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Large-seeded plant species tend to be restricted to late-seral and mature forests, yet the reason for this habitat specificity is often not understood. The typical absence of these species from younger forests may be due to either their ineffective seed dispersal to early-seral habitats or postdispersal factors such as life history traits and physical and biotic variables, or both. Two large-seeded palm species, Iriartea deltoidea and Astrocaryum murumuru var. javarense, were used to experimentally evaluate the role of postdispersal limitation by testing whether the species exhibit differential seedling survivorship in forest stands of different ages. Under natural conditions, both palm species are largely absent from early- and mid-seral floodplain forest but are common in late-seral and mature forest. Iriartea seedlings and juveniles are found occasionally in early- and mid-seral forest, whereas Astrocaryum are almost never found there. To assess the degree to which postdispersal factors could account for these patterns, seeds of the two palm species were transplanted into four zones in the successional floodplain forest of Manu National Park, Peru. Three experiments quantifying seedling establishment and survivorship were carried out : a 3-yr experiment using Iriartea, in which flooding during the 1st yr was lower than average (Iriartea Dry Experiment) ; a 1-yr experiment using Iriartea, in which flooding during the 1st yr was higher than average (Iriartea Wet Experiment) ; and a 2-yr experiment using Astrocaryum, in which flooding during the 1st yr was also higher than average (Astrocaryum Wet Experiment). For each experiment, four or five plots, each containing 75 seeds, were placed in each of four zones from early to late succession. The entire design was replicated in two successional transects that were separated by 6 km. Seedling survivorship of Astrocayum was highest in the late-seral zones of both transects, which corresponded closely to its restricted natural distribution. Hence, postdispersal limitations, perhaps in conjunction with restricted seed dispersal, apparently contributed heavily to the general absence of Astrocaryum from the early- and mid-seral floodplain forests. Flooding did not appear to influence Astrocaryum seedling survivorship. Postdispersal factors also seemed to influence strongly Iriartea establishment, as evidenced by the significant variation in seedling survivorship across seral zones and between transects. Moreover, in the Iriartea Dry Experiment, seedling survivorship was negatively correlated with level of flooding. During the Iriartea Wet Experiment, survivorship was substantially lower in all seral zones, probably due to the heavy flooding. Thus, flooding, as a postdispersal factor, appeared to play a major role in shaping the natural distribution of Iriartea in the successional floodplain forests. Because seedling survivorship in one mid-seral zone was substantially higher than would be predicted from the natural Iriartea seedling density, results from transplant experiments also suggest that limited seed dispersal may contribute to this palm's early-seral distribution. For Iriartea, seed dispersal limitation may play a role complementary to that of flooding. In Amazonian primary-successional floodplain forest, the habitat specificity of at least one, and perhaps two, large-seeded species appears to result from both dispersal limitation and postdispersal limitation factors.

A sagebrush steppe community in northwestern Colorado was disturbed in 1984 and subjected to annual applications of nitrogen and phosphorus, and successional responses were studied over a 5-yr period. Phosphorus was not found to be significant but nitrogen did significantly affect succession for all years except the first. Three seral groups developed on the non-fertilized plots, the first two dominated by annuals and lasting 3 yr, the third transitional and dominated by perennials. The addition of N altered this successional pattern by allowing annuals to remain as site dominants through the 5th yr. Results of this study suggests that dominance of a site by annuals in early stages of secondary succession is related to high nutrient availability.

We examined 4 yr of intensive census records for 72 line transects in contiguous riparian vegetation. Across all transects the number of bird species differing between pairs of suc- cessive years followed a random distribution. For any season, from one-quarter to over one-third of the species differed. There were weak tendencies for specific plant communities and seral stages to have high or low turnover rates. The proportion of avian species in a community changing between years was lower in summer than in other seasons but was similar between years for any specific season. Locally breeding species showed slightly more stable communities than did nonlocally breed- ing species. These high turnover rates in bird community composition between years bring into question assumptions underlying current theories of avian habitat selection, as well as assumptions essential when competition theory is used as the framework to account for community organization. Furthermore, there are substantial empirical similarities between these species turnovers in contig- uous habitats and species turnovers on island and island-like patches of habitat.

To establish plausible explanations of the factors determining patterns of local distribution and abundance of white-footed mice, Peromyscus leucopus, concurrent measures of habitat structure, plant species composition, and mouse density were performed in several seral stages at Point Pelee National Park, southern Ontario. Population density covaries with foliage profile structure among habitats in which P. leucopus occur, whereas floristic com- position is unimportant. White-footed mouse distribution and restriction to nongrassland habitats may be due to a significant structural difference between grassland and nongrassland habitats.

Species diversity of vascular plants was determined in 51 seral communities ranging from 0.2-200+ yr old. Species richness (S = number of species), information content (OFPOP = -E p loge pi), redundancy R = (1'pop - H'iax)/(H'max - Hm in), and evenness ('pop = f'pop/lOge S) were calculated for numbers of individuals in four strata (ground layer, shrub, understory, and canopy. Richness (S) in the strata and major growth forms (herbs, woody vines, shrubs, and trees) increased rapidly following their establishment, then at a decreasing rate throughout the remainder of succession. Equitability, (I - R, J'pop), on the other hand, increased to near maximum levels immediately after establishment but changed little thereafter. Contrasts in seral richness and equitability trends suggest differing regulatory mechanisms-equitability being regulated primarily by short term factors (resource levels) and richness by long term factors (community stability and evolutionary time).

I analyzed food habits and habitat utilization patterns of deer mice (Peromyscus maniculatus) in seral stages of coastal coniferous forest in southeast Alaska. Adult deer mice consumed a higher proportion of hard—bodied arthropods than did juveniles. Juveniles consumed a lower proportion of soft—bodied arthropods in high—density populations than in low—density populations. High—and low—density habitats were described for adults and juveniles using discriminant function analysis. Adult high—density habitat had more cover than juvenile high—density habitat and was more favorable, as evidenced by a greater overwinter survival of both juveniles and adults. Intraspecific competition appeared to responsible for niche displacement of juvenile deer mice along food and habitat dimensions. See full-text article at JSTOR

A species—rich small—mammal community on 7 ha of diverse coastal heath in Myall Lakes National Park, New South Wales, Australia, was studied for 7 mo before the area burned in a wildfire (August 1974) and has subsequently been monitored for 5 yr since the fire. Species regularly trapped were the dasyurids Antechinus stuartii and Sminthopsis murina, the peramelid Isoodon macrourus, and the native murids Pseudomys novaehollandiae and P. gradcilicaudatus, together with the introduced Mus musculus. Pseudomys species, M. musculus, and S. murina reached greater abundance on early seral stages, while the abundance there of both Rattus fuscipes and R. lutreolus was much reduced. Species reach peak abundance in an orderly replacement sequence exhibiting a mammalian secondary succession. A habitat accommodation model is proposed with species entering the succession and reaching peak abundance as externally controlled changes in the vegetation fulfil the habitat requirements of each species. Species leave the succession or are greatly reduced in abundance when these local physical conditions move out of the optimal range for the species. This study shows that a major perturbation of a small—mammal community can produce a variety of responses among species, suggesting that regeneration time may represent a resource axis subdivided by community members in this secondary succession. The rapid recovery illustrated by the total number of individuals, as a measure of community response, support the suggestion that fire and fire frequency have been major factors in producing a fire—adapted, species—rich small—mammal community on this heathland.

Avian community structure was studied along a meadow-aspen-fir-spruce subalpine sere in northern Utah and southern Idaho during the breeding seasons of 1976, 1977, and 1978. During 1977 one of the worst droughts of this century occurred in the western United States, and comparative changes in avian community structure were documented during and after drought in the four seral stages. The number of breeding species declined most markedly during drought in aspen. Breeding communities on the forested plots during drought were least similar to predrought communities; pre- and postdrought communities were consistently most similar. Densities of singing males declined more markedly on all plots during drought than did number of species, and remained below predrought levels in 1978. Changes were also noted in avian trophic structure during drought: insectivores gen- erally declined in number, nectivorous hummingbirds completely disappeared, and the number of granivorous cardueline finch species increased. These changes can be related to changes in food resources. During drought, insect species composition and densities changed, flower phenology was 5 wk early, and one of the best coniferous cone crops in 30 yr occurred in northern Utah. Direct effects of lack of water were observed, and many bird species probably experienced water stress. Although difficult to document, indirect effects of drought on food resources are suggested for insectivores, nectivores, and possibly carnivores. The results indicate that a drought can represent an 'ecological crunch" to, and affect the structure of, temperate avian communities. However, separating the variation due to drought from inherent variation is difficult without comparative long- term studies. Avian communities in deciduous vegetation may be more greatly affected by drought than those in coniferous vegetation.

A abstract. A nested quadrat pattern analysis suggests that the adult members of early seral tree species exhibit maximal clumping at a quadrat size corresponding to the sizes of natural lightgaps created by treefalls. However, the dominant species show a pattern of randomness at nearly all quadrat sizes. Some seral characteristics of forest trees support the idea that the beech-maple forest is a mosaic of species of different seral stages.

The floodway zone of the Hoh River exhibits four terrace levels of different ages, formed by erosional activity of the river on valley fills. The vegetation in this valley is in a long—term seral sequence as shown by the zonal pattern in relation to aging and development of these land surfaces. Succession starts on gravel bars, which are dominated by Alnus rubra and Salix scouleriana. The following sequential forest communities, and associated ages of land surfaces, are found: Alnus rubra on alder flats (80—100 yr); Picea sitchensis—Acer macrophyllum—Populus trichocarpa on first terraces (400 yr); Picea sitchensis—Tsuga heterophylla on second terraces (750 yr); and Tsuga heterophylla on third terraces. The latter represents the climax community for the river terrace sere, and it occurs on surfaces exposed by retreating Pleistocene alpine glaciers. The first three terraces are derived from Neoglacial alluvial fills. There is a strong correlation among zonation patterns, forest succession, age of terraces, soil moisture, and soil profile development. Available soil moisture is an important factor governing the zonal sequence. The younger land surfaces are significantly drier than the older terraces. Plants on alder flats and first terraces must withstand greater moisture stress than those of second and third terraces. As the land surface ages, the soil profile develops; deeper, more mature soils are found away from the river. The term "Olympic rain forest" is inappropriately applied to this vegetation; "temperate moist coniferous forest" is more appropriate not only for forests in the Hoh Valley, but also for the rest of the Olympic Mountains and vegetation along the northern Pacific coast.

Theoretical considerations and evidence from the literature suggest that early successional plant species should make a lesser commitment of resources to defense against herbivores, and should then provide better food sources for generalized herbivores than later successional and climax plants. Commitment to defense by plants is estimated by determining short-term palatabilities to two slug species; one native to western Washington, Ariolimax columbianus, and one introduced from Europe, Arion ater. Results of tests with 100 plant species of three growth forms and from different seral stages indicated that early successional annuals were significantly more palatable than early successional perennials which were sig- nificantly more palatable than later successional species. No correlation was found between palatability and evolutionary association of the herbivores with the plant species.

Results from an extensive vegetation survey of 197 boreal forest stands, encompassing a full spectrum of succession and site types in the regions of Ontario and Quebec south of James Bay, are reported. Non-centered principal component analysis plus varimax rotation (nodal component analysis) is applied to overstory and understory data in order to detect vegetational noda. The over- story data are inherently more structured (i.e., contain more distinct subgroups) than those of the understory. An exception is seen with groups in which Abies balsamea plays a prominent role. These are interpreted as stages in various successions of which only one, a Betula papyrifera to A. balsamea sequence, represents the complete transition from one canopy dominant to another. The understory noda are summarized in terms of the compositional and environmental features of stands belonging to each nodum. Relationships among the understory noda are summarized in a multidimensional scaling ordination which is derived directly from similarity values (conjunction coefficients) representing the overlap between pairs of noda. Two major environmental gradients seem to affect understory composition. These are a site moisture-nutrient concentration gradient and a general fertility-productivity gradient. Canopy composition and understory vegetation are compared by nodal conjunction between the two analyses. Groups of noda, representing wet bog forests and also upland mesic forests, show moderate to good coincidence but beyond this little canopy specificity emerges. These results indicate that overstory-understory coincidence is due primarily to similar site requirements. Understory species' response to an overstory succession is examined. Many abundant herbs seem indifferent to dramatic canopy change. This observation and results from nodal component analysis are discussed with respect to forest fire.

Major post-burn plant communities were characterized and environmental rela- tionships investigated on an area burned by forest fires in 1933, 1939, and 1945. Results reveal that seral vegetation developing after three forest fires is classifiable, and the commu- nities show consistent relationships to environmental factors. Both shade-intolerant, early seral species and shade-tolerant, late seral or climax species revealed specific environmental requirements for growth and survival. Species composition and dominance data were re- corded in 42 stands. Six associes were recognized. The Alnus rubra/Polystichutm munitum associes occurs predominantly below 1,200 ft elevation, on north-facing, lower slope positions. These stands usually occupy the stony phase of the Hembre or the Astoria soil series. The Alnus rubra/Rubus parviflorus associes is found on steep, north-facing slopes usually at slightly higher elevations than the Alnus/Polystichurm associes. These stands are predominantly asso- ciated with the stony phase of the Hembre soil series. The Acer circinatum/Polystichumn mnuniturm associes, found on all aspects between 700 and 1,200 ft, was arbitrarily classified into xeric and mesic phases. However, the community is usually associated with steep, lower slope positions. It is also found on the stony phase of the Hembre or the Astoria soil series. The Rubus parviflorus/Trientalis latifolia associes is found on all aspects, on steep, upper slope positions and above 1,200 ft elevation. It occurs predominantly on the Kilchis soil series. Stands of the Pteridium aquilinunm/Lotus crassifolius associes usually occupy gentle, middle, and upper slope positions on all aspects above 1,200 ft elevation. It is found on the deep, stone-free Hembre soil series. The Vaccinium parvifolium/Gaultheria shallon associes is found on south-facing, convex slopes or ridgetops from 700 to 2,100 ft. It occurs to some degree on all soil series in the area. Two provisional associes were recognized: the Acer inacrophyllutnI/Symphoricarpos mollis associes occupying partially-vegetated, south-facing, rock outcroppings and talus slopes, and the Acer macrophyllutm/Alnus rubra associes limited to stream bottoms. Some of the causes of vegetation heterogeneity are discussed, and a dichoto- mous key to the vegetation is presented.

Ecological succession, or the orderly change and development of biotic communities and the ecosystems of which they are a part, is one of the important principles of ecology. Plant succession has been subject to much investigation since 1900, but animal succession is less well-known, studies of it being mostly qualitatively descriptive. Due to the great mobility of animals and the general lack of knowledge dealing with taxonomy and life histories of a large part of the fauna, animal succession in terrestrial communities is more difficult to study than plant succession. At present, the most profitable line of approach is to select for study some significant part of the community or a "population" composed of species groups for which good census methods have been worked out. In terrestrial communities, birds are usually conspicuous components, and the territorial behavior of many species makes possible relatively accurate field determinations of population density during the breeding season. Furthermore, community selection by birds is most pronounced during this critical period in their life history. Since animals, as well as plants, may be active agents in bringing about community changes, quantitative data on population size should help in the understanding, prediction, and control of the changes which we designate as "ecological succession. The present paper deals with the breeding bird populations of areas representing seral stages in secondary succession on the upland of the Piedmont physiographic region. A similar study in the Mountain region has been published (Odum 1950) and one for the Coastal Plain is in progress. For aid in the location and botanical description of study areas we are indebted to the following: Dr. Wilbur H. Duncan, Dr. Don L. Jacobs, Depart1 Present address: Dept. of Biology, Mercer University, Macon, Ga. ment of Botany, and Dr. L. W. R. Jackson, School of Forestry, University of Georgia; Dr. Catherine Keever, State Teachers College, Millersville, Pennsylvania; and Mr. Jack Brown, Soil Conservation Service, Athens, Georgia.

Quiercus garryana forests, prominent at low elevations throughout the Willamette Valley, Oregon, have developed from oak savanna subsequent to settlement of the valley in the mid-nineteenth century. Interruption of the ground fires that were common in the pre- settlement environment probably caused the change. The understory of the oak forest is dominated by shrubs, and well-defined strata are present. Four plant communities occur: (1) Quercus garryana/Corylus cornuta var. californica/Polystichum munitum (most mesic) (2) Quercus garryana/Prunus avium/Symphoricarpos albus; (3) Quercus garryana/Arne- lantchier alnifolia/Symphoricarpos albus; and (4) Quercus garryana/Rhus diversiloba (most xeric). All are in seral condition because of their relatively recent development and because they have been disturbed throughout their existence by man's activities. The soils supporting the oak forest are generally deep and well drained and have developed profiles with illuvial horizons and acidic reaction. They are derived from sedimentary and basic igneous rocks and old valley-filling alluvium. Seven established soil series are present: Steiwer, Carlton, Peavine, Nekia, Dixonville, Olympic, and Amity. The Steiwer series and its catenary associate, Carlton, are the most common soils.

As a means of studying inter— and intrazonal invasion in black sagebrush (Artemisia nova A. Nels) communities six maturity classes were established for pinyon (Pinus monophylla Torr. and Frem.) and juniper (Juniperus osteosperma (Torr.) Little) in east—central Nevada. Pinyon and juniper invade and increase in black sagebrush communities until the understory, except for a few hardy plants, is eliminated. Juniper invades first and tends to be eventually replaced by pinyon. Accelerated invasion by both species started about 1921 and is closely related to overgrazing, fire suppression, and climatic change. See full-text article at JSTOR

A comparison of climate, soils, vegetation, and biotic history of mediterranean ecosystems revealed closest ecological equivalence between the blue oak grassland in California and the vallonea oak grassland in Israel, both mediterranean oak savannas in which overall environmental resemblance seems closest. Ecological amplitude and syndynamics in most other comparable types are similar, but the chamise chaparral on non-calcic brown upland and lithosols differs from its maqui counterpart by its one-layered structure and by its adverse influence on the ecosystem. Annual grasslands in California foothills are comparable to seral batha dwarfshrub and grassland in Israel as human-induced degradation stages of chaparral and maqui. For such ecological comparisons a holistic ecosystem approach seems more suit- able than any preconceived phytoclimatic and climax concepts.

A study of bird species diversity (BSD) on three seral stages characteristic of secondary succession on the New Jersey Piedmont was done during the winter of 1968—69, the spring of 1969, and the summer of 1969. The seral studies were a 2— to 33—year—old field (the herbaceous field), a 30—year—old field (the cedar field), and a climax oak—hickory forest (the oak forest). Two study plots, each with an area of 2 hectares, were chosen within each seral stage. Diversity indices were calculated using the Shannon—Weaver information formula, H'=—-Σpilogepi. The species count (species richness) was found to account for many of the differences in BSD between the seral stages. The evenness with which species were numerically distributed (equitability) was found to be lowest and to be lowest and to have its greatest influence on the diversity index in the herbaceous field, due to the presence of large flocks of non—nesting species. Equitability was higher and more constant in the cedar field and oak forest. Territoriality was thought to account for the higher equitabilities observed in summer. In winter, the more rigorous environment was thought to be a factor in lowering the equitability at least in the cedar field.Equitability was not lowered as much in the oak forest, possibly due to aggregations of birds into mixed species flocks. The cedar field and oak forest were qui te different in the seasonal patterns of equitability. Both species richness and equitability were concluded to be important parameters in ecological study.

A gradient analysis and description was made of forest succession among the Thuja plicata—Tsuga heterophylla communities in the vicinity of Lake McDonald in Glacier National Park Montana. Thirty—three pioneer, seral, and climax communities located on well—drained slopes at elevations between 3,200 and 3,500 ft (1,050—1,150 m) were sampled. Through the calculation of indices of community similarity and dissimilarity, the stands were objectively arranged along a unidimensional gradient. The data summarized along the resulting ordination gradient provide a quantitative description of the basic successional pattern existing among these cedar—hemlock communities. Typically, following burning Pinus contorta communities become established, and these in turn are gradually replaced by Pinus monticola and Pseudotsuga menziesii in various proportions. Climax communities on the upland sites become dominated by Tsuga heterophylla, with smaller, but self—reproducing populations of Thuja plicata also persisting. See ful...

This study is the second of a series dealing with aspection and fluctuations in animal populations of wooded areas. The data were collected in connection with a study of prairie uplands in McClain County, Oklahoma (Carpenter, '36b). The topography of the region is characterized chiefly by rolling hills separated by ravines. In some places gullying has greatly increased during the period of heavy grazing prevailing since the latter portion of the last century. The consequent succession and the seasonal aspects of the more distinct seral communities are described.

Overstory and understory data were collected from 49 forest stands in 27 small stream bottoms in the Gulf Coastal Plain region of southwestern Alabama. The stands were arranged in a single—dimensioned ordination on the basis of the importance values of the persistent species in the overstories. Leading dominant species, from the dry end to the wet end of the ordination gradient, were Cornus florida, Pinus palustris, Quercus nigra, Liquidambar styraciflua, Nyssa sylvatica v. sylvatica, Magnolia virginiana, and N. sylvatica v. biflora. Two important seral species, most prominent at the middle of the ordination gradient and of relatively little importance at either end, were Pinus elliottii and Liriodendron tulipifera. The stand position on the ordination gradient, referred to as the moisture—regime index, was significantly related to water—table depth, soil—surface gradient, and soil pH at 63.5 cm. Failure to obtain significant relationship with other soil variables was attributed to the high frequency of fresh soil deposition in the small stream bottoms. As a check on the ordination analysis, species—present data were used to construct a species—correlation diagram. When species moisture—regime numbers from the ordination analysis were inserted in this diagram, good agreement was revealed in the results of the two independent analyses.

An investigation of the Tomocerinae was concducted in a selected series of old field successional .stands in the Piedmont of North Carolina to determine the variability in size and trivial composition of populations in different seral stages of old field communities. An analysis of seasonal fluctuations in density and frequency of the several species was computed to decide what microclimatic factors affected each member of the .subfamily; stratal sampling was employed to establish the possibility of vertical migrations in the litter-humus layer and underlying soil strata. The Piedmont region of North Carolina presents an orderly secondary succession of vegetation following the abandonment of upland fields (Oosting 1942). Five types of old field communities were chosen for study with paired stations established for each successional stage with most stations located in the Duke University Forest (Figure 1). The author is grateful to Dr. I. E. Gray of the Department of Zoology, -Duke University, for guidance and helpful criticisms, anid to Dr. David Wray of the North Carolina Department of Agriculture for confirming the -identifications of the Tomocerinae.

The pifion pine (Pinus monophylla) dominates a belt of vegetation in the mountains of the southwestern deserts which falls altitudinally between the higher, montane associations, such as yellow pine and Douglas fir, and the lower desert scrub and Joshua tree associations. Typically pifions grow in open stands. with tracts of shrubs of seral type interspersed. Junipers (Juniper utahensis) are intermixed in varying degree but occur most commonly on arid ridges and benches with shallow soil. In zonal classification, the pifion belt falls in the Upper Sonoran Life-zone. In terms of biomes it is related to the woodland formations because of the ample spacing and small stature of the trees. The pinon in this area seldom assumes the aspect of a full dominant in its association; a climax condition as typified in coniferous forest formations, with which the association has many floral affinities, is rarely attained. Because of its decidedly mixed relationships, as well as its distinctive aspects, the pifion-juniper community is often usefully regarded as a major biotic unit or formation. In a survey of the higher parts of the Grapevine Mountains, Death Valley National Monument, during the first ten days of June, 1940, I became impressed with the unusually heavy stand of pifions there and with the presence of birds not normally found in association with this tree. The Grapevine Mountains border the north arm of Death Valley on the east, along the California-Nevada boundary; their crests are east of the line in Nye County, Nevada. Two high points, Grapevine Peak, 8,705 feet, and Wahguyhe Peak, 8,590 feet, dominate the center of the range and are but three miles apart. The crest between them is nowhere less than 7,500 feet. On lower peaks to the north and south some pifion woodland occurs, but the peculiarly heavy tracts of pifion are scattered about the high peaks on the northeast slope of the range. The lowest pifions on this slope are at about 6,000 feet. Only near the summits of the two high points are there small numbers of limber pine (Pinms flexilis) and these are so sparse and so intermixed with pifions as scarcely to form a distinctive association. Further attention devoted to the vertebrate fauna of these mountains, and particularly to the birds, has convinced me that some kinds unexpected in the region occur there because of the unusual density of the pifions. This density provides "life-forms" or physical aspects of vegetation that normally are found only in forests of other kinds of conifers. Another group of animal species seems to be present primarily because of the high elevation and consequent conditions of temperature and perhaps moisture. In mountains such as the Toyabe Range, 100 miles north, there are tracts of mountain mahogany (Cercocarpus) between the pifion belt and the limber pines, that may be classed as Transition Zone (see Bailey, '36, p. 24). The comparable altitudinal range in the Grapevine Mountains is occupied by what seems to be an unusual upward extension of the pinions so that they actually mingle with and surround the limber pines. Transition-zone trees such as yellow pine (Pintis ponderosa) and Douglas fir (Pseudotslfga taxifolia) are wholly lacking. The pinons then range into a high altitudinal belt that is correspondingly cool in summer and they attain a climax stand, in places, which provides plant-growth forms usually lacking in this association. Both factors con