Slope position influences vegetation-atmosphere interactions in a tropical montane cloud forest
Por:
Berry, Z. Carter, Gotsch, Sybil G., Holwerda, Friso, Munoz-Villers, Lyssette E., Asbjornsen, Heidi
Publicada:
1 may 2016
Resumen:
Throughout a single day, the microclimatic conditions in tropical
montane cloud forests vary from strong solar radiation with simultaneous
strong atmospheric water demand (high vapor pressure deficit, VPD,
values), followed quickly by clouds and fog events drastically reducing
both of these environmental variables. Due to the complex topography and
weather patterns in these regions, microclimate, including fog events,
can vary strongly across very small spatial scales as well, leading to a
highly dynamic and compelling environment to examine how environmental
variables influence tree water use across space and time. Due to this
variation, the present study examines how environmental drivers of tree
water use varies across three slope positions (upslope, midslope,
low-slope) in a tropical montane cloud forest in Veracruz, Mexico.
Measurements of sap flow using the heat ratio method were conducted on
three dominant canopy species along with simultaneous measurements of
microclimate within each site. To assess the relative importance of
microclimatic variables in explaining tree water use across diurnal
periods, data were separated into day and night periods and fog and
clear events. Multiple regression models were conducted for each tree
with input variables of VPD, solar radiation, air temperature, shallow
soil moisture, deep soil moisture, and leaf wetness. We found that VPD
explained a large majority of the variation in tree water use during
daytime fog periods, particularly at the upslope and midslope sites.
During nighttime periods, VPD was the dominant driver of water use
variation during clear periods while a combination of VPD and leaf
wetness explained variation during night, fog periods. Additionally,
tree water use was more decoupled from environmental variables at the
low-slope site. Finally, a separation of model components into fog and
clear periods improved model outputs particularly at low flow
conditions, highlighting the differential interactions between tree
water use and environment during night and fog periods. Results from
this study provide new insight into the importance of fog events, low
VPD, and leaf surface wetting at controlling tree water use in cloud
forests. The variation in drivers of water use across short spatial
scales demonstrate the importance of considering individual and species
level variation across fog and clear periods in predicting physiological
responses of species to climate in cloud forests. (C) 2016 Elsevier B.V.
All rights reserved.
Filiaciones:
Univ New Hampshire, Dept Nat Resources & Environm, Durham, NH 03824 USA
Franklin & Marshall Coll, Dept Biol, Lancaster, PA 17604 USA
Univ Nacl Autonoma Mexico, Ctr Ciencias Atmosfera, Ciudad Univ, Mexico City 04510, DF, Mexico
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