MORRISON, JANET A. Department of Biology, The College of New Jersey, P.O. Box 7718, Ewing, NJ 08628-0718. - Dogwood decline in the urban New York Botanical Garden Forest.
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.
Key words: Cornus florida, dogwood anthracnose disease, plant-pathogen interactions, recruitment, spatial analysis, Urban forest ecology