Remnant Tree Research Articles

Revised slip rates for the Alpine fault at Inchbonnie: Implications for plate boundary kinematics of South Island, New Zealand

The northeast-striking, dextral-reverse Alpine fault transitions into the Marlborough Fault System near Inchbonnie in the central South Island, New Zealand. New slip-rate estimates for the Alpine fault are presented following a reassessment of the geomorphology and age of displaced late Holocene alluvial surfaces of the Taramakau River at Inchbonnie. Progressive avulsion and abandonment of the Taramakau floodplain, aided by fault movements during the late Holocene, have preserved a left-stepping fault scarp that grows in height to the northeast. Surveyed dextral (22.5 ± 2 m) and vertical (4.8 ± 0.5 m) displacements across a left stepover in the fault across an alluvial surface are combined with a precise maximum age from a remnant tree stump (≥1590–1730 yr) to yield dextral, vertical, and reverse-slip rates of 13.6 ± 1.8, 2.9 ± 0.4, and 3.4 ± 0.6 mm/yr, respectively. These values are larger (dextral) and smaller (dip slip) than previous estimates for this site, but they reflect advances in the local chronology of surfaces and represent improved time-averaged results over 1.7 k.y. A geological kinematic circuit constructed for the central South Island demonstrates that (1) 69%–89% of the Australian-Pacific plate motion is accommodated by the major faults (Alpine-Hope-Kakapo) in this transitional area, (2) the 50% drop in slip rate on the Alpine fault between Hokitika and Inchbonnie is taken up by the Hope and Kakapo faults at the southwestern edge of the Marlborough Fault System, and (3) the new slip rates are more compatible with contemporary models of strain partitioning presented from geodesy.

Timber management with variable retention in Nothofagus pumilio forests of Southern Patagonia

Forestry practices integrating ecological and social criteria have been replacing those based only on economic values. Traditional silviculture, such as shelterwood cuts ( SC), transforms uneven-aged original stands to an even-aged managed forest. Recently, other methods have proposed to conserve some of the original heterogeneity of the old-growth forests. One proposal leaves 30% of the timber quality forest area as aggregated retention and 20% basal area as dispersed retention. The aim of this study was to analyze the feasibility of timber management with aggregated and dispersed retention in Nothofagus pumilio old-growth forests by analyzing timber and harvesting yield potential compared with traditional regeneration systems. Also, remnant tree stability of aggregated retention was analyzed. Timber yield potential of old-growth forests varied from 136 to 479 m 3 ha −1 across a site quality gradient. High grading cutting improved yield index (timber volume and harvested basal area ( HBA) ratio of 7.9 m 3 m −2). In contrast, this index decreased in clear-cuts (4.7 m 3 m −2) and shelterwood cuts (4.9 m 3 m −2). The index also decreased in the aggregated and dispersed retention treatment (5.1 m 3 m −2), but with higher timber harvested volumes. Windthrow of remaining trees in aggregated retention was related to time, being significantly higher during the first year after harvesting. Windthrow was affected by crown class and position into the aggregates of the remnant trees as well as site quality of the stand. Regeneration methods with aggregated retention were feasible across the entire site quality gradient, and economic losses were not significant when compared to shelterwood cuts. The method also resulted in stability of the remnant overstory, which maintained the ecological conditions to ensure biodiversity conservation and continuity of harvested stands.

Remnant tree effects on soil microbial carbon and nitrogen in tropical seasonal pasture in western Mexico

Selection of plant species for agro-silvo-pastoral or ecological reclamation programs must be based on a deeper knowledge of the existing relationships between plant species and soil nutrient dynamics in each ecosystem. We evaluated the seasonal pattern of soil microbial carbon (C) and nitrogen (N) under two remnant tree species ( Caesalpinia eriostachys and Cordia elaeagnoides) in a tropical seasonal pasture dominated by Panicum maximum in western Mexico. Soil samples were taken from under two arboreal species and P. maximum in rainy and dry seasons. The soil C:N ratio was higher under P. maximum [17] than under both tree species [15]. The soil microbial C (Cm) was higher under C. elaeagnoides than under C. eriostachys and P. maximum. Magnitude and direction of effect of the two remnant tree species on soil biogeochemistry changed with seasonal rainfall. The interaction of plant species and seasonal rainfall did have an effect on soil microbial N (Nm). Soil samples from April and July had the lowest microbial N concentrations under the three plant species, increasing four fold in September under C. elaeagnoides and P. maximum. At the end of the wet season, C. elaeagnoides clearly had the highest Nm values (130 μg N g −1), suggesting that this tree species has a higher capacity to protect soil N within microbial biomass than C. eriostachys, because under C. elaeagnoides the soil had more organic matter due a higher input of litter and root chemical quality. Therefore, C. elaeagnoides would be the best plant species to implement in agro-silvo-pastoral programs or ecological reclamation of TDF pastures.

Epiphytic lichens along gradients in topography and stand structure in western Oregon, USA

Epiphytic macrolichen communities were compared among forest stand types in the Blue River watershed of western Oregon. Stand types were defined by stand structure, according to age classes of the younger tree cohort and remnant tree retention. Remnant trees were those in an older cohort that remained following a stand disturbance that initiated tree regeneration, such as a timber harvest or natural forest fire. Stands were located in upland and riparian forests of two vascular plant series (western hemlock and true fir). Presence and abundance of all epiphytic macrolichen species were sampled in a 0.4 ha circular plot in 117 stands. Nonmetric multidimensional scaling (NMS) ordination revealed that the strongest differences in lichen community composition were related to elevation, which was correlated with vascular plant series. Cyanolichens were largely limited to lower elevation forests (470 – 950 m) of the western hemlock series, while matrix lichens and forage lichens with green-algal photobionts dominated high elevation stands (950 – 1470 m) of the true fir series. Lichen communities differed with stand age. In even-aged young stands, lichen communities were species poor and lichen community composition differed from all other stand types. In general, macrolichen species richness varied little among stand types. However, cyanolichen species were most diverse in old-growth and mature stands at lower elevations. Lichen communities in young stands (< 20 yr) with remnants differed from those in even-aged young forests in both plant series. As a stand develops, the presence of remnant trees may accelerate the development of the lichen community towards those found in older stands. We infer that remnant trees serve as refugia for lichens through a disturbance and provide lichen inoculum to younger trees. Hardwood patches were hotspots for lichen diversity, particularly cyanolichens that are infrequent on conifers. Hardwood patches were most prevalent along perennial streams. To maintain and enhance lichen communities at a landscape level, forest managers must consider the importance of features such as late-successional stands, remnant trees, hardwoods, and riparian areas to lichen communities. These features are especially important to retain in or near regenerating forests to promote colonization by dispersal-limited lichens.

Patterns and implications of transformation in semi-arid succulent thicket, South Africa

Transformation of South African succulent thicket in response to grazing is widespread and characterized by the extensive replacement of dense closed-canopy thicket with a ‘pseudo-savanna’ of remnant trees with an ephemeral field layer. In this study, we examined the patterns of transformation in a semi-arid succulent thicket ecosystem using replicated fence line contrasts. We quantified the changes in plant species and functional diversity, physiognomy and biomass. We tested whether the remnant tree guild of the transformed thicket is in a stable state, using aerial photographs and ground-truthing to track the survivorship of canopy trees over 60 years in transformed landscapes. We investigated the impacts of transformation on recruitment into the canopy tree guild by measuring seedling establishment across the fence line contrasts. Transformation results in a significant loss of plant and functional diversity. There is a significant reduction in the biomass and structural complexity of the vegetation, both vertically and horizontally. The canopy tree guild in transformed thicket is not stable owing to ongoing adult mortality and little successful recruitment. These results are interpreted in a framework of ecosystem functioning and long-term stability. We suggest that the pseudo-savanna typical of transformed succulent thicket is not a stable alternative state to intact thicket, but rather an intermediate stage in a trajectory towards a highly desertified state where only the ephemeral grasses and forbs persist.

The effects of C, N and P additions on soil microbial activity under two remnant tree species in a tropical seasonal pasture

Although the availability of soil nutrients can constraint microbial activity, little is known about the interactive effects on soil microbial activity in tropical soils of nutrient addition and plant species. To test this effect, incubation experiments were carried out to assess the effects of C, N and P addition in soil samples from under two remnant tree species ( Caesalpinia eriostachys and Cordia elaeagnoides) and a dominant grass species ( Panicum maximum) in a tropical seasonal pastures in western Mexico. Substrate-induced respiration method was used to determine microbial activity in soil samples from dry and rainy seasons. In the dry season, the addition of C, N and P had no effect on the soil microbial activity, but this activity was strongly influenced by the plant species. The soil associated with C. elaeagnoides had a higher C mineralization and a lower net C immobilization in microbial biomass than the soil associated with C. eriostachys. In contrast, in the rainy season soil microbial activity was influenced by the interaction between the nutrient addition treatments and plant species. The addition of P enhanced microbial activity under C. elaeagnoides, while under C. eriostachys, added N increased accumulation of C in the microbial biomass. The differential response of soil microbial populations under both remnant tree species was explained by the soil’s pH buffering capacity and by the amount of microbial biomass. However, under the grass species the addition of CNP and N increased C mineralization, but C and CNP addition treatments decreased net C immobilization. These results suggest that nutrient addition increased the decomposition of soil organic C, but the released C was not stabilized in the pasture soils. Thus, the fertilization of pasture soils is not a reliable soil management practice, because it does not contribute to sustaining the availability of soil C and nutrients during the growing season. The utilization of silvo-pastoral systems can be a better alternative for the management of the tropical pastures, but the selection of tree species is critical for successful results.

Efecto de dos especies de árboles remanentes y de un pasto en la capacidad amortiguadora del pH del suelo

La capacidad amortiguadora del pH del suelo fue afectada por dos especies de árboles remanentes de la selva y por una especie de pasto. La diferencia más importante entre las dos especies de árboles remanentes fue el grado de neutralización del complejo de intercambio catiónico: el suelo de C. elaeagnoides estuvo dominado por los cationes alcalinos (i.e. Ca2+, Mg2+ , K+) a diferencia del suelo de C. eriostachys, que estuvo dominado por H', debido a su mayor tasa de nitrificación. En contraste, la especie de pasto tuvo una menorcapacidad de amortiguamiento del pH y el factor principal que controló el pH en la solución del suelo fue la fuerza del ácido. Esto sugiere, que las condiciones de manejo en este ecosistema han reducidos los mecanismos de protección de nutrientes del suelo, asociados principalmente a las especies vegetales

Spatial distribution of late-successional coniferous species regeneration following disturbance in southwestern Québec boreal forest

Remnant tree stands left intact following a disturbance constitute the sole seed banks available for regeneration of coniferous species that neither bear serotinous cones nor reproduce vegetatively. The success of regeneration of tree species on these disturbed sites is, therefore, dependent on the distance from potential seed sources. The regeneration of balsam fir ( Abies balsamea (L.) Mill.), white spruce ( Picea glauca (Moench) Voss) and white cedar ( Thuja occidentalis L.) was studied at two sites in Québec’s southwestern boreal forest in order to quantify the influence of remnant stands on spatial distribution of regeneration. The first site is located in an area that burned in 1944 while the second site is located in an area that was clear-cut in the mid-1980s. Canonical correspondence analyses were used to determine the respective contributions of environmental data and spatial variables to the pattern of spatial distribution of regeneration. The results reveal that distance from a remnant stand is the most important variable in explaining spatial distribution of regeneration when compared to environmental variables such as soil type, drainage, slope and altitude. The plots of regeneration density against distance from a remnant stand for both the burned site and logged site show that regeneration density decreases abruptly with distance from a remnant stand. Furthermore, spatial autocorrelation analyses (Moran’s I) indicate that even small remnant zones can significantly influence the pattern of spatial distribution of regeneration for the three species studied. The results presented here suggest that where preestablished regeneration is not abundant enough, alternative silvicultural systems such as strip clear-cutting or seed-tree systems could be used instead of cuts with protection of regeneration and soils (CPRS).

Wind and remnant tree sway in forest cutblocks. II. Relating measured tree sway to wind statistics

New silvicultural designs use unharvested forest strips to provide wind shelter in harvest cutblocks, and reduce windthrow of remnant trees. In this study we attempted to quantify wind shelter in terms of tree sway. We investigated the relationship between wind statistics and tree sway in two cutblocks in northern Alberta, Canada: a narrow cutblock (1.7 canopy heights in width, X c = 1.7 h), and a wide cutblock ( X c = 6.1 h). We focused on the case of winds oriented across the cutblock width. The instantaneous across- and along-cutblock wind `forces' acting on an understory white spruce ( Picea glauca) were considered as proportional to u| u| and v| v| , where u and v are the across- and along-cutblock wind velocities at height z = 0.4 h. A simple mass–spring–damper displacement model, calibrated to tree sway measurements, was used to diagnose the sway response of a `characteristic' remnant spruce (damping coefficient ζ = 0.11, natural frequency ω n = 0.4 Hz). We determined that in the cutblocks this characteristic tree: (i) had a small average angular displacement 〈 θ〉 relative to its maximum displacement θ max; (ii) exhibited `resonant sway,' where the interaction of tree dynamics and turbulence increased sway by 10–35% over that expected if displacement was proportional to the instantaneous wind force; and (iii) had sway statistics which correlated well with the standard deviation of wind force σ u|u| . Modelled tree sway was used to infer the degree of windthrow protection in the sheltered cutblocks. Our approach was to predict a threshold average wind velocity in the open ( U w, essentially a weather station windspeed) which correlates with the occurrence of windthrow of remnant spruce in the cutblock. Our assumption was that an average velocity of 10 m s −1 causes windthrow of unprotected trees in the open. Larger windspeeds ( U w) are needed to cause windthrow in the cutblocks. In the wide cutblock U w varied from 13 m s −1 near the downwind forest edge to 25 m s −1 near the upwind edge. In the narrow cutblock U w varied from 19 m s −1 at the downwind edge to 30 m s −1 at the upwind edge. The most effective wind shelter, as given by the highest U w, was within three tree heights of the upwind forest. In designing harvest cutblocks to reduce windthrow, we suggest that cutblocks not exceed three tree heights in width.

Wind and remnant tree sway in forest cutblocks.: I. Measured winds in experimental cutblocks

New silvicultural techniques use unharvested forest strips to provide wind shelter in harvest cutblocks, and reduce windthrow for remnant trees. The objective of this paper was to characterise the winds across two such sheltered cutblocks: a narrow cutblock whose width ( X c) was 1.7 canopy heights ( h), and a wide cutblock with X c = 6.1 h. Our focus was on the winds affecting understory trees, when the wind direction was across the cutblock width. Propeller and cup anemometer measurements were made along transects across the cutblocks, at height z = 0.4 h. These data were normalised using windspeeds measured simultaneously in a much larger, nearby `reference' clearing. In both cutblocks the best wind shelter was near the upwind forest edge, where the average cup windspeed ( S) was reduced to approximately 20% of its value in the reference clearing, the average across-cutblock wind velocity ( U) was approximately 10% of its clearing value, and the turbulent kinetic energy (TKE) was approximately 20% of its clearing value. Both U and S increased slowly with downwind distance ( x) across the cutblocks. The pattern of turbulence was different, as TKE increased rapidly with x immediately downwind of the forest, then attained near-constancy beyond x = 3 h downwind of the forest edge (in the wide cutblock), at a value slightly above the clearing value. Based on these observations, we conclude that effective wind shelter in a cutblock occurs within three tree heights of the upwind forest edge (for understory trees of height z ≈ 0.5 h), where both the average wind velocity and the turbulence are reduced relative to their levels in larger clearings.

Wind and remnant tree sway in forest cutblocks. III. a windflow model to diagnose spatial variation

Root-mean-square tree sway angle ( σ θ ) can be related to the r.m.s. value ( σ u| u| ) of the wind `force' u| u|, specified nearby. Therefore the spatial pattern of wind statistics over the landscape, if known, arguably maps the relative risk of windthrow – suggesting a wind model can provide the basis to interpret spatial patterns of windthrow, and guide strategies with respect to that concern. To test this idea, we adopt a simple flow model able to describe both the mean wind ( U) and kinetic energy of the turbulence ( k), viz. Reynolds' equations closed using eddy-viscosity K∝ λk 1/2, where λ is the turbulence lengthscale. We first compare this model with others' measurements of wind near forest edges, then simulate our own observations, which spanned arrays of cutblocks and intervening forest blocks in the Boreal forest (periodic spacing 1.7 h or 6.1 h, where h is mean tree height). We show that the model predicts well the spatial variation of the mean windspeed and turbulent kinetic energy, these being the wind statistics having greatest impact upon tree sway. Model-implied spatial patterns of r.m.s. wind force ( σ u| u| ) agree closely with those observed, and in conjunction with a tree-motion model, imply tree sway ( σ θ ).