Branch mass allocation increases wind throw risk for Fagus grandifolia

Wind is a major force of disturbance in forests throughout the world, causing trees to break or uproot and topple over, depending on tree morphology and growing conditions. Previous research has suggested that trees that are more massive or which have lower height–diameter ratios are less at risk to wind throw, but the influence of crown size and branching architecture has been more difficult to elucidate. In general, there has been more research on coniferous trees, which have more simplified and symmetrical crown structures, relative to broad-leaved, deciduous trees. Here, we modelled the probability of wind throw for American beech (Fagus grandifolia Ehrh.), a broad-leaved, deciduous species common in the eastern USA, for trees covering a broad range of sizes (5.6–79.8 cm, diameter at breast height), in two nearby stands, in an experimental forest in southwestern Michigan, USA, where a wind event occurred. After a major blow-down of more than 200 trees in one of the stands, a subset of trees was destructively sampled after the storm. Analysis of the characteristics of the wind-thrown versus non-wind-thrown, residual trees, indicated that a very large branch fraction of total tree mass was a key factor leading to toppling of the wind-thrown trees. This study provides new empirical data related to the characteristics of wind-thrown American beech trees and suggests a potentially important role for branch to stem mass ratios as a predictor of wind throw risk for this species and possibly other broad-leaved, deciduous tree species, with a deliquescent branching architecture.

Performance of jack pine (Pinus banksiana) rooted cuttings from proliferated dwarf shoots versus seedlings 8 years after planting

Growth and tree form characteristics of jack pine (Pinus banksiana Lamb.) rooted cuttings propagated from proliferated dwarf shoots (PDS) were compared with seedlings in two field trials 8 years after establishment. Results indicated that jack pine rooted cuttings from PDS can grow as well as seedlings and maintain acceptable tree form. Rooted cuttings of progeny from the 22 top-ranking open-pollinated families in a seedling seed orchard of jack pine were 4.2% taller and 10% larger in diameter at breast height than commercial seedlings tested on the same sites, which indicates that rooted cuttings have potential in realizing genetic gains in jack pine tree improvement programs. Rooted cuttings increased the proportion of trees with normal branching characteristics and reduced the percentage of trees with excessive heavy branches in the Sault St. Marie trial, which had larger tree sizes. However, longer term monitoring (20 to 25 years) is needed to determine stability of jack pine rooted cuttings planted on sandy soil where wind throw may become a problem as tree size increases.

Reconstruction of mixed hemlock–spruce stands in coastal southeast Alaska

Stands of western hemlock (Tsugaheterophylla (Raf.) Sarg.) and Sitka spruce (Piceasitchensis (Bong.) Carr.) on low-elevation, upland sites in coastal southeast Alaska develop as single-generation stands after stand-replacing disturbances and as multiple-generation stands after minor disturbances. Both stand types were studied. Spruce grew rapidly after major and minor windthrow events and reached the mid to upper canopy of the stand. Hemlock showed variable growth patterns and occupied both upper and lower canopy positions. Unlike forested regions containing more tree species, the species compositions and stand structures were similar among both the single- and multiple-generation stands. Hemlock and spruce occupied unique yet similar canopy and stand structural positions in both single- and multiple-generation stands because they had distinctly different regeneration and development patterns. Regardless of the frequency or intensity of the disturbance, spruce usually regenerated on mineral or mixed-soil microsites created by wind-throw events, and hemlock usually regenerated on organic substrates. Hemlock regeneration was prolific and tended to dominate sites by sheer number. Mortality rates were extremely high, but the large number of hemlock seedlings guaranteed many surviving stems. Spruce regeneration was much lower, but this species had higher survival rates and generally more rapid height growth. An important stand component was the advance hemlock regeneration that existed prior to the new stand; they formed a significant and dominant position in the future stand.

THE INFLUENCE OF LOGGING ON DOUGLAS FIR BEETLE POPULATIONS

All species of bark beetles of economic importance prefer to attack freshly-killed host material. Logging slash, wind-throw, and fire-killed timber provide ideal breeding grounds for bark beetles. A few species, mostly in the Dendroctonus group, are able to attack and kill living trees. When beetles in this group, raised in preferred host material, cannot find any or enough freshly-killed trees, logs, or slash to enter, they may attack living trees. In the interior of British Columbia, infestations of the Douglas fir beetle can often be traced to logging disturbance.The regulation or control of bark beetle populations involves several generally accepted principles:(a) The removal or destruction of beetle broods in infested material in time to prevent the new adult beetles from emerging to attack fresh material.(b) Continuous logging in time and area will tend to keep the beetles in the slash.(c) Keep suitable breeding material to a minimum.(d) The use of trap trees or trap logs for remedial action in trouble areas.