A model relating transpiration for Japanese cedar and cypress plantations with stand structure

Abstract

Previous studies have revealed that changes in forest structure due to management (e.g., thinning, aging, and clearcutting) could affect the forest water balance. However, there are unexplained variability in changes in the annual water balance with changing structure among different sites. This is the case even when analyzing data for specific species/regions. For a more advanced and process-based understanding of changes in the water balance with changing forest structure, we examined transpiration (E) observed using the sap-flux method for 14 Japanese cedar and cypress plantations with various structure (e.g., stem density and diameter) in Japan and surrounding areas and developed a model relating E with structural parameters. We expressed E using the simplified Penman-Monteith equation and modeled canopy conductance (Gc) as a product of reference Gc (Gcref) when vapor pressure deficit is 1.0 kPa and functions expressing the responses of Gc to meteorological factors. We determined Gcref and parameters of the functions for the sites separately. E observed for the 14 sites was not reproduced well by the model when using mean values of Gcref and the parameters among the sites. However, E observed for the sites was reproduced well when using Gcref determined for each site and mean values of the parameters of the functions among the sites, similar to the case when using Gcref and the parameters of the functions determined for each site. These results suggest that considering variations in Gcref among the sites was important to reproduce variations in E, but considering variations in the parameters of the functions 3 was not. Our analysis revealed that Gcref linearly related with the sapwood area on a stand scale (A) and that A linearly related with stem density (N) and powers of the mean stem diameter (dm). Thus, we proposed a model relating E with A (or N and dm), where Gcref was calculated from A (or N and dm) and the parameters of the functions were assumed to be the mean values among the sites. This model estimates changes in E with changing structure from commonly available data (N and dm), and therefore helps improve our understanding of the underlying processes of the changes in the water balance for Japanese cedar and cypress plantations.

Relationship between stem diameter and transpiration for Japanese cypress trees: Implications for estimating canopy transpiration

“…Contrary, solar radiation at the other seven sites was measured at an open space. This difference in the measurement settings should not affect our results seriously because of small spatial variations in solar radiation and low sensitivity of transpiration to solar radiation for Japanese cypress trees (Komatsu et al, 2014). Soil water potential was measured using a tensiometer at a depth of 10, 30, and 55 cm for the Kiryu_upper and at a depth of 10, 30, 60, and 90 cm for the Kiryu_lower (Table S1).…”

Conversion of natural forests to managed forest plantations decreases tree resistance to prolonged droughts

“…In Piedmont sites, the need to modify current practices such as an increase in thinning activities to reduce stand density and increase water and other resources available to the residual trees (Newton, 2009;Zhao et al, 2010) is advisable. This, in turn, will result in more vigorous trees and thus higher ability to resist and recover from drought (McDowell et al, 2009;Komatsu et al, 2014) and probably of damage or mortality from insects, diseases, and other agents (Desprez-Loustau et al, 2006;Jactel et al, 2009). Additionally, the management of tree density in natural systems relies on the balance between the facilitation and competition processes necessary to provide optimal conditions for tree growth.…”

Seasonal changes of azimuthal, radial, and tree-to-tree variations in sap flux affect stand transpiration estimates in a Cryptomeria japonica forest, central Taiwan

“…Our estimates of annual E (=83.5 mm of 211 fine days) was relatively small compared with that of other Japanese cedar forests in Japan (e.g., Kumagai et al 2007;Komatsu et al 2014). Komatsu et al (2014) compared canopy conductance estimated with the sap flux method for nine Japanese cedar forests including our site.…”

“…Komatsu et al (2014) compared canopy conductance estimated with the sap flux method for nine Japanese cedar forests including our site. Canopy conductance standardized by sapwood area for our site (referred to as XT in the paper) was comparable to those for the other sites.…”