DISCUSSION AND RESULTS. DESCRIPTION OF PLANT COMMUNITIES
15. Populion fremontii alliancia nova hoc loco
Typus nominis: Platano racemosae-Populetum fremontii associatio nova hoc loco.
Cottonwood and other riparian wet deciduous forests, spreading into Californian and Great Basin territories in the Pluviseasonal, Xeric and Desertic, Oceanic and Continental, Mediterranean bioclimate belt areas (thermo-, meso-, and supramediterranean thermoclimatic belts) and growing along the river banks, flood plains, streams, water courses, etc. on fluvisols and occasionally, on gleysols.
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Figure 39. Distribution of the cottonwood and riparian deciduous forests belonging to the order Vg. Populetalia fremontii. 15. Populion fremontii (California and Great Basin Regions; Mediterranean macrobioclimate): 15a. Platano racemosae-Populetum fremontii (California), 15B. Populion mesetae prov. (Madrean and Mexican Xerophitic Regions; Xeric and Desertic Tropical bioclimates).
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Bioclimatic diagnosis: Ic 6-28, Io 0.3-3.6, Itc 200-450, Tp 1200-2200, Tps 500-850, Tmin < 12, m < 8. [Mepo, Mepc, Mexo, Mexc, Mdc-Tme, Mme, Sme-Dry, Sar, Ari].
Within the alliance Populion fremontii we clearly recognize the Californian association 15a. Platano racemosae-Populetum fremontii, characterized by California sycamore (Platanus racemosa), and by a particular geographical race in the Great Valley Sector (typical subassociation) characterized by Hinds walnut (Juglans hindsii). Throughout the continental Great Basin territories, a floristically poor association could be interpreted, mainly discriminated by an unpublished nothosubsp. of Populus xhincleyana (Populus fremontii subsp. fremontii x angustifolia).
Characteristic species: Acer negundo var. californicum, Carex barbarae, Junglans californica, Juglans hindsii, Platanus racemosa, Populus fremontii subsp. fremontii, Salix hindsiana, Vitis californica.
15a. Platano racemosae-Populetum fremontii associatio nova hoc loco
Mediterranean Pluviseasonal and Xeric Oceanic (barely continental in Northern Sacramento Valley); thermo- and mesomediterranean; dry and semiarid; cottonwood and other riparian deciduous forests growing in flood plains, valleys, river banks, etc., on deep fluvisols. These forests are distributed throughout the oceanic territories of the California Region, mainly in the Great Valley Sector.
Bioclimatic diagnosis: Ic 6-22, Io 1.2-3.6, Itc 300-450, Tp 1600-2200, Tps 500-800, Tmin < 12, m < 8. [Mepo, Mepc, Mexc-Tme, Mme-Dry, Sar].
Table 65 gives six relevés from Sacramento Valley Subsector territories. The most characteristic trees are Populus fremontii subsp. fremontii, Platanus racemosa, Juglans hindsii and Acer negundo var. californicum. Oregon ash (Fraxinus latifolia) could be accepted as a territorial Californian characteristic species of this association, in despite of their territorial characteristic value in the Oregon white oak (Quercus garryana) and Oregon ash deciduous flood plain forests (Querco garryanae-Fraxinetum latifoliae) of Willemette Valley (Pluviseasonal Oceanic Mediterranean humid). In the understory are common some native and introduced plants such as Artemisia douglasiana, Carex barbarae, Rubus ulmifolius, Salix lasiolepis, Toxicodendron diversilobum, Vitis californica, etc.
Table 65
15a. Platano racemosae-Populetum fremontii
(Populion fremontii, Populetalia angustifolio-deltoidis)
| Altitude (1=10m) | 8 | 11 | 8 | 11 | 9 | 9 | 9 |
| Number of species | 14 | 14 | 15 | 19 | 20 | 20 | 17 |
| Ordinal number | 1 | 2 | 3 | 4 | 5* | 6 | 7 |
| Trees: |
| Platanus racemosa | 3 | 2 | 3 | 3 | 1 | 1 | V |
| Populus fremontii | 2 | 4 | 2 | 4 | 3 | 4 | V |
| Fraxinus latifolia | 1 | 1 | 1 | 2 | + | 1 | V |
| Juglans hindsii | + | 2 | + | 2 | 2 | 3 | V |
| Acer californicum | + | + | + | 1 | 2 | 2 | V |
| Cercis occidentalis | + | + | + | + | . | . | IV |
| Salix gooddingii | . | + | . | 1 | 1 | 1 | IV |
| Characteristic species: |
| Carex barbarae | + | . | + | + | 1 | 1 | V |
| Vitis californica | 1 | . | 1 | . | 2 | 3 | IV |
| Salix lasiolepis | . | 1 | + | + | . | 1 | IV |
| Salix exigua | . | 1 | . | 1 | 1 | 1 | IV |
| Cephalanthus occidentalis | + | . | 1 | + | . | . | II |
| Prunus emarginata | . | . | . | + | . | . | I |
| Companion species: |
| Rubus ulmifolius | 1 | 1 | 1 | 2 | 1 | 2 | V |
| Artemisia douglasiana | 1 | 1 | 1 | 1 | + | 1 | V |
| Toxicodendron diversilobum | 1 | 1 | . | 1 | . | + | IV |
| Iris douglasiana | . | . | + | + | 1 | 1 | IV |
Other species. Trees: Alnus rhombifolia + in 1, 3 and 5. Quercus lobata + in 2 and 4. Ficus carica + in 5 and 6. Morus alba + in 5 and 6. Companion species: Piptatherum miliaceum 1 in 2, 4, 5 and 6. Torilis arvensis 1 in 1 and 3. Xanthium strumarium + in 4 and 5. Hedera helix 1 in 5 and 6. Sambucus mexicana + in 5, 1 in 6. Phytolacca americana + in 5 and 6.
Localities: 1. California: Shasta Co. Anderson. Parkville Road, Ash Creek close to Sacramento River. 40º25'N-122º12'W. 30 m, 50 cm, 500 m2 (reg. Sánchez-Mata CA97-222). 2. California: Tehama Co. Red Bluff, Jellys Ferry Road close to Sacramento River. 40º19'N-122º13'N. 20 m, 50 cm, 400 m2 (reg. Sánchez-Mata CA97-226). 3. California: Shasta Co. Anderson. Balls Ferry, Sacramento River. 40º26'N.122º12'W. 30 m, 50 cm, 500 m2 (reg. Sánchez-Mata CA97-221). 4. California: Tehama Co. Red Bluff, Bend Ferry Road close to Sacramento River. 40º15'N-122º13'W. 20 m, 50 cm, 400 m2 (reg. Sánchez-Mata CA97-224). 5. California: Tehama Co. Red Bluff. William B. Ide State Historic Park, Sacramento River. 40º12'N-122º13'W. 25 m, 60 cm, 500 m2, holotypus ass. (reg. Sánchez-Mata CA 97-224). 6. California: Tehama Co. Red Bluff. William B. Ide State Historic Park, Sacramento River. 40º12'N-122º14'W. 25 m, 60 cm, 500 m2 (reg. Sánchez-Mata CA 97-225). 7. Synthesized table.
Type relevé (holotypus): Table 65, relevé n. 5. Sánchez-Mata reg. CA97-224. 19.09.97. Site: California: Tehama Co. Red Bluff. William B. Ide State Historic Park, Sacramento River. 40º12'N-122º13'W. 25 m, 60 cm, 500 m2. Estimated bioclimatic factors: Pluviseasonal Oceanic Mediterranean (Ic ~ 21), lower mesomediterranean (Itc ~ 330), lower dry (Io ~ 2.6), Positive Summer Temperature Tps ~ 800. Biogeographic location: Californian Region, Northern Californian Province, Great Valley Sector, Sacramento Valley Subsector. Floristic combination: Linnaeo-Piceetea characteristic species, trees: 2 Acer negundo var. californicum, + Alnus rhombifolia, + Ficus carica, + Fraxinus latifolia, 2 Juglans hindsii, + Morus alba, 1 Platanus racemosa, 3 Populus fremontii subsp. fremontii, 1 Salix gooddingii. Others: 1 Carex barbarae, 1 Salix exigua, 2 Vitis californica. Companion species: + Artemisia douglasiana, 1 Hedera helix, 1 Iris douglasiana, + Phytolacca americana, 1 Piptatherum miliaceum, 1 Rubus ulmifolius, + Sambucus mexicana, + Xanthium strumarium.
15B. Populion mesetae alliancia prov.
Typus nominis: non published.
Xeric and Desertic Tropical; upper thermo- and meso- as well as lower supratropical; arid, semiarid and dry; Mexican Xerophytic and Madrean cottonwood and other riparian deciduous forests, developing along streams, river banks, water courses, flood plains, etc.,and growing on fluvisols and other wet soils. In the eastern Mexican Xerophytic Region territories (Tamaulipan Province) a riparian mesoforest community could be recognized and probably it could be included in a new alliance characterized by Fraxinus berlandierana and Celtis lindheimeri.
Bioclimatic diagnosis: Ic 6-22, Io 0.3-3.6, Itc 300-520, Tp 900-2800, Tps 700-1000, Tmin < 14, m <9. [Trxe, Trde-Uttr, mtr, Lstr-Ari, Sar, Dry-Pse].
Characteristic species: Juglans major, Juglans microcarpa, Platanus wrightii, Populus fremontii subsp. mesetae, Salix taxifolia.
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