摘要:

Strong onshore winds and airborne sea salt can gradually defoliate trees at the exposed margin of temperate pine stands in New Zealand and induce a slowly moving front of dieback and regeneration. Overcrowded mature stands are vulnerable to crown abrasion: abrasion affects trees 20 m ahead of the dieback front; suppressed trees 12 m ahead die before the front reaches them. At the stand margin, trees die from abrasion and salt wind induced dieback. The dieback zone lets sunlight enter the stand; light-demanding pine seedlings establish, but a gradient of increasing litter depth from the dieback front and summer dryness restrict successful seedling establishment to a narrow zone that moves parallel with the dieback front and 11-13 m ahead of it. Further seedlings establish for 4-10 years before the juveniles form a closed canopy; competing vegetation is partly suppressed by infrequent cattle browsing. Regenerating juvenile maritime pine (Pinus pinasterAit.), show a strict age-related gradation from the dieback front and indicate that wind and salt deposition have been constant for 30 years. Stands further from the sea, with lower stocking rates and other pine species, did not have a clear-cut regeneration zone, because there were no strong gradients of litter depth and light intensity.

ISSN:0045-5067    

DOI:10.1139/x98-073

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Spread ofHeterobasidion annosum(Fr.) Bref. was investigated in a 60-year-old Norway spruce (Picea abies(L.) Karst.) stand in central Lithuania. Of the 375 trees sampled,H. annosumwas isolated from 85 (22.7%). Forty nine (56.3%) of the isolates belonged to the S group and 38 (43.7%) to the P group. Among the S-group isolates, 35 genets occupied 49 trees (1.4 trees per genet on average). In the P group, 24 genets were detected in 37 trees (1.5 trees per genet on average). The largest S and P genets were 21 and 20 m in diameter, respectively. The S group spread was more extensive within stems than for the P group; mean length of the decay column for S-group isolates was 459 ± 159 cm (mean ± SD), and it was 327 ± 101 cm for P-group isolates (p= 0.0001). Average stump area affected by decay was 56 ± 15%for the S group, and 47 ± 16% for the P group (p= 0.016). This is the first published field data on intersterility group related difference in decay extension in tree stems. The S group is better adapted than the P group to growth in Norway spruce

ISSN:0045-5067    

DOI:10.1139/x98-071

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Interactions between soil nutrient cycling processes are likely to influence N losses following disturbance in forest ecosystems. During a 340-day laboratory incubation, we examined C and N transformations in three sandy soils of different N status fromPinus radiataD. Don plantations before clear-cutting. The soils were a high N status Andisol (losing -N in streamwater) and a fertilized and unfertilized Entisol. In contrast to other forest ecosystems, -N accumulated readily in all mineral soils and in the Andisol forest floor but did not accumulate until day 63 and 210 in the fertilized and unfertilized Entisol forest floor, respectively. However, gross nitrification occurred from day 42 in both Entisol treatments. Net nitrification in the Entisol forest floor began when substrate C/N ratio declined to about 40, possibly because of decreased C availability and decreased competition for both -N and -N in conjunction with a lower microbial C/N ratio. Carbon and gross N mineralization rates (per unit of C or N, respectively) correlated positively (r2= 0.93) in mineral soil but correlated negatively in the forest floor, probably because of major differences in C and N quality and potential differences in microbial community structure. The mean residence time of N in mineral-N pools was higher for soils from the N-rich site, in part because of lower microbial N demand. These results suggest that sudden removal of C inputs (such as at harvest) may cause greater disruption of internal soil N cycles on nutrient poor sites, increasing the proportional losses of N as compared to nutrient-rich sites.

ISSN:0045-5067    

DOI:10.1139/x98-067

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A half-sib progeny trial with single-tree plots on one test site of various environmental variations is simulated to examine the relative statistical efficiencies of randomized incomplete block designs (ICBs) over their corresponding randomized complete block design (RCB) in estimating family means. The ICBs with full constraint (FC), half constraint (HC), and no constraint (NC) over replicates and an alpha design (Alpha) are considered. A geostatistical spatial model is employed, which allows specifications of patchy and systematic environmental variations across the test site and estimations of block and error components with SAS PROC MIXED. The simulation shows that Alpha is the most efficient ICB in the 21 scenarios of patchy and systematic site variations, followed by NC and HC, and these ICBs (except FC) are generally more efficient than RCB in terms of the average variance of a family mean contrast. The gains in statistical efficiencies with implementations of Alpha and NC (rather than RCB) in forest genetic testing can be high, depending largely on the nature (and level) of spatial environmental variation. Practical implications of these simulated results for forest genetic trials are discussed.

ISSN:0045-5067    

DOI:10.1139/x98-072

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Discrete generation and rolling front breeding strategies are compared in terms of gain and inbreeding over a period of 40 years using stochastic simulation. In the rolling front strategy, crosses are made between the best available trees in each year, and new progeny trials are established using the crosses done in the previous year, rather than waiting for all crosses in that generation to be completed. For a given amount of resources, the rolling front strategy resulted in 25-35% greater gains per year, mainly due to a shorter generation interval. Inbreeding was also higher in the rolling front, although gains per unit of inbreeding were consistently greater than with the discrete generation strategy. Despite the smaller size of trials and greater imbalance between trials in rolling front, the results suggest that breeding value estimation using mixed-model BLUP is robust enough to ensure accurate prediction of breeding values and maintain the advantage of the rolling front strategy.

ISSN:0045-5067    

DOI:10.1139/x98-075

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Heartwood ellagitannins and volatile extractives were studied by high-pressure liquid chromatography and gas chromatography - mass spectrometry after extraction of wood samples taken from 54 mature trees of pedunculate oak (Quercus roburL.) and sessile oak (Quercus petraea(Matt.) Liebl.) from 14 mixed stands located in the forest of Cîteaux (Bourgogne). These same trees had been previously subject to detailed study of leaf morphology and wood anatomy. Over 50 compounds, of diverse chemical types, were identified in the wood extracts and over 30 of these compounds were quantified. No species-specific extractives were identified, but the amounts of ellagitannins and a small number of volatile compounds, includingcis- andtrans-&bgr;-methyl-&ggr;-octalactone isomers, were found to vary significantly between the two species. Multivariate analyses of these extractives allowed the classification of samples according to species, although less distinctly than similar analyses using leaf morphological characteristics. No strong intraspecific correlations between chemical constituents and anatomical or morphological characteristics were found that were common for both species. Nonetheless, sessile oaks displaying atypical wood anatomy were also less morphologically and chemically representative of their species. Trees possessing the lowest levels ofcis- andtrans-&bgr;-methyl-&ggr;-octalactone are found to be those with a morphology the least distinct of either species

ISSN:0045-5067    

DOI:10.1139/x98-066

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Height and lateral growth, biomass distribution, leaf morphology, and crown architecture were studied in yellow birch (Betula alleghaniensisBritton), sugar maple (Acer saccharumMarsh.), and beech (Fagus grandifoliaEhrh.) seedlings growing under 1-50% of above-canopy light in a sugar maple stand, in Quebec. All three species showed increasing growth with increasing light, but growth of yellow birch was higher and more responsive than that of sugar maple and beech. All three species showed typical sun-shade morphological responses, such as decreasing specific leaf area and leaf area ratio, and increasing leaf area index, with increasing light availability. Sugar maple was morphologically more plastic than the other species. It showed variations in biomass allocation to leaves and branches, a decrease in branch length to seedling height ratio, and a marked increase in the ratio of leaf area to stem length. Although our results clearly demonstrate the ability of these three species to modify several of their morphological features in response to variations in light, they do not show a clear relationship between species shade tolerance and morphological response to light variations. We suggest that species-specific developmental patterns may act as important constraints to morphological acclimation to light variation.

ISSN:0045-5067    

DOI:10.1139/x98-077

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The distribution of canopy heights obtained with an airborne laser scanner over a field trial with Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco) was a function of the vertical distribution of foliage area. Over a wide range of canopy structures, the proportion of laser pulses returned from or above a given reference height was proportional to the fraction of leaf area above it. We hypothesized that the quantile of the laser canopy heights matching in probability the fraction of leaf area above a desired height would be an unbiased estimator of same. This was confirmed in 36 (20 × 20 m) plots and 6 older validation plots. Canopy-based quantiles of the laser canopy height data were within 6% (mean 3%) of the field estimates. Laser and field estimates were strongly correlated (r~ 0.8), and statistical tests supported the null hypotheses of no difference in mean stand height (P> 0.3). A geometric model successfully predicted the mean difference between the laser canopy heights and the mean tree height. Our results explicate why estimation of stand heights from laser scanner data based on the maximum canopy height value in each cell of a fixed area grid has been successful in practice

ISSN:0045-5067    

DOI:10.1139/x98-078

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The core area concept is proposed as a criterion promoting the formation of contiguous areas of old growth over time in the landscape. Core area is defined as the area of old forest, free of edge effects, where the edge effect is a function of the state of the surrounding habitat. The core area measure is evaluated by solving a long-range planning problem for a landscape consisting of 200 stands, where the net present value of forest management is maximized under the constraint of a certain amount of core area in the landscape over a time horizon of 100 years. Simulated annealing is used as the solution technique. The results indicate that the degree to which stands are clustered depends on the amount of core area demanded and the extent of the edge width. The amount of new core area that is allocated adjacent to existing core area, indicating a continuity of core area formation, is increased with core area demand, the minimum age of old forest, and the existence of a U-shaped initial age structure. The cost of attaining the spatial patterns appears to be low compared with the cost of retaining the old forest.

ISSN:0045-5067    

DOI:10.1139/x98-076

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Damage by the southern pine beetle (SPB) (Dendroctonus frontalisZimm.) occurs frequently in the southeastern United States and can result in tree death over large areas. A new technique for detection of SPB activity was tested for shortleaf pine (Pinus echinataMill.) in the Caney Creek Wilderness, Ouachita National Forest, Arkansas. Digital images with 1-m pixel resolution were acquired from a light aircraft in 6- to 10-nm bandwidths centered at wavelengths of 675, 698, and 840 nm. The 675-nm band was selected to yield a maximum contrast between yellow or brown versus green foliage. The 698-nm band was selected based on its high sensitivity to leaf chlorophyll content to enable detection of less severe chlorosis in more recently damaged trees. The 840-nm band was used as a reference band that is not sensitive to chlorophyll. Images acquired within each band were calibrated to percent reflectance based on the known reflectances of a gray scale placard located on the ground. Individual trees with yellow to brown foliage were easily located in the 675- and 698-nm images. Milder chlorosis in more recently damaged pines was detected by a normalized difference vegetation index (NDVI) that was derived from 698- and 840-nm reflectances. Although statistically significant, the contrast of recently infested trees versus undamaged trees was generally visually poor in NDVI or color composite images. This was apparently a result of the inherent variability in leaf chlorophyll content throughout the forest. The increased reflectance near 700 nm characteristic of recent damage likely would be resolved more easily in pine plantations of low species diversity. Images of a NDVI that was based on 675- and 840-nm reflectances produced the strongest contrast between heavily damaged and undamaged trees.

ISSN:0045-5067    

DOI:10.1139/x98-079

出版商:NRC Research Press    

年代:1998

数据来源: NRC