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NATURAL HISTORY OF PACIFIC MADRONE, ITS DISEASES AND INTERACTION WITH GLACIAL SOILS OF THE PUGET SOUND A.B. ADAMS POSSIBLE ESC 110 PROJECT BACKGROUND Pacific madrone (Arbutus menziesii) is in decline in urban areas of the Puget Trough. This Puget Sound region is characterized by young glacial soils of mixed mineralology and texture. Associated with the decline of madrones is infestation by fungal pathogens that most likely are of native origin. The slow demise or death of the madrones occurs over a time period of years or even decades suggesting that plant nutrition, habitat or root function may play a role in the pathology of this plant. In other well-known tree/fungal pathogen interactions, death of the tree host is abrupt and certain. Such is the case with the American chestnut, Dutch elm and more recently oak infestations California. From the standpoint of pathology and co-evolution this tree is most interesting to study. This is especially true when soils are considered as a factor in pathology. Phytophthora (root rot) seems to infect roots in soil of poor drainage. Fungal hyphae move rapidly into the vascular tissue of the plant and young saplings at least die within weeks of the infection. Death occurs for the top of the plant downward. This sudden death results in leaves remaining on the plant after death, thus providing a field method for identifying the disease. Soils with poor drainage are more likely to have trees that die young with Phytophthora. Nattrassia mangiferia, on the other hand, infects the stem as a surficial depression of the bark. The fungus grows actively from the circumference of the depression leaving a black hollow hole behind. Although this fungus directly takes nutrients from the plant, it also damages its host indirectly by girdling branches thus denying transport of water and soil nutrients to the leaves and sugar products of photosynthesis from the leaves to the roots. Unlike Phytophthora, madrone trees often coexist with Natrassia cankers; in some cases, they even reverse the spread of disease. On many urban soils and natural soils in which topsoil has been removed or modified, nonetheless, the Nattrassia fungus has slowly decimated some madrone populations. HYPOTHESES • Madrone diseases are related to soil type – Soil structure and function (for instance, drainage) – Soil chemistry (for example, pH and nutrients) • Madrone diseases are related to community physical structure • Madrone diseases are related to disturbances (fire) • Madrone fruits provide a scarce resource for migratory and resident birds during a critical time period (late fall) in Puget Sound Pure Broadleaf Evergreen Forest of Pacific Madrone SAND QUARRIES ALLOW FOR STUDY OF BASAL ROOTS IMPORTANT FOR WATER UPTAKE , SLOPE STABILITY AND ANCHORING PLANT PIT SHOWING ESPERENT SAND WITH Bw/Bs? Hypothesis: natural soil series supports healthy madrones • Lower left - Nattrassia induced branch cankers produced black sunken centers with areas of active pathogen growth on the borders • Upper right - Cankers may completely girdle branches • Lower right - Competition for nutrients between the tree and fungus and girdling of vascular tissue ultimately may cause death in major branches or trunks of large trees. Here the two madrone trunks to the right (one dead with leaves, the other alive) are from the same tree; the dead trunk was girdled by Nattrassia. A TYPE OF ROOT ROT (PHYTOPHTHORA) INFECTS POTTED AND FIELD PLANTS THAT ARE PERIODICALLY FLOODED. BELOW SHOWS THE PROGRESSION OF PHYTOPHTHORA SYMPTOMS IN OVERWATERED POTTED PLANTS. FLOODING IS COMMON IN URBIC (CONSTRUCTION FILL) SOILS • Left most plant showed initial signs of infection, but the watering regime was made drier and it recovered • Second from left - fungus spreads from root clogging vascular system killing plant from top down. • Middle - the rapidity of death caused by root rot aids in identifying it because the leaves remain on the plant at the time of death. • Far right - all leaves eventually abscise. LAWTON CLAY FOUND BELOW LAWN AT LAURELHURST PARK, SEATTLE. IS THIS IMPERMEABLE STRATA RESPONSIBLE FOR DISEASED MADRONES GROWING HERE? MAGNOLIA BLUFFS HAS A COMPACTED CAP OF GLACIAL TILL. MADRONES ARE BELIEVED TO PLAY A ROLE IN STABILIZING THESE SLOPES WITH THEIR ROOTS, BUT THE SHALLOW HARDPAN MAY CAUSE MADRONES TO BECOME SICK? • Undisturbed, natural soils with madrones are very uncommon in the urban areas. • Compaction and erosion destroy upper soil surfaces crucial for ion exchange and plant nutrient uptake SOME POSSIBLE PROJECT TOPICS • • • • Help in field work to determine the relationship of depth to hardpan to madrone health at Magnolia Bluffs Characterize construction fill material (urbic soil) at Warren Magnunson and NorthSeattle Community College wetland fill Characterize soil profiles beneath sick madrone trees at Laurelhurst Park. Take part in a soil and leaf sampling project at a natural, healthy madrone site. • • • • Conduct literature research on Phytophthora infestations at other places and on other plants (for instance, California oaks) and relate it to Pacific madrone problems. Conduct literature research on Nattrassia (stem cankers) infections at other places and on other plants and relate it to Pacific madrone problems Analyze results of studies on previous bird frugivore studies, develop hypothesis and design your on bird study. Plant/pathogen coevolution