Analysis of floristic diversity of Ailanthus altissima (Mill.) Swingle (tree of heaven) and co-occurring native tree species in Northeastern Maryland
Date
2010
Authors
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Publisher
University of Delaware
Abstract
Invasive species, along with habitat loss and fragmentation, are major factors attributed to biodiversity decline and ecosystem alteration (Vitousek, 1996; Williamson, 1996; Pimentel, 2000; Flory, 2009). Ailanthus altissima (Mill) Swingle, an invasive tree species, has been regarded as the “most serious threat to natural areas” both damaging and strongly invasive to native Maryland habitats (McKnight, 2004). In order to preserve biodiversity in Maryland forested habitats, biodiversity studies incorporating Geographic Information Systems (GIS) with traditional inventory methods need to be completed. The purpose of this work is to study a suburban habitat that has experienced an influx of A. altissima. This thesis incorporates historic aerial imagery, shapefile production and plot inventories which included identifying tree species and measuring diameter at breast height (dbh).
The study was conducted in two forested plot areas located in Fair Hill Natural Resources Management Area in northeastern Maryland. The two plot areas were similar in size, but differed in shape and proximity to transportation routes. Nineteen circles measuring 314m2 in area were studied in total. A tree inventory was taken for each circle with the species, and dbh in cm recorded for all tree species greater than 5cm dbh. Other data resources included historic aerial imagery and dendrochronological data. The aerial images were used to view forest cover of image year, and used to develop GIS layers of forest edges. The data layers of the forests were used to calculate area, perimeter, and shape index. Dendrochronological data were also collected and allometric age equations were developed.
The hypotheses in this study involved examining the diversity, and the year of entry of A. altissima. Due to the effects of A. altissima and its ability to form monocultures, areas where the species are present should have values that indicate levels of lower biodiversity compared to areas where the species is not present (Hypothesis one(H1)). Hypothesis two (H2) concerns edge effects acting on the forest plot and greater stand densities and dbh of A. altissima should be seen in edge circles compared to interior circles. Due to a sale from private ownership to the state of Maryland, the sale could have ushered in the species. If the entry of A. altissima was prior to 1975, then hypothesis three (H3) will be disproved while if the year of entry is after 1975 then H3 would be confirmed. The fourth and final hypothesis (H4) investigates shape indices and years with higher shape indices would indicate entry periods for the species. Data involved in examining this hypothesis involves shapefile examination, tree ring analysis and historic aerial imagery analysis.
It was found that H1 was confirmed by the means that circles with A. altissima possessed lowered diversity in general than circles without the species. It was found that A. altissima were contained in 12 out of the 19 circles sampled and of the 12 circles, only three circles contained less than 50% of the circle as A. altissima. Results in this study did not confirm that interior circles had greater biodiversity and smaller dbh than exterior circles. However, only two interior circles were present in this study, and each varied in biodiversity and age of circle. Circle C contains 68% of the total species as A. altissima and contains dbhs of trees estimated of having an age of 45 years while the other interior circle, circle E, contains 52% of the species A. altissima and has trees estimated at 24 years. It was found that the sale of ownership did not clearly support the introduction of A. altissima, which does not support H3. However, for plot R273 circles 8 and 9, it was estimated that year of entry of A. altissima was around 1980, which could support H3, but entry of trees in Gallaher Rd Plot were estimated prior to 1970. The final hypothesis, H4, was found to be validated and years with higher shape indices indicated entry time frames for A. altissima. For GALRD plot, a general trend of shape indices from more distended shapes to more compact shapes were seen over the imagery time frame, while for R273 plot, shape indices fluctuated over the time period and years with higher indices saw introduction of A. altissima in the following years.