Frost Rings and White Earlywood Rings in Picea Mariana trees from the boreal plains, Central Canada

Abstract

Dendroecological analysis of tree-ring anomalies can facilitate better environmental reconstructions provided that conditions leading to their formation are well understood. White earlywood rings (WER) constitute an anomaly not previously described and, like frost rings (FR), occur often in boreal coniferous species in central Canada. the objectives of this study were i) to examine the distribution of FR and WER in black spruce trees, ii) to measure and compare tracheid dimensions in WER and control rings and iii) to investigate potential causes of WER formation. sampling was conducted in two regions of western Manitoba. At each of four sampling sites, ten black spruce trees were selected for stem analysis. Results indicated that FR were mainly formed in the smaller diameter, thin barked portion of the stem up to a height of 16m, whereas WER were almost uniformly distributed along the stem. tracheids were measured for WER occurring in 1916WER occurring in , 1943WER occurring in and 1970 and WER were found to have earlywood tracheids with significantly thinner cell walls compared to control rings. It is speculated that the formation of WER may be related to reduced hormone and carbohydrate availability in the early growing season. the potential linkage between WER and frost events, or other agents of defoliation, prior to ring formation merits further investigation.

Fire Regime in Marginal Jack Pine Populations at Their Southern Limit of Distribution, Riding Mountain National Park, Central Canada

“…Dormant season fires were assumed to be spring fires due to the relative absence of fires or area burned in the fall in the recent written fire record (Cornelsen, unpublished data). This interpretation is supported by the occurrence of WER, which was often synchronized with fire years, and this anomaly has been associated with crown and/or foliage damage during the dormant season prior to the onset of radial growth [56]. Their high frequency in fire years suggests crown damages associated with low intensity fires prior to the onset of growth.…”

“…White earlywood rings were observed in both jack pine trees bearing fire scars and in unscarred trees within LKFMU ( Figure 3B,C). The presence of WER could provide an indication of crown scorch as they have been associated with crown damages during the dormant season, presumably leading to a carbohydrate deficit responsible for the production of earlywood tracheids with thin secondary walls [56]. The absence of WER in jack pine trees growing outside the LKFMU would support this hypothesis.…”

“…This interpretation is also supported by the absence of WER in jack pine trees growing outside the LKFMU. This is in contrast with the WER of 1943 and 1954, which were also observed outside the LKFMU (and in DMPF and PPF), and were most probably associated with winter and/or spring regional frost damages [56]. Fire data indicate that RMNP has a spring-dominated fire regime, with 6% of fires occurring in April, 90% in May, and 3% in June [36].…”

“…Given that the absence of fire scars does not necessarily imply that an area did not burn at a given time [52], white earlywood rings (WER; [56]) were also systematically compiled. White earlywood rings were observed in both jack pine trees bearing fire scars and in unscarred trees within LKFMU ( Figure 3B,C).…”

Microscopic Examination of Wood: Sample Preparation and Techniques for Light Microscopy

“…Soft non-lignified cells (i.e., cambial cells, differencing xylem cells, parenchyma cells) may also be squeezed, torn, and distorted [10,72]. Sectioning artifacts constitute a problem when cell measurements are to be obtained and time-consuming corrections often need to be applied manually to digital images to avoid generating erroneous data [66,92]. Potential sectioning artifacts are associated to a certain degree with the specimen itself, cell wall density, wood block size, blade type and sharpness, blade angles, and human dexterity/experience.…”