|
Study Number: |
1035 |
|---|---|
|
Project Title: |
Gap PAR (Photosynthetic Active Radiation). |
|
Investigator(s): |
Barry Clinton E-Mail | Tel. 828.524.2128 | Biographical Sketch |
| Affiliated Institution(s): | USDA Forest Service |
| Address: |
Coweeta Hydrologic Laboratory
3160 Coweeta Lab Road Otto, North Carolina 28763 USA |
| Study Type: | Terrestrial |
| Project Type: | Coweeta Core Research |
| Study Period: |
04/1993-04/1997 |
| Status/Notes: | |
| Funding Sources: |
National Science Foundation, DEB-9632854 (Text Version) and DEB-0218001 (Text Version) to Coweeta LTER. |
| Abstract: |
Small canopy openings often alter understory
microclimate, leading to changes in forest structure and composition. It
is generally accepted that physical changes in the understory (i.e.,
microclimatic) due to canopy removal drive changes in basic forest
processes, particularly seedling recruitment which is intrinsically
linked to soil moisture availability, light and, to a lesser extent,
temperature. We examined the impact of small canopy gaps of the type
(snags) and size (~300 m2) most frequently observed in the southern
Appalachians on the understory microclimate. We created artificial
canopy gaps at two elevations (a.m.s.l.) by girdling trees in areas with
and without a Rhododendron maximum L. (rosebay rhododendron) understory.
Soil and air temperature (degrees C), photosynthetically active radiation (PAR;
mmol m-2s-1), and volumetric soil water content (WC%) in the upper 15 cm
of soil were measured along transects generally running north to south
through each gap. Overall, PAR was substantially less in rhododendron
gaps than in non-rhododendron gaps. We found a slight increase in PAR in
non-rhododendron gaps during spring and summer compared to controls.
Very little seasonal variation in PAR was observed in rhododendron gaps
compared with non-rhododendron gaps. In general, %WC in rhododendron
gaps was lower than in non-rhododendron gaps and less variable. We also
found a gap response in incident PAR during the spring and summer
seasons. There was no significant effect of gap creation on %WC, nor
were there site (elevation) differences or effects due to the presence
of rhododendron. Further, there was no significant gap effect on mean,
maximum, or minimum soil and air temperature; however, there were
significant effects from the presence of rhododendron and between sites
for PAR and soil and air temperature during certain seasons of the year.
Although there is some certainty about measurable responses in key
microclimatic variables in rhododendron and non-rhododendron gaps found
in this study, we could not be certain if responses represent a
significant enough departure from values in undisturbed conditions to
elicit a tree recruitment response. Our results indicate that for
openings of the size examined here, topography and evergreen understory
are the primary determinants of spatial and temporal heterogeneity in
understory microclimate. Resources
for students about terms used in this study:Succession in canopy gaps - Source: Coweeta LTER Environmental heterogeneity-tree gaps research - Source: Coweeta LTER Rhododendron maximum - Source: USDA Plants Database Photosynthetically Active Radiation (PAR) - Source: Old Dominion University |
| Location(s), Described: | Watershed 18 and Watershed 27. |
| Location(s), Download GPS: | ArcView Shape Files (shp.): UTM, NAD83, Zone 17 | Lat/Lon |
| Location(s), Online Maps: |
 Online Map |
| Methods/Experimental Design: |
Photosynthetically active radiation (PAR,
400-700 nm) was measured on cloudless days between the hours of 1030 and
1330 on approximate 2-week intervals using a sunfleck ceptometer
(Decagon, Inc.) in the PAR function for estimates of quantum flux. We
recorded the average of four measurements at 1 m above the forest floor
for each location along the transects; measurements of full sun were
made in open locations near each study site for calculations of percent
full sun. The height of 1 m above the forest floor for PAR measurements
is well within the 2-8 m high rhododendron subcanopy.
Site IDs: |
| Sampling Frequency: | Approximately biweekly. |
| Data Columns: |
Site - Site ID where measure was taken.
Site IDs are defined in Methods/Experimental Design. |
| Publications: |
Clinton, Barton, D. 2003.
Light,
temperature, and soil moisture responses to elevation, evergreen
understory, and small canopy gaps in the southern Appalachians.
Forest Ecology and Management. 186(1-3): 243-255. |
| Data Restrictions: | Users must adhere to the Coweeta LTER Data Policy. |
| Metadata: | EML Format (XML Schema) | Information about EML |
| Data Downloads: |
Microsoft® Excel (.xls) Text Comma Delimited (.csv) DBase (.dbf) |