Showing papers by "Thomas T. Veblen published in 1995"

Sapling diameter growth in gaps for two Nothofagus species in New Zealand

Abstract: We quantified the effects of position within treefall gaps, gap size, and sapling size on sapling radial increment (most recent 5 yr, using tree cores) for two species of Nothofagus (southern beech) on the South Island, New Zealand (42 13' S). Mean radial growth rates of the two species and characteristics of the gaps in which they occurred were similar. Based on regression analysis, stems (1.4-26 m tall) of both species grew faster in larger gaps than smaller gaps (canopy gap area range 16-528 m2) and larger stems grew faster than smaller ones, the latter more true of N. fusca than N. menziesii. N. fusca grew fastest near gap center; N. menziesii grew fastest south of gap center. Smaller stems of both species grew faster south of gap center and large ones faster at, or even north of, gap center. For all size classes, the optimum location for N. menziesii growth was further south than for N. fusca. N. fusca grew faster than N. menziesii near gap center; N. menziesii grew faster than N. fusca south of gap center. These results are intermediate between literature predictions of best growth in gap center (based on soil moisture, soil nutrients and diffuse radiation) and best growth near the south gap edge (based on direct beam radiation and without considering shading).

Tectonic influences on tree growth in northern Patagonia, Argentina: the roles of substrate stability and climatic variation

Abstract: In northern Patagonia, Argentina, we examined the influences of climatic variation and inter-site variation in substrate stability on the dendroecological effects of earthquakes. In association with the great earthquake in 1960 centered off the coast of nearby Valdivia, Chile, extensive tree mortality occurred in northern Patagonia in Nothofagusdombeyi–Austrocedruschilensis stands on unstable debris fans. To examine the effects of the 1960 and earlier earthquakes on tree growth, we developed tree-ring chronologies from samples of the surviving A. chilensis on unstable debris fan sites and at adjacent nonfan sites of more stable substrates. For controlling the effects of regional climatic variation, we also produced a tree-ring chronology from this species in a more distant and undisturbed stand. Strong variations in tree-growth patterns on fan sites were associated with the historically documented major seismic events of south central Chile that occurred in 1737, 1751, 1837, and 1960. Tree-ring chronologi...

Attributes of reliable long-term landscape-scale studies: Malpractice insurance for landscape ecologists

Abstract: Monitoring long-term change in forested landscapes is an intimidating challenge with considerable practical, methodological, and theoretical limitations. Current field approaches used to assess vegetation change at the plot-to-stand scales and nationwide forest monitoring programs may not be appropriate at landscape scales. We emphasize that few vegetation monitoring programs (and, thus, study design models) are designed to detect spatial and temporal trends at landscape scales. Based primarily on advice from many sources, and trial and error, we identify 14 attributes of a reliable long-term landscape monitoring program: malpractice insurance for landscape ecologists. The attributes are to: secure long-term funding and commitment; develop flexible goals; refine objectives; pay adequate attention to information management; take an experimental approach to sampling design; obtain peer-review and statistical review of research proposals and publications; avoid bias in selection of long-term plot locations; insure adequate spatial replication; insure adequate temporal replication; synthesize retrospective, experimental, and related studies; blend theoretical and empirical models with the means to validate both; obtain periodic research program evaluation; integrate and synthesize with larger and smaller scale research, inventory, and monitoring programs; and develop an extensive outreach program. Using these 14 attributes as a guide, we describe one approach to assess the potential effect of global change on the vegetation of the Front Range of the Colorado Rockies. This self-evaluation helps identify strengthes and weaknesses in our program, and may serve the same role for other landscape ecologists in other programs.