David R. Vann

Transpiration rate relates to within- and across-species variations in effective path length in a leaf water model of oxygen isotope enrichment

Stable oxygen isotope ratio of leaf water (δ(18)O(L)) yields valuable information on many aspects of plant-environment interactions. However, current understanding of the mechanistic controls on δ(18)O(L) does not provide complete characterization of effective path length (L) of the Péclet effect,--a key component of the leaf water model. In this study, we collected diurnal and seasonal series of leaf water enrichment and estimated L in six field-grown angiosperm and gymnosperm tree species. Our results suggest a pivotal role of leaf transpiration rate (E) in driving both within- and across-species variations in L. Our observation of the common presence of an inverse scaling of L with E in the different species therefore cautions against (1) the conventional treatment of L as a species-specific constant in leaf water or cellulose isotope (δ(18)O(p)) modelling; and (2) the use of δ(18)O(p) as a proxy for gs or E under low E conditions. Further, we show that incorporation of a multi-species L-E scaling into the leaf water model has the potential to both improve the prediction accuracy and simplify parameterization of the model when compared with the conventional approach. This has important implications for future modelling of oxygen isotope ratios.

Reconstruction of Tertiary Metasequoia forests. II. Structure, biomass, and productivity of Eocene floodplain forests in the Canadian Arctic

Abstract Abundant fossil plant remains are preserved in the high-latitude middle Eocene deposits of the Buchanan Lake Formation on Axel Heiberg Island, Nunavut Territory, Canada. Intact leaf litter, logs, and stumps preserved in situ as mummified remains offer an opportunity to determine the structure, biomass, and productivity of two Taxodiaceae-dominated forests that grew north of the Arctic Circle (paleolatitude 75–80°N). We excavated fossil tree trunks and treetops to develop equations that describe the height, structure, and mass of the aboveground components of Eocene-age Metasequoia trees. We combined those data with surveys of in situ stumps to determine the structure, biomass, and productivity of two fossil forests, “N” and “HR.” We calculated a canopy height of 40 ± 3 m for the N forest and 25 m ± 2 m for the HR forest. Buried knots in dissected logs and abundant branch-free bole wood indicate that these were tall, closed-canopy forests. Stem tapers indicate that the overstory was of uniform height. Stem volume equaled 2095 m3 ha−1 and stem biomass was 628 Mg ha−1 in the N forest. Volume and biomass in the HR forest were much smaller, 211 m3 ha−1 and 63.3 Mg ha−1, respectively. We estimated understory tree biomass to be 40 Mg ha−1 in the N forest and 3.5 Mg ha−1 in the HR forest. Recovery of seven fossil treetops with exposed branch stubs enabled us to make estimates of branchwood and foliar biomass using allometric equations derived from modern, plantation-grown Metasequoia glyptostroboides. Estimated stand-level branch biomass was 13 and 6.7 Mg ha−1 in the N and HR forests, respectively. Standing foliar biomass was estimated to be 3.2 and 2.1 Mg ha−1 in the N and HR forests, respectively. Using annual ring widths, the reconstructed parabolic stems, and wood density of modern Metasequoia, we calculated annual wood production to be 2.3 Mg ha−1 yr−1 for the N forest and 0.55 Mg ha−1 yr−1 for the HR forest Assuming that the ancient Metasequoia were deciduous like their living relatives, annual aboveground net primary productivity was 5.5 Mg ha−1 yr−1 for the N forest and 2.8 Mg ha−1 yr−1 for the HR forest. Our estimated biomass and productivity values for N are similar to those of modern old-growth forests of the Pacific Northwest of the United States and old-growth coastal Cordillera forests of southern Chile.

Effects of ambient levels of airborne chemicals on freezing resistance of red spruce foliage

Abstract Repeated, severe winter injury incited and sustained the decline of red spruce ( Picea rubens Sarg.) in the mountain forests of the northeast. Some experiments have shown that acidic mist comparable to ambient cloud water reduces frost tolerance of red spruce seedlings. To help bridge the gap between seedling studies and mature spruce growing under field conditions, we excluded airborne chemicals from the foliage of red spruce 75 years old or more, growing on Whiteface Mountain, New York in cloud-immersed forests at 1170 m. Polyethylene and Teflon chambers with multi-stage filters excluded ambient cloud water and charcoal-reactive gases (e.g. ozone) in different combinations from the distal meter of exposed branches in the upper crown. Three months of exclusion in the summer of 1988 improved several needle characteristics, including midwinter cold tolerance. Resistance to freezing injury measured experimentally in midwinter was a good predictor of the degree of natural winter injury which occurred in late winter. Artificial freezing of shoots in situ reproduced the symptoms of naturally occurring winter injury. Thus, freezing injury appears to be important for the development of the type of winter injury observed at Whiteface Mt. In experimental trees which sustained natural winter injury, exposure to charcoal-filtered air and deionized water mist during the preceding summer improved resistance to freezing injury compared with ambient air and cloud water. The loss of freezing resistance attributed to ambient conditions was about 10°C, sufficient to increase substantially the risk of winter freezing damage.

Allometric equations for two South American conifers: Test of a non-destructive method

Non-destructive biomass estimation for protected tree species is necessary to understand their population dynamics and the ecological factors affecting species scarcity. We present a method for estimating aboveground biomass of bole, branches and foliage, using data obtained by climbing live trees to collect limited samples and measurements. This method was . applied to 26 individuals of Fitzroya cupressoides Mol. Johnston, a protected Chilean conifer, and to 12 individuals of a . second, morphologically similar, but unprotected species, Pilgerodendron u˝iferum D. Don. Florin. Trees were climbed, ´ basal diameter of all branches ) 1 cm were recorded and four branches per tree were removed for further measurement. The sampled branches were used to develop allometric equations predicting branch, twig and foliar biomass from branch basal diameter. These equations were used to generate whole tree canopy biomass estimates based on climbers measurements of branch basal diameter. Bole biomass was estimated from serial measurements of height, diameter and wood density. Whole tree canopy and bole biomass estimates were then used to develop allometric equations predicting wood and foliar biomass from diameter at breast height. Five of the P. u˝iferum trees were felled and weighed by conventional methods, and the data used to evaluate error in the non-destructive technique. Although the technique was labor intensive, it was found to yield mean estimates for canopy components that are expected to be within 10% of the true mean for large populations of trees .watershed level studies . Accurate estimation of individual trees may be less reliable, as the amount of dispersion about . some of the regressions was quite high ) 20% . q 1998 Elsevier Science B.V.

Phosphorus fractions in montane forest soils of the Cordillera de Piuchué, Chile : biogeochemical implications

The Hedley fractionation procedure as modified by Tiessen and Moir (1993) was used to evaluate the amounts of P in several soil chemical pools in an old, unglaciated landscape at 600 m elevation in the Cordillera de Piuchué, Chile (42° 30′ S. 74° W). This is an area of primary forests which have escaped disturbance from forest harvesting, land clearing and the deposition of anthropogenic chemicals. Two study watersheds are conifer-dominated with moorland on wind-exposed ridgetops. In a third study watershed, vegetation is dominated by evergreen broadleaf trees. Soils are thin (ca. 40 cm) and have a high organic matter content. Across all communities, most of the soil P is in non-labile forms in organic combinations or in combination with secondary soil minerals. Little P was present in primary minerals. The remainder (ca. 20%) was in labile forms extractable with anion exchange resin or bicarbonate solution. From litterfall and allometric relationships, we estimated the annual P requirement of growing vegetation to be <1 kg ha-1 in the moorland and < 3 kg ha-1 in the conifer and mixed forests. This is substantially less than the standing pool of resin-extractable P (ca. 20 kg ha-1), which is considered to be P fraction most readily available to plants. Resin-extractable P was strongly correlated with soil carbon content ( R2 =0.72 − 0.87, p < 0.001) suggesting that soil organic matter is the likely proximate source of plant-available P. On a kg ha-1 basis, the most labile forms of P did not differ significantly across 3 of the 4 community types despite dramatic differences in species, live biomass and annual P requirement, suggesting little control of available P pools by forest vegetation type. On a more detailed level, resin-extractable P was strongly correlated with HCO3-extractable organic (and inorganic) P. This is consistent with other findings of P behavior in acid soils high in organic matter in which microbial transformations are key in regulating pools of plant-available P.

Structure, allometry, and biomass of plantation Metasequoia glyptostroboides in Japan

We quantified structural features and the aboveground biomass of the deciduous conifer, Metasequoia glyptostroboides (Hu and Cheng) in six plantations in central Japan. In order to derive biomass estimates we dissected 14 M. glyptostroboides trees into three structural components (stem wood, branch wood and foliage) to develop allometric equations relating the mass of these components and of the whole tree to diameter at breast height (DBH). We found robust relationships at the branch and whole tree level that allow accurate prediction of component and whole tree biomass. Dominant tree height was similar within five older (>40 years) plantations (27‐33 m) and shorter in a 20-year-old plantation (18 m). Average stem diameter varied from 12.8 cm in the youngest stand to greater than 35 cm in the oldest stand. Metasequoia have relatively compact crowns distributed over the top 30% of the tree although the youngest stand had the deepest crown relative to tree height (up to 38%). At the individual tree level in older stands, 87% of the aboveground biomass was allocated to the stem, 9% to branch wood and 4% to foliage. We found little difference in the relative distribution of above ground biomass among the stands with the exception of lower foliage biomass in larger diameter trees. Total aboveground biomass of the older stands varied twofold, ranging from a maximum of 450 Mg ha ! 1 in a 42-year-old stand to a minimum of 196 Mg ha ! 1 in a 48-year-old stand. Total above ground biomass of the 20-year-old stand was 176 Mg ha ! 1 .

Distribution and cycling of C, N, Ca, Mg, K and P in three pristine, old-growth forests in the Cordillera de Piuchué, Chile

We assessed a number of biomass and soil parameters in order to examinerelationships among nutrient availability, forest productivity and vegetationpatterns in two old-growth forested watersheds in a pristine montane landscapeon Isla de Chiloé, Chile. We selected watersheds in both gymnosperm- andangiosperm-dominated forests and determined tree species, d.b.h. and health forall trees < 2 cm d.b.h. in plots established at 50m intervals. Soils were sampled at two depths in each plot andanalyzed for total C and N, and for exchangeable Ca, K, Mg andresin-extractableP. Allometric relationships and vegetation nutrient concentrations were used todetermine above-ground pools from the vegetation survey data. Growth rates werederived from increment core measures. Soil pools of most elements measuredappear adequate to support forest growth indefinitely. Mineralized nitrogen,which is similar in quantity to the annual demand for nitrogen from the soil isthe exception, consistent with the possibility of N limitation in two of theforest types studied. A third type, an evergreen broadleaved forest, appears torequire substantially more nitrogen than would appear to be available from netmineralization measurements. Productivity per unit of nitrogen required fromthesoil is quite high, largely as a consequence of the evergreen habit of thespecies in these forests. Compared to other temperate montane forests in theNorthern Hemisphere, nutrient pools and cycling characteristics were found tobemostly similar across forest types, in spite of considerable variation invegetation and soils.

Cytological and ultrastructural preservation in Eocene Metasequoia leaves from the Canadian High Arctic.

The ultrastructural examination by transmission electron microscopy of 45-million-year-old mummified leaves of Metasequoia extracted from the Upper Coal member of the Buchanan Lake Formation in Napartulik on Axel Heiberg Island revealed the preservation of intact chloroplasts and chloroplast components. Abundant tanniferous cell inclusions may indicate that the 3-mo period of constant daylight during the Artic summer induced high concentrations of tannins in the leaf tissues, which may have arrested microbial degradation of the litter. Quantified differences in the extent of chloroplast preservation through a vertical section of the lignite suggest that short-term shifts in the depositional environment took place, perhaps influencing the exposure of the leaf tissues to conditions that would either promote or inhibit decomposition.

Reconstruction of Tertiary Metasequoia forests. I. Test of a method for biomass determination based on stem dimensions

Abstract Accurate reconstruction of the biomass, structure, and productivity of ancient forests from their fossilized remnants remains an interesting challenge in paleoecology. In well-preserved Tertiary fossil Metasequoia forests of Canadas Arctic, in situ stumps and fragments of stems, treetops, and branches contain substantial information about tree dimensions that can be used to determine tree height, stand biomass, and other characteristics such as canopy depth and structure, and the history of stand development. To validate a method for reconstructing the biomass of the Eocene floodplain Metasequoia forests of Axel Heiberg Island, we measured stump diameters and spacing, and stem, branch, and treetop characteristics in living Metasequoia glyptostroboides and Chamaecyparis thyoides stands in ways that simulate the limited measurements that can be made in well-preserved fossil forests in Canada and probably elsewhere. We used those limited measurements to estimate tree height and volume, branch and foliar dry weights, and tree biomass. The estimates derived from the limited data set are usually within 15% of the estimates derived from the methods currently used in forest ecology for determining those metrics in modern forests. Under appropriate conditions, the biomass of ancient forests can be estimated with reasonable confidence.

Structure, Biomass, and Productivity of a Late Paleocene Arctic Forest

ABSTRACT. Abundant fossil plant remains are preserved in the high-latitude late Paleocene Iceberg Bay Formation on Ellesmere Island, Nunavut, Canada. Intact leaf litter lenses and permineralized, in situ logs and stumps offer for the first time an opportunity to determine the structure, biomass, and productivity of a redwood-dominated forest that grew in the polar regions of Nunavut (paleolatitude 75–80° N). Well-preserved fossil tree trunks were excavated to develop equations that describe the height, structure, and mass of the aboveground components of late Paleocene-age (approximately 55.8 to 58.7 million years old) Metasequoia (redwoods) trees. We then combined those data with measurements of the in situ stumps to determine the structure, biomass, and productivity of this polar fossil forest. The height of the canopy trees in the forest was calculated to be 32 ± 2 m. Abundant branch stubs that represent the remnants of living branches were found on a wide range of stem sizes including larger logs from the lower portions of the fossil trees indicating a relatively deep canopy. The branch lengths predicted from allometric relationships developed on modern Metasequoia trees are consistent with the stump spacing measured at Stenkul Fiord. The stem volume equaled 1,632 m3 ha-1 and stem biomass was a minimum of 490 Mg ha-1. Recovery of an incomplete treetop with exposed branch stubs enabled us to make minimum estimates of branch wood and foliar biomass using allometric equations derived from extant Metasequoia glyptostroboides trees in Japan. Estimated stand-level branch biomass was at most 19 Mg ha-1 and standing foliar biomass was estimated to be a maximum of 4 Mg ha-1. We adjusted the derived stemwood biomass estimates to account for a potential bias against sapwood and bark preservation. This adjustment increased our stemwood biomass estimates by 17% to 576 Mg ha-1. Using the annual ring widths of the tree stems, the reconstructed parabolic stems, and wood density of modern Metasequoia, we calculated the annual wood production of the Stenkul Fiord forest to be 3.8 Mg ha-1 yr-1. Assuming the ancient Metasequoia trees were deciduous like their living relatives, the annual aboveground net primary productivity was between 5.8 and 7.8 Mg ha-1 yr-1. These estimated biomass and productivity values fall within the range for those obtained for modern old-growth forests of the Pacific Northwest (USA) and old-growth coastal Cordillera forests of southern Chile and are near the average values for temperate freshwater floodplain forests in North America.