Due to its dry climate and limited vegetation, desert areas of Arizona
were once a haven for individuals seeking allergen-free environments. Landscaping
in the rapidly growing Phoenix metropolitan area has altered the pollen
composition of this desert environment, with implications for allergy sufferers.
Using pollen and vegetation data from a random sample of 200 sites in
the CAP LTER study area, CAP LTER scientists Glenn Stuart, Corinna Gries,
and Diane Hope sought to investigate the relationship between pollen as
measured from surface sediments (soil) and extant vegetation. They focused
their work on four research questions:
- How does pollen abundance map against plant abundance across agricultural
versus desert versus urban landscapes?
- How well defined or delineated are the pollen-plant relationships? Can
plant taxa be grouped according to the degree of correlation between pollen
and plant cover abundance?
- Can plant taxa be grouped depending on how well the presence or absence
of the extant plant taxa correlate with the presence or absence of pollen
across the entire study area?
- Are the findings of the relationships between extant vegetation and
pollen and the distribution of pollen in line with expected results or
are these relationships confounded by disturbance and manipulation of plant
diversity in the agro-urban environment?
Data analysis focused on the entire suite of perennial
plant taxa found across the study region with a detailed analysis of spatial
and numerical patterns for select taxa including Ambrosia (bursage
or ragweed), a plant native to the Sonoran Desert, and Pinus (pine),
an introduced tree species. CAP scientists chose these taxa because they
display a range of pollen-dispersal mechanisms as well as different distributions.
They examined the pollen-plant relationships for these using maps, in addition
to other analyses of variations in pollen concentration and plant cover
between agricultural, desert and urban landscapes.
These analyses show some striking patterns. Ambrosia, a wind-pollinated
genus, displayed the highest pollen concentrations of any genus in the study,
although these are highest in the desert environment where the plant is
mostly found (Fig. 1). Pinus pollen shows up in abundance in urban
areas where the tree has been planted as a non-native species. Pinus pollen
was also found in 94% of desert samples. Pollen from the Chenopodiaceae-Amaranthus group
(a group of mostly annuals with similar pollen grains) is also present in
relatively high concentrations across the three land-use types, particularly
in agricultural landscapes.
The map of pollen concentration versus plant cover for Pinus (Fig.
2) shows a marked contrast with the Ambrosia map (Fig. 1), illustrating
the differences in plant cover percentages. Furthermore, the spatial distribution
of Pinus pollen within the urban area reflects historical patterns
of growth with higher concentrations of Pinus cover in older parts
of the metropolitan area. |
