Estimation of Tree Crop Size across Multiple Taxa: Generalization of a Visual Survey Method

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.

Influence of Food Availability on Matrilineal Site Fidelity of Female Asian Black Bears

“…We then used the conversion formula developed by Nakajima et al (2015) to obtain the number of acorns produced per unit area (m 2 ) (Apa):…”

Horizontal and elevational patterns of masting across multiple species in a steep montane landscape from the perspective of forest mammal management

“…We monitored fruit production in August (Castanea, Swida, and Prunus) or September (all other species), depending on species-specific phenology. We used the visual survey method (Nakajima et al 2015) to monitor the fruit production of each selected tree; an observer scanned the crown of the tree using a binocular and counted fruiting units for a fixed time interval three times per tree. The morphological fruiting unit differed among taxa: acorn for Quercus, cupule for Castanea and Fagus, fruit for some species of Prunus, and the infructescence for remaining species.…”

Detection of arboreal feeding signs by Asiatic black bears: effects of hard mast production at individual tree and regional scales

“…See the work of Nakajima et al . () for details of this method. There are three seeds in a cupule of C. crenata ; therefore, we calculated the number of seeds by multiplying the counted number of cupules by three.…”

“…Two or three people each counted the number of fruits on each tree three separate times from different angles, using binoculars. See the work of Nakajima et al (2015) for details of this method. There are three seeds in a cupule of C. crenata; therefore, we calculated the number of seeds by multiplying the counted number of cupules by three.…”

“…We transformed these data to the count per second (C) and substituted into the following equation to estimate the number of seeds per unit crown projection area (F; number m À2 ), F = a C b , where a and b are species-specific parameters (Nakajima et al, 2015). We also calculated the basal area (BA) from the diameter at breast height (DBH) of each tree to estimate its crown projection area (CA; the area of an irregular circle when the tree crown is projected on ground) by using the equation CA = a BA b , where a and b are species-specific parameters (Nakajima et al, 2015). We then calculated the mast energy per tree by multiplying CA (m 2 ) by F (number m À2 ) and the energy content of a seed (kJ).…”