TITLE:
Estimation of Tree Crop Size across Multiple Taxa: Generalization of a Visual Survey Method
AUTHORS:
Ami Nakajima, Takashi Masaki, Shinsuke Koike, Koji Yamazaki, Koichi Kaji
KEYWORDS:
Forest Regeneration, Fruit Production, Observation Error, Seed Production, Wildlife Management
JOURNAL NAME:
Open Journal of Forestry,
Vol.5 No.7,
September
21,
2015
ABSTRACT: Estimating
tree fruit production is important for various purposes; however, no consensus
has been established on which method is appropriate over different tree
species. Here the aim of this study was to assess whether the tree crop size of
taxa with different fruit morphology could be accurately estimated using the
visual survey method (VSM), taking into consideration errors due to the
participation of different observers. Eight main tree species of temperate
deciduous forests of Japan were used. Using a hierarchical Bayesian framework,
the model parameters were estimated to convert the number of fruits counted by
VSM to the fallen fruit density. The estimated model had a high accuracy for
seven of the eight tree species. The trees of the outlier species had the
smallest diameter and height, presumably resulting in false-positive errors.
The model could be easily generalized for other species that were not tested in
this study by adjusting the model parameters to the size of the unit used in
the visual survey. The bias caused by errors depending on the observer (likely
false-negatives) was not substantial. Thus, the generalized VSM proposed in
this study should be useful to accurately estimate the crop size across various
tree taxa with low workload.