Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

71
CLIMATE
The climate of Coastal Delaware is milder than that of sites directly northward
or inland. Detailed climatological data for Lewes, Delaware where Cape Henlopen is
located found in the monthly publication of the National Oceanic and Atmospheric
Administration 1 . Mean annual temperature at Lewes is 56.1 o F (13.3 o C), and the
annual precipitation is about 44.9 inches (1140 mm). The average length of the
frost-free period at the coastal parks exceeds 200 days. Nor’easters may occur from
late fall to mid spring. Though not as potentially severe as hurricanes, nor’easters
may cause dune damage from strong northeast or east winds. Strong winds may
account for unusually high tides that produce severe dune erosion. Drought is
frequent and may be especially injurious to vegetation if it is prolonged and occurs
during the growing season. Fenwick island has the states’ highest minimum
temperature, 31 o F (-0.4 o C), and the state’s lowest annual snowfall, 4.01 inches
(101.9 mm).
METHODS
Collecting trips were made to the study areas approximately once a month
during the growing seasons from April 2006 through October 2006. Objectives for
each trip included the collection of voucher specimens and accumulation of
information on abundance and apparent habitat preference for each species.
Classification and determination of non-native status of vascular plant species were
according to Gleason and Cronquist 2 and Bailey 3 .
RESULTS AND DISCUSSION
The flora of Delaware is composed of 2,175 species of which 610 are not
native 4 . Dicots, 1,411 taxa, are more numerous than monocots (669 species). The
Asteraceae, Poaceae and Cyperaceae are the largest families in the flora with 238,
237 and 237 species respectively. The percentage of non-native species, 22
percent, of the parks’ flora, was slightly less than the states’ as a whole. Grasses
(Poaceae) and composites (Asteraceae) contain the greatest number of species at
the state parks, which is similar to the state's largest plant families.
Seventy three non-native vascular plant species have been identified at the
three coastal Delaware state parks. Dicots (55 species) were more numerous than
monocots (17 species). The total number of vascular plant species collected from
April through October 15, 2006 includes 335 species in 183 genera in 92 families.
Non-native species composed 22 percent of the flora.
The greatest number of non-native species were found in the Poaceae (n=
13) and the Asteraceae (n= 11) (Table 2). Five families were composed exclusively
of non-native taxa: Commelinaceae (1/1), Elaeagnaceae (2/2), Liliaceae (3/3),
Molluginaceae (1/1), and Oleaceae (1/1).
Several alien taxa, Celastrus orbiculatus, Eragrostis curvula, and Phragmites
australis, pose a threat to native vascular plants. Celastrus may grow up and over
53