Abstracts of Papers - Harvard Forest - Harvard University

ent dominants. Monitoring during the ensuing 20
years recorded the spread of Typha, changes in
density and productivity of other dominants, and
minor shifts in understory species. Analysis of
alterations in species composition can be used to
predict vegetation responses after flooding in
similar marshes. Phragmites, Typha, Scirpus and
Scolochloa life cycle characteristics and biomass
have been monitored in a number of sites. Variations
between sites and years will be compared with data
from a transect from lat 51?N to lat 56?N.
VAN DER VALK, ARNOLD G. Department of Botany,
Iowa State University, Ames, IA 50011.
- Vegetation dynamics in freshwater wetlands.
Vegetation change in freshwater wetlands will be
reviewed as well as theories put forth to explain
it. This review will focus on two basic questions:
(1) What are the mechanisms that enable the
establishment and persistence of wetland vegetation?
(2) What are the mechanisms that cause the com-
position and structure of wetland vegetation to
change? A new model is presented in which all
vegetation change is due to one of three phenomena
or a combination of them: Gleasonian succession,
maturation, and fluctuation. These three phenomena
are defined and then illustrated using data from
prairie glacial marshes.
Poster Session
AARSSEN* LONNIE W. & ROY TURKINGTONo Botany Dept.,
University
V6T 2B1.
of British Columbia, Vancouver, B.C.
- Temporal vegetation patterns in three different
aged pastures.
Three adjacent pastures (planted in 1977, 1958 and
1939) on a farm in the lower Fraser Valley of British
Columbia were surveyed periodically over a 3 year
period. In each survey, species cover was recorded
in quadrats and contact sampling was used to investigate
temporal patterns of fine-scale association
between species. Ordination of time-series percentage
cover surveys showed a trend of increasing community
constancy in older pastures and suggested that
the three communities have a developmental relationship.
Soil analyses showed little correlation with
species cover and the fewest correlations in the
oldest pasture. Interspecific associations in
younger communities were predominantly temporary in
nature while older communities had more associations
which persisted essentially unchanged. This data
formed the basis of a qualitative model of pasture
community evolution which attributes within-community
temporal changes to the selective forces accruing
from biotic interactions.
ATKINS, TREVOR A.** Dept. of Botany, U. of Manitoba,
Winnipeg, Manitoba, R3T 2N2; PETER F. LEE, Dept. of
Biology, Lakehead U., Thunder Bay, Ontario, P7B 5E1;
JOHN M. STEWART, Dept. of Botany, U. of Manitoba,
Winnipeg, Manitoba, R3T 2N2.
-Environmental interactions influencing the growth
and development of Zizania aquatica.
Two sites on Lake of the Woods, Ontario were monitored
Ecological Section 41
bi-weekly in the summer of 1982. Wild rice growth
(density, biomass, phenophase) and tissue nutrition (9
elements) were measured through sampling in randomized
complete block experiments. Water depth was used as a
blocking factor in both sites: One site also included
blocking on the presence of lily pad (Nuphar) competit-
ion. The physical environments of the two sites were
monitored for water depth, water column temperature and
dissolved oxygen concentration profiles; and soils for
pH, conductivity, bulk density and nutrient regime.
Biomass, density, and nutrient contents of competing
macrophytes were also measured. The growth and devel-
opment of the wild rice population was then related
to its physical environment through multi-variate
analysis. Growth was found to be influenced by enviro-
mental factors common to other studies. The previously
unexplored interactions amongst variables yielded
inLsight into the growth and development of wild rice.
Interactions with oxygen are of significant interest.
BARNES, FAIRLEY J.*, and GARY L CUNNINGHAM. Dept.
Biology, New Mexico State University, Las Cruces,
NM 88003. - Water status of dominant species in
pinyon-juniper habitat types.
Pinus edulis and Juniperus monosperma have overlapping
distributions in the pinyon-juniper woodland of
northern New Mexico. Forty sites representing the
range of pinyon-juniper habitats in the Jemez
Mountains were analyzed using vegetative and physical
site characteristics. Three habitat types (HT) were
distinguishable primarily on the densities of mature
and seedling P. edulis and J. monosperma, and
secondarily on the presence of specific perennial
grasses. Sites within each HT were ranked using the
same criteria and six sites selected to form a
presumptive moisture gradient characteristic of the
woodland. Predawn leaf water potentials of P. edulis
and J. monosperma did not vary significantly among
the sites. This may indicate that these dominant
trees are occupying microsites of favorable moisture
and that their densities within the various HT's are
a reflection of the availability of such microsites.
BIGLEY, RICHARD E. and PAUL G. HARRISON*. Depart-
ment of Botany, University of British Columbia,
Vancouver, B.C., Canada V6T 2B1. - The population
biology of two intertidal seagrasses, Zostera
japonica and Ruppia maritima, at Roberts Bank,
British Columbia.
Vegetative and flowering components of co-occurring
intertidal populations of Zostera japonica Ascherson
and Graebner (a recent introduction) and Ruppia
maritima L. s.l. (more commonly found in inland
brackish water) were studied in southwestern British
Columbia. Results from one year of repeated mapping
and examination of shoots in permanent plots on a
tidal gradient showed that shoot flux, age structure,
survivorship, growth of leaves and rhizomes, and seed
production all were affected by the amount of expos-
ure to the air. Plots having the greatest exposure
had fewer shoots (of both species), a greater percent
of shoots flowering early in the season, and lower
seed production than plots with less exposure. The
length of the life cycle of R. maritima was the same
regardless of differences in exposure, while plants
of Z. japonica subject to the longest exposure to the
air initiated and ended flowering and entered a qui-
escent overwintering state earlier than plants lower
in the intertidal zone.