For Botanical Society of America Annual Meeting 2000
Dogwood decline in the urban New York Botanical Garden Forest
Jante A. Morrison, Department of Biology, The College of New Jersey
Much of the forest in the eastern United States exists as fragments surrounded by urbanizing development, yet little explicit attention has been paid to plant ecology in forests embedded in an urban matrix. In the 16 ha old-growth New York Botanical Garden Forest, in Bronx, NY, many native tree species exhibit decline and/or lack of recruitment. Cornus florida shows distinct symptoms of decline that may be due to dogwood anthracnose disease, age-related senescence, and/or environmental stress. In order to investigate spatial factors often associated with disease, such as host density and distance from the forest edge, I characterized spatial patterns of symptoms and mortality from 1995 to 1998, using GIS with positional data from a sub-meter accurate GPS. Most dogwoods in the forest were mature; only 2% had DBH < 3 cm in 1998 and no seedlings were found in either year. In both years the fungal pathogen Discula destructiva was present. Nearly all trees showed some symptoms (lower branch and twig die-back, conidiomata on leaves, leaf blotch). Of 219 trees found alive in 1995, 12% were dead by 1998, 80% were alive, but another 8% were not relocated. Dead trees had a smaller DBH on average, suggesting that older trees were not more likely to die. No clear spatial pattern was evident for symptoms, but there were patterns for mortality. Only one of the 41 trees at or close to the forest edge (within 15 m) died. The 81 trees within 2 m of another dogwood were also less likely on average to die (only 8.6%). So, the interior of this urban forest appears to present a challenge to isolated young dogwoods in particular. At the observed mortality rates, and without recruitment, the interior of the NYBG Forest may lose half of its dogwood trees by 2013.