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Overstory and regeneration dynamics in riparian management zones of northern Minnesota forested watersheds

Publication year: 2012
Source:Forest Ecology and Management, Volume 271
Brian Palik, Michelle Martin, Eric Zenner, Charles Blinn, Randy Kolka
We quantified tree regeneration under different riparian management zone (RMZ) treatments along first-order streams in Minnesota, USA. A primary objective for long-term management of RMZs in the study region is to maintain some tree cover and promote establishment of later successional tree species and conifers. We also compared regeneration response to contrasting harvesting systems that differed in expected soil disturbance and impact on residual vegetation. Riparian treatments included: (1) full control (no cutting in RMZ (60 m-wide in all treatments) or adjacent upland stand), (2) riparian control (RMZ uncut; adjacent upland stand clearcut); and partially-harvested RMZs (RMZ basal area reduced from 29 to 13 m²/ha, adjacent upland stand clearcut) and using (3) cut-to-length or (4) tree-length harvesting. Nine years after treatment, basal area of the full control had not changed appreciably, while basal area of the riparian control had declined by 28% and basal area of the two partial-harvest treatments had decreased by 54%; reductions were due to blowdown of residual trees. Total regeneration density was stable over time in the full control and riparian control, but increased substantially in the two RMZ treatments. Regeneration response was driven by early successional species, mostly Populus tremuloides and Betula papyrifera , and shrubs. Responses were similar between the two harvesting systems. Our results show that regeneration does increase with partial harvesting of RMZs, that the response is mostly due to early succession, shorter-lived deciduous species, and that harvest systems that differ in expected site and vegetation impact elicit similar results. A lack of significant increases in conifers and longer-lived trees in the RMZs following treatment, and the substantial increases in shrubs which may inhibit establishment of these species, suggests a need for more active approaches to establish these species, for example through under planting and competition control.

Interactions between soil gravel content and neighboring vegetation control management in oak seedling establishment success in Mediterranean environments

Publication year: 2012
Source:Forest Ecology and Management, Volume 271
Carlos J. Ceacero, José Luis Díaz-Hernández, Antonio D. del Campo, Rafael M. Navarro-Cerrillo
Restoration of vegetation in Mediterranean areas is limited by several factors, some of which are poorly understood, such as soil stoniness and competition with natural vegetation. This paper analyzes the interaction between weed management treatments (cultivation, herbicide, mulch and tree shelter) and the profile stoniness in Holm oak ( Quercus ilex L. sub. ballota (Desf.) Samp.) seedling establishment in Mediterranean areas. Our experimental trials show that profile gravel content is a key factor in seedling survival, in which optimal reforestation sites would be defined by gravel content <5%; transitional sites by 5% ⩽ gravel content ⩽ 15% and excluded sites by gravel content >15%. The soil profile gravel content caused severe water limitations, especially important in the first year after planting, which influenced the effectiveness of neighboring vegetation control techniques for seedling establishment success. This study also confirms the positive effect of competition management techniques on survival. The treatments tested showed an improvement in the survival rate, but not in growth rate, over the control treatment throughout the monitoring period. We have obtained a vegetation response model in which the beneficial effects of competition control on the success of oak seedling establishment are distorted by soil gravel content.

Partitioning vascular understory diversity in mixedwood boreal forests: The importance of mixed canopies for diversity conservation

Publication year: 2012
Source:Forest Ecology and Management, Volume 271
Virginia Chávez, S. Ellen Macdonald
Progress in understanding the patterns of plant diversity requires a conceptualization and quantification of the hierarchy of patch configuration that exists in plant communities across levels of observation. In order to identify the scales at which vascular plant diversity is maximized, we investigated the hierarchical organization of understory vascular plant diversity in relation to canopy patch types in mature boreal mixedwood forests in western Canada. In each of two study areas within a 30 km² landscape (55° N, 112° E) we sampled four canopy patch types: conifer, mixed conifer-broadleaf, broadleaf and canopy gaps. Understory diversity (richness and Shannon’s ( H ′) index) was additively partitioned in relation to these four canopy patch types across a hierarchy of four scales; α -individual patch + β 1-among patches within canopy patch type + β 2-among canopy patch types within area + β 3-between areas . We also examined understory species abundance patterns by means of rank-abundance plots fitted to relative abundance models. The largest partition of species richness was among patches within canopy patch type (β 1 ). For Shannon diversity index, the largest partition was at the within-individual patch level (α 1 ) indicating that evenness was high at the patch level but that dominance increased at higher levels in the hierarchy. The assessment of relative abundance by means of rank abundance plots suggested that the canopy patch types differed in terms of the ecological mechanisms influencing diversity patterns. Considering plant diversity within a hierarchical framework is critical for the understanding and management of biodiversity as maximum levels of plant richness and evenness do not necessarily occur at the same observational scales. Management practices which retain the natural hierarchies of vegetation patches will help conserve plant community richness and diversity.

Logging scars in Ghanaian high forest: Towards improved models for sustainable production

Publication year: 2012
Source:Forest Ecology and Management, Volume 271
W.D. Hawthorne, D. Sheil, V.K. Agyeman, M. Abu Juam, C.A.M. Marshall
We analyse data from 12 permanent sample plots (PSPs) in Ghana to determine recovery rates of skid trails and gaps in forest logged 10–30 years previously. We examine four key indicators of recovery – basal area, mortality rate, diameter increment and changes in the balance of tree guilds (Pioneer Index) – to compare the forest directly affected by logging (the apparent extraction network, AEN), with adjacent, less damaged forest. Data are presented on gaps created by felling individuals of different species and diameter, with a view to refining existing yield allocation procedures. Our results indicate that forest recovery is slower than predicted by commonly used yield models. The basal area of AEN forest is below 23 m² ha⁻¹ in all 12 plots, even 30 years after logging, and is not obviously increasing. Initially elevated annual mortality rates return to normal rates of less than 2% after 15 years in the non-AEN forest, and after 22 years in the AEN forest. Diameter increments peak early for pioneers, and increase linearly for shade-bearers across the 10–30 year period, but are not translated into gains in basal area. Only in one plot does the Pioneer Index of the AEN approach that of the less disturbed surrounding forest, implying inertia against canopy closure, as pioneers replace pioneers. We conclude that Ghana’s commercial logging practices are not sustainable on the current 40-year felling cycle. A different approach is required to achieve a sustainable harvest. Yield models will need to account for reduced site productivity. We suggest improved yield allocation through: (i) the development and use of electronic stock-maps to plan yield allocation, and as a basis for monitoring, (ii) accounting for species–specific differences, and (iii) collecting further data on the varied productivity of old extraction routes. Future studies should try to relate soil type to logging-impacts and recovery.

Associations between crossbills and North American conifers in Scotland

Publication year: 2012
Source:Forest Ecology and Management, Volume 271
Ron W. Summers, Alice Broome
Understanding the habitat requirements of the Scottish crossbill Loxia scotica is fundamental to the conservation of this endemic bird which, like other crossbills, specialises in feeding on conifer seeds extracted from cones. Habitat associations of Scottish crossbills and common crossbills Loxia curvirostra were determined from a systematic survey of conifer woodland within the range of the Scottish crossbill during January to April 2008. All the commonly planted conifers were producing cones. Scottish crossbills were associated with the amount of coning lodgepole pine Pinus contorta , whilst common crossbills were associated with coning Sitka spruce Picea sitchensis , lodgepole pine and to a small extent with larches Larix spp. The Scottish crossbill’s association with lodgepole pine is interesting in view of the notion that Scottish crossbills are adapted to Scots pine Pinus sylvestris . Likewise, there was no evidence that common crossbills in the study area during January to April 2008 had an association with Norway spruce Picea abies , the tree with which they are normally associated in continental Europe. Lodgepole pine and Sitka spruce cones have thinner scales than those of Scots pine and Norway spruce, respectively, so are probably easier to exploit for seeds than the conifers to which they are assumed to be adapted. This may explain the associations we found. North American crossbills that specialise on lodgepole pine and Sitka spruce have smaller bills than even common crossbills (the smallest of the western Palearctic crossbills, apart from the two-barred crossbill Loxia leucoptera bifasciata ). Adaptation to Sitka spruce by common crossbills is unlikely because common crossbills in Scotland largely arrive during irruptions from continental Europe, after which they return in a subsequent season. Therefore, their association with North American conifers in Scotland is temporary. For the resident Scottish crossbills, there is a greater possibility of adaptation to lodgepole pine. However, given the difficulties in identification of old specimens in museums, it was not possible to examine trends in bill size; the prediction is that bill size should decline. Future research needs to distinguish which conifer Scottish crossbills are adapted to as opposed to those which may be temporarily preferred when most profitable.