Leaning Trees Research Articles

Righting response of artificially inclined maritime pine (Pinus pinaster) saplings to wind loading

To determine if trees respond to dynamic and static loading in the same manner, 2-year-old maritime pine (Pinus pinaster Ait.) trees were subjected to different types of mechanical loading in the field. One block of trees (the control) were kept in pots and planted in the field at an angle of 0 or 45 degrees to the vertical. A similar block of leaning potted trees was planted nearby and subjected to frequent, unilateral wind loading for a period of 1 s every 2 min. Half the leaning trees were oriented toward the direction of wind loading and half were oriented along the axis of wind loading. The stem profile was measured three times during the growing season to quantify the rate of stem straightening. Compression wood formation and stem shape were measured in all plants. No differences in mean height or diameter were observed between blocks and all leaning trees straightened, but not at the same rate. Although no difference in the rate of apical straightening occurred between control and wind-treated trees, the righting response of the basal part of the stem of leaning trees subjected to wind was four times greater than that of leaning trees without wind. No differences in the righting response were observed between leaning trees growing toward and trees growing away from the source of wind. No significant differences in compression wood formation were found between control trees and wind-treated trees, indicating that other factors must determine the reorientation rate of leaning trees. Results are discussed with reference to the quality of compression wood in conifers and the mechanotransductive pathway in plants.

Woodpecker Nest Tree Characteristics in Upper Midwestern Oak Forests

Characteristics of woodpecker nest trees have been widely studied in some regions of North America. However, there is little research from the Upper Midwest. Forest managers need information on woodpecker nest tree characteristics so they can recommend leaving during harvest trees that meet the needs of cavity-dwelling wildlife. Information specific to the Upper Midwest is especially important given that declines in several species of cavity nesting birds have been predicted by an environmental analysis of timber harvest in Minnesota. Our purpose was to identify attributes of nest trees used by primary cavity-nesting birds. We compared nest trees to unused trees and examined differences in nest trees among woodpecker species. We found 166 active woodpecker nests in upper midwestern oak forests in 1997 and 1998. For each nest tree, we recorded height, diameter, status, and aspects of tree decay. We also measured four potential nest trees (non-nest trees, within size requirements of cavity-nesting birds, with at least 2 indicators of heartwood decay) closest to each active nest tree. Additionally, we recorded these measurements for 137 randomly selected potential nest trees. Using paired t-tests and chi-square analysis, we found each woodpecker species had a unique set of characteristics that separated nest trees from potential nest trees. Using an extension of the McNemar test for related samples, we found woodpeckers as a group used trees that were larger, both in diameter and height, more often elm (Ulmus americana, U. rubra) or aspen (Populus tremuloides, P. grandidentata), more likely to have old cavities present, and with more decay indicators than adjacent potential nest trees. The Yellow-bellied Sapsucker (Sphyrapicus varius) differed from the other woodpecker species by nesting in living Trembling Aspens (Populus tremuloides) with intact tops, complete bark cover, and heartwood fungus. Diameters of nest trees differed significantly among woodpecker species, but unlike findings from other studies, the height of nest hole and nest tree did not. Woodpecker nest entrances faced south or southeast significantly more often than by chance alone, even when excluding leaning trees. This study suggests that generic forest management for all woodpecker species may not be adequate because individual species have specific nest tree requirements. Management recommendations for cavity-nesting birds need to be tailored to meet the needs of a diversity of species.

COLONIZATION–EXTINCTION DYNAMICS OF AN EPIPHYTE METAPOPULATION IN A DYNAMIC LANDSCAPE

Metapopulation dynamics have received much attention in population bi- ology and conservation. Most studies have dealt with species whose population turnover rate is much higher than the rate of patch turnover. Models of the dynamics in such systems have assumed a static patch landscape. The dynamics of many species, however, are likely to be significantly affected by the dynamics of their patches. We tested the relative im- portance of local conditions, connectivity, and dynamics of host tree patches on the meta- population dynamics of a red-listed epiphytic moss, Neckera pennata, in Sweden. Repeated surveys of the species and its host trees were conducted at three sites over a period of six years. There was a positive effect of connectivity, and colonizations mainly occurred in the vicinity of occupied trees. Colonizations were also less likely on strongly leaning trees. Local extinctions sometimes occurred from small trees with low local abundances but were most often caused by treefall. Simulations of the future (100 years) dynamics of the system showed that the metapopulation size will be overestimated unless the increased local ex- tinction rate imposed by the dynamics of the trees is accounted for. The simulations also suggested that local extinctions from standing trees may be disregarded in dynamic models for this species. This implies that the dynamics of N. pennata can be characterized as a patch-tracking metapopulation, where local extinctions are caused by patch destruction.

Distribution pattern of the epiphyteNeckera pennataon three spatial scales – importance of past landscape structure, connectivity and local conditions

We tested which factors explain the distribution pattern of the epiphytic mossNeckera pennataon three spatial scales using the framework of generalized linear models. First, we tested which factors explained its occurrence in forest stands in a 2500 ha landscape. At this scale, we also tested the effect of the historic landscape structure. We recorded its occurrence in all suitable stands. The occurrence probability increased with increasing present quantity ofAcer platanoides, and with increasing present and past quantity ofFraxinus excelsior. The probability also increased with increasing connectivity to occupied stands. However, the connectivity to stands present in 1977 (recorded from infra‐red aerial photographs) explained more of the variation. This suggests that the regional metapopulation size ofN. pennatahas decreased during the past decades, and that its present distribution pattern reflects the age of the remaining stands, and the distribution of past dispersal sources in the landscape. Second, we tested which factors explained the occurrence and abundance on individual trees in three forest stands.Neckera pennatamainly occurred onAcerandFraxinusstems. The most important variable in explaining occurrence probability was connectivity to surrounding occupied trees, which probably reflects the restricted dispersal range in this species. The abundance on occupied trees was also explained by this variable. The occurrence probability and abundance also increased with increasing tree diameter, probably reflecting the time that a tree has been available for colonization and the time since colonization, respectively. The occurrence probability and abundance furthermore decreased on strongly leaning (and deteriorating) trees. The occurrence probability increased with increasing bark roughness, probably reflecting increasing suitability regarding bark chemistry and moisture. Third, we tested its vertical distribution on occupied trees. The main distribution was below 1.6 m.

WITHIN-TREE VARIATION IN ANATOMICAL PROPERTIES OF COMPRESSION WOOD IN RADIATA PINE

Two trees of radiata pine, one showing severe lean, the other growing almost vertically, were assessed for the presence and anatomical properties of compression wood, including anatomy, lignin distribution, microfibril angle, basic density, radial and tangential lumen diameter and cell wall thickness. Both trees contained significant amounts of compression wood although the severity and amount of compression wood was greater in the leaning tree. Changes in lignin distribution seem to be characteristic of the mildest forms of compression wood with reduced lignification of the middle lamella representing the earliest change observed from normal wood. An increase in microfibril angle was associated with both mild and severe compression wood although examples of severe compression wood with the same or smaller microfibril angles than opposite wood, or with very small microfibril angles, were found. When segregated into mild and severe compression wood the average difference in microfibril angle was 4° and 8° respectively compared with opposite wood. Within-ring distribution of microfibril angle was different in severe compression wood compared to opposite wood with higher angles in the latewood. Severe compression wood showed a 22% increase in basic density compared to mild compression wood and opposite wood. The increased density was accounted for in terms of a 26% increase in tracheid wall thickness throughout the growth ring, offset by a 9% increase in radial lumen diameter, slightly greater in the latewood. There were no significant changes in density or cell dimensions in mild compression wood compared with opposite wood.

Growth stress distribution in leaning trunks of Cryptomeria japonica.

The distribution of growth stresses in leaning trunks of Cryptomeria japonica (L.f.) D. Don was determined by measuring the stresses released by the kerf method with strain gauges glued at specified positions along the trunks. Effects of both tree height and peripheral positions on the surface of leaning trunks on surface growth stress were determined. The inner residual growth strains in leaning trunks were also measured. We found high compression stresses in the lower side of leaning trunks that differed greatly from the tensile stresses in normal erect trunks. However, transverse compression stress was found around the tree trunk in both normal and compression wood. In leaning trees, the distribution of internal stresses in the bent trunk portion differed from that in the erect trunk portion, being compressive on the outside and tensile on the inside. The resistant moment introduced by compression stress generated in compression wood is released by the bending of the leaning trunk. The bending stresses are then superimposed on the original internal growth stress. We demonstrated that Poisson's effect of longitudinal stresses should be considered when evaluating transverse surface growth stresses. The existence and intensity of compression wood development can be assessed by growth stress measurements. We conclude that the compressing force of compression wood functions physiologically to give an upward righting response in a leaning trunk.

Irregular heartwood formation in Pinus pinaster Ait. is related to eccentric, radial, stem growth

In order to determine whether the distribution of heartwood in Maritime pine, Pinus pinaster Ait., is affected by stemlean stem, cross sections of trunks at different heights were taken from fifteen 52-year-old leaning trees (angle of lean varied from 0 to 20°). Cross sections were found to be eccentric in shape. However, this eccentricity was not correlated to tree lean, but was related to wind direction. Heartwood was not found to form regularly with tree age and its production regressed significantly with stem eccentric growth. A significantly larger number of annual rings were transformed into heartwood on the compression (underneath the lean or leeward) side of the tree than the opposite or perpendicular sides of the tree. The proportion of heartwood was found to be significantly smaller at the base of the tree, where it accounted for 45% of the cross section, compared to further up the tree at 2.5 and 5.0 m, where it accounted for 57% of the cross section. The proportion sapwood:heartwood remained constant around the cross section, regardless of the direction of lean or wind. Therefore, early heartwood formation on the compressed sides of leaning trees may be due to a developmental process, which allows the tree to maintain a constant, optimal volume of sapwood around the trunk. Further investigations into the physiological and biochemical changes incurred during heartwood formation are needed to explain this phenomenon.

Ice Storm Damage to a Sweetgum Plantation Fertilized with Nitrogen and Phosphorus

Abstract Ice storm damage to a 19-yr-old sweetgum plantation (Liquidambar styraciflua L.) fertilized with nitrogen (N) and phosphorus (P) at age 4 was evaluated. Stem breakage was 39%, compared to 6% leaning, and 55% no damage. Fertilization did not influence the breakage, but dbh, crown diameter at age 15, and predicted dbh at the ice storm related to breakage. Overall, the mean dbh and crown diameter were greater for trees with breakage than those without breakage. The dbh of the leaning trees was smaller than that of the undamaged trees. Although trees with greater dbh had a greater probability for breakage, mean plot dbh may be more important than the individual trees' dbh. A tree with greater dbh compared with the adjacent trees has a greater probability of breakage. The results also show that although severely damaged, this plantation appears to have sufficient undamaged trees for recovery to levels described by others for thinned stands. South. J. Appl. For.(23)4:224-229.

Dendrogeomorphological analysis of a slope near Lago, Calabria (Italy)

The dendrogeomorphological analysis has been used to investigate the periods of disturbance on a slope affected by deep-seated gravitational movements. The method proved to be of great help in determining the temporal sequence of diffused slope movement in the study area, and, though to a lesser extent, to find out the possible causes of triggering the mass-movement. In general, leaning trees indicate that the movement is active. The visual growth analysis indicates that anomalies consisted of sudden decreases of the growth (suppression of tree-rings) induced by stress consequent on ground disturbance, followed in some cases by sudden increases of tree-ring width induced by the higher moisture content in the landslide body. By anomaly analysis, an increase of the anomaly index (It) occurred between 1840 and 1860; subsequently, a period of strongly oscillating values of It occurred that levelled off around 1950. It also appears that mass-movements began to affect this zone soon after 1850s, thus, we can tentatively assume that they have been the cause of the growth anomalies, with a maximum influence in the period between 1860 and 1895. As regards the causes for mass-movement, we inquired about timing of extreme meteorological events and earthquakes. The meteorological data obtained from raingauging stations are not so well related to mass-movement reactivation as the seismic data are. However, only a minority of extreme meteorological events may produce such a disturbance that can be recorded in the tree-ring record. Indeed, only 30% of anomalies can be explained in terms of extreme events. On the other hand, the continuous creeping of the sackung might irregularly trigger the movement of shallower landslides in non extreme-events years. We obtained, instead, a higher degree of coincidence between disturbing causes and anomalous tree growth using archive reports on extreme rainfall periods.

672 The Impact of East Coast Hurricanes on Apples

Hurricanes or strong winds occasionally damage apple trees in the northeastern and mid-Atlantic regions of the U.S. Following the wind event, trees may be leaning or may be lying flat on the ground with extension root damage. Commercial growers generally pull trees upright while the ground is still moist and support the tree or just the trunk with various types of posts providing support to a height of about 60 to 200 cm above ground. In some cases the trees are pulled partially upright and propped up with boards or sand bags may be placed on the upwind side of the tree. Research data are not available for comparing various methods of treating the trees following wind damage, but field observations indicate that trees perform well if trees are pulled upright within 2 or 3 weeks after the wind event. Data from rootstock research plantings from several states indicate that tree anchorage is influenced by the combination of scion cultivar and root-stock. In Virginia in 1989, Hurricane Hugo brought wind gusts of about 95 km·h–1 when the ground was completely saturated by heavy rains. Trees in several plantings designed to evaluate rootstocks or cultivars were evaluated for the extent of leaning following the storm. The percentage of leaning trees on M.26 EMLA was <10% for `McIntosh' and `Golden Delicious' and 40% for `Delicious'. Susceptibility of trees on M.7A was also influenced by scion cultivar, with 0% for `Golden Delicious' and `Empire', 2% for `Redchief Delicious', and 88% for `TripleRed Delicious'.

THE EFFECT OF WIND ON THE MECHANICAL PROPERTIES OF THE WOOD OF BEECH (FAGUS SYLVATICA L.) GROWING IN THE BORDERS OF SCOTLAND

Summary To test the hypothesis that wind exposure affects the wood properties of trees, a preliminary study was made of the longitudinal and radial wood strength of fourteen wind-exposed beech trees (Fagus sylvatica) growing in the Borders of Scotland. Measurements were made on both the leeward and windward sides of the trees and the leeward sides were found, on average, to be stiffer and stronger than the windward sides. The effect was more pronounced in leaning trees than in straight trees. The measurements were compared with similar measurements of beech growing in a sheltered part of Germany and showed that the timber from the Scottish beech trees was stronger.

The adaptive significance of trunk inclination: a further thought

A recent paper in this journal has criticized our previous study, in which we identified an adaptive significance of trunk inclination on slopes. Our main argument was that a tree on a slope may gain some benefit by leaning, which provides the tree with shorter access to the canopy light, and thus a better chance for survival, and that if this benefit outweighs the cost involved in leaning, trunk inclination will be favoured by selection. Although the criticisms are based on some misunderstandings, the situations considered in the critique, which are different from ours, have inspired us into an extension of our previous study. In the course of a reply to the criticisms, we present a further thought on the adaptive significance of trunk inclination in a broader scope. Specifically, we show that our model, with its modified formulation of the benefit component of tree leaning, may evaluate the fitness of a tree with its trunk inclined. It can also be used to examine the conditions for tree leaning, and make predictions on the optimal tree leaning in any situations, including canopy gaps and permanent openings, which the critique is mainly concerned with.

The Possible function of Buttresses in Caryocar Nuciferum (Caryocaraceae) in Guyana: Ecological and Wood Anatomical Observations

This paper describes the microscopic structure and morphology of stern and buttresses of swamp-grown Caryocar nuciferum L. and discusses the function of buttresses. Buttresses are mainly found at the opposite side of the leaning direction of a tree and thus could function as tension members. In contrast to the stern wood, which exhibits a moderate amount of tension wood fibres with a gelatinous layer, the wood of the buttresses on the tension side and the compression side of the leaning tree is characterised by thick-walled tension wood fibres. In addition, the number of vessels in the buttresses is substantially higher than that in the stern wood. The preferential direction of the buttresses and the anatomical differences in the various parts of the tree are discussed.

Recovery and morphology of Pinus resinosa Ait. trees 50 years after they were displaced by a hurricane

Leaning red pine ( Pinus resinosa) trees at Harvard Forest in Petersham, Massachusetts, USA, were studied 50 years after they were displaced from the vertical by a hurricane. Objective methods of characterizing leaning trees in process of reorientation to the vertical were developed. The trees were sigmoid- or sinuous-shaped because their upper parts tended to regain vertical growth along a direction that was approximately a continuation of their original vertical growth path before they were displaced. There were large between-tree variations in (i) bole angle of displacement, (ii) external morphological parameters, and (iii) degree of recovery. On average, 63.6% of the leaning tree total height had regained vertical growth, 26.7% of the total weight was leaning toward the direction from which the hurricane came, while the remaining 9.7% was still leaning in the leeward direction in which it was displaced. The effect of angle of displacement was significant only on maximum bole displacement on the horizontal plane (positive), concave sweep length (positive), length of bole leaning windward (positive), length of corrected portion (negative) and curvature index (positive). Important relationships were observed (a) among indices of bole and crown size (positive), (b) between curvature index and length of corrected portion (negative), and (c) among indices of bole shape (positive).

Tilted Tree Hypsometry

Abstract State-of-the-art technique for measuring height of leaning, forked, crooked, or curved trees is briefly reviewed. The most efficient method employs an expensive tiltable range- finding dendrometer which can measure various types of leaning or nonlinear trees. However, a much less expensive tiltable nonranging hypsometer can be employed on straight leaning trees. This recently developed technique uses spherical triangulation observation points to eliminate bias attributable to lean in the slant plane toward or away from the observer. Necessary formulae and many numeric examples are given to aid in understanding the computational process. For. Sci. 37(6):1581-1590. 12

Species and Stand Response to Catastrophic Wind in Central New England, U.S.A.

(1) The effect of catastrophic hurricane wind on forest vegetation in central New England was examined at the species and stand level. (2) Species susceptibility to wind is largely explained by canopy position: fast-growing, pioneer species that form overstorey dominants (Pinus strobus, P. resinosa, Populus spp. and Betula papyrifera) suffered much greater damage than slower growing, or tolerant species occurring primarily in codominant, intermediate and suppressed canopy positions (Carya spp., Acer rubrum, Quercus alba, Q. velutina and Tsuga canadensis). Uprooting was much more important than breakage as the primary form of damage. This result, which contrasts with the findings of most studies of wind damage, may perhaps be explained by the very high levels of precipitation that accompanied the storm, saturating the soil and loosening the roots. (3) Damage to forest stands exhibits a positive, linear relationship with stand age and height and negative relationship with density. Conifer forests are significantly more susceptible than hardwood forests. Pinus strobus and P. resinosa stands are susceptible to wind at 15 years of age and are completely destroyed at 30 years; hardwood stands exhibit increasing damage from age 20 years, but are not completely blown down until age 80-100 years. (4) Within stands, damage shifts progressively from the dominant trees in young stands to include trees in the codominant, intermediate and suppressed layers in older forests. Parallel changes with age in the type of damage include a decline in the number of leaning trees and increase in uprooting. (5) Damage to species and stands from a catastrophic windstorm occurs quite predictably and specifically within the forests studied. This discriminating impact of wind has profound consequences on the vegetation at a range of spatial scales and is largely mediated by historical factors and structural and compositional aspects of the vegetation mosaic.

Epiphytic vegetation on Acer macrophyllum: a multivariate study of species-habitat relationships

Multivariate methods were used to examine epiphytic species composition on the lower trunk of Acer macrophyllum at five sites in south-coastal British Columbia, Canada. Differences in species composition and abundance between sites were attributed mainly to variation in relative humidity and light conditions. Bark chemistry differences accounted for only a small portion of the observed variation in epiphytic composition between sites. Within sites, compositional variation was examined over 0.5–5 m from ground level on the upper, vertical, and lower trunk surfaces of leaning trees. Compositional variation of the epiphytic vegetation with height and inclination tended to be more strongly developed at drier sites. Furthermore, at all sites compositional variation tended to be greater on upper (wetter) than on lower (drier) surfaces. Particular epiphytic species tended to occur in similar locations on the trunk surface at different sites, suggesting that some microhabitat specialization has occurred. Observed distributional shifts of epiphytic species appeared to be greatest among sites differing widely in prevailing microenvironmental conditions.

Soil movements on permafrost slopes near Fairbanks, Alaska

Many north-facing slopes in the Yukon–Tanana Uplands of Alaska show signs of downhill movements in the form of hummocky surface and leaning trees. Measurements of movements and pore pressures were made at several sites in the Caribou–Poker Creek Research Watershed. It was found that, on slopes with inclinations near 30°, most of the movements occurred immediately after thaw when pore pressures were high.To evaluate the slope stability, the soil strength was measured by direct shear tests. The strength of the moss layer and tree roots was evaluated by performing tension tests on the roots and the moss–root complex. Results of stability analyses show that local failures involving individual wedges are likely. The displacements associated with a wedge slide would result in a hummock or step. The strength of the moss–root complex was found to be a significant factor in the stability of the wedge and of the step. Key words: moss, roots, permafrost, pore pressure, shear strength, slope stability, thaw.

Measuring Trees That Lean, Fork, Crook, or Sweep

Abstract Until recently there was no fully satisfactory solution to the broad problem of measuring standing trees whose axes leaned, forked, crooked, or curved. Analysis of a spherical model has led to revision of a well-known computer program (STX) that will now process standard rangefinder-dendrometer measurements of straight leaning trees without bias, and similar measurements of forked, crooked, or curved trees with negligible bias. More field effort is required if instruments lack rangefinding capability. Azimuth of crosslevel axis and tilt of hypsometer aligned with tree axis must then be measured from each of two separate observation points to enable computation of a constant correction angle to be added algebraically to each tilted elevation angle. Corrected elevation angles together with a single range (measured parallel to the ground} will then allow unbiased computation of other elevated slant ranges, slant heights, and diameters.

Relationship between fibre morphology and shrinkage of wood

This is a study on the shrinkage of wood representing the wide range of morphology variation in leaning trees. It involved 13 trees of Eucalyptus regnans, one of Eucalyptus sieberi and four of Pinus radiata, and specimens taken at close intervals around the circumference of each. Data indicated a systematic modulation, between extremes at upper and lower sides of each stem, in longitudinal growth strains, relative proportions of thin, medium and thick-walled fibres, microfibril angle in the S2 layer of these, and both Klason and acid-soluble lignin content. Analyses indicated that the microfibril angle in S2 was a prime factor in influencing both longitudinal and volumetric shrinkage reactions; proportion of thick-walled fibres in the tissue, thickness of S2 relative to S1, and variations in lignification also were involved. Unusually thick-walled fibres were associated with visco-elastic strain recovery effects, which could form a substantial part of dimensional changes apparently attributable to shrinkage.