Mixture Of Trees Research Articles

Effects of mixture of broad-leaved trees on the chemical characteris-tics of the soil in Japanese cypress stand

Effects of mixture of broad-leaved trees on the chemical characteris-tics of the soil in Japanese cypress stand

A PROPOSED PLANTING MATRIX FOR NATURE CONSERVATION AND AMENITY

Summary Despite the wholesale destruction of Britain's ancient woodland over the centuries and the neglect of the surviving remnants, this paper suggests that locally grown indigenous planting stock can be planted in appropriate locations in order to create a close replica of semi-natural woodland. The planting of suitable mixtures of trees and shrubs in well structured plantations is an appropriate approach to the establishment of woodlands in the British Isles but could be equally used elsewhere in the temperate world. This paper examines and discusses an establishment practice to create a woodland, based largely on natural processes with adaptations for human implementation. It is argued that woodlands created in this manner are robust enough to remain intact should management be delayed and are both aesthetically pleasing and good for wildlife. A model specification and examples of woodland communities are given.

Soil andLeucaena leucocephala L. growth variability underFaidherbia albida Del. andZiziphus spina-christi L. Desf.

In order to obtain data which will facilitate the scientific development of multiple intercropping of trees in agroforestry systems, the effects ofFaidherbia albida Del. orZiziphus spina-christi L. Desf. on soil quality and on yield of interplantedLeucaena leucocephala L. were investigated. The distance to which bothFaidherbia albida andZiziphus spinachristi trees improved soil quality as well asLeucaena leucocephala andSorghum vulgare L. production around them was about two times the radius of the tree crown. Higher yields of plants underZiziphus spina-christi thanFaidherbia albida were explained by similarly higher concentrations of available phosphorus (P). Other soil parameters, including total nitrogen (N), were similar under both species; being higher under the tree canopies than away from them. The study identified optimum tree spacing for agroforestry to be twice the tree crown radius. It also demonstrated the advantages of multiple tree mixtures over pure stands in improving soil quality and productivity.

Some Aspects of Polya Tree Distributions for Statistical Modelling

Polya tree distributions are defined. They are generalizations of Dirichlet processes that allow for the possibility of putting positive mass on the set of continuous distributions. Predictive and posterior distributions are explained. A canonical construction of a Polya tree is given so that the Polya tree has any desired predictive distribution. Choices of the Polya tree parameters are discussed. Mixtures of Polya trees are defined and examples are given.

Phase transition in diffusion-limited aggregation with two immiscible components.

A diffusion-limited-aggregation (DLA) model with two immiscible components (A and B atoms) is presented to investigate a phase transition in morphological changes. A segregation occurs where the DLA pattern is constructed by a mixture of trees consisting of only A atoms and trees consisting of only B atoms. Above a critical concentration ${\mathit{p}}_{\mathit{c}}$, trees with only A atoms exceed trees with only B atoms, and the DLA with only A atoms dominates. It is found that a phase transiton between A-DLA and B-DLA occurs at the critical concentration ${\mathit{p}}_{\mathit{c}}$, where A-DLA and B-DLA represent, respectively, DLA with only A atoms and DLA with only B atoms. The phase transition is analyzed by making use of the real-space renormalization-group method. The correlation length \ensuremath{\xi} scales as \ensuremath{\xi}\ensuremath{\approxeq}(p-${\mathit{p}}_{\mathit{c}}$${)}^{\mathrm{\ensuremath{-}}\ensuremath{\nu}}$, where ${\mathit{p}}_{\mathit{c}}$=0.5 and \ensuremath{\nu}=1.85 on the square lattice.

The Effect of Resource Depletion on the Feeding Behaviour of a Browser: Winter Foraging by Moose on Scots Pine

(1) The foraging dynamics of a browser, the moose Alces alces L. exploiting depleting resources was studied experimentally. It was hypothesized that: (a) differences in the intake of twig biomass between tree stands in early foraging sessions would tend to even out as resource depletion progressed; (b) food item selectivity within stands would decrease, and (c) bite diameters would increase with time. (2) Artificial stands, composed of one browse species or a mixture of species, were set up in a forest area. The species included were Scots pine Pinus sylvestris L., aspen Populus tremula L. and grey alder Alnus incana (L.) Moench. Special attention was paid to the analysis of the pattern of Scots pine exploitation because this tree is of commercial interest. Moose browsing was assessed by counting bites and by measuring bite diameters. (3) Initially the total consumption of twig biomass in the pine + aspen stand was twice as high as that in the other two stands. This difference remained until almost half of the available biomass in the pine + aspen stand had been consumed. Within stands the preference for aspen over pine increased over time, whereas the preference for pine over alder decreased. Bite diameter on Scots pine showed a significant decline over time. (4) Browsing on Scots pine was only slightly affected by the species composition of the tree mixtures. Browsing intensities on individual pines was positively correlated with the amounts consumed on adjacent stems.

Metabolic and faunal activity in litters of tree mixtures compared with pure stands

Foresters are showing increasing interest in the advantages to timber production of certain mixtures of plantings. We have studied decomposition and nutrient release in litters from tree mixtures compared with pure stands. Comparisons have been made of nutrient dynamics in pure and two-species mixtures of oak ( Quercus petraea), alder ( Alnus glutinosa) and Norway spruce ( Picea abies), planted in a replicated design in 1955. Nutrient availability and tree growth were enhanced in the spruce/pine and depressed in the spruce/alder and spruce/oak mixtures compared with single-species stands. Increased mobilization rates in the spruce/pine and decreased rates in the spruce/alder and spruce/oak were correlated with increased and decreased metabolic activity, respectively, and changes in the decomposer community of the forest floor. It is suggested that a species of litter with a relatively high nutrient concentration, when added to a low-quality litter may enhance decomposition and nutrient release of the latter. It is concluded that part of the explanation for modified growth of trees in mixtures compared with pure stands is to be found in the interactions between invertebrates and microorganisms in the litter, which result in changes in nutrient dynamics.

Fire and the Forest History of the North Cascade Range

Postglacial vegetation changes are often ascribed to the direct effects of climate change. I studied pollen, plant macrofossils, and sediment charcoal in order to determine the potential role of changes in the disturbance (fire) regime in the postglacial development of local vegetation at Kirk Lake in the foothills of the North Cascade Range in northwestern Washington. Five pollen assemblage zones are recognized: a Pinus–Populus zone >12 000 BP, a Picea—Alnus sinuata zone from >12 000 to 11 030 BP, an Alnus rubra—Pteridium zone from 11 030 to 6830 BP, a Cupressaceae zone beginning at 6830 BP, and a late Holocene Pinus—Alnus rubra zone from 2400 to 900 BP. The first forests (>12 000 BP) were an open mixture of conifers and deciduous trees, chiefly Tsuga mertensiana, Abies, Pinus contorta, and Populus on a landscape subject to erosion. Just before 12 000 BP, the pioneer species Picea sitchensis, Alnus rubra, and A. sinuata became important constituents of the forest. Although pollen accumulation rates were high, the abundance of Alnus sinuata indicates an open—canopy forest. Beginning °11 200 BP, climatic warming initiated major changes in forest composition and the fire regime. Tsuga heterophylla migrated into the region, rapidly expanded, then declined shortly thereafter, while Pseudotsuga menziesii, Alnus rubra, and Pteridium expanded, and Pinus contorta, Picea sitchensis, Populus, and Alnus sinuata declined. The abundance of Pseudotsuga, Alnus rubra, and pteridium between 11 030 and 6830 BP corresponds with increased influxes of charcoal into the sediment; this zone is interpreted as a closed forest with a relatively high fire frequency and composed of a mosaic of postfire successional communities in which fire—adapted Pseudotsuga and Alnus rubra predominated over fire—sensitive Tsuga heterophylla. Pinus monticola became locally important °800 BP. Between 6800 and 6400 BP Thuja plicata arrived, Tsuga heterophylla expanded, and Alnus rubra, Pseudotsuga and Pteridium declined. These changes are accompanied by a reduced fire frequency, inferred from lower charcoal accumulation rates, and they indicate a shift to wet—temperate climate similar to today's. The late Holocene fossil record shows the development of the adjacent peatland, which Pinus contorta eventually invaded.

Response of messmate stringybark regrowth to release in irregular stands of mixed eucalypts

Summary The response in basal area and height of messmate stringybark regrowth stems to release from competition over a period of ten years was examined in irregular stands of mixed eucalypts in the Wombat and Creswick Forests. These stands contained a mixture of small trees (dbhob <30 cm) less than 40 years old (regrowth), with larger trees (dbhob to 80 cm) 80 to 100 years old (overwood). Competing stems were identified by the ‘zone count’ method using a 9.2 m2 ha-1 optical wedge. Basal area increment (bai) and height increment of regrowth stems was reduced by competing overwood and regrowth, but regrowth stems retained a capacity to respond when released from this competition. Regardless of crown position within the regrowth stratum, regrowth responded to the reduction in competition, with the magnitude of the response in bai and height increment generally increasing with the degree of release and increasing crown dominance. These results indicate that in the mixed eucalypt forests of central Victoria, where partial cutting is practised, selected regrowth stems, preferably of good form and in the dominant crown position class, can be released from their competitors to reduce the production time for the new crop.

Experiences with genetically mixed forest plantations in the Netherlands

The use of the genotype mixtures, including species mixtures of trees, may be indicated on forest planting sites of variable or uncertain quality and/or when the reactions of components of the mixture to these sites are imperfectly known; that is, in cases where predictability is low. Four examples are given of planting practice in the Netherlands with species mixtures on such sites. The development of stands was monitored. This led to increased knowledge of the sites and of the reaction of the mixture components to them. On certain sites the planting of some species had been superfluous and a waste of money, as they rapidly disappeared from the mixture. Increased knowledge reduced the need for mixtures. Where the site or its vital weather characteristics remained unpredictable, the planting of a mixture retained its value. It proved difficult to maintain a particular mixture over an appreciable part of the rotation, in spite of careful thinnings. Some individual mixtures developed into pure stands, others into a mosaic of more or less pure stands of different species. In Dutch poplar culture, enough is known about sites and clones and their interaction to make the planting of single clones in pure stands attractive. If several clones are suited to the site, a mosaic of pure stands is preferred over an individual mixture.