Woodland Trees Research Articles

Seedling ecology of two miombo woodland trees

The development of seedlings of two miombo trees, Brachystegia spiciformis Benth. and Julbernardia paniculata (Benth.) Troupin, was studied during two growing seasons (December 1989–April 1991) at a Zambian grassland site. Seed germination rates under laboratory and field conditions were not significantly different although germination in the field was delayed by 1–2 weeks due to insufficient rainfall. After one year of storage J. paniculata seed germination had declined from 67% to 17% while germination of B. spiciformis seeds remained at about 83%.

Recruitment of Seedlings and Vegetative Sprouts in Unburned Chaparral

Age structure of 12 stands of chaparral, unburned for 56—120 yr, was investigated. All shrubs produced discernible growth rings, and ring counts on stems from stands of known age, plus synchrony in annual growth ring width among species in the same stand, were taken as evidence that growth rings represented annual rings. Species that survive fire by vegetative regeneration from the root crown were capable, in the absence of fire, of continuously regenerating their canopy with basal sprouts. These multistemmed resprouting species had an uneven age structure, indicating continuous recruitment of new stems into the population. The predicted age distribution for resprouting shrub stem populations illustrated very different patterns for species within the same stand and for the same species in different stands. In most resprouting shrubs, <15% of the stems dated back to the first decade after fire, and in many species the majority of stems were <10 yr of age. This contrasts with obligate seeding shrubs that do not initiate new stems from the root crown, and for which, in undisturbed chaparral, 100% of the stems date back to the years immediately following the last fire. Seedling recruitment was abundant in seven of these old chaparral communities. Species with abundant seedling populations, ranging from 1000 to 37 500 individuals/ha, were Quercus dumosa, Q. wislizenii, Rhammus crocea, Prunus ilicifolia, Heteromeles arbutifolia and Cercocarpus betuloides. These species share the characteristic of regenerating after fire solely by resprouting, and seldom recruit seedlings during the first few decades after fire. Thus, it is concluded that these postfire obligate resprouters require long fire—free periods for successful reproduction and potential population expansion. For all but the last species, seedlings were most abundant in stands with a closed canopy and deep litter layer. Safe sites for establishment were not in gaps, although gaps may be important for successful recruitment of saplings into the adult population. For all sprouting species the actual age distribution of seedlings and saplings indicated that recruitment did not occur every year; mortality was high but most populations had some saplings that survived beyond the first decade. For all postfire seeding taxa, viz., Adenostoma, Arctostaphylos, and Ceanothus, no significant seeding recruitment was observed in these ancient communities. Seedlings of woodland tree species had colonized several of these old chaparral communities; however, even in stands a century old, successional replacement of chaparral was not imminent.

Demographic structure of California chaparral in the long‐term absence of fire

Abstract. Demographic structure of 12 chaparral sites unburned for 56 to 120 years was investigated. All sites were dominated by vigorous shrub populations and, although there was colonization by seedlings of woodland tree species in several stands, successional replacement of chaparral was not imminent. Although successional changes in community composition were evident, there was no indication of a decline in species diversity. Non‐sprouting species of Ceanothus suffered the greatest mortality at most, but not all, sites. Sprouting shrubs, such as Quercus and Heteromeles had very little mortality, even in stands more than a century old. All postfire resprouting species had multiple stems of different ages indicating these shrubs were capable of continuously regenerating their canopy from basal sprouts. Ceanothus populations were highly clumped and there was a significant correlation across all sites between variance/mean ratio and percentage mortality. As Ceanothus populations thinned, they became less clumped. In mixed chaparral stands, Quercus and Heteromeles were significantly taller than associated Ceanothus shrubs and overtopped the Ceanothus; at two sites, the density of live Quercus per plot was correlated with the density of dead Ceanothus. Thus, mortality of Ceanothus stems is likely related to both intra and interspecific interations.Seedling recruitment was observed for most shrub species that regenerate after fire by resprouting; seedling and sapling densities ranging from 1000–36 500 ha‐1 were recorded for Quercus dumosa, Rhamnus crocea, Prunus ilicifolia, Heteromeles arbutifolia and Cercocarpus betuloides. For all but the last species, seedlings and saplings were most abundant beneath the canopy cover and not in gaps. Across all sites, recruitment was significantly correlated with depth and bio‐mass of the litter layer. Cercocarpus betuloides was present in several stands, but seedling establishment was found only in one very open, disturbed stand. Regardless of stand age, taxa such as Adenostoma, Arctostaphylos and Ceanothus, which recruit seedlings after fire, had no significant seedling production.

Phenology of Acacia albida trees in Zambezi riverine woodlands

SummaryThe phenology of Acacia albida trees was studied over eight years in Mana Pools National Park, Zimbabwe. Leaf flush occurred towards the end of the rains. It was followed by flowering, with ripe fruit‐fall in the late dry season. Leaf‐fall occurred early in the following wet season. After seasons of low rainfall, trees were severely defoliated by caterpillars soon after leaf flush and this prompted a second flush of leaves. In these years there were also two periods of flowering and fruit production. During dry years, the proportion of trees which failed to set fruits after flowering increased, fruit production by those trees which did bear fruit was reduced and fruit‐fall started earlier in the year.

Fruit production by Acacia albida trees in Zambezi riverine woodlands

ABSTRACTFruit production by Acacia albida (Leguminosae: Mimosoideae) trees in Mana Pools National Park, Zimbabwe, was monitored over eight years. Timing of ripe fruit-fall varied between years, as did fruit production: production of ripe fruits by the same tree varied from 5.4 kg in 1983 to 290.1 kg in 1988. Baboons reduced fruit production by feeding on unripe fruits and the mass eaten each year was negatively correlated with rainfall. Potential fruit production (i.e. production in the absence of baboons) was high when the late wet season was wet or cool and when fruit production in the previous year was low. Late wet season rainfall and temperature probably determined the degree of defoliation by caterpillars: in 1983 and 1987, when the late wet season was hot and dry, the trees were almost completely defoliated. During the late dry season, A. albida fruits were an important component of the diets of waterbuck, eland, elephant, buffalo and kudu; they were seldom eaten by hippopotamus and were ignored by zebra and warthog.

15 N natural abundance as a possible marker of the ectomycorrhizal habit of trees in mixed African woodlands.

The partial contribution by fixed nitrogen in N2 -fixing plants can be estimated if the 15 N natural abundance of non-N2 -fixing reference species, which derive their N from the soil, deviates from that of atmospheric N2 (the 15 N natural abundance method). Data from Tanzanian miombo woodland showed a significant difference (= 1.0-2.5 δ15 N%0 ) in 15 N abundance between ectomycorrhizal and vesicular-arbuscular (VA) mycorrhizal reference species. This finding casts doubt upon arbitrary selection of reference species, and also raises the possibility of using 15 N abundance as a marker of the ectomycorrhizal habit. It is suggested that the higher 15 N abundance of ectomycorrhizal tree species could result from differences in discrimination during uptake or from greater utilization of organic N.

Measuring the risk of predation in an energy currency: field experiments with foraging blue tits, Parus caeruleus

A technique for measuring the ‘risk of predation’, in an energy currency, is described. Experiments on free-living blue tits determined the extent to which feeding in a risky site was compensated by making food easier to obtain. The birds were trained to use operant feeding devices which were placed at different distances from the edge of woodland tree cover. The reward schedules at the feeders were controlled by a computer, which adjusted the number of hops required to obtain a food reward in relation to the extent to which each feeder was used. When the feeders were used equally the reward schedules stabilized and were recorded. There was little difference in the final reward schedules of feeders placed under the cover of trees, but the frequency of reinforcement required to persuade the birds to feed in the open rose dramatically at relatively short distances (1·5m) from cover.

Size distribution and density of trees in bogs and pine woodlands in west central Louisiana

Size distribution and density of trees in bogs and pine woodlands in west central Louisiana

Use of nestboxes by the Dormouse Muscardinus avellanarius

Nestboxes, with their entrance holes facing inwards, were fixed to trees in deciduous woodland in Somerset. Their use by dormice Muscardinus avellanarius L. was monitored monthly through three summers, 1986–1988. At the principal study site, more than 60% of the boxes had been found by dormice by the end of the first summer and the dormice themselves had been recorded in more than 40% of them. Trapping revealed that numbers of dormice present in areas with nestboxes were greater than in similar areas without boxes. Nestboxes thus appear to support enhanced populations and offer a means of assisting the conservation of this species. Dormice successfully reared young in the boxes, which also provided a means of access for basic studies on biology of this scarce and poorly known British mammal.

Breeding Parameters of the Brown Goshawk Accipiter fasciatus in South-eastern Australia

Sixty-seven breeding attempts of the Brown Goshawk Accipiter fasciatus were investigated on 26 temtories. Incubation generally commenced in October, although as early as mid-September and as late as early December. Incubation took 30- 35 days, most young hatching in November. The nestling period was usually 28-35 days; males generally fledged earlier than females. No breeding occurred outside the springlsummer period. Nests were placed high in mature Eucalyptus trees in woodland within 200 m of pasture. Nest trees were commonly on sheltered slopes of southerly or easterly aspect. Approximately 30% of nests were beside the trunk of the nest tree, the remainder being in branch forks 1-12 m from the trunk. Active nests were never closer than 1.6 km apart. Breeding density and success declined from 31.3 active nests1100 km², 2.31 young fledgedlactive nest in 1981 to 20.3 active nests1100 km², 1.54 young fledgedlactive nest in 1983. From 50-77% of territories held active nests in any one year during 1981-83. Particular nests were used for several years in succession on some territories, however there was no correlation between nest re-use and prior breeding success. Limited evidence was found for territory fidelity from year-to-year.

Some ecological characteristics of the primary trophic level of a secondary succession

Simultaneous studies have been made of the macroscopic organisms of a series of sites in a secondary succession to determine the extent to which the bionomic strategies of the organisms and the features of the com­munities show consistent patterns or trends. In the estimation of primary productivity allowance was made for turnover. Although standing crop and litter biomass increased through succession, the level of primary production remained within the range 750–980 g m-2. The following trends, with successional age, were recorded: leaf life expectancy in­creased, the amount of biomass allocated to reproduction fell, as did the ratio of flowering to reproductive structures in the herb layer, average germinule size increased and seedling survival fell. The flowering struc­tures of the dicotyledons were predominantly hermaphrodite in the field seral stages, but monoecious in the woodland trees; dioecious plants were relatively rare. The early successional plants were often self pollinated; this mechanism is characteristic of very few of the plant species found in the other seral stages. Insect pollination was the most frequent mechanism in the forbs of the old field and wind for the woodland trees. In the assessment of these characters, from direct observation or from existing published information, frequency was expressed not only simply as species presence, but also by weighting the different species for their relative abundance in the vegetation of that site: the patterns revealed by these approaches differed in emphasis. The seed bank closely predicted the composition of the early successional flora. The pattern of succession in these sites would seem to conform most closely to the initial floristic composition model of Egler (Vegetatio4, 412 (1954)), with a tolerant stage followed by an inhibitory stage, the latter in the old field. Here the conditions provided by the thick grass vegetation maintain large popu­lations of small mammals and molluscs that increase the mortality of seedlings, including tree seedlings, and so retard the rate of succession. Non-native (immigrant) plant species contributed up to 16% of the vegetation cover in the first two years of the succession, but thereafter they were rare or absent. Because the comprehensive nature of the study often precluded elaborate replication, the general conclusions could be limited by the extent that the findings were site specific, therefore com­parisons have been made with other studies of particular features to evaluate the biological robustness of the findings. Within the trends and patterns summarized above there were interesting exceptions, but the life-history traits observed conformed to previously published predic­tions for habitats with similar levels of productivity, but varying levels of disturbance.

Variation in Betula pubescens Ehrh. (Betulaceae) in Scotland: its nature and association with environmental factors

A classification, based on climatological, topographical and geological attributes and developed by Bunce, Barr & Whittaker (1981: Annual Report of the Institute of Terrestrial Ecology, U.K. 1980) for stratifying the U.K. into 32 land classes, was used to ensure objectivity when sampling the range of variation within Betula spp. in northern Britain. Seeds of Betula spp. were collected, wherever possible, from each of ten woodland trees in three geographically distinct locations of each of 12 land classes known to ‘carry’Betula species. Trees in a thirteenth land class, restricted to the west of Scotland, were inaccessible. Seedlings from 170 of 196 trees were attributed to B. pubescens which occurred in all 12 land classes: the remaining 26 trees were identified as B. pendula which is restricted to five land classes in southern and eastern Scotland. Detailed analyses of plant morphological and phenological features using principal component analyses, cluster analyses and canonical variance analyses showed that leaf size, shape and hairiness were good discriminators of variation, as was the occurrence of fruitbodies of Laccaria proxima, a sheathing (ecto-)mycorrhizal fungus. These discriminators enabled the seedlings to be arranged in a nuniber of distinctive groups: sredlings with drooping branclirs and small laves, chararteristics of B. pubescens subspecies tortuosa, originating from westerly and wet locations to seedlings with upright branches and large leaves originating from easterly and dry locations. Leaf lengths and the increasing frequency of petiolar hairs were related to maximum July temperatures and measures of oceanicity (at the sites of origin).

Holocene Vegetation and Climate in the Puerto Blanco Mountains, Southwestern Arizona

AbstractPlant macrofossils from 21 pack rat (Neotomasp.) middens at 535–605 m from the Puerto Blanco Mountains, southwestern Arizona, provide and excellent history of vegetation and climate for the last 14, 120 yr B.P. in the Sonoran Desert. A late Wisconsin juniper-Joshua tree woodland gave way to a transitional early Holocene desertscrub with sparseJuniperus californica(California juniper) by 10,540 yr B.P. Important Sonoran Desert plants includingCarnegiea gigantea(saguaro) andEncelia farinosa(brittle bush) were dominants. Riparian trees such asAcacia greggii(catclaw acacia),Prosopis velutina(velvet mesquite), andCerdicium floridum(blue palo verde) grew on dry, south-facing slopes in a middle Holocene Sonoran desertscrub in a warm, wet summer climate with frequent winter freezes. Modern subtropical Sonoran desertscrub formed about 4000 yr B.P. as summer rainfall and winter freezes declined.Cercidium microphyllum(foothills palo verde),Sapium biloculare(Mexican jumping bean),Olneya tesota(ironwood) andStenocereus thurberi(organ pipe cactus) became dominant as riparian trees retreated to wash habitats. The inferences of a latest Wisconsin/early Holocene summer monsoonal maximum by J. E. Kutzbach (1983), Modeling of Holocene climates.In“Late-Quaternary Environments of the United States,” Vol. 2, “The Holocene” (H. E. Wright, Ed.), pp. 271–277. Univ. of Minnesota Press, Minneapolis) are not supported for the Southwest. Apparently the persistence of late Wisconsin circulation patterns offset any increases in insolation.

The Herbivorous Insect Communities of Open and Woodland Bracken: Observations, Experiments and Habitat Manipulations

In this paper we examine how the insect herbivores that feed on bracken fern, Pteridium aquilinum (L.) Kuhn., are influenced by open and woodland habitats. Most, but not all herbivore species in Britain are commoner on open bracken. We examined three possible causes of these distributions: differences in host plant phenology between the two habitats, the effect of shade per se, and differences in host plant quality. Woodland bracken emerges earlier, but unshaded bracken grows more rapidly, so that by mid-season both have attained a similar stage of development. Nevertheless, we found that the abundances of some herbivore species were correlated with the date of emergence, regardless of habitat, although others were not. Thus plant phenology was one of several factors that might explain differences between open and woodland herbivore assemblages. The effects of shade per se were examined by removing woodland trees and artificially shading open areas for comparison with unmanipulated controls. Again some species responded by changing their distributions according to their known preferences for light or shade, whilst others did not. Finally we examined feeding preferences, growth and mortality rates of a sawfly caterpillar, Strongylogaster lineata, on open bracken, where it is common, and on woodland bracken where it seldom occurs. However, the type of habitat proved to have no effect on the performance of the caterpillar. We conclude that the degree of shading of the host plant has pronounced, but variable effects on the distribution of bracken herbivores. While it was possible to identify some of the factors influencing some species along the light-shade gradient, it is apparent that processes determining the distributions and abundances of each species are both complex and idiosyncratic.

Patterns of Variation in Eucalyptus sideroxylon A. Cunn. Ex. Woolls. I. Variation in Adult Morphology

Eucalyptus sideroxylon, a woodland tree occumng in an arc from central and southern Victoria to south-eastem Queensland, is currently divided into subsp. slderoxylon to the north, and subsp. tricarpa to the south. Thirty populations were sampled throughout the range of the species and studied for adult leaf and fruit characters. There were found to be very marked and highly significant morphological differences between the two subspecies, more especially in the fruit characters. Within subsp. sideroxylon there was a general distinction between the inland populations and the more coastal populations, while within subsp. trlcarpa there was similarly a general differentiation of the coastal populations from the northern and north-central Victorian populations. The extent and general pattern of these various differences are documented as a prelude to further studies.

Collar Rot and Basal Canker of Sugar Maple

Two types of trunk symptoms are associated with urban maple decline in Wisconsin. One is a "basal canker," caused by Fusarium spp., and the other is a "collar rot" caused by a Phytophthora sp. Phytophthora collar rot appears to be more destructive. Trunk girdling by these diseases, both occasionally observed on the same tree, was greatest on trees with severe decline (Class V) and least on trees with initial decline (Class II). Incipient cankers were found on trees still healthy in outward appearance (Class I). Buttress roots of planted trees were deeper than the roots of naturally seeded, woodland trees. Moreover, woodland trees exhibited no similar cankers. We believe that the fungi and the diseases they incide are causes of urban maple decline in Wisconsin. They may be associated with maple tree production in nurseries or with planting practices in urban situations.

Parmotrema arteagum, a New Lichen Species from Mexico

Parmotrema arteagum Egan is described from west-central Mexico. This new species belongs to the Parmotrema perforatum complex and is charac- terized by a robust thallus, the production of marginal cilia, perforate apothecia, a white lower surface, large spores and conidia, and atranorin and salazinic acid. Soredia and isidia are lacking. Parmotrema arteagum grows on branches of oak and other deciduous trees in woodlands between 600 and 900 m elevation in the state of Michoacan.

Influence of stemflow on the representation of pollen oftiliain soils

Abstract The pollen distribution in mineral soil in woodland containing Tilia × europaea L. was studied in an attempt to explain abnormally high percentages of Tilia pollen found in some podzol profiles. It was shown that a greater concentration of pollen containing greater proportions of Tilia pollen occurred in a narrow zone (c. 30 cm) around the trunk of Tilia trees than in the soil further from the trunk. This is attributed to the effect of stemflow concentrating pollen and possibly increasing the preservation of pollen at the trunk base. The percentages of Tilia pollen found were similar to the abnormally high values from the podzol profiles. It is suggested that these profiles mark the precise locations of trees in an earlier woodland. The implications of this to the interpretation of soil pollen diagrams are discussed.

Baboon sleeping site preferences and relationships to primate grouping patterns.

Baboons choose sleeping sites in the following descending order of preference: (1) steep cliff faces and caves, (2) taller emerging trees in continuous forests, (3) the canopy of contiguous forest without emerging trees, and (4) open woodland trees. Choice of sleeping sites in an order appearing to agree with degree of inaccessibility to most predators suggests the hypothesis that predation avoidance is the major basis for use and choice of particular sleeping sites. If this preference order for kinds of sleeping sites is applicable to other large primates, it suggests that spacing of adequate sleeping sites relative to the distribution and density of food resources is one factor contributing to group size and possibly other features of primate social structure. The relatively even distribution of numerous adequate sleeping sites in tropical forests may be one factor permitting evolution of small social units. By contrast, sparse distribution of sleeping sites relative to resource field may permit the development of large social groups.

Reducing Damage to Shade and Woodland Trees from Construction Activities

Guidelines are given for reducing damage to trees from installing underground utility lines, making road and grade cuts and fills, and constructing home developments. Observations and experience, especially in supervising construction that affected trees on rights-of-way in Maryland, and the available literature provide the basis for the guidelines. Case histories are cited illustrating a range from no apparent injury to extensive damage.