Windthrow Damage Research Articles

Development and long-term evaluation of harvesting patterns to reduce windthrow risk of understorey spruce in aspen-white spruce mixedwood stands in Alberta, Canada

Summary The Hotchkiss River Mixedwood Timber Harvesting Study developed new approaches to harvesting systems for western Canada’s boreal mixedwood forests. Conventional harvesting equipment was used to test 11 harvesting and silvicultural systems over a 530-ha site. These include one- and twopass modifi ed uniform shelterwoods, two- and three-pass strip shelterwoods, two-pass alternate strip shelterwoods and four-pass progressive strip shelterwoods. These were used to test varying levels of wind protection designed to protect and minimize wind damage to understorey (immature) white spruce residuals following harvest of the aspen overstorey. Ongoing monitoring of wind dynamics and associated windthrow patterns since 1992 have provided clear management practice guidelines for reducing windthrow of immature spruce and residual aspen following harvesting. There are thresholds related to spruce height and distance from aspen residuals, beyond which windthrow damage increases signifi cantly. The infl uence of topography, timing of harvest and the spatial confi gurations of multiple harvests on windthrow dynamics have been clarifi ed through this research. These results have provided valuable information to help forest planners to utilize harvesting and silvicultural systems that best reduce windthrow damage to understorey spruce, following harvest of overstorey aspen.

Windthrow resistance of apple trees grafted in an orchard

Pull-down tests were conducted for apple trees grafted in an orchard and for support posts in order to discuss the failure mode in windthrow damage, the effect of rootstock types on the uprooting strength, and the reinforcing effect of support posts on young trees. The test samples were ten mature trees (20–23 years old) of three varieties grafted on two types of rootstocks, three young trees (7 years old) grafted on dwarf rootstocks, and nine support posts of larch logs and steel pipes. The failure modes were found to be uprooting for mature trees and rootstock breakage for young trees. The uprooting strength of apple trees was considerably smaller than the uprooting strength of forest trees reported in previous studies. However, the windthrow resistance of the apple trees with respect to the critical wind velocity was estimated to be sufficient despite their low uprooting strength because of their small height. Young trees should be supported with wooden posts for a few years after grafting so that they acquire sufficient windthrow resistance.

Windthrow damage in Picea abies is associated with physical and chemical stem wood properties

On 26 December 1999, the windstorm “Lothar” hit large parts of western and central Europe. In Switzerland, windthrow losses reached 12.7 Mio m3 of timber, corresponding to 2.8 times the annual national timber harvest. Although these exceptional losses were due to extreme peak velocities, recent changes in tree nutrition may have increased forest susceptibility. Previous controlled environment experiments revealed that wood density (associated with wood stiffness) tends to increase in elevated CO2, and to decrease when N-availability is enhanced (e.g., by soluble N-deposition). Such changes in wood quality could theoretically influence the risk of wind damage. We used the “Lothar” windstorm as a “natural experiment” to explore links between damage and wood properties. In 104 windthrow sites across the Swiss Plateau, more than 1,600 wood cores from (1) broken, (2) uprooted and (3) still standing (not damaged) spruce trees (Picea abies) were collected in February and March 2000. Wood properties, treering width and chemistry of the wood samples were analysed. Broken trees showed wider treerings in the decade 1990–99 compared to non-broken trees (either uprooted or undamaged trees). Broken trees also showed lower non-structural carbohydrate (NSC) concentration in sapwood, reflecting active structural carbohydrate sinks associated with fast growth. There was also a trend for higher tissue N-concentrations in broken trees. No significant differences between damage types were found in wood density and wood shrinkage during desiccation. We conclude that stem breakage risk of P. abies is associated with a stimulation of growth in the past decade and with changes in tree nutritional status. However, the risk for windthrow of whole spruce trees (uprooted but not broken) was not related to the studied wood parameters.

Variable Retention Forestry Science Forum April 21-22, 2004

As a result of criticism of past forest management in coastal British Columbia, there was a shift away from the traditional clearcutting system to the retention system. In April 2004, FORREX, in partnership with the Canadian Forest Service, the British Columbia Ministry of Forests, the Forest Engineering and Research Institute of Canada (FERIC), Weyerhaeuser Canada, Madrone Consulting, and Malaspina University–College, hosted a science forum on Variable Retention Forestry. The forum provided an opportunity to discuss the latest findings, issues, and challenges of retention practices. This paper summarizes the important messages from the forum, including the following:• The importance of developing and implementing adaptive management monitoring and evaluation frameworks.• The use of variable retention (VR) as a tool that should be guided by goals and philosophies.• Consideration of the costs of implementing VR.• The importance of understanding disturbance patterns and their impact.• The importance of an awareness of the possible effects on stand development of any insects and diseases.• The importance of an awareness of local site and regional conditions when attempting to predict the outcomes of windthrow damage.• Consideration of public perception of forest management practices.Outstanding issues and questions are also summarized, and a list of resources outlining the latest research findings in the area of variable retention is provided. It is important to invest in monitoring and understanding the biological implications of VR practices while addressing the social issues around forestry on a public land base—the original rationale for the retention system.

Vascular plant response to windthrow severity in Norway spruce—dominated Myrtillus site type forests in Estonia

:Species composition and number of species in ground vegetation after windthrow varies depending on damage severity and management actions after a storm event. In this paper we seek to determine the changes in species composition depending on the severity of storm damage. The vegetation response was studied by comparing areas with different levels of windthrow damage (undamaged, partly damaged, totally damaged, and totally damaged and harvested) in Norway spruce–dominated forests in Estonia. A total of 108 herbal and shrub species were found in all areas. Species number was lowest in the control areas and highest in the harvested plots. The number of species that responded to disturbance severity, when compared to the control plots, increased during the second year of the two-year survey period. The groups of species responding to different degrees of storm severity and silvicultural treatments were identified. Early invasion after a storm was observed in the case of several species, such as Epilobium angustifolium, Rubus idaeus, and Ranunculus repens. All the ferns that responded to damage extent seemed to be most favoured in totally damaged areas. Rubus saxatilis showed the clearest response trend, with higher coverage in response to increasing wind severity.

Effects of windthrow on a stand of Eucalyptus delegatensis (Myrtaceae) and early understorey succession at Snowy River National Park, Victoria

Summary During June 1998 a very strong windstorm at the Snowy River National Park near Mt Gelantipy caused severe damage to a stand of Eucalyptus delegatensis. Little is known about the impact of windthrow on E. delegatensis and subsequent seedling recruitment. This study was undertaken 4.5 y later to examine (i) windthrow damage to E. delegatensis and the understorey Acacia dealbata, (ii) the influence of tree size on the pattern of tree damage, (iii) the undergrowth in the windthrow area compared with that in control plots, and (iv) species composition of the soil-stored seed-bank in windthrow and control plots. We found that high winds toppled virtually all trees regardless of size and species, damaging 99% of the E. delegatensis. In windthrow plots there were 49 seedlings ha-1 of E. delegatensis and 2210 ha-1 of A. dealbata. No E. delegatensis or A. dealbata seedlings were recorded in the control plots. In the soil seed-bank study five species were recovered from soil samples collected from the control, and six from the windthrow-damaged sites. The canopy species E. delegatensis recruited only from the windthrow site. The exotic Rubus fruticosus was found to be colonising the windthrow site, but was not present in the control site. Results show that E. delegatensis recruitment is very poor in the damaged area, and species colonising within that area are light demanding or early succession species. It is proposed that seedling recruitment in the windthrow sites be accelerated by burning the site and broadcasting E. delegatensis seed, or transplanting seedlings.

Financial impact evaluation of catastrophic storm damage in Irish forestry: a case study. II. Future revenue losses

Summary The objective of the research reported in this article was to identify factors influencing the economic impact of catastrophic storm damage in forestry. The study was based on data from stands which were wind thrown in the south of Ireland during the storm of 24 December 1997. The study area covered all forests in Counties Cork and Waterford, most in County Kerry and some in County Limerick. This, the second of two articles, focuses on the future revenue losses in the current and the subsequent rotation. The results of the analysis on short-term impacts (presented in the first article) are combined with these long-term impacts to produce a comprehensive estimate of the financial losses due to catastrophic wind damage. Two forests (Midleton and Skibbereen) were selected for detailed stand-level analysis. This analysis showed average combined stumpage and growth losses per ha of IR£1778 for Midleton forest and IR£4141 per ha for Skibbereen forest. These losses were for the current wind-thrown rotation only. As a consequence of the wind throw, the next rotations will commence earlier than planned, resulting in a reduction in these losses. Taking both the current and next rotation into account, the losses per ha were IR£1649 for Midleton forest and IR£3668 per ha for Skibbereen forest. The total wind-throw loss in Midleton of IR£163 252 amounted to 28 per cent of the average annual stumpage value of IR£583 700. For Skibbereen forest, the total windthrow loss of IR£641 900 was 126 per cent of the average annual stumpage value of IR£511 110. The reasons for this much higher percentage loss in Skibbereen forest were: a higher proportion of blown stands; a lower average annual stumpage value in the years prior to the storm; and a greater difference between target rotation length and the age at which the stands were wind blown. These results show clearly that the financial impact of wind-throw damage can vary greatly depending on the local stand and forest characteristics. Consequently, any accurate estimates of financial losses due to catastrophic wind throw have to be based on detailed stand-level analysis.

Windthrow damage 2 years after partial cutting at the Date Creek silvicultural systems study in the Interior Cedar–Hemlock forests of northwestern British Columbia

Windthrow damage 2 years after partial cutting at the Date Creek silvicultural systems study in the Interior Cedar–Hemlock forests of northwestern British Columbia

Windthrow damage 2 years after partial cutting at the Date Creek silvicultural systems study in the Interior Cedar–Hemlock forests of northwestern British Columbia

Partial cutting that removed either 30 or 60% of the volume as single trees or small groups up to 0.5 ha had little effect on wind damage to merchantable trees (≥17.5 cm diameter). On average, 6.7 stems per hectare of windthrow occurred across unlogged and logged units, representing approximately 1.9% of the standing trees. Over 2 years, 0.63 m 2 ·ha n1 of merchantable basal area was damaged, or 1.5% of the original standing basal area. In the partial cuts, 2.2% of the trees were damaged compared with 1.1% in unlogged areas. The 1.1% increase in damage in partial cut units was well below the 10% effect size considered large enough to warrant either management intervention or to deem the partial cutting a failure. The greatest wind damage occurred in the old-growth stands. For 8 of the 9 tree species examined, no individual tree characteristics seemed to predispose them to wind damage. Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes, Populus tremuloides Michx., and Abies lasiocarpa (Hook.) Nutt. were the most susceptible species to windthrow.

Effects of partial bark removal on the growth of Pacific yew

Whole-tree harvest of Pacific yew (Taxusbrevifolia Nutt.) to provide bark for production of the new anticancer drug taxol may adversely affect stand structure where yews provide thermal cover, browse, or riparian benefits. Harvesting only a portion of the bark on standing trees would maintain existing stand structure if the affected trees continued to grow, but partial bark removal seldom has been applied because its long-term effects are unknown. We measured 121 yews that had been scarred by windthrow or logging damage 3–92 years ago and found that their growth did not differ significantly from the growth of nearby unscarred yews. Radial growth of the scarred trees was strongly correlated with growth before scarring; it was slightly associated with overstory canopy density, elevation, and the amount of bark removed. Partial bark removal from one side of the tree probably will not seriously affect the growth of Pacific yew if less than 50% of the bark is removed.