Evaporation and canopy characteristics of coniferous forests and grasslands

Evaporation and canopy characteristics of coniferous forests and grasslands Canopy-scale evaporation rate (E) and derived surface and aerodynamic conductances for the transfer of water vapour (g s and g a , respectively) are reviewed for coniferous forests and grasslands. Despite the extremes of canopy structure, the two vegetation types have similar maximum hourly evaporation rates ( E max ) and maximum surface conductances (g smax ) (medians = 0.46 mm h -1 and 22 mm s -1 ). However, on a daily basis, median E max of coniferous forest (4.0 mm d -1 ) is significantly lower than that of grassland (4.6 mm d -1 ). Additionally, a representative value of g a for coniferous forest (200 mm s -1 ) is an order of magnitude more than the corresponding value for grassland (25 mm s -1 ). The proportional sensitivity of E, calculated by the Penman-Monteith equation, to changes in g s is >0.7 for coniferous forest, but as low as 0.3 for grassland. The proportional sensitivity of E to changes in g a is generally ±0.15 or less. Boundary-line relationships between g s and light and air saturation deficit (D) vary considerably. Attainment of g smax occurs at a much lower irradiance for coniferous forest than for grassland (15 versus about 45% of full sunlight). Relationships between g s and D measured above the canopy appear to be fairly uniform for coniferous forest, but are variable for grassland. More uniform relationships may be found for surfaces with relatively small g a , like grassland, by using D at the evaporating surface (D 0 ) as the independent variable rather than D at a reference point above the surface. An analytical expression is given for determining D 0 from measurable quantities. Evaporation rate also depends on the availability of water in the root zone. Below a critical value of soil water storage, the ratio of evaporation rate to the available energy tends to decrease sharply and linearly with decreasing soil water content. At the lowest value of soil water content, this ratio declines by up to a factor of 4 from the non-soil-water-limiting plateau. Knowledge about functional rooting depth of different plant species remains rather limited. Ignorance of this important variable makes it generally difficult to obtain accurate estimates of seasonal evaporation from terrestrial ecosystems. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Oecologia Springer Journals

Evaporation and canopy characteristics of coniferous forests and grasslands

Oecologia, Volume 95 (2) – Aug 1, 1993

Loading next page...
 
/lp/springer-journals/evaporation-and-canopy-characteristics-of-coniferous-forests-and-3coZEkslBa
Publisher
Springer Journals
Copyright
Copyright © 1993 by Springer-Verlag
Subject
Life Sciences; Ecology; Plant Sciences
ISSN
0029-8549
eISSN
1432-1939
D.O.I.
10.1007/BF00323485
Publisher site
See Article on Publisher Site

Abstract

Canopy-scale evaporation rate (E) and derived surface and aerodynamic conductances for the transfer of water vapour (g s and g a , respectively) are reviewed for coniferous forests and grasslands. Despite the extremes of canopy structure, the two vegetation types have similar maximum hourly evaporation rates ( E max ) and maximum surface conductances (g smax ) (medians = 0.46 mm h -1 and 22 mm s -1 ). However, on a daily basis, median E max of coniferous forest (4.0 mm d -1 ) is significantly lower than that of grassland (4.6 mm d -1 ). Additionally, a representative value of g a for coniferous forest (200 mm s -1 ) is an order of magnitude more than the corresponding value for grassland (25 mm s -1 ). The proportional sensitivity of E, calculated by the Penman-Monteith equation, to changes in g s is >0.7 for coniferous forest, but as low as 0.3 for grassland. The proportional sensitivity of E to changes in g a is generally ±0.15 or less. Boundary-line relationships between g s and light and air saturation deficit (D) vary considerably. Attainment of g smax occurs at a much lower irradiance for coniferous forest than for grassland (15 versus about 45% of full sunlight). Relationships between g s and D measured above the canopy appear to be fairly uniform for coniferous forest, but are variable for grassland. More uniform relationships may be found for surfaces with relatively small g a , like grassland, by using D at the evaporating surface (D 0 ) as the independent variable rather than D at a reference point above the surface. An analytical expression is given for determining D 0 from measurable quantities. Evaporation rate also depends on the availability of water in the root zone. Below a critical value of soil water storage, the ratio of evaporation rate to the available energy tends to decrease sharply and linearly with decreasing soil water content. At the lowest value of soil water content, this ratio declines by up to a factor of 4 from the non-soil-water-limiting plateau. Knowledge about functional rooting depth of different plant species remains rather limited. Ignorance of this important variable makes it generally difficult to obtain accurate estimates of seasonal evaporation from terrestrial ecosystems.

Journal

OecologiaSpringer Journals

Published: Aug 1, 1993

There are no references for this article.

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create folders to
organize your research

Export folders, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off