Natural forest regeneration-soil relationships in a fire disturbed urban natural area forest.
Sustainability for urban natural area forests can be achieved with extensive natural regeneration of the native canopy species. A new urban forest management protocol "SAFE" (Soils Aliens Fire Exclosure) has the goal of increasing natural regeneration through: soil treatments; alien species treatments; fire surveillance; and large herbivores exclosure fencing. This research reports on the initial stages of the iterative process for the SAFE protocol. The soils and fire components of the SAFE protocol were examined for the seedlings and saplings of the seven canopy taxa growing in a loam and an extremely stony loam of the same soil series in the Good Woods, Philadelphia, Pennsylvania. Comparisons are made with data before and after an arson caused fire in 2015. Before the fire, seedlings for Carya spp., Prunus serotina, Quercus alba, and Quercus rubra and Q. velutina as well as Liriodendron tulipifera saplings had larger populations in the loam. The seedling populations for all seven taxa and saplings for Carya spp., Liriodendron tulipifera, and Prunus serotina were different in the burned and unburned areas of both soils. Post-fire sprouts, which were considered separately, had low survival rates four years after the fire. In the four combinations of soils and burned and unburned areas, pH, phosphorus, potassium, magnesium, and calcium were deficient except for phosphorus in the burned extremely stony loam. Negative binomial regression equations for seedlings of all seven taxa with the soil nutrients indicate fertilizer treatments to increase phosphorus, potassium, magnesium, and calcium would cause no change in natural regeneration. Regression variable estimates indicate increasing the pH would result in forest regeneration decreases for Acer rubrum, Fraxinus americana, and Prunus serotina. The next research steps for SAFE in the Good Woods are to monitor seedling populations changes after: a soil treatment; alien species control; a fire, and large herbivores exclusion.