Types of Vegetation in the San Joaquín Valley of California and Their Relation to the Beet Leafhopper

TECHNICAL BULLETIN NO. 557 JUNE 1937

TYPES OF VEGETATION IN THE SAN JOAQUÍN VALLEY OF CALIFORNIA AND THEIR RELATION TO THE BEET LEAFHOPPER

By R. L. PIEMEISEL Physiologist Division of Sugar Plant Investigations Bureau of Plant Industry and F. R. LAWSON Junior Entomologist Division of Truck Crop and Garden Insects Bureau of Entomology and Plant Quarantine

UNITED STATES DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C.

For lale by the Superintendent of Documenti. Washington, D. C Price 10 cenu Technical Bulletin No. 557 June 1937

UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C.

TYPES OF VEGETATION IN THE SAN JOAQUÍN VALLEY OF CALIFORNIA AND THEIR RELATION TO THE BEET LEAFHOPPER

By R. L. PiEMEiSEL, physiologist, Division of Sugar Plant Investigations, Burean of Plant industry, and F. R. LAWSON, junior entomologist, Division of Truck Crop and Garden Insects, Bureau of Entomology and Plant Quarantine ^

CONTENTS Page Introduction 1 Types of vegetation—Continued. Definition of types of vegetation and their Plant communities along washes and relationships 3 stream beds 16 Relation of types of vegetation to climate and Plant communities of minor importance.. 17 topography 4 Changes in weedy plant cover _ 18 Types of vegetation ^ 6 Principal species of present plant cover 20 Tree savanna 6 Possibilities of reduction of weedy areas and Pacific grassland 8 the effect on leafhopper population and curly Desert saltbush 10 top damage 24 Spiny saltbush 13 Summary 27 Lowland types 14 Literature cited 28

INTRODUCTION Earlier studies by a number of investigators have determined that in the San Joaquin Valley of California the virus disease curly top causes damage every year to sugar beets, tomatoes, beans, melons, and squash, as well as to other truck crops and to ornamental plants, and that severe crop losses have occurred in years of high population of the beet leafhopper {Eutettix tenellus (Baker)), only known vector of the curly top disease. The life history and general movements of the leafhopper are also known. In the spring at the time of the drying of winter annuals on the range lands of the western side of the valley, the insect moves clown into the valley onto green summer annuals or onto crops, where it remains during the summer. In the fall, at the time of harvesting beets and when the summer annuals dry, the leafhopper moves back to the range lands onto

1 The authors are indebted to Eubanks Carsner, senior pathologist, Division of Sugar Plant Investigations, Bureau of Plant Industry, and W. C. Cook, entomologist, Division of Truck Crop and Garden Insects, Bureau of Entomology and Plant Quarantine, for suggestions during the course of the work and for their criticism of the manuscript ; also to the late A. S. Hitchcock, principal botanist, and Agnes Chase, associate botanist, Divi- sion of Plant Exploration and Introduction, Bureau of Plant Industry, for identification of the grasses, and to S. F. Blake, senior botanist, and Ivar Tidestrom, formerly assistant botanist, of the latter division, for identifying plants other than grasses. 112826°—37 1 1 2 TECHNICAL BULLETIN 5 5 7, U. S. DEPT. OF AGRICULTURE whatever host plants are green and feeds on these until the winter rains again bring on the growth of winter annuals. When this study was begun it was not known whether the present breeding grounds and food supplies of the beet leafhopper were static in location and area or whether they were temporary in nature and might be subject to great changes in both location and area. It has recently been shown by Piemeisel (8)- that the annuals serving as spring and summer hosts do not form a large part of the original vegetation in the southern Idaho area, that their great abundance is the result of overgrazing and abandonment of plowed lands, and that if abandonment ceased and grazing were restricted the host plants would be replaced by nonhost plants, chiefly grasses, and eventually by the original vegetation. A similar situation exists in the San Joaquín Valley. However, since the reestablishment of the original vegetation, and also to some extent the stands of host plants, depended on what the original type had been, it was necessary to know, insofar as possible, the extent and composition of the present vegetation and of the original types. This information was not available in published works. Jeps(}n (5) gives the zonal arrangement, a brief description, and the principal species of some of the types in California, but most of these are at a higher altitude than the area considered here. Other authors, mentioned later, discussed one or more of the types with the characteristic species. No detailed maps of the vegetation oí the valley were available. Accordingly, the types of original vegetation were reconstructed a« far as they could be from the studies made, and their probable boundaries were mapped (fig. 1). The present vegetation was also mapped (figs. 2 and 3). In the following pages each of the principal original types, shown on the map, is briefly described. The derivation of present stands from the original, through modification or destruction, is also discussed, as well as the relation of the present stands of each particular type to the beet leafhopper. To show these interrelationships for the valley as a whole, a diagrammatic representation was made (fig. 4). The more important relationships are discussed in more detail later. To facilitate the use of figure 4, the names of the plants used are here given in full: Desert saltbush, also known as allscale {Atnplex folycarpa (Torr.) S. Wats.) ; spiny saltbush, also known as spine- scale (Atriplex spinifera Macbride) ; bract scale (A. hracteosa S. Wats.) ; saltgrass {DisticMis npicata (L.) Greene) ; Kussian-thistle {Salsola pestifer A. Neis.) ; seepweed, also known as alkali blite (Dondia moquini (Torr.) A. Neis.) ; alkali heath (Frankenia grandi- folia C. and S.) ; and pickleweed {AUenroIfea occidentalis (S. Wats.) Kuntze). The following treatment of the types of vegetation is far from complete from a broad ecological viewpoint, since features closely related to the beet leafhopper are stressed and others omitted. Never- theless it is hoped that the information given may be of use to future investigators of the plants and animals of the section and that it will fill a need such as that experienced by the writers when the present study was begun.

2 Italic numbers In parentheses refer to Literature Cited, p. 28. imuUITree Savanna ^3 Desert Soitbush E^Pacific Gross I ond ^S! Spiny Soltbush ES] Lowland Types Scale of mi les o 5 10 15 FiacBE 1,—Map showing jirinoipal oriKinal types of vegetation in the San Joaquín Valley» (Coiiilai-e with fig. 2.) 112Si:(i°—37 (!■"«<•'■ p. 2) No. 1 ^Winter Annuals ^Desert SoItbush QUID] Form Land ^ Spiny Soltbush ES Lowlond Types Scale of miles IIii'i I I 0 5 10 15 FiocRE 2.—Map of Togetation of the San Joaciuin Valley as it is at present. The boundary lines were drawn from surveys in addition to those made from the original vegetation types. Solid lines indicate boundaries actually surveyed. Dotted Unes show estimated boundaries Ijttwren parts surveyed. (Mapped by F. B. Lawson.) 112820=—37 -Far-ep. 2) X.,. 2 O FOGWEED C BRACT SCALE {Atriplex expanse) (A. bracfeosa) • RUSSIAN-THISTLE (Sa/so/c7 pesfifer) Each dof represents 500 ocres Scale of miles

FiGCHE 3.—Map slio^iug tiistribution of su:!;nier weed hosT.s in 1933. 1128-0°^-37 iFa-,<'i'--) N'J. •; VEGETATION IN THE SAN JOAQUÍN VALLEY 3

DEFINITION OF TYPES OF VEGETATION AND THEIR RELATIONSHIPS Throughout this bulletin the common terms "weedy areas" and "types of original vegetation" are used. "Weedy areas" refers to the

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vegetation" is used to designate the vegetation as it existed preceding the intensive disturbances caused by the white man. The "types' are tlie stabilized units that together formed the original vegetation. Their composition and extent are reconstructed insofar as possible for the period given above. The San Joaqnin Valley is a meeting place of the desert formations of the interior, the Mohave and Colorado Deserts, and the grassland and broad sclerophyll formations of the Pacific slope. The outline given below shows the relation of the units of vegetation of this valley to the classifications made by previous investigators for the sections just mentioned. Cooper (5), who dealt chiefly with the Coast Eange area, divided the broad scleroplij-ll vegetation into the broad sclei'ophyll formation and the chaparral formation. The tree savanna of this bulletin is probably a nearly related, more arid form of his Qnei'(.'UH agrifolm-lohata association included in the broad sclerophyll formation. Clements {2) classifies the grassland as a Stipa-Poa association of the Stipa-Bouteloua formation. 81iantz and Piemeisel (11) have specified rank for a number of units of vegetation in the southwestern desert region that are common to the San Joaquin Valley. These belong to the two formations—the southwest desei't shrub or creosotebusn formation, and the salt desert shrub formation described by Shantz {10). Units of original Vegetation Ciassiflcation Tree savanna Quercus agrifoUn-lohnta association ; broad sclerophyll formation. Paoiflc grassland .Siiprt-Poa-association ; Gra.ssland (Stipa-Boutclmm) formation. Desert saltbusli Atrlplex polycarpa association; southern desert shrul> or ereosotebush formation. Spiny saltbush Atriplex spmifera association; salt desert shrub formation. Pickleweed Allenrolfea association; salt desert shrub formation. Seepweed Dondia association; salt desert shrub formation. Saltgrass Distichlis association; salt desert shrub formation. Alkali heath Franhenia association ; salt desert shrub formation. Clements' classification arranges these units somewhat diiferently. He designates the grassland a.s the climax and the only association. The other units become developmental units, "associes." Thus desert saltbush becomes a subclimax and an "associes" rather than an association. In addition to the types or units of original vegetation given above, there are listed under miscellaneous plant communities those of slight extent, of a mixed nature, or of undetermined stability, that cannot be related to any system of classification with the information available at present.

RELATION OF TYPES OF VEGETATION TO CLIMATE AND TOPOGRAPHY

The San Joaquin Valley is separated from the more humid coastal section of California by the Coast Eange on the west and the Tehachapi Mountains on the south. This separation is complete except for the break opposite San Francisco Bav, where the drainage from the Great Valley^ cuts a broad gap "through the Coa.st Eange. The influence of the coast through this opening causes a

= The Great Valley includes both the Sacramento and the San Joaquin Valleys. VEGETATION IN THE SAN JOAQUÍN VALLEY 5 gradient of temperature and rainfall from Stockton, with a mean annual temperature of 60.1° F. and a mean annual rainfall of 14.57 inches, to a hotter and drier climate at Bakerefield, which has a mean annual temi)erature of 65.1° and a mean annual rainfall of 5.39 inches. The effect of this gradient of temperature and rainfall is reflected in the distribution of the types of vegetation (fig. 1). The mean annual rainfall for the vegetation types, as indicated by 27 stations in the valley, is shown in table 1. Stations near the borders of types and stations where distui'barice had been so great that there was nuich doubt as to the original type were not included. All stations had a record of at least 20 years, and the longest was 65 years. The annual rainfall as shown in table 1 by both the mean and the range fi'om the highest to the lowest station in the ty])e is least for desert saltbusli, the driest type, and most for tree savanna, witli Pacific grassland in an intermediate position. The distribution of lowland types, discussed in more detail later, is dependent on under- ground water rather than directly on precipitation.

TAHI.E t.—Coinpiirison (if mean rai-nfall' of stations in the Sail Joaiiidii Vallen ill relation to types of original ref/elatioii

Mean annual ra infall

Type of vegetation Stations Average .\t wet- of all test At driest stations station station

Nu víbcr Incites Iitclirx Im-hr.s 6 15. 22 19. 35 12 10. 35 12. 35 Desert saltbush 5 5. 83 0. 3'! 5. 15 I>owland tyjtes and spiny saltbush 4 '7.15 8. 13 0.30

1 Data from reports of the Weather Bureau. IJ. S. Department of .Agriculture. ' The soil moisture in these types is augmented by a high water table.

The tree savanna occupies the higher hills in the southern part, gradually descends to the lower hills, and finally (in the north) crosses the valley floor. The Pacific grassland type descends to lower altitudes and crosses the valley floor in a similar numiier. Desert saltbush, which occupies the drier portions of the valley, becomes nar- rower in the north until it is finally pinched out just north of the Fresno-Merced County line. The apparent discrepancy between the belts of vegetation and topography, in that tree savanna and grassland, which cover respec- tively the lower foothills and the higher slopes of the valley in the central and southern parts of the valley, also cover the lowest portion of the valley in the north, is better understood if the two belts are imagined not as concentric belts parallel to the valley floor but as dipping downward as one goes north and finally reaching the valley floor. The reason for this has already been given, namely, that the north end, although it is the lowest part of the valley, is onen to the sea, and has lower temperatures and higher rainfall than trie central and southern portions. 6 TECHNICAL BULLETIN 5 5 7, U. S. DEPT. OF AGRICULTURE

From Suisun Bay south to the Tehachapi Mountains the Coast Range becomes higher with a steeper slope. The valley floor rises gradually in the same direction, that is, the altitude at the lowest point in the southern part (Buena Vista Lake) is 291 feet, and at Stockton, in the north, 23 feet. However, this slope is very gentle, being only 268 feet in nearly 225 miles. The streams south of Fresno either flow into the now dry lakes of Tulare and Buena Vista or empty into the valley floor. Although these two lakes are connected with each other by Goose Lake Slough and with the San Joaquín River by Fresno Slough, there is no flow except in seasons of very heavy rainfall. In the northern half of the valley the course of the San Joaquin, from Mendota to Modesto, is sluggish and divided. Thus the floor of the valley in its southern and central portions is poorly drained and has a high water table and its soils have a high salt content. The vegetation of this section consists of plants adapted to the high water table and high salt content. TYPES OF VEGETATION

TREE SAVANNA

LOCATION AND EXTKNT Since most of the tree savanna lies above the breeding territory of the leafhopper, less efi'ort has been made to fix the boundaries of this type than of some of the others. The upper limits are nowhere shown, whereas the lower are given only where tree savanna enters the valley or where it is present on the nearby hills. Generally tree savanna is bordered on its upper boundaries by chaparral and on its lower by grassland. In going south from Bakersfield and up the Tehachapi Mountains, tree savanna is reached in a short distance, owing to the steep slope and its northerly exposure (fig. 1). On the other hand, west and somewhat south of Bakersfield, in the Taft-McKittrick district, there IS a wide belt of low hills on which tree savanna does not appear, and the type comes in only after the range west of the Carrizo plain is reached. Just north of the Carrizo plain tree savanna again appears on the higher hills bordering the San Joaquin Valley and continues northward, gradually descending to the lower hills and finally cross- ing the valley floor just below Stockton to join with a tree savanna belt on the western slopes of the Sierra Nevada. On the Sierra Nevada side the lower boundary of tree savanna is very irregular. It may be high up the slopes, as at the town of Friant, or may swing far out on the plains, as it does near Tulare. The marked extension of the tree savanna area into the valley near Tulare (fig. 1) is probably due to the broad alluvial fan formed by the many branches of the Kaweah River. It is quite likely that close study of the tree savanna that is dependent on ground water would result in its separation from the tree savanna dependent on rainfall. Lacking such information, the two have been grouped together in this bulletin since they are much more closely related to each other than to any of the other types. On the valley floor the northward extent of tree savanna has not been determined. From Lathrop north large portions have been VEGETATION IN THE SAN JOAQUÍN VALLEY 7 cleared and farmed, but groves of oaks occur along watercourses, and occasional trees are present in fields, i)asture lands, and farmyards. The size and arrangement of these scattered trees indicate that they are part of an original growth rather than plantings or a recent growth. Moreover, the scattering of trees is lacking south of this belt, except for limited areas along the streams. The northern portion of the tree savanna, which extends across the valley, covers, for the most part, sandy loams, while the portion in the foothills of the central and southern part commonly occupies rough lands with coarse and often stony soils.

BOTÁNICA!, COMPOSITION The tree savanna originally consisted of a scattered growth of oak trees and an undergrowth of perennial grasses (fig. 4). The oaks were chiefly Quercus lohata Née (valley white oak), Q. douglanii Hook, and Arn. (California blue oak), and Q. wislizeni A. DC. (highland live oak). On the valley floor Q. lohata is the most common. The perennial grass cover is discussed under the next type, Pacific grassland.*

DESTRUCTION OR MODIFICATION OP ORIGINAL VEGETATION AND RESUI.TING STAND In the tree savanna type, modification of the original stand has been general, while complete destruction has taken place in a comparatively small area. That is, over most of the area originally covered by the type the perennial grass cover among the scattered growth of oaks has been destroyed by grazing, but the trees over this portion are, for the most part, standing. The perennial cover among the oaks has been replaced by an annual cover of grasses and herbs, such as wild oats {Avena fatua L.), three alfilerias"^ {Erodium cifíutarium (L.) L'Hér., E. hotryu BertoL, and E. moschatum (L.) L'Hér.), annual barley grasses {Hordeum niuHnum L., and related species), and others. (See lists, figs. 11 and 12.) The part almost completely destroyed is the valley portion in the north. Here cultivation has destroyed all but a scattering of trees around farm build- ings, in pastures, and occasionally in fields. Fallow lands and neglected croplands are covered with annuals, of which the principal species are the following: Fiddleneck {AmAncMa si)p.), common mustards {Braf

RELATION OF PLANT COVEE TO LEAFHOPPEK POPUT^ATION

Although important hosts are found in the tree savanna, the type as a whole is not of importance as a breeding area. In the hilly higher portions, although winter annuals are abundant, the leafhopper is not found in large numbers. In the smaller valley portion

PACIFIC GRASSLAND

LOCATION AND EXTENT Pacific grassland, as shown in figure 1, forms a continuous belt which completely surrounds the central and southern portions of the valley. North of Fresno the type drops farther down the sides of the valley and finally covers the valley floor just south of the tree savanna area. The narrowest portions of the belt are in the southern sections where the rise from valley floor to high hills is abrupt. In the hills, at its upper limits, grassland irregularly occupies the exposed slopes and the tree savanna the protected slopes. The lower limits between grassland and desert saltbush on the western side are not well defined at present, and originally they probably overlapped to a considerable extent. Below approximately 1,500 feet, in the southern portion of the valley, bunch-grass tufts exist at present only on the north slopes of the hills and in diminishing abundance as one approaches the edge of the plains. Desert saltbush occurs on both north and south slopes below approximately 1,500 feet. The soil types most prevalent in the grassland area are sandy loams. On such soils grassland originally extended far down into the valley on the eastern side. On the western side the plains are of a heavier soil type and are covered with desert saltbush (fig. 1).

BOTANICAL COMPOSITION The type was; originally a cover of perennial bunch grasses, but it is now almost entirely destroyed. Weaver and Clements {1^) con- sider '■'•Stifa setigera''' (a name formerly used for S. pulohra Hitchc, purple needlegrass) as the former dominant of the Pacific prairie, with which were associated S. eminen,s Cav. (formerly used for S. lepida Hitchc, foothill needlegrass), Koeleria cristata (L.) Pers. (junegrsiss), Poa scabrella (Thurb.) Benth. (pine bluegrass), ^e/éc?« imperfecta Trin. (California melic), Elymnjbs sitanion (now referred to Sitanion hyst/rix (Nutt.) J. G. Smith, squirreltail), and E. triti- coides Buchl. (beardless wild-rye), with species of Danthonia (oat- grass), Bronrns (bromegrass), and Festwoa (fescue) under moister and cooler conditions. Species of Stipa, Poa, Mélica, and Danthonia can still be found on northern slopes or in protected places. Where scattered stands remain it is rare to find these grasses in head, since they are eaten off to the ground. A description of the former stands of grasses in the moister coastal districts of northwestern California, together with an account of the changes resulting from excessive grazing, is given by Burtt Davy {1).

DESTRUCTION OK MODHTCATION OF ORIGINAL VEGBJTATION AND RESULTING STANDS The major portion of the grassland belt northward from a point west of Los Banos, then eastward across the valley, and finally south along the east side of the valley, has been destroyed by cultivation VEGETATION IN THE SAN JOAQUÍN VALLEY 9 and is farmed at the present time (figs. 1 and 2). The portion that has not been ploAved has been greatly modified by overgrazing. The bunch-grass area south from Los Banos on tlie west side of the valley has likewise been greatly modified by overgrazing and some of the small valleys have been cultivated. On the more exposed slopes in this ovei'grazed section destruction of the original stand has been almost complete and such areas are now occupied by winter annuals, annual grasses where not too heavily grazed, but herbaceous annuals over most of the area. Chief of the annual grasses are wild oats.

FKíTKH 5.—A winter ainiuul ouxcr (durk poi-tiun in iorcKfound) willi nearly Ijai'e areas (middle) on wliieh lartre leafhoi)pei- i>(>pnlations are bred. In the l)aek;.:round are bare, eroded soutliern slopes. The tall plant in the foreground is Aploptiiipus, a perennial weed, common on heavily grazed land.s. (liig I'anoehe Canyon. Calif.. January 1924.) wild baideys (Ilordcum, s])p.), and foxtail chess {Bromun riihciiK L.), while the principal herbaceous annuals are alfilerias (M rod him cicutarimn. and K. hotryis), peppergrass [Lepidium nitidum Nutt.), and plantain {Flautado erecta Morris). The most generally distributed of these are Ihe two s])ecies of alfileria and foxtail chess. Locally, peppergrass, plantain, fiddleneck, and popcorn floAver {PJagiohotht^s vothofulvus A. Gray) occur in great abimdance (fig. 5). Perennial weeds such as matchweed {Gutierresia ealiforniea (DC.) T. and G.) and Aplopappm venetus vernonioides (H. B. K.) Blake {Isocoma véneta) are contmon, forming sparse stands. In some years the summer annuals, bluecurls or vinegarweed (IVicho-^teiiia lanceolatum Benth.), and tarweeds {Hemizonia spp.), form oi)en stands over a considerable area. Russian-thistle forms sparse, (¡pen stands on ¡Jortions of the overgrazed range west of Los Banos (fig. 6). 112826°—37 2 10 TECHNICAL BULLETIN 5 5 7, U. S. DEPT. OF AGEICULTURE

With respect to both area covered and numbers of plants, winter annuals form the bulk of the secondary growth. The more protected slopes show stands of bunch grasses of varying density but never a complete cover. The tufts of the perennial grasses are usually closely clipped and always mixed with a secondary growth of annuals or perennials.

riGURE 6.—Russian-tllistle on bunch-Kra.ss range as a result ot destructive grazing. Sucli stands are favorable for high leafhopper populations. (North o£ Ortigalita Creek, Calif., September 1931.)

BEILATION OF PL.\NT COVEM 10 LEAFHOPPiJK POPULATION In the uncultivated portions of the grassland type, plantain and peppergrass form short open stands on the overgrazed southern slopes (fig. 7). Where such stands are near patches of fall hosts, such as Lepidospartum squamatum A. Gray, or California sagebrush (Artemisia californica Less.), or scattered desert saltbush in the grassland area, they form the most favorable winter breeding grounds of the leafhopper. DESERT SALTBUSH

LOCATION AND EXTí;NT Desert saltbush occupies the hot, dry plains of the southern and western portions of the valley. On the western side the type is pinched out near Los Banos between Pacific grassland and lowland types (fig. 1). South of this the type extends in a narrow strip to Oro Loma and then broadens to a belt 10 to 20 miles wide which extends south to Buena Vista Lake. From there east the belt narrows to a few miles in width, reaches across the southern end of the valley, and then north to Bakersfield. From there it forms an irregular area to about 40 miles north. Originally it may have extended considerably beyond this, but here the changes following cultivation have been too great to obtain definite evidence on this point. Changes have not been so great over the desert saltbush area as a whole and there is sufficient evidence for mapping the original extent of this VEGETATION IN THE SAN JOAQUÍN VALLEY 11 type as shown. There is no indication that any considerable portion of the large desert saltbush area is a secondary succession following the destruction of a former grassland. Bunch grass probably occupied none of this area with the possible exception of small particularly favorable localities, such as portions of alluvial fans. Ex- isting remnants of the desert saltbush indicate occupancy of the area for a long period. The appearance and size of the bushes themselves, the presence of dead wood, and the appearance of the hummocks of soil surrounding the bushes all indicate a considerable age.

FIGURE 7.—Hilly bunch-grass liind with slirnbby perennials, chiefly i;okJen-aster (Chry- sopnifi rillosa) aUma the wash. The hills on both sides of the wash are covered with winter annuals. Leafhoppers are bred in large numbers on the south-facing, nearly denuded slopes (upper portion) adjacent to the shi-ubby growth of the wash (middle portion). (Lone Tree Creek, San Joaquin County, ('alir.. May 15, 1934.)

In addition, the mean annual rainfall in the two types shows a well-defined difference (table 1). Probably there was originally a wide transition area in which the two types overlapped. The lower limits of desert saltbush, that is, the spiny saltbush border, is quite distinct, for here the types have been disturbed much less. The large desert saltbush plains on the western side of the valley are composed mainly of two types of soil, Panoche loam and Panoche clay loam, as shown on the soil map by Holmes et al. (4). Of these, the Panoche loam occupies the greater area. Panoche sandy loams cover a comparatively small section.

COMPOSITION AND APPBUBANCE No adequate description of the original stand of desert saltbush has been found, and at present it is diíBcult to determine what the former composition was. It is likely that the stand was one of desert saltbush with a scattering of herbaceous plants in the interspaces. At the lower elevations the bushes were probably larger and nearer together, so that the herbaceous plants were fewer, whereas 12 TECHNICAL BULLETIN 5 5 7, TJ. S. DEPT. OF AGRICULTURE in the upper portion, toward the bunch grass, the bushes were more widely spaced, the interspaces containing more herbaceous plants and some perennial grasses.

DKSTBUCTION OR MODIFICATION OF ORIGINAL VEGETATION AND KESUI^TING STAND In some localities the shrubs have been removed by dragging, to lessen fire hazard in the vicinity of oil fields, but the largest portion has been killed off either by farming or attempts at farming or by trampling and browsing. This is true of the large plains area of the desert saltbush land, though considerable tracts still exist as remnants of the original vegetation (figs. 1 and 2). However, these are greatly modified by grazing. The bushes are severely browsed and reduced in size, and the herbaceous cover has been extended. Where tlie shrubs have been removed the cover is entirely a herbaceous one. Thus all gradations are present—areas where the bushes are intact, scattered stands of dead or half-dead shrubs, large tracts with only stumps left, and areas with only a herbaceous cover. The herbaceovis cover consists largely of winter annuals, princi pally alfileria, peppergrass, foxtail cliess, plantain, and others given m the lists (figs. 11 and 12). The growth is somewhat similar to that on bunch-grass land, but here it is shorter, sparser, and less uniform, in the drier years, often forming patches rather than a continuous cover. Tlie mnnber of species is less here than on bunch-grass land. Two species of alfileria {Erodium hotrys and E. moHchatum) that occur in bunch grass do not occur or are rare. In the desert saltbusli area proper, summer annuals do not occur to any extent. Kussian- thistle does not occur outside of recently abandoned lands. In the transition belt between desert saltbush and bunch grass it normally forms sparse open stands on alluvial fans in the Coalinga area and the area innnediately south of Little Panoche Creek, and in some years it occurs on extensive tracts in these areas.

Eia^\TION OF PLANT <'OVKR TO LELiJ-HOPFlCB POPULATION Over the entire area where desert saltbush occurs it is the principal fall host for the beet leafhopper. After the fall movement from desert saltbush onto the sprouting winter annuals, plantain, peppergrass, and other less abundant hosts carry the leafhopper through the winter and spring. The first two plants are widely distributed and very abundant over the entire area of the desert saltbush type. On those areas from which desert saltbush has been removed the populations of leafhopj^ers are small, owing to the absence of suitable hosts to carry the insects through the period between the drying of summer hosts and the sprouting of winter aimuals. On the plains where desert saltbush is still present, significant numbers of leafhoppers are car- ried through the fall on desert saltbush and breed in the spring on winter annuals. However, in the drier seasons the annuals of this type dry up early before the leafhopper can produce a spring genera- tion. Consequently, the highest sprmg populations are produced in the hdls below 1,500 feet in the transition belt between the desert saltbush and bunch-grass types where the annuals do not often dry so early. During the summer leafhoppers breed in abundance on Rus- VEGETATION IN THE SAN JOAQUÍN VALLEY 13 sian-thistle, which occurs in the desert saltbush type on abandoned lands. SPINY SALTBUSH

LOCATION AND EXTENT

The spiny saltbush type forms an almost continuous belt of varying width from Gustine south to Buena Vista Lake, then east across the end of the valley and north beyond Bakersfield, where it swings west, almost forming a loop. The belt in its entire length skirts the lower edge of the desert saltbush, separating it from the lowland types. The type is lacking on the east side of the valley north of Tulare Lake. ït occurs outside of the area shown on the map in scattered stands mixed with desert saltbush on some of tlie hills in the Tumey Gulch area where gypsum is evident. Spiny saltbush covers the lower portion of the Panoche clay loam area, roughly that part below the alkali line on tlie soil map by Holmes et al. (4).

APPEARANCE AND BOTANICAL t'OMPOWITION The general appearance of a spiny saltbush cover somewhat re- sembles that of desert saltbush. It is likely that the numbers of herbaceous plants in the original stand of spiny saltbush were even fewer than in desert saltbush, since over most of the area the bushes were nearer together and the upper soil layer is often covered with a crust of "alkali" soil. In the remnants of this type that exist today the winter annuals are scarce when the bushes are in a good healthy condition and with their original spacing. Winter annuals appear in the spots where the bushes have been removed, though the stand is often sparse and consists of few species.

DESTRUCTION OK MODIFICATION OF ORIGINAL VEGETATION AND RBSULTING STAND

A large proportion of the spiny saltbush cover has remained intact, the proportion being greater than in any of the other types, hence remnants form the bulk of the area shown as spiny saltbush on the map (fig. 1). In these, winter annuals, chiefly peppergrass and goldfielcls {Baeria spp.), form scattered patches, and summer annuals are lacking. The portions that have been cleared and cultivated are comparatively small, but, where abandoned, bract scale, fogweed {Atriplex expansa (Dur. and Hilg.) S. Wats.), spikeweed {Hemizonia pungens (H. and A.) T. and G.), and Banda hyssopifolia (Pall.) Kuntze are common, with Russian-thistle less so. Browsing by sheep has had a much less serious effect on spiny saltbush than on desert saltbush, and no large areas of it have been destroyed in this manner. Spiny saltbush seeds and dries in the spring and early summer and does not start growth again until late fall (the latter part of November or first of December), consequently it is not browsed so heavily. Moreover, some protection is afforded by the spiny nature of the plant. Desert saltbush, on the other hand, flowers in the spring or early summer and is still green and succulent in the fall when sheep are brought down from the mountains and before the range normally starts growing. Over 14 TECHNICAL BULLETIN 5 5 7, V. S. DEFI. OF AGRICULTURE large areas at this time of the year it is the only green feed and consequently is heavily browsed.

EEI^TION OF PLANT COVEB TO LEArHOPPER POPULATION The most important sections of the spiny saltbush land, with respect to leafhopper populations, are abandoned lands that produce stands of summer annuals, such as fogweed and bract scale. On these are bred large numbers of beet leafhoppers during the summer. In the area where spiny saltbush is intact or on the older abandoned lands where winter annuals have replaced summer annuals, very little breeding of the leafhopper occurs.

LOWLAND TYPES There are several of the lowland types that are closely related, and as far as this study is concerned they can be grouped together. They are seepweed, alkali heath, pickleweed, and saltgrass. Originally they occupied the lower portions of the valley, as here the soils are usually of the heavier type, loam and clay loam, with considerable accumulation of soluble salts and a high water table. Measure- ments of the soluble salts and soil moisture of .these types in the southwestern desert region have been made by Shantz and Piemeisel (IJ). Ihe loAvland types have been greatly modified as a result of cultivation, irrigation, drainage, and grazing. On lands once farmed there are at present considerable areas of saltgrass, alkali heath, and .seepweed that are definitely secondary successions. To what extent original stands covered the area shown in the map (fig. 1) as lowland types is difficult, if not impossible, to determine at present, but that the areas are far greater than they were previous to the beginning of cultivation is quite certain. Statements made in the reports of soil surveys—Lapham and Jensen (7) 1904 ; Holmes et al. (4) 1916; Kelly (6) 1920—point out the large increase in the area of alkali. Owing to the great changes that have taken place and to the destruction of all evidence of former stands, the eastern boundary of lowland types (fig. 1) must be considered an arbitrary line.

APPEARANCE AND BOTANKJAL COMPOSITION Seepweed forms a hummocky soil, each small mound topped by a plant. The purer stands may form a belt bordering the spiny saltbush type or may grow in patches within one of the other lowland types. Alkali heath may form pure, rather open stands a few inches in height, or it may occur scattered throughout one of the other lowland types. Saltgrass may form a sod in situations where the water table is high (fig. 8). In drier places there are scattered small tufts of a few blades each. Though saltgrass, seepweed, and alkali heath occur mixed in any one of the other lowland types, each one also forms very large areas of pure stands. In wetter situations pickleweed forms a rank growth several feet high (fig. 9). Where drier, the shrubs are smaller and widely spaced. In any of the types, when the perennials reach their normal abundance and development, annuals are few or lacking entirely, indicating that this was the condition in the original stands. VEGETATION IN THE SAN JOAQUÍN VALLEY 15 PHHRPPH HHHHH h ^'"^^I^H^B

*"^ - ^1' -' 'iV.ii i ' *¿-v ^-"SfeöVflPi' ■

FiGUKK 8.—A stand of saltgra.ss on formerly cultivated land where the previous season's growth had been burned off. In the background is one of the dikes set up for irrigation. Such a stand has no significance with regard to leafhoi>i)er populations. (Three miles west of Lament, Calif.. Aug. 30, 1934.)

"■-■'■'" " ? , t*:^^ '•'-)..

W^-• '' ■'■ ■:■ -**•_.-.,_ ^

^ V. ,»•■

FiauRE 9.—Pickleweed land with sali-ciifrustcd soil in tlie interspacfs. Sui'li land has few or no weed hosts and there is no breeding of leafhoppers. (28 miles west of Fresno, Calif., Aug. I'O, 1934.) 16 TECHNICAL BULLETIN 55 7, U. S. DEPT. OF AGRICULTURE

DESTRUCTION OB MODIFICATION OF ORIGINAL VEGKTATION As previously stated, the changes in the extent of the stands of the lowland types have undoubtedly been great. (Compare figs. 1 and 2.) Where there has been plowing alone, without an accom- panying change in the water table, the land is quickly covered again with lowland types. Whether or not intermediate stages of either summer or winter annuals appear is dependent locally on the amount of soluble salts. Because of the greater probability of lessening the amount of soluble salts in the topsoil after plowing, the intermediate stages are nuich more likely to occur than after overgrazing. Thinning of the perennials by overgrazing sometimes results in a thin stand of summer annuals, almost never a dense stand. Where summer annuals appear, jackass clover (WMizenia refracta Engelm.) is a common one. If winter annuals occur, peppergrass {Lepidium ■nitidum Nutt., and more abundantly L. latipes Hook.), alfileria, and goldfields {Bueña spp.) are the connnonest.

BiXATION OF PLANT 0OVi:B TO UiiFHOPPEB POPULATION The lowland types are similar to sj)iny saltbush with respect to leafhopper populations, in that there is very little breeding except on summer weeds on recently abandoned lands.

PLANT COMMUNITIES ALONG WASHES AND STREAM BEDS On the basis of the area covered, the communities included under this general heading belong under the next heading, Plant Comnmni- ties of Minor Importance. However, because of their importance in relation to the leafhopper, they are treated separately. The heading suggests their mixed and varied nature. They represent for the most part various stages of i^rimary successions occurring on tlie washed, gravelly, or stony soils of intermittent streams that drain from the Coast Range into the valley (fig. 7). Some of the plant species found ill the dry stream beds occupy considerable areas higher up in the hills. Such are California sagebrush, wild buckwheat {Enogonum faticictilatum Benth.), juniper {Juniperm sp.), and many annuals. Other plants are quite closely confined to stream beds. Among these &v^Lepidofipartu7n,gQ\ú(in-ií&iftv {Chrysopsis villosa (Pursh) Nutt.), mule fat {Bacchmis vimin-ea DC), and arrowweed {Pluchca sericea (Nutt.) Cov.). The more stable soils of the benches slightly above the stream beds may be covered with plants from the adjoining vegetation types. At the borders of the stream bed there is often a scattermg of trees, usually Fremont cottonwood {Populm fremontii S. Wats.) and the California sycamore, often called planetree {Plata- nus racemosa. Nutt.). Occasionally the sides of the canyons have seepage areas where plants characteristic of lowland types occur such as alkali heath and saltgrass. ' There is much variation in the plants of the stream beds, and often creeks near to one another and apparently similar have very different dominants. The principal streams from the Altamont Pass south to Kern County are given below, together with the commonest and most characteristic plants. VEGETATION IN THE SAN JOAQUÍN VALLEY 17

Streams Common or characteristic plants Buenos Ajres Creek Mule fat, golden-aster. Lone Tree Creek Golden-aster. Hospital Creek Lepidospartum. Puerto Creek Mule fat. Orestimba Creek (iolden-aster. San Luis Creek Do. Los Banos Creek Golden-aster, mule fat. Ortigalita Cre«;k Saltgrass, alkali heath. Little Panoflie

PLANT COMMUNITIES OF MINOR IMPORTANCE

Here are grouped and briefly described the plant communities that are relatively unimportant both as to area covered and as to .significance in connection with leafhopper populations.

Ditches and sloughs support hydrophytic communities that are not a part of the lowland types, though they are in the same general area. These communities occupy lands that are covered with water for at least part of the year. In this respect they differ from the lowland types that occupy soils where the water table may be high but where there is no surface water for any length of time. The characteristic species are marsh plants, such as tules {Scirpus spp.) and cattails {TypJia. spp.). The original area has been greatly reduced as a result of draining and cultivation of the lakes and sloughs. To a slight extent only has this been offset by an extension along canals 18 TECHNICAL BULLETIN 5 5 7, U. S. DEPT. OF AGRICULTURE and ditches as a result of irrigation. The communities are of no economic significance from the standpoint of the leafhopper.

ME8QUITB AND QUAILBBUSH Mesquite and quailbrush constitute a mixed and very variable comnmnity covering a small area on the lower benches along the rivers and streams of Kern County. It is composed of mesquite {Prosopis glandulom Torr.), quailbrush or lenscale {Atri/plex lenti- formis (Torr.) S. Wats.), and various admixtures of other plants. The comnmnity overlaps on the one hand the desert saltbush type and is mixed with it, and on the other the lowland types, saltgrass and seepweed. Neither mesquite nor quailbrush in the San Joaquin Valley occurs in extensive communities as they do in the Gila River Valley in Arizona and in the Coachella Valley in California.

OTHER MINOB COMMUNITIES The hog wallows have been briefly described by Jepson {5). They are seasonal by nature. In the present study they are of lui significance. There remain two shrub communities of the foothills. California ephedra, often called Mormon tea or jointfir {Ephedra califomica S. Wats.), is the principal shrub over a considerable area of the clayey Panoche Hills surrounding Panwhe Valley as far north as Ortigalita Creek, an area of many square miles. It is also found in typical scattered stands between the Taft-McKittrick Hills and the Carrizo plain, almost to Antelope Valley, and is found occasionally between there and Coalinga. California sagebrush and wild buckwheat are constituents of the coastal sagebrush and are frequently found on steep rocky slopes in the tree savanna, and sometimes they extend on such slopes down into the bunch-grass type. California ephedra, California sagebrush, and wild buckwheat in these localities sometimes hold ccmsiderable numbers of the leafhopper during the fall before germination of the winter hosts. CHANGES IN WEEDY PLANT COVER The stands of plants that follow destruction of the original vegetation as a result of man's activities are not stable plant communities. They may change from season to season. The changes follow general trends that depend largely on the use made of the land, as shown diagrammatically in figure 10 and discussed below. If detailed information were available to represent these trends for each type of original vegetation separately, the several diagrams would undoubtedly show some significant differences. However, figure 10 has been made general enough to include most of these, while the known outstanding exceptions, such as that for the lowland types, are pointed out later. The left half of figure 10 shows the changes resulting from a continuous disturbance, the first column from alternating plowing and temporary abandonment, and the second from continuous excessive grazing. The stands listed in the first column do not de- VEGETATION IN THE SAN JOAQUÍN VALLEY 19 velop beyond the summer annual stage if the abandonment is only for 1 or 2 years. If it is much longer than this, the changes take place as shown either in the next column or in the right of the figure, depending on whether or not there is excessive grazing. The de- terioration of the range, as shown in the second column, is a gradual change over large areas, but in smaller areas where stock is concen- trated in large numbers year after year the entire process may take place in a few seasons.

DESTRUCTION OF ORIGINAL VEGETATION DEVELOPMENT OF VEGETATION AND CHANGES IN WEEDY STANDS UNDER PROTECTION FROM RESULTING FROM REPETITIVE PLOWING REPETITIVE PLOWING AND AND ABANDONMENTOR WITH CONTINUED ABANDONMENT OR FROM EXCESSIVE GRAZING EXCESSIVE GRAZING

ORIGINAL VEGETATION BARE SOIL BARE OR NEARLY PERMANENTLY BARE SOIL I i ABANDONED AFTER DESTROYED BY PLOWING DESTROYED BY EXCESSIVE FARM LAND EXCESSIVE GRAZING AND GRAZING AND ON SUBSEQUENTLY ABANDONEO EXCESSIVE GRAZING RANGE LAND FOR CONTINUED THEREAFTER I TO 3 YEARS

SPARSE STAND OF LUXURIANT SUMMER ANNUALS STAND OF WITH SUMMER ANNUALS WINTER ANNUALS

AGAIN PLOWED AND ABANDONED SHORT STAND OF SUMMER ANNUALS WITH SPARSE STAND SHORT STAND OF WINTER ANNUALS OF WINTER ANNUALS APPEARING WINTER ANNUALS

ENDLESS GOOD STANO OF WINTER ANNUALS REPETITION

POISONOUS PLANTS, WITH SPARSE STAND PERENNIALS APPEARING OF IN STANDS OF WINTER ANNUALS WINTER ANNUALS

ORIGINAL VEGETATION

FIGURE 10.—Diagrammatic representation of the changes in the stands that follow the destruction of the original vegetation. The left half of the figure deals with the changes as a result of continuous disturbance, and the right half with the changes taking place under protection from disturbances and leading to a reestablishment ol tlie original cover. Tlie right half of figure 10 begins where the first half leaves off, with the disturbing influences eliminated. In the case of permanently abandoned lands the recovery to the final stage of original vegetation will necessarily be very slow except for outlying areas that are more or less surrounded by the original vegetation. The development to a good stand of wniter annuals takes place quite rapidly, in 1 to 3 years. This winter annual stage might be sub- divided into two, with annual grasses poorly represented in the first but dominant in the second. The rate of recovery on tlie bare soil resulting from overgrazing depends on the damage done by erosion. Where the topsoil has been removed the recovery is exceedingly slow, 20 TECHNICAL BULLETIN 5 5 7, U. S. DEPT. OF AGRICULTUEB

but where the top layer is intact or nearly so the recovery at least to a stand of -winter annuals may take place in a few seasons. Be- fore the stand of winter annuals is reached there may be an intervening? stand of sparse summer annuals, as shown in %ure 10, but this summer annual stage does not develop on desert saltbush land. Under present conditions the reestablishment of the original vegetation is arrested by grazing on the range lands and by intermittent farming of the poorer cultivated lands. Over an enormous area overstocking prevents the replacement of the winter annual cover by perennials (fig. 2). Indeed, over most of this area stocking is so heavy at the present time that the stand of winter annuals is deteri- orating rapidly into range weeds and in some places bare soil. It is the range weeds, such as plantain and peppergrass, that are the chief spring hosts of the beet leafhopper and on which the insect builds up the enormous populations that migrate to crops in the spring. Summer annuals cover a smaller area in comparison with winter annuals. They are mostly confined to recently plowed and abandoned lands. Even here there is a continuous replacement of summer annuals by winter annuals. If it were not for repeated plowing and subsequent abandonment of these lands, the area of summer animals would in a short time be reduced to unimportant proportions. Since it is these summer annuals growing on intermittently farmed land that are the principal summer hosts of the leafhopper, if intermittent farming were discontinued a necessary link in the chain of food and breeding plants of the leafhopper would be greatly weakened.

PRINCIPAL SPECIES OF PRESENT PLANT COVER The lists of species shown in figures 11 and 12 include tlie principal plants of the present plant cover, chiefly unstable ¡jlant communities. As for the original vegetation types, the dominant perennials have been discussed and these are not included in the lists. The portions of the original vegetation existing today, as sliown in figure 2, have been greatly modified by grazing. Tlie stands have become either a dense cover of the dominant perennials or more often a thinned stand of these with a cover of winter annuals in the interspaces. The plants composing this winter annual cover are included in figure 11. Aside from the exception just made, the dense stand of perennials, and the well-farmed lands which have no direct bearing on the problem, the entire area of the present plant cover in the San Joaquin Valley can be divided into two classes, namely, the plant cover on grazing lands and that on recently abandoned farm lands. Both are unstable plant covers. That on grazing lands is for the most part one of winter annuals with comparatively small areas where perennial range weeds, such as unpalatable plants, are abundant ; the other, on recently abandoned farm lands, is chiefly one of summer annuals. These overlap to some extent, since winter annuals may also appear on recently abandoned farm lands. Likewise certain portions of the range may show a cover of summer annuals. But these exceptions form a small part of the whole. Accordingly, the list of species is divided into figure 11, the species found on grazing lands, COMPARATIVE ABUNDANCE IN AREAS INDICATED CLASS AND SPECIES TREE PACIFIC DESERT SPINY MIXED SAVANNA GRASSLAND SALTBUSH SALTBUSH LOWLAND TYPES

SUMMER ANNUALS: SJiLSOLA P£STfFER (RUSSIAN-THISTLE) 1,2

WISUZENIA REFRACTA íJACKASS CLOVER) EREMOCARPUS SETIGERUS (TURKEYMULLEIN)

TRICHOSTEMA LANCEOLATUKê (BLUECURLS OR VINEGARWEEO)

HEMIZONIA SPP.

WINTER ANNUALS:

AVENA FATUA (wiLD OATS)

BROMUS RUBENS (FOXTAIL CHESS),2 BROMUS SPP. (B.RIGIDUS,B.MOLUS, B.ARENARIUS) (SROMEGRASS), 2 FESTUCA OCTOFLORA (SLENOER FESCUE) HORDEUM GUSSONEANUM (MEDITERRANEAN BARLEY), 2 HORDEUM MURINUM (MOUSE BARLEY), 2 ~

HOLLISTERIA LAN ATA, I

CALANDRINIA CAULESCENS, I —

MC NT/A PERFOUATA (MINER'S LETTUCE) ~~

ALSINE MEDIA (CHICKWEEO), 2 '

HERN! AR IA CINéREA ,1

MECONELLA UNEARIS

PLATYSTEMON CAUFORNICUS (CREAMCUPS)

ATHYSANUS PUSLLLUS -•

BURSA BURSA-PASTORIS (SHEPHERDS- PURSE),2 " LEPIDIUM LATIPES (PEPPERGRASS), I ~ LEPIDIUM NITIDUM (PEPPERGftASS),I

THELYPODIUM LASlOPHYLLUM

TROPIDOCARPUM GRACILE, I

LOTUS SP.(BIRDSF00T TREFOIL)-.

LUPINUS NANUS. L. BICOLOR (LUPINES) MEDICAGO DENTICULATA (BUR-CLOVER),2

ERODIUM BOTRYS, 2

ERODIUM CICUTARIUM (REOSTEM ALFILERIA),2 ERODIUM MOSCHATUM . (WHITESTEM ALFILERIA), 2~ SPHAEROSTIGMA DENTATUM (EVENING-PRIMROSE)

SPHAEROSTIGMA PUBENS —

CiLIA TRICOLOR

LINANTHUS OICHOTOMUS (EVENING-SNOW)

NEMOPHILA S PP.

NYCTELEA MEMBRANACEA- [ I

PHACELIA TANACETIFOLIA'- ! 1

ALLOCARYA STIPI7ATA

AMSINCKIA DOUGLASIANA, A. INTER- MEDIA, A. TESSELATA (FIDDLE-NECK)

PECTOCARYA PENICILLATA, 2 !■ : \ PLAGlOeOTMRYS NOTHOFULVUS (POPCORN FLOV^ER) S&LVIA CCLUMBARIAE, SCARDUACEA (THISTLE SAGE) ORTHOCARPUS PURPURASCENS (OWLCLOVER)

PLANTAGO ERECTA, P. INSULARLS (DESERT PLANTAIN), I

BAERIA GRACILIS, B. ULIGINOSA (GOLDFIELDS)

LAYIA GLANDULOSA

UALACOTHRIX CALIFORNICA, »¡.COULTERI (SNAKE'S-HEAD)

MON O LO PI A MAJOR

PERENNIALS:

ÂLLIUM SPP. (WILD ONION) •\ I étOOKERA CAPlTATA (BLUEOICKS)

HOOKERA LAXA (GRASSNUT) ATRLPLEX SEMIBACCATA (AUSTRALIAN SALTBUSM). Z" eSCMSCHOLZiA CALIFORNICA (CALIFORNIA-POPPY)

ASTRAGALUS SPP. (A.PREMQNTII, A.OxrPHrsuS) CCHINOCYSTIS SP. ÍBIGR00T)

C06SWELLIÂ BICOLOR-

CUTl£RR£ZlA CALlFCRNICA (MATCHWEED) J^LOPAPPUS VENETUS V£Rt^NfOiDES

FicrRE 11.—List of plant species found on graiing lands, with an indication of thi; comparative abundance of each spedes in the various areas formerly occupied by the nriclTial rpireration rvrv>«». Thf» Íprieth of thp hnr* shown !n how tnsnT of the arpa.i VEGETATION IN THE SAN JOAQUÍN VALLEY 21

COMPARATIVE ABUNDANCE IN AREAS INDICATED CLASS AND SPECIES TREE PACIFIC DESERT SPINY MIXED SAVANNA GRASSLAND SALT BUSH SALTBUSH LOWLAND TYPES

SUMMER ANNUALS: ATRIPLEX BRACTEOSA ^m (BR4CT SCALE), 1 1 J ATRIPLEX EXPANSA ^^^^^ä§g^^^^^§^ (FOGWEEO), 1 1 r BASS/A HYSSOPIFOLIA, 1,2 1 1 SALSOLA PESTIFER fRUSSIAN-THISTLE), 1,2 1 m^m^mm 1 WISLIZEHIA REFRACTA W/////////M EREMOCARPUS SETIGERUS 1 1 1 TRICHOSTEMA LANCEOLATUM 1 1 fBLUECURLS) 1 1 HEMIZONIA PUNCENS 1 (SPIKEWEED) w///W//^WMmmmmmm _ ._j (HORSEWEED), 2 1 wimmiMM 1 HELIANTHUS AHNUUS 1 1 (SUNFLOWER) ,2 1 mmmmmmmmmmm. 1 1 HETEROTHECA GRANDIFLORA- — 1 mmm. 1

WINTER ANNUALS: 1 (FOXTAIL CHESS), 2 [ f HORDEUM MURINUM 1 \MM3WM:iMM. (MOUSE BARLEY), 2 I V' ' mmm^/zMMmm \ (CREAM CUPS) 1 i 1 1 (SHEPHERDS-PURSE), 2 \ \ LEPIDIUM LATIPES ^-•■p-;v

' Unpublished data. ' Erodium cicutarium is not included, since the worlc mentioned above indicates that this species IS of very little importance as a winter breeding host in the San Joaquín Valley VEGETATION IK THE SAN JOAQUÍN VALLEY 23 the soil. In the case of summer annuals the number of species is greater on recently abandoned lands, though the number of species of winter annuals is reduced. Moat of the species of winter annuals are native. However, where tlie winter annual stage of succession has developed, introduced species such as alfileria and foxtail chess are ever present and are usually dominant. Native winter annuals, such as plantain and peppergrass, form almost pure stands in localized areas where conditions are least favorable for the other winter annuals. The summer annual species are mostly native, though Russian-thistle, the one of greatest importance as a bi-eeding host of the leafhopper, is an intríxluctiou. The other two important summer plants, fogweed and bract scale, are native. In glancing at the list of species on grazing lands (fig. 11) it is seen that by far the largest innnber of the species of winter annuals is shown (at the left) under the two closely related types of vegetation, tree savanna and Pacific grassland. Desert aaltbiish is a poor third, while spiny saltbush and the lowland types show very few species. This is probably the proportion that existed at the time when the stands of original vegetation were intact. Not only was there a larger number of species of winter annuals in Pacific grassland and tree savanna, but also the number of individuals was much greater in these two types than on the heavier, more or less salt- encrusted soils of the lowland types and spiny saltbush. Neverthe- less, even in the types where tlie numbers of winter annuals were greatest, they were comparatively few as long as the normal stand of the original type was maintained. The 23resent-day distribution and extent of the winter and summer hosts of the leafhopper will be better understood by referring to figures 1, 2, and 3. At least one of the three important winter hosts (plantain, peppergrass, nuistard) can be found abundantly in any of the types as they exist today. However, as has previously been stated (under Desert Saltbush, p. 12), there is very little leafhopper repro- duction in the winter and spring except where the winter annual stage occurs on former bunch-grass or desert-saltbush land below 1,500 feet. Some idea of the wide extent of such breeding grounds can be obtained from figure 2. Tlie distribution of the three important summer hosts of the beet leafhopi)er in 1933 is shown in figure 3. It is seen that only comparatively small areas of these summer hosts are to be found on overgrazed range lands, such as those in the vicinity of Coalinga and in the Los Banos Hills. Most of the simimer hosts occur on the valley floor on plowed lands, particularly fallow or recently abandoned lands. Considerable data (not here presented) have been gathered on the distribution of summer host plants, the location and extent of the areas, and the variations of these areas from year to year. Here it is sufficient to point out that the total acreage is dependent on several fac- tors, namely, climatic conditions, available irrigation water supply, and economic conditions. Of these the last two are the most important, since the available irrigation water supply and economic conditions (prices paid for agricultural products) determine the amount of tilled lands left idle and since the total acreage of summer hosts is largely dependent on the amount of such idle lands. 24 TECHNICAL BULLKTI>r 5 5 7, U. S. DEPT. OF AGRICULTURE

The composition of the summer weed host areas is considerably in- fluenced by the type of soil. Fogweed is most abundant near Tulare Lake on the heavier soils. Kussian-thistle, with the exception of com- partively small areas near Mendota, Los Banos Hills, and Coalinpa, is most commonly found on the sandy soils. Bract scale is less confined to definite soil types and is often mixed with the other two summer hosts. The occurrence, to any considerable extent, of any of the three summer hosts on soils of the valley floor is dependent on plowing (fallow and recently abandoned lands). POSSIBILITIES OF REDUCTION OF WEEDY AREAS AND THE EFFECT ON LEAFHOPPER POPULATION AND CURLY TOP DAMAGE

The statement has been made previously that present conditions (large weedy areas and large leafhopper populations) are due to disturbances caused by tillage and grazing. However, the enormous breeding areas are not due to farming and grazing as such, but rather to their uneconomical practices. Thus the districts in the San Joaquin Valley that consist of good soils, with a sufficient supply of good irrigation water, and consequently are well farmed, do not produce leafhopper hosts in sufficient abundance to breed economically significant populations of beet leafhoppers. It has been shown tliat the summer hosts of the leafhopper are weeds forming the first stage of the succession on fallow or abandoned lands. Thus, the large areas of weed hosts and the very high sunmier populations of leafhoppers occur in the sections of the valley where, from time to time, lands are allowed to lie idle. Likewise, the improper use of the range results in large areas of winter hosts and high spring leafhopper populations. The original range and the range maintained in nearly its original condition consists principally of perennial plants not favorable to the production of high popnlations of leafhoppers. With overstocking of the range, the first effect is a reduction of the forage value of the land by I'eplacement of good forage plants with those of less forage value. The final effect is the disappearance of practically all of the vegetation, the loss of the topsoil, and eventually the formation of wortli- less, badly eroded lands. It is the plants of little or no forage value growing on the nearly bai-e areas that are the important winter breeding hosts of the beet leafhopper. Tlie belief that the correction of the two misuses of the land just discussed will lessen and eventually reduce to an insignificant ]Joint the damage to crops from curly top is based on the following facts, most of Mdiich have been discussed separately in the foregoing pages. Here they are brought together to show the relation of one to the other. The first is that the years in which great damage is done to curly-top-susceptible crops are those in which there are enormous populations of beet leafhoppers, and the years in which damage is slight are those when the leafhopper populations are small. The second is that the enormous populations of leafhoppers come from vast areas of weeds. The third, that if the areas of weeds are reduced the leafhopper populations will also be reduced, is obvious from the first two. Tlie first and the second are based on the observations and field collections of numerous workers over a period VECJEÏATIOÎi IN THE SAX JOAQUÍN VALLEY 25 of many years. The third is well demonstrated ^yhenever drought greatly reduces the areas of \yeeds. Moreover, the reduction of the weed areas by the natural supplanting of one stand of plants by another and the interruption of this process by excessive grazing or repetitive plowing have been fully discussed in the preceding section and illustrated by a diagram (fig. 10). The basic principles under- lying this change are now generally accepted in plant ecology. The application and effects of a contemplated reduction of weed- host areas will be better understood if the interrelationships of the insect's food and breeding habits and the sequence of host plants are reviewed. In the California area under consideration there is no single set of plants capable of sujjporting economic populations throughout the year. Instead, there are necessary two sets of breeding hosts that are green at different seasons of the year, one in tlie Ninnmer-fall season and one in the winter-spring season. Also in the San Joaquín Valley there must be in most years a third set of i)lants which function as food plants, not breeding hosts. These support the insect temporarily durhig late fall when neither of the other two sets of breeding hosts is green. It is clear that a contemplated reduction of weed-host areas need operate on only one of the two sets of breeding hosts. However, it is extremely probable that if both sets of hosts were reduced in area the reduction of either need not be so complete. The situation at present with respect to the acreage of the two sets of hosts is that the sunmier host ac'reage is small as compared with that of winter hosts. On this basis alone the reduction of the sununer weed-host area is less of a problem than that of the winter- host area. The other consideration is the removal of the factor (hat maintains the weed areas. The summer-host acreage is due almost entirely to intermittent farming—repeated plowing with intervening periods of temporary abandonment. The portion of summer-host acreage attributable to excessive grazing is comparatively small (fig. 3). That this type of intermittent, speculative farniing is uneconomical has been pointed out for some time by economists. If tliese lands could be taken out of private ownership iind allowed to revert to grazing lands the stands of summer annuals covering them would shortly (in 1 to 3 years) be replaced by winter iunmals (fig. 13). This would increase the acreage of winter hosts, but the great reduction of one set of hosts, the summer hosts, wouhl ]nake it impossible for the leafhopper to build up high populations. Moreover, this increase in winter annual acreage would be temporary if the.se lands were transferred to grazing lands and treated as stated in the next paragraph. The possibility of a reduction of the winter host area (fig. 2) directly depends on the prevention of destructive grazing (fig. 14). Since most of the land is privately owned, it would mean either taking the land out of private ownership so that some sort of public control could be set up or persuading the owners to maintain a voluntary control of the range. If a control of grazing were estab- lished that would place emphasis on the restoration and maintenance of the full forage value of the range, instead of attempting to keep a definite number of stock, the possibilities for reducing the winter host acreage would be veiy good. For the greater part of the total 26 TECHNICAL BULLETIN 5 5 7, U. S. DEFT. OF AGRICULTURE

FIGURE 13.—A stand of winter annuals, chiefly foxtail chess and nionse barley, rephiciiiii Kussiiui-thistle, a scattering of which still appears on the field. (Near Arvin, Calif., Mar. 2(i, 1932.)

FiGURK 14.—Bunch-grass land protected from grazing. A dense growth of annuals, species of Festuca, Jiromiis, and Gilia, with frequent tufts of perennial grasses, species of Poa and Stipa. BU11)üUK plants, such as species of Hookera {Brodiaea) and Allium, are common. Blossoms of the former are conspicuous. Stands such as this are not favorable for high leafhopper populations. (Lone Tree Canyon, San Joaquin County, CaUf., Apr. 10, 1934.) VEGETATION IN THE SAN JOAQUÍN VALLEY 27 area it would not mean that a complete reestablishment of the original perennials would be necessary for the reduction of the winter hosts. Particularly in the portions (fig. 1) where grassland and tree savanna were the orignial types, a stand of annual grasses could be expected in a much shorter time. Both of the suggestions made above, the elimination of intermittent farming and the prevention of excessive grazing, to reduce leaf- liopper populations and the curly top damage to crops, have also been recommended for some time as sound principles of conservation. SUMMARY A map of the original vegetation of the San Joaquin Valley was made, and the following five principal types of vegetation were described: (1) Tree savanna, a cover of scattered oak trees and an undergrowth of perennial grasses and herbs; (2) Pacific grassland, a stand of bunch grasses and perennial herbs; (3) desert saltbush, a growth of well-spaced desert shrubs; (4) spiny saltbush, also a desert shrub growth, but occurring on more saline soils; (5) lowland types, several types grouped together, such as saltgrass, pickleweed, etc., all of which occur on the lower lands where there is a high water table and high salt content. To a large extent all of the original types have been greatly modified or destroyed by cultivation and grazing. Pacific grassland has been all but obliterated. Tree savanna has been almost entirely destroyed in the flat valley portions, while in the hilly portions the oak trees remain to a large extent, but the undergrowth of perennial grasses and herbs has been greatly modified. Desert saltbush remains on a considerable portion, but even this area has been considerably modified by grazing. Spiny saltbush has probably been least disturbed, and the stands of today are probably more nearly like the original cover than in any of the other types. The lowland types, because of cultivation and a change in the level of the water table as a result of irrigation, have extended far beyond the original borders. As a result of the great modifications of the land itself, the borders of the lowland types, as shown in figure 1, are considered less reliable than those of the other types. The kind of plant cover resulting from the destruction of the original stands is dependent on the use made of the land and to a less extent on the type of vegetation destroyed. Thus, of the lands used for grazing, the excessively grazed areas produce a stand of winter annuals, and, if too heavy grazing continues, the stand is reduced and finally the soil may be bare. Of the lands used for farming, the intermittently farmed lands (alternate plowing and temporary abandonment) produce for the most part the present large acreage of summer annuals. The continuance of these two misuses of the land, excessive grazing and intermittent farming, maintains large acreages of winter annuals (fig. 2) and summer annuals (fig. 3). If these abuses were discontinued, a natural supplanting of one stand of plants by another would take place that would eventually lead to a reestablishment of the original cover. Under present conditions this reestablishment rarely takes place except in the lowland types, where it may be very rapid. 28 TECHNICAL BULLETIN 5 5 7, U. S. DEPT. OF AGRICULTURE

The beet leafhopper, which transmits the curly top disease of beets, tomatoes, ancl other crops, utilizes in California two sets of breeding host plants. One set, the summer host plants, chiefly Rus- sian-thistle, bract scale, and fogweed, is found to the greatest extent on intermittently farmed lands, while the other set, the winter host plants, such as plantain, peppergrass, and some species of minor importance, is found where grazing is heaviest and the plant cover is thin or the soil nearly bare. A contemplated reduction of hosts need operate on only one of these sets, although it is extremely probable that if the acreage of both were reduced the reduction of either need not be so complete. The correction of the two uneconomical practices, intermittent farming and destructive grazing, is in accordance with the general principles of land conservation. Such a correction would also result in greatly reducing leafhopper populations and the curly top damage to crops. LITERATURE CITED

(1) BuETT DAVY, J. li}02. STOCK KANGES OF NOKTHWESTEKN CALIFORNIA : NOTES ON THE GRASSES AND FORAGE PLANTS AND R.\NGK CONDITIONS. U. S. Dept. Agr., Kur. I'laiit Indus. Bull. 12, 81 pp., illus. (2) CLEMENTS, F. E. 1Ü28. PLANT SUCCESSIONS AND INDICATORS ; A DEFINITIVE EDITION OF PL.\NT SUCCESSION AND PLANT INDICATORS. 453 pp., ilUis. New York. (3) COOPEB, W. S. 192'J. THE BROAD-SOLI';ROPHYLL VEGETfATION OF CALIFORNIA ; AN ECOLOGICAL STUDY OF THE CHAPARRAL AND ITS RiCL.ATED CflMMUNITIES. 124 pp., lllius. (Ciirnosie Inst. Wash. Pnli. :!1!).) (4) HOLMES, L. C, BCKM.\NN, E. C, NELSON, J. W., and GUERNSEY, J. E. 1Ü21. RECONNOISSANCE SOIL SURVEY OF THE MIDDLE SAN .JOAQUÍN VALLEY, CALIFORNIA. U. S. Dept. Agr., Bur. Soils Field Oper. (1916), Kept. 18:2421-2529, illus. (5) JEPSON, W. L. 1!)25. A MANUAL OF THE FLOWERING PL\NTS OF C.M.IFOENIA. 1238 pp., illUS. Berkeley, Calif. (6) KELLY, W. P. 1920. THE PRESENT STATUS OF ALKALI. Calif. Agr. Expt. Stil. Clrc 219 10 pp. (7) LAPHAM, M. H., and JENSEN, C. A. 1905. SOIL SURVEY OF THE BAKEBSFIELD AREA. U. S. Dept. Agr., Bur Soils Field Oper. (1904) Kept. 6: 1089-1114, illus. (8) PlEIMEISEL, R. L. 1932. WEEDY ABANDONED LANDS AND THE WEED HOSTS OP THE BEET LELiF HOPPER, U. S. Dept. Agr. Circ. 229, 24 pp., illus. (9) SEVERIN, H. H. P. 1933. "FIELD OBSERVATIONS ON THE BEET LEAFHOPPER, EUTF;TTIX TENELLU8, IN CALIFORNIA. Hilgardla 7: [281]-3fiO, illus. (10) SHANTZ, H. L. 1925. PLANT COMMUNITIES IN UTAH AND NEVADA. U. S. Nati. MuS Cou- trib. U. S. Nati. Herbarium 25:15-23. (11) and PiEMEisEL, R. L. 1924. INDICATOR SIGNIFICANCE OF THE NATURAL VEGETATION OF THE SOUTH- WESTERN DESERT REGION. Jour. Agr. Researeli 28: 721-802, illus. (12) WEAVER. J. E., and CLEMENTS, F. E. 1929. PLANT ECOLOGY. 520 pp., illus. New York and London.

U. S. GOVEBt.MENT PRINTING OFFICE; 1937