(1)
Diurnal and seasonal patterns of nitrogenase activity of red alder in comparison
with white clover in silvopastoral agroforestry systems
Teklehaimanot
Z, Martin R
BIOLOGY
AND FERTILITY OF SOILS
28 (3): 267-270 JAN 1999
Abstract:
Simultaneous
measurements were made to assess the diurnal and seasonal patterns of nitrogenase
activity of red alder (Alnus rubra Bong.) and white clover (Trifolium repens
L.) growing together in a silvopastoral agroforestry system using the acetylene
reduction assay. Diurnal measurements were made in the summer and autumn at
3-h intervals whereas seasonal nitrogenase activity was assessed based on
observations made at midday in July, September and January to represent the
summer, autumn and winter seasons, respectively. No obvious diurnal patterns
of nitrogenase activity were found in either red alder or white clover in
summer and no significant variations in nitrogenase activity were observed
between day and night. However, in autumn, pronounced diurnal patterns were
observed in both species. Significantly higher rates of nitrogenase activity
per unit dry weigh (dwt) of nodules were detected at 1500 hours in red alder,
whereas, in white clover: significantly higher rates were obtained at 2100
hours. There was no significant correlation between diurnal nitrogenase activity
and air temperature, photosynthetically active radiation and soil temperature
at 10 cm depth in either red alder or white clover. Seasonal rates of nitrogenase
activity showed significantly higher activity in summer, which subsequently
decreased in autumn, to reach very low levels in the winter. The rates of
nitrogenase activity of white clover were consistently higher than those of
red alder both diurnally and seasonally. In the three seasons sampled, the
average nitrogenase activity for white clover was 66.42 mu mol C2H4 g dwt(-1)
h(-1), which was 3.5 times higher than the 18.67 mu mol C2H4 g dwt(-1) h(-1)
obtained for red alder.
(2) Effect of tree spacing on form and phenology of sycamore and
red alder
Sk. Ahiul Islam, 2000, 202 pp.
MPhil
Thesis
The
effect of spacing, planting pattern and sheep on tree form and phenology was
investigated using four treatments with sycamore (Acer pseudoplatanus L.) and two with red alder (Alnus rubra Bong.) in a silvopastoral agroforestry
experiment at Henfaes Farm, North Wales, UK up to seven years after planting
(in 1999).
Height
and diameter did not vary significantly with treatments in sycamore or red
alder seven years after planting. Height:diameter ratio was not influenced
by treatment in sycamore but a significantly higher ratio was found in the
closely spaced 2500 stems ha-1 treatment than in the widely spaced
400 stems ha-1 treatment in red alder. The number of shoot reiterations
per tree (in total and the number of adaptive reiterations) were significantly
lower in the 2500 stems ha-1 treatment than in two of the widely
spaced treatments of both species (100 stem ha-1 for sycamore and
400 stems ha-1 for red alder) but in red alder the 2500 stems ha-1
treatment resulted in a significantly larger number of traumatic reiterations per tree than in the
400 stems ha-1 treatment .
There
were large variations in tree crown size amongst the treatments in 1999. The
closely spaced 2500 stems ha-1 treatment had longer
crown height than in two of the widely spaced treatments of both species.
In sycamore the 2500 stems ha-1 treatment resulted in greater crown
diameter, crown volume, crown surface area and crown shape ratio than in the
100 stems ha-1 treatment. In red alder the 400 stems ha-1
treatment resulted in greater crown shape ratio than in the 2500 stems ha-1
treatment but treatment had no significant effect on other crown variables.
Treatment
had significant effects on a range of branch characteristics in both species
in 1999. In sycamore the greatest branch length, branch reach and branch diameter
were found in the 2500 stems ha-1 treatment and a greater number
of buds per branch was found in the closely spaced clump treatment than in
the 100 stems ha-1 treatment. In red alder the 400 stems ha-1
treatment resulted in greater angle of branches, number of buds per branch
and living shoots:dead shoots ratio than in the 2500 stems ha-1
treatment. Also in red alder the number of dead branches and the rate of branch
mortality were significantly higher in the 400 stems ha-1 treatment
than in the 2500 stems ha-1 treatment.
Spacing
also had significant effects on different phenological variables of both species.
Shorter winter shoot dormancy periods were found in the 2500 treatment than
in the 100 stems ha-1 treatment in sycamore, and a longer period
of leaf production and a shorter winter dormancy period were found in the
400 than in the 2500 stems ha-1 treatment in red alder. In red
alder the 400 stems ha-1 treatment resulted in a greater number
of male catkin clusters and fruit clusters.
In
sycamore significantly lower crown dimensions and branching traits mentioned
above in the 100 stems ha-1 agroforestry treatment were caused
by sheep grazing/browsing. In red alder crown development, branching traits,
flowering and fruiting phenology were affected by canopy competition in the
closely spaced forestry control treatment (2500 stems ha-1) but
not affected much by sheep gazing/browsing in the widely spaced agroforestry
treatment (400 stems ha-1).
(3)
Tree and livestock productivity in relation to tree planting configuration
in a silvopastoral system in North Wales, UK
AGROFORESTRY
SYSTEMS
56:
47-55, 2002
Abstract
Silvopastoral
systems in Europe offer the potential of introducing environmental benefits
while at the same time increasing the diversity of farm outputs. The establishment of new silvopastoral systems
by planting young trees into existing pasture was investigated at a site in
North Wales, UK. Two tree species,
sycamore (Acer pseudoplatanus L.) and red alder (Alnus rubra
Bong.), were planted into pasture at a range of densities and planting arrangements.
Growth of trees planted in farm woodland blocks (2500 stems ha-1)
was compared with the growth of trees planted at 400 stems ha‑1
in clumps and dispersed throughout the plot and at 100 stems ha-1
(dispersed). Over the first six years
after planting, alder trees were significantly taller and larger in diameter
than sycamore. Sycamore trees planted
at close spacing in farm woodland or clumped arrangements were significantly
larger in diameter than widely spaced sycamore at 100 and 400 stems ha-1. Livestock productivity was unaffected by the
presence of trees during the six-year establishment phase of the system. The planting of trees in a clumped pattern
appears to combine silvicultural benefits to tree growth with agricultural
benefits of maintaining livestock production while trees are established.
Studies on Alnus rubra Bong. (red alder) and Acer pseudoplatanus L. (sycamore)
were carried out to assess their timber and wood fuel properties when grown
at wide spacing as in a silvopastoral system. Initial tree planting density
had significant effects on modulus of elasticity (MOE) in red alder and on
compression strength in sycamore. Wood samples taken from red alder trees
in the high-density plots of 2500 stems ha-1 gave significantly higher MOE
than trees in the low-density plots of 400 stems ha-1 (silvopastoral system).
Wood of sycamore in the high-density plots had significantly higher compression
strength than sycamore wood in the low-density plots. There was, however,
no significant effect of planting density on modulus of rupture (MOR) in either
species. On average, red alder had lower wood density, MOR and compression
strength than sycamore. There was, however, no significant difference in MOE
between the two species. Planting density did not have any effect on wood
fuel Higher Heating Value (HHV) of either red alder or sycamore. There was
also no significant difference in wood fuel HHV between the two species. Red
alder wood, however, had significantly higher fuel value index (FVI) than
sycamore due to its lower ash content. (5)
Contribution of red alder to soil nitrogen input in a silvopastoral system
Teklehaimanot
Z, Ronnie M. Mmolotsi
BIOLOGY
AND FERTILITY OF SOILS 43: 843-848
Abstract: Studies
on Alnus rubra Bong. (red alder) were carried out to assess its potential
for use as a component of a silvopastoral system. Comparison was between two
treatments: red alder 400 stems ha-1 (silvopasture) and red alder 2500 stems
ha-1 (forestry control). d15N values close to zero were recorded in all red
alder plant parts except for root nodules, indicating that a large proportion
of N in red alder was fixed from the atmosphere. Overall, it was estimated
that there was 63.45 kg N ha-1 fixed N accumulated in red alder trees and
the rate of N fixation was estimated at 30.95 kg ha-1 yr-1 in the silvopasture
treatment. The total amount of N that could potentially be added to the soil
in the silvopasture treatment as a result of decomposition of senescent leaves,
roots and dead nodules was estimated at 40.56 kg ha-1 yr-1. Of the total N
added to the soil, 27.1 kg ha-1 yr-1 was due to N fixation from the atmosphere.
These results show that red alder has a potential to improve and maintain
soil fertility in a silvopastoral system.
6)
Developing silvopastoral systems and their effects on diversity of fauna J.H. Mcadam, A.R. Sibbald,
Z. Teklehaimanot, W.R. Eason AGROFORESTRY SYSTEMS 70: 81-89, February 2007 Abstract: