469 research outputs found
Structure and canopy tree species regeneration requirements in indigenous forests, Westland, New Zealand
This report reviews the literature on regeneration requirements of main canopy
tree species in Westland. Forests managed for production purposes have to be
harvested in an ecologically sustainable way; to maintain their natural character, harvesting should facilitate regeneration of target species and ensure that their recruitment is in proportion to the extent of extraction. The reasons for species establishing at any point in time are unclear; however, they are probably related to the availability of suitable microsites for establishment, the size of the canopy openings formed by disturbance, and whether or not seeds are available at or around the time of the disturbance. Age structures from
throughout Westland show that extensive, similar-aged, post-earthquake cohorts of trees are a feature of the region. This suggests that infrequent, massive earthquakes are the dominant coarse-scale disturbance agent, triggering episodes of major erosion and sedimentation and leaving a strong imprint in the forest structure. In other forests, flooding and catastrophic
windthrow are major forms of disturbance. The findings suggest that, in general, large disturbances are required for conifer regeneration. This has implications for any sustained yield management of these forests if conifers are to remain an important component. Any harvesting should recognise the importance for tree establishment of: forest floor microsites, such as fallen logs
and tree tip-up mounds; and the variable way in which canopy gaps are formed. Harvesting should maintain the 'patchy' nature of the natural forest—large patches of dense conifers interspersed with more heterogeneous patches of mixed species.This is a client report commissioned by West Coast Conservancy and funded from the Unprogrammed Science Advice fund
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Forest structure and regeneration in the Tsuga heterophylla - Abies amabilis transition zone, central Western Cascades, Oregon
The dynamics of stands in the mid-elevation old-growth
Douglas-fir (Pseudotsuga menziesii) forests of the central western
Oregon Cascade Range were investigated using stand structure
analysis. Trees with different growth rates were commonly present
in the same stand, which resulted often in a weak correlation
between tree diameter and age. Thus, age data and information on
spatial dispersion and disturbance history were collected to aid in
interpreting stand development.
The population structures described were influenced by periodic
fires of variable intensity and extent that resulted in a mosaic of
relatively even-aged patches of different conifer species. The
overall pattern depends on stochastic factors, species' life history
attributes, and the nature of the fire events. The species that
first dominates a site following a disturbance profoundly affects
subsequent stand composition and development. If Pseudotsuga
menziesii or noble fir (Abies procera) dominate early, then tree
regeneration of western hemlock (Tsuga heterophylla) and often
Pacific silver fir (Abies amabilis) will rapidly occur. Conversely,
if Tsuga heterophylla establishes first, regeneration will be absent
or minimal until canopy openings are formed. Several factors that
influence regeneration depend on the main canopy composition.
Canopy density determines how much light reaches the understory
which in turn influences the abundance of tree seedlings and
herbaceous species. Secondly, windfalls of old trees, branches, and
snags often create canopy openings that are colonized by new
seedlings or filled by previously established individuals. Lastly,
decaying logs and stumps provide important substrates for tree
seedling establishment, especially for Tsuga heterophylla. In
stands without fire for at least several centuries, canopy openings
are critical for the successful regeneration of the shade tolerant
species Tsuga and Abies amabilis. The amount of direct beam
radiation during the growing season is correlated with numbers and
height growth of seedlings and saplings in larger openings.
These interactions demonstrate the need for successional schemes
to include the effects of different canopy species, in addition to
various disturbances, as factors controlling the rate and nature of
forest succession
Urban ecology and ecological design: New Zealand perspectives and future pathways
The main goals of the workshop were to identify ways in which ecology and design can be successfully integrated and to determine future research and teaching directions in urban ecology and ecological design. Now more than ever we need to understand the role of urban ecology and design in dealing with social, climatic, economic and biodiversity crises in a rapidly changing world. This presentation identifies New Zealand perspectives and future pathways
The HLA class II allele DRB1*1501 is over-represented in patients with idiopathic pulmonary fibrosis
Background: Idiopathic pulmonary fibrosis (IPF) is a progressive and medically refractory lung disease with a grim prognosis. Although the etiology of IPF remains perplexing, abnormal adaptive immune responses are evident in many afflicted patients. We hypothesized that perturbations of human leukocyte antigen (HLA) allele frequencies, which are often seen among patients with immunologic diseases, may also be present in IPF patients. Methods/Principal Findings: HLA alleles were determined in subpopulations of IPF and normal subjects using molecular typing methods. HLA-DRB1*15 was over-represented in a discovery cohort of 79 Caucasian IPF subjects who had lung transplantations at the University of Pittsburgh (36.7%) compared to normal reference populations. These findings were prospectively replicated in a validation cohort of 196 additional IPF subjects from four other U.S. medical centers that included both ambulatory patients and lung transplantation recipients. High-resolution typing was used to further define specific HLA-DRB1*15 alleles. DRB1*1501 prevalence in IPF subjects was similar among the 143 ambulatory patients and 132 transplant recipients (31.5% and 34.8%, respectively, p = 0.55). The aggregate prevalence of DRB1*1501 in IPF patients was significantly greater than among 285 healthy controls (33.1% vs. 20.0%, respectively, OR 2.0; 95%CI 1.3-2.9, p = 0.0004). IPF patients with DRB1*1501 (n = 91) tended to have decreased diffusing capacities for carbon monoxide (DLCO) compared to the 184 disease subjects who lacked this allele (37.8±1.7% vs. 42.8±1.4%, p = 0.036). Conclusions/Significance: DRB1*1501 is more prevalent among IPF patients than normal subjects, and may be associated with greater impairment of gas exchange. These data are novel evidence that immunogenetic processes can play a role in the susceptibility to and/or manifestations of IPF. Findings here of a disease association at the HLA-DR locus have broad pathogenic implications, illustrate a specific chromosomal area for incremental, targeted genomic study, and may identify a distinct clinical phenotype among patients with this enigmatic, morbid lung disease
Search for Production via Trilepton Final States in collisions at TeV
We have searched for associated production of the lightest chargino,
, and next-to-lightest neutralino, , of the
Minimal Supersymmetric Standard Model in collisions at
\mbox{ = 1.8 TeV} using the \D0 detector at the Fermilab Tevatron
collider. Data corresponding to an integrated luminosity of 12.5 \ipb
were examined for events containing three isolated leptons. No evidence for
pair production was found. Limits on
BrBr are
presented.Comment: 17 pages (13 + 1 page table + 3 pages figures). 3 PostScript figures
will follow in a UUEncoded, gzip'd, tar file. Text in LaTex format. Submitted
to Physical Review Letters. Replace comments - Had to resumbmit version with
EPSF directive
Search for Top Squark Pair Production in the Dielectron Channel
This report describes the first search for top squark pair production in the
channel stop_1 stopbar_1 -> b bbar chargino_1 chargino_1 -> ee+jets+MEt using
74.9 +- 8.9 pb^-1 of data collected using the D0 detector. A 95% confidence
level upper limit on sigma*B is presented. The limit is above the theoretical
expectation for sigma*B for this process, but does show the sensitivity of the
current D0 data set to a particular topology for new physics.Comment: Five pages, including three figures, submitted to PRD Brief Report
Measurement of the Boson Mass
A measurement of the mass of the boson is presented based on a sample of
5982 decays observed in collisions at
= 1.8~TeV with the D\O\ detector during the 1992--1993 run. From a
fit to the transverse mass spectrum, combined with measurements of the
boson mass, the boson mass is measured to be .Comment: 12 pages, LaTex, style Revtex, including 3 postscript figures
(submitted to PRL
Measurement of the Top Quark Mass Using Dilepton Events
The D0 collaboration has performed a measurement of the top quark mass based
on six candidate events for the process t tbar -> b W+ bbar W-, where the W
bosons decay to e nu or mu nu. This sample was collected during an exposure of
the D0 detector to an integrated luminosity of 125 pb^-1 of sqrt(s)=1.8 TeV
p-pbar collisions. We obtain mt = 168.4 +- 12.3 (stat) +- 3.7 (sys) GeV/c^2,
consistent with the measurement obtained using single-lepton events.
Combination of the single-lepton and dilepton results yields mt = 172.0 +- 7.5
GeV/c^2.Comment: 12 pages, 3 figure
Measurement of Dijet Angular Distributions and Search for Quark Compositeness
We have measured the dijet angular distribution in =1.8 TeV
collisions using the D0 detector. Order QCD
predictions are in good agreement with the data. At 95% confidence the data
exclude models of quark compositeness in which the contact interaction scale is
below 2 TeV.Comment: 11 pages, Latex, 3 postscript figure
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