Agriculture Reference
In-Depth Information
drawdown issues were identified that were later resolved. A primary issue was
transmission through dense vegetation to the local server. To solve this prob-
lem, we placed two wireless routers in strategic positions to avoid tall vegeta-
tion between the sensor and local server.
Interpretation of Spatial and Temporal Change in Acoustic Observations
The analytical component of the AAOS automatically computes Power Spectral
Density (PSD) values (Welsh 1967) for each of 10 frequency intervals between
1 and 11 kHz. These values were normalized (0-1 range) so that soundscape
energy could be compared between locations. In addition, acoustic indices were
developed from these values. One index, the Normalized Difference Soundscape
Index (NDSI), was used to examine spatial and temporal variability of the KBS
LTER soundscape (Kasten et al. 2012, Gage and Axel 2013). The mean NDSI
was positive in all systems, indicating that biophony dominated the soundscape
everywhere. The means (±standard errors) of the NDSI for the winter wheat
(Conventional and No-till combined), Poplar, and Early Successional communi-
ties were 0.52 ± 0.01, 0.79 ± 0.01, 0.52 ± 0.08, respectively. Poplar had the highest
mean NDSI among the three habitat types and was significantly different from the
winter wheat and Early Successional systems (
F
= 348.81,
p
<0.001), indicating
that the Poplar system was more dominated by biological sounds compared to the
other communities.
Although overall mean NDSI values are informative, acoustic energy pat-
terns (expressed as watts kHz
−1
) vary depending on the source of the sound as
well as the time of day and the season. The acoustic frequencies and patterns of
the frequencies may provide insight into ecological phenomena. The patterns of
acoustic energy (watts kHz
−1
) in each system are shown for four different acous-
tic frequency intervals (1-2 kHz; 2-3 kHz; 3-4 kHz; and 4-5 kHz) in Fig. 14.6.
Both human activity (anthrophony) and some other organisms signal at lower
frequencies (e.g., some amphibians, larger birds). Note the precipitous change in
acoustic energy at 1-2 kHz (Fig. 14.6A) in all three systems at dawn and dusk.
Also note the rise and fall in acoustic energy that can be attributable to human
activity during daylight hours (08:00-20:00 h), especially in open areas (wheat
and Early Successional systems) compared to Poplar where sound is buffered
by vegetation. At the next highest frequency interval (2-3 kHz; Fig. 14.6B), we
observe moderately high levels of soundscape energy in all systems during night-
time. At this frequency, the Early Successional community has the highest acous-
tic energy during the daytime compared to wheat or Poplar. In the next frequency
interval (3-4 kHz; Fig. 14.6C), there is a precipitous rise in acoustic energy at
dawn (0530 h) and a sharp decline at dusk (2100 h). It is within this frequency
range that many species of birds signal. Relatively high levels of energy due to
birdsong are sustained during the day. Although the energy in the frequency range
of 4-5 kHz (Fig.14.6D) is less than that in the lower frequencies (Figs. 14.6A-C),
energy is higher at night in wheat and Poplar and relatively constant in the Early
Successional community.
