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Dendroecological methods play a critical role in developing our understanding of forest processes by contributing historical evidence of climate variability and the temporal characteristics of disturbance. We seek to contribute to these methods by developing a research protocol for decoupling radial-growth signatures related to climate, fire, and insect outbreaks in central Oregon. Our methods are based on three independent, crossdated tree-ring data sets: 1) a 545-year tree-ring climate reconstruction, 2) a 550-year fire history, and 3) a 250-year pandora moth outbreak history derived from host (Pinus ponderosa) and non-host (Abies grandis-Abies concolor) tree-ring chronologies. Based on these data, we use visual criteria (marker and signature rings), statistical comparisons, and Superposed Epoch Analysis (SEA) to identify the timing of growth anomalies and establish the temporal relationships between drought, climate variation (ENSO and PDO), fire events, and pandora moth (Coloradia pandora) outbreaks. Our results show pandora moth outbreaks generally coincide with periods of below-average moisture, whereas fire in central Oregon often follows a period of wetter than average conditions. Fire events in central Oregon appear to be related to shifts in hemispheric climate variability but the relationship between fire and pandora moth outbreaks remains unclear.
During the late 19th Century there was considerable debate in the United States among members of the legal profession, the general public and even some scientists about the validity of using tree rings to determine tree age. In an earlier boundary dispute case in Maryland (1830) the Honorable Theodorick Bland rejected the use of tree rings to establish the date when a purported witness tree was marked with an identifying blaze. Bland did not believe that there was enough scientific evidence or legal precedent to support this idea. A review of the current scientific literature of the time, however, indicates that most scientists, especially in Europe, accepted that tree rings could be used to determine age. In the United States, however, this idea was debated, particularly in the late 19th Century, in both the popular press and scientific publications. The main argument of opponents such as A. L. Child was that the number of tree rings was often wildly in excess of the known age of the tree. These inconsistencies were likely because of the inexperience of the observer, mistaking earlywood and latewood for separate rings, and the presence of a small number of false rings, sometimes called secondary rings. The great ages reported for the giant sequoias may have also raised doubts among the public. Among scientists, however, the relationship between ring number and tree age and between ring width and climate became widely accepted. Several cases heard in both Federal and State Courts as well as Bernhard E. Fernow's Age of Trees and Time of Blazing Determined by Annual Rings laid to rest any doubt of the relationship between tree rings and age in temperate forests, i.e. one ring equals one year's growth, and showed that the date when a witness tree was blazed could be easily determined from a cross-section of the trunk.
In 1982, several rectangular openings were cut in a 100 year old sub-alpine Norway spruce forest stand to initiate regeneration at the Lusiwald site at Davos, Switzerland. The openings on the steep, north-facing slope created rapid changes to the environment of the border trees. Growth reactions of these border trees were compared and analysed with reference trees from the adjacent closed canopy stand in 1997. The radial growth pattern of the two data sets differed within the 14-year period since the openings were cut; the border trees showed growth releases. The growth reaction at the stem base was larger than at breast height. Changes in wind exposure may have influenced border trees to adapt their root systems. Sub-alpine Norway spruce stands aged around 100 years, which are usually considered slow-growing on a north aspect, still seem capable of reacting to greater resource availability such as sudden light changes.
This study presents the first annually-resolved chronology using Salix alaxensis (Anderss.) Cov from Victoria Island, Northwest Territories, Canada, an area well north of treeline. Forty-one samples were collected and examined for subsequent analysis. However, crossdating was difficult because of locally absent or missing rings and the narrowness of the rings, and ultimately thirteen stems were crossdated and used to evaluate their dendroclimatological potential. The chronology spans 74 years (1927–2000) and could potentially be extended further using subfossil wood. Precipitation data from December of the previous year to March of the current year were the most consistently and highly correlated with ring width. This suggests that the recharge of the soil moisture by early summer snowmelt is a key factor limiting growth of these shrubs.
The dimensions, manufacture and application of a mini-borer to take 3-mm cores are described. This new instrument seems particularly well-suited to determining ages of saplings in situations where collection of cross-sections and coring with standard increment borers are too destructive, and where node-counting may not be sufficiently accurate. The design has resulted in trouble-free use in the field, and the mini-cores can be stored in the straws, and mounted and sanded in the core mounts used for collections of the standard 4–5-mm increment cores.
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