R. H. Whittaker

Vegetation of the Siskiyou Mountains, Oregon and California

II. PROCEDURE .................................. 285 Study Areas ................................. 285 Vegetation Samples and Soil Data ..... ..... 286 Arrangement of Samples in Transects .... . 286 Evaluation of Transect Techniques . ..... . 288 Transect Tables ................... ....... 289 III. VEGETATION DESCRIPTION ...... ............. 291 Low Elevations on Diorite . ... ......... .. 291 Low Elevations on Gabbro ..... ........ 297 Low Elevations on Serpentine and the Two-Phase Ef fect .......... .............. . 299 Forest Vegetation of Higher Elevations on Diorite ......................... ....... 302 Vegetation of Higher Elevations on Serpentine . . 305

GRADIENT ANALYSIS OF VEGETATION

CONTENTS

The Hubbard Brook Ecosystem Study: Forest Biomass and Production

A small watershed in the White Mountains of New Hampshire bearing meso- phytic, cool-temperate, broadleaf-deciduous forests was studied. Acer saccharum, Betula lutea, and Fagus grandifolia are dominant, but toward higher elevations Picea rubens and A bies balsamea also occur and indicate the transition toward subalpine climate. The stands are young (following cutting in 1909-17) but contain older trees; stand composition is thought reasonably representative of the climax. For application of the Brookhaven system of forest dimension analysis, 93 sample trees of major species were cut and roots excavated. Mean dimensions of sample trees, and the constants for the system of logarithmic regressions relating volume, surface, mass, and growth to diameter at breast height and other independent vari- ables, show decrease in tree sizes and height/diameter ratios toward higher elevations. Stand characteristics, based on application of the regressions to forest samples, show trends of decrease for the elevation belts from low to high: stem basal area 26.3, 23.7, and 22.0 m2/ha, weighted mean tree height 16.9, 16.7, and 10.8 m, weighted mean age 124, 95, and 83 yr, stem wood volume 176, 155, and 103 m3/ha, aboveground biomass (dry matter) 162, 152, and 102 t/ha, estimated volume increment 379, 365, and 223 cm3/m2/yr, aboveground net primary productivity (1956-60) 1127, 1041, and 790 g/m2/yr, and leaf area ratio 6.2, 5.7, and 5.5 m2/m2. Biomass (and, presumably, production) of root systems is 18%-21% of that aboveground. Different estimations suggest that a mean climax biomass for the watershed may be around 350 t/ha, aboveground. Net ecosystem production (i.e., addition to the pool of woody biomass in the community) is estimated as 350 g/m2/yr aboveground and 85 below- ground for 1956-60, 238 and 52 g/m2/yr for 1961-65. Analysis of stem wood volume incre- ments reveals an abrupt and striking (18%) decrease in volume growth and productivity from 1956-60 to 1961-65. The net primary productivity of the former period, with a weighted mean for the watershed of 1110 g/m2/yr above and below the ground, is thought more nearly normal for the forest. Both drought and effects of increasing air pollution (notably increasing acidity of rainfall) may be responsible for the recent decrease in productivity.

Vegetation of the Santa Catalina Mountains, Arizona: A Gradient Analysis of the South Slope

Vegetation of the southwest slope of the Santa Catalina Mountains of southeastern Arizona was sampled and transects prepared for 1,000—ft (305 m) elevation belts on granite and gneiss soils from the summit forests (2,440—2,750 m) to the base of the mountains (900 m). Transects also represented subalpine forests above 2,750 m in the Pinaleno Mts. and vegetation of the valley plain or bajada below the mountains, and samples were taken from volcanic soils below 900 m in the Tucson Mts. Principal community—types from high elevations to low are: subalpine forest (Picca engelmanni in the Pinaleno Mts. and Abies lasiocarpa), montane fir forest (Abies concolor, Pseudotsuga menziesii), pine forests (Pinus ponderosa, P. strobiformis), pine—oak forests (P. ponderosa, Quercus hypoleucoides), pine—oak woodlands (P. ponderosa, P. chihuahuana, Q. hypoleucoides, Q. arizonica), pygmy conifer—oak scrub (Pinus cembroides, Juniperus deppeana, Q. arizonica, Q. emoryi, Arctostaphylos pringlei, A. pungens, monocot shrubs), open...

DIMENSION AND PRODUCTION RELATIONS OF TREES AND SHRUBS IN THE BROOKHAVEN FOREST, NEW YORK.

Extensive tracts of oak-pine forest grow on the level, sandy soils of glacial outwash derivation on Long Island, New York (Conard 1935). The forests are small and unimpressive to a forester. In mature stands older and larger pines (Pinus rigida Mill.) rise above a canopy of oaks (Quercus alba L., Q. coccinea Muench, and few Q. velutina Lam. and other species). The canopy is open, with light intensity below the trees sufficient to support a shrub stratum of small Vacciniaceae of high coverage (Reiners 1965). These forests are floristically related to the pine forests of New Jersey and the Coastal Plain southward, and to the pine heaths of the Great Smoky Mountains (Whittaker 1956), with which they share a number of major species. All of these forests have been subject to repeated fires, and dense, immature successional stands with Pinus rigida and scrub oak (Qtiercus ilicifolia Wang.) occur over extensive areas. The small size of the trees at Brookhaven has facilitated development of a system of detailed dimension analysis useful for various problems related to forest volume, biomass, production, surface and nutrient circulation. The methods are developments from forest measurements used by Burger (1929, 1953), Boysen Jensen (1932), Moller (1945, 1947), Ovington (1957), Ovington & Madgwick (1959a, b) and others, but are intended to advance beyond those measurements in important respects. They use the wood rings and bud-scale scars which mark annual increments of growth in some climates for assessment of current net production and nutrient movement in forests. They are designed specifically to deal with the complexities of many-aged stands including climaxes, as distinguished from plantations. The work is part of a long-term study of various aspects of the Brookhaven forest as an ecosystem, a study which includes experimental irradiation of a segment of the forest with gamma radiation from a cesium soturce (Woodwell 1962, 1965). The plants of the present study have been taken from the forest outside the area of radiation effects. Included in this report are results of dimension analysis of trees and shrubs as a first phase of the research on bio mass, production and nutrient circulation.

The role of mosaic phenomena in natural communities.

Abstract Interrelations among three groups of ideas are considered. (1) The place where a plant is rooted, or a sessile animal is attached, may be termed a microsite. The microsites for a community form a mosaic that is differentiated by physical environment or biological effects or both. Population function and regulation, and community self-maintenance and response to environmental fluctuation, can be approached in terms of the flow of reproducing populations through the mosaic. (2) Most communities are subject to disturbance followed by succession. Communities are diverse in the kinds and frequencies of disturbances and in kinds of successions and climaxes; and the species of a biota diversify in their relationships to successional time and patterns of successional and climax communities. (3) Although mosaic phenomena are general, two broad groupings may be recognized: intracommunity patterns that relate to microsite differentiation and species response to this, and intercommunity successional mosaics and climax complexes for which community disturbance is a major determining force. Relationships between elements of a mosaic can often be formulated in terms of a chain or network of replacement rates, but formulations should allow for the influence of bath terms and occurrence of semipermanent plateau stages in some successions.

The Biosphere and Man

Preceding chapters in this volume have dealt with the history of productivity study, methods of measurement, patterns of productivity in different kinds of communities, and some applications in research. Two topics remain: the characterization of the biosphere as a whole in terms of productivity and related properties, and consideration of man’s relationship to the biosphere. The first topic is the focus of the book as a whole, and it is summarized here as well as in Chapters 10 and 13. The second topic is inescapably problematic; we can offer only a viewpoint on it.

VEGETATION OF THE SANTA CATALINA MOUNTAINS, ARIZONA. V. BIOMASS, PRODUCTION, AND DIVERSITY ALONG THE ELEVATION GRADIENT'

Measurements were taken in 15 communities along the elevation gradient from fir forest at high elevations, through pine forest, woodlands, and desert grassland, to deserts at low elevations in the Santa Catalina Mountains, Arizona, and in a Cercocarpus shrubland on limestone. Eight small-tree and shrub species of woodlands and deserts were subjected to dimension analysis by the Brookhaven system. Aboveground biomass decreased along the elevation gradient from 36-79 dry kg/M2 in fir and Douglas-fir forest to 0.26-0.43 kg/M2 in the desert grassland and two desert samples. Net aboveground primary productivity similarly decreased from 1,050-1,150 g/m2 * yr in mesic high-elevation forests to 92-140 g/m2 - yr in desert grassland and deserts. Both biomass and production show a two-slope relation to elevation (and, probably, to precipitation), with a steeper decrease from the high-elevation forests to the mid-elevation woodlands, and a less steep decrease from dry woodlands through desert grassland into desert. The two groups of communities at higher vs. lower elevations also show different relations of leaf area index and chlorophyll to elevation and to productivity. The two groups may represent different adaptive patterns: surface-limiting, with low pro- ductivity in relation to precipitation but high production efficiency in relation to surface in the more arid lower elevations, vs. surface-abundant, with high productivity relative to pre- cipitation based on high community surface area, but lower production efficiency in relation to this area, in the more humid higher elevations. Vascular plant species diversity shows no simple relation to productivity, but decreases from high-elevation fir forests to the pine forests, increases from these to the open woodlands, and decreases from dry woodlands through the desert grassland and mountain slope desert to the lower bajada (creosotebush) desert.

Classification of Plant Communities

12 Approaches to Classifying Vegetation.- 13 The Physiognomic Approach.- 14 Dominance-Types.- 15 The Finnish School and Forest Site-Types.- 16 Synusial Approaches to Classification.- 17 Russian Approaches to Classification.- 18 North European Approaches to Classification.- 19 Numerical Classification.- 20 The Braun-Blanquet Approach.

A COMPARATIVE STUDY OF RECIPROCAL AVERAGING AND OTHER ORDINATION TECHNIQUES

SUMMARY Reciprocal averaging is a technique of indirect ordination, related both to weighted averages and to principal components analysis and other eigenvector techniques. A series of tests with simulated community gradients (coenoclines), simulated community patterns (coenoplanes), and sets of vegetation samples was used to compare ordination performance of reciprocal averaging (RA) with non-standardized and standardized principal components analysis (PCA) and polar or Bray-Curtis ordination (PO). Of these, non-standardized PCA is most vulnerable to effects of beta diversity, giving distorted ordinations of sample sets with three or more half-changes. PO and RA give good ordinations to five or more half-changes, and standardized PCA is intermediate. Sample errors affect all these techniques more at low than at high beta diversity, but PCA is most vulnerable to effects of sample errors. All three techniques could ordinate well a small (1-5 x 1-5 half-changes) simulated community pattern; and PO and RA could ordinate larger patterns (4 5 x 4-5 half-changes) well. PCA distorts larger community patterns into complex surfaces. Given a rectangular pattern (1-5 x 4-5 halfchanges), RA distorts the major axis of sample variation into an arch in the second axis of ordination. Clusters of samples tend to distort PCA ordinations in rather unpredictable ways, but they have smaller effects on RA, and none on PO. Outlier samples do not affect PO (unless used as endpoints), but can cause marked deterioration in RA and PCA ordinations. RA and PO are little subject to the involution of axis extremes that affects nonstandardized PCA. Despite the arch effect, RA is much superior to PCA at high beta diversities and on the whole preferable to PCA at low beta diversities. Second and higher axes of PCA and RA may express ecologically meaningless, curvilinear functions of lower axes. When curvilinear displacements are combined with sample error, axis interpretation is difficult. None of the techniques solves all the problems for ordination that result from the curvilinear relationships characteristic of community data. For applied ordination research consideration of sample set properties, careful use of supporting information to evaluate axes, and comparison of results of RA or PCA with PO and direct ordination are suggested.