 30. R. O. Curtis, F. R. Herman, D. J. De Mars, For. ley, Can. J. For. Res. 7, 400 (1977). forests [W. S. Overton, D. P. Lavender, R. K. Sci. 20, 307 (1974); D. J. De Mars, F. R. Her- 44. R. H. Waring, S. W. Running, S. W. Hallgren, Hermann, “S.4.01 Mensuration, Growth, and man, J. F. Bell, “Preliminary site index curves unpublished data. Yield,” in IUFRO Biomass Studies (Univ. of for noble fir from stem analysis data,” U.S. For. 45. D. N. Gates, Annu. Rev. Plant Physiol. 19, 211 Maine Press, Orono, 1973), p. 91]. Serv., Res. Note PNW-119 (1970), pp. 1-9. (1968); __ and L. E. Papian, Atlas of Energy 52. On one old-growth tree of Pseudotsuga men- 31. G. M. Woodwell and D. B. Botkin, in Analysis Budgets of Plant Leaves (Academic Press, New ziesii, 16 percent of the 61 million needles were of Temperate Forest Ecosystems, D. F. Reichle, York, 1971). 1-year-old [L. H. Pike, R. Rydell, W. C. Deni- Ed. (Springer-Verlag, New York, 1970), p. 73; 46. L. Chalk and J. M. Bigg, Forestry 29, 5 (1956); J. son, Can. J. For. Res. 7, 680 (1977)]. P. Sollins, D. E. Reichle, J. S. Olson, “Organic Clark and R. D. Gibbs. Can. J. Bot. 35, 219 53. L. E. Rodin and N. I. Bazilevich, Production matter budget and model for a southern Appala- (1957); R. D. Gibbs, in The Physiology of Forest and Mineral Cycling in Terrestrial Vegetation, chian Liriodendron forest,” Oak Ridge Nat. Trees, K. V. Thimann, Ed. (Ronald, New York, G. E. Fogg, Ed., translated by Scripta Technica Lab. Rep. ORNL-IBP-73-2 (1973). 1958), p. 43. (Oliver and Boyd, London, 1967). 32. J. Ungerson and G. Scherdin, Flora 157, 391 47. R. Fogel and K. Cromack, Jr., Can. J. Bot. 55, 54. J. Rennie, Plant Soil 7, 49 (1955). (1968). 1632 (1977). 55. R. F. Fisher and E. L. Stone, Soil Sci. Soc. Am. 33. R. E. Neilson, M. M. Ludlow, P. G. Jarvis, J. 48. J. Turner and M. J. Singer, J. Appl. Ecol. 13, Proc. 33, 955 (1969); J. Turner, For. Sci. 23, 307 Appl. Ecol. 9, 721 (1972). 295 (1976). ( 1977). 34. O. Hagem, ”The dry matter increase of conifer- 49. N. M. Stark, Ecology 58, 16 (1977). 56. D. W. Cole, J. Turner, S. P. Gessel, “Elemental ous seedlings in winter. Investigations in ocean- 50. An interesting feature of the Pacific Northwest cycling in Douglas fir ecosystems of the Pacific ic climate,” Medd. Vestl. Forstl. Forsoeksstn. is the large array of organisms associated with Northwest: a comparative examination,” pre- 26, 1-317. (1947); “Additional observations on nitrogen fixation. Nitrogen, an important nutri- sented at the Twelfth International Botanical the dry matter increase of coniferous seedlings ent and one to which young forests typically Congress, Leningrad, 1975 (in press). in winter. Investigations in an oceanic climate,” show a growth response, is also the nutrient 57. C. C. Grier, personal communication. ibid. 37, 253 (1962); A. J. Rutter, Ann. Bot. most severely affected by the wildfires typical of 58. F. H. Bormann, G. E. Likens, J. M. Melillo, (London) 21, 399 (1957); D. F. W. Pollard and the region. A broad array of higher plants have Science 196, 981 (1977). P. F. Wareing, ibid. 32, 573 (1968). nitrogen-fixing microbial associates [H. J. 59. H. A. Moonev and P. W. Rundel. Bot. Gaz., in 35. I. K. Bradbury and D. C. Malcolm, Can. J. For. Evans, Enhancing Biological Nitrogen Fixation press. Res. 8, 207 (1978). (National Science Foundation, Washington, 60. J. Turner and J. N. Long, Can. J. For. Res. 5, 36. This is equally true of soil and air temperatures. D.C., 1975)], mostly successional pioneers such 681 (1975). Frozen soils are extremely uncommon, even in as Alnus rubra and Ceanothus velutinus. Large 61. Anonymous, Am. For. 79, 21 (1973). subalpine environments. Water uptake is, there- amounts of nitrogen-50 to 300 kg/ha per year- 62. H. A. Fowells. “Silvics of forest trees of the fore, not a major problem. can be fixed during early stages of forest devel- United States” (U.S. Forest Service Agents 37. W. H. Emmingham and R. H. Waring, Can. J. opment, thereby balancing major losses associ- Handbook No. 271, Washington, D.C., 1965), p. For. Res. 7, 165 (1977). ated with forest destruction by fire. Foliose li- 762. 38. L. S. Jahnke and D. B. Lawrence, Ecology 46, chens endemic to the large, massive crowns of 63. Tables of Temperature, Relative Humidity, and 319 (1965)--,- old-growth trees provide further nitrogen inputs Precipitation for the World (Meteorological Of- 39. S. W. Hallgren, thesis, Oregon State University, of 5 kg/ha per year. Finally, large boles contain fice, London, 1958). Corvallis, (1977). substantial nitrogen; as snags and logs, these 64. Many scientists have participated in discussions 40. C. S. Tan and T. A. Black. Boundary-Layer Me- structures survive major disturbances, provid- of the material presented here and contributed teorol. 10, 475 (1976). ing a slowly available source of nitrogen as well significant ideas and data. We thank W. H. Em- 41. S. W. Running, R. H. Waring, R. A. Rydell, as sites for bacterial fixation [B. W. Cornby and mingham, W. A. McKee, G. M. Hawk, K. Cro- Oecologia 18, l(1975). J. B. Waide, Plant Soil 39,445 (1973); M. J. Lar- mack. Jr., and P. Sollins who reviewed earlier 42. R. H. Waring and S. W. Running, Plant Cell En- son, M. F. Jurgensen, A. E. Harvey, Can. J. drafts of the manuscript and C. C. Grier and viron. 1, 131 (1978). For. Res., 8, 341 (1978)]. All these pathways for W. Denison. This work was conducted under 43. J. Grace, D. C. Malcolm, I. K. Bradbury, J. fixation and retention of nitrogen may represent the auspices of the Coniferous Forest Biome, Appl. Ecol. 12,931 (1975); R. E. Neilson and P. adaptations to catastrophic wildfires and related U.S. Analysis of Ecosystems, IBP (NSF grant G. Jarvis, ibid., p. 879; W. R. Watts, R. E. Neil- nitrogen deficiencies in a region otherwise favor- GB-20963). contribution number 304. This is pa- son, P. G. Jarvis, ibid. 13, 623 (1976); W. J. able to vegetative growth. per 1229 of Forest Research Laboratory, Ore- Davies and T. T. Kozlowski, Can. J. Bot. 92, 51. Current foliage may represent less than 15 per- gon State University, Corvallis 9733 I.

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