Amounts of litter fall in some pine forests in a European transect, in particular Scots pine.

Pine litter fall data, mainly needle litter, were available for 64 plots in a transect from the Arctic Circle in Fennoscandia (41 plots) to southern Spain (22 further plots in continental Europe) and one in the American Midwest). Data originated from a total of eight pine species. Regressions were calculated mainly for needle litter fall and to some extent for total litter fall. We obtained a highly significant linear relationship for needle litter fall and latitude (R 2adj = 0.285; n = 58; P < 0.001) when using needle litter fall data from all pine species. Combining sites in the boreal and Atlantic climates gave an R2 adj of 0.732 with n = 45 (P < 0.001). A multiple linear relationship using stand age, latitude and basal area was highly significant and gave an R2adj value of 0.412 (n = 54; P < 0.001). For the amount of Scots pine needle litter in Fennoscandia, the best simple linear relationships were obtained with site index (H 100) (R2 adj = 0.349), latitude (R2adj = 0.331) and basal area (R2adj = 0.324) as predictor variables, whereas the regressions on altitude and stand age were significant only with P < 0.01. An X2 function for stand age improved the relationship with age to R2adj = 0.243. Multiple regression relationships for Fennoscandia between needle litter fall and latitude plus basal area and that to latitude plus basal area plus age were highly significant (R2adj = 0.605 and 0.661, respectively, with n = 41). In a stepwise procedure using data from the same sites, combinations of the factors latitude, site index, basal area and stand age could explain as much as 78 % of the needle litter fall. For total litter fall as measured by the same method as needle litter we related data from 32 sites to that of needle litter fall and obtained highly significant relationships indicating that needle litter fall may be used as an index for total litter fall. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS.Chute de litière dans quelques forêts de pins, en particulier du Pin sylvestre, le long d'un transect européen. Les données de chute de litière, essentiellement des chutes d'aiguilles, étaient disponibles pour 64 sites le long d'un transect depuis le cercle polaire en Scandinavie (41 sites) jusqu'au Sud de l'Espagne (22 sites supplémentaires en Europe continentale) et un site dans le midouest américain. Les données proviennent de huit espèces de Pin. Des régressions ont été calculées principalement pour la chute d'aiguilles et dans certains cas pour la chute totale de litière. Il existe une relation linéaire hautement significative entre la chute des aiguilles et la latitude (R2adj = 0.285 ; n = 58; p < 0,001) lorsque l'ensemble des données pour toutes les espèces sont utilisées. La combinaisons des sites en climat boréal et atlantique donne un R2adj de 0.732 pour n = 45 (p < 0,001). Une relation linéaire multiple, utilisant l'âge du peuplement, la latitude et la surface terrière est hautement significative et donne un R 2∼ de 0.412 (n = 54; p < 0.001). La meilleure relation linéaire, pour les retours d'aiguilles chez le Pin sylvestre en Scandinavie a été obtenue en utilisant comme variables prédictives l'indice de fertilité stationnelle « H 100 » (R2 adj = 0.349), la latitude (Radj = 0331), et la surface terrière (R2adj = 0.324 ; alors que la régression sur les variables altitudes et âge des peuplements n'était significative seulement à p < 0,01. Une fonction X2 pour l'âge du peuplement améliore la relation avec l'âge, R2adj = 0,243. Les relations multiples entre la chute des aiguilles et la latitude associée à la surface terrière et celle associée à la surface terrière plus l'âge, pour les sites Scandinaves, sont hautement significatives (R2 adj = 0,605 et R2adj = 0,661, respectivement, avec n = 41 ). La procédure de régression progressive sur les données des mêmes sites, combinaisons des variables latitude, indice de fertilité, surface terrière et âge du peuplement permet d'expliquer 78 % de la variation de la chute des aiguilles. Des relations hautement significatives ont été calculées sur les données des retours totaux de litière, utilisant la même méthodologie sur 32 des sites. Elles démontrent que la quantité des chutes des seules aiguilles peut être utilisée comme indice pour la chute totale de la litière. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS

Accounting for photodegradation dramatically improves prediction of carbon losses in dryland systems

Traditional models of decomposition fail to capture litter mass loss patterns in dryland systems. This shortcoming has stimulated research into alternative drivers of decomposition, including photodegradation. Here, we use aboveground litter decomposition data for dryland (arid) sites from the Long-term Intersite Decomposition Experiment Team data set to test hypotheses (models) about the mechanisms and impacts of photodegradation. Incorporating photodegradation into a traditional biotic decomposition model substantially improved model predictions for mass loss at these dryland sites, especially after four years. The best model accounted for the effects of solar radiation via photodegradation loss from the intermediate cellulosic and lignin pools and direct inhibition of microbial decomposition. Despite the concurrent impacts of photodegradation and inhibition on mass loss, the best photodegradation model increased mass loss by an average of 12% per year compared to the biotic-only decomposition model. The best model also allowed soil infiltration into litterbags to reduce photodegradation and inhibition of microbial decomposition by shading litter from solar radiation. Our modeling results did not entirely support the popular hypothesis that initial lignin content increases the effects of photodegradation on litter mass loss; surprisingly, higher initial lignin content decreased the rate of cellulosic photodegradation. Importantly, our results suggest that mass loss rates due to photodegradation may be comparable to biotic decomposition rates: Mass loss due to photodegradation alone resulted in litter mass losses of 6–15% per year, while mass loss due to biotic decomposition ranged from 20% per year during early-stage decomposition to 3% per year during late-stage decomposition. Overall, failing to account for the impacts of solar radiation on litter mass loss under-predicted long-term litter mass loss by approximately 26%. Thus, not including photodegradation in dryland decomposition models likely results in large underestimations of carbon loss from dryland systems

Effects of Land Crabs on Leaf Litter Distributions and Accumulations in a Mainland Tropical Rain Forest 1

The effect of the fossorial land crab Gecarcinus quadratus (Gecarcinidae) on patterns of accumulation and distribution of leaf litter was studied for two years in the coastal primary forests of Costa Rica's Corcovado National Park. Within this mainland forest, G, quadratus achieve densities up to 6 crabs/m 2 in populations extending along the Park's Pacific coastline and inland for ca 600 m. Crabs selectively forage for fallen leaf litter and relocate what they collect to burrow chambers that extend from 15 to 150 cm deep ( N = 44), averaging (±SE) 48.9 ± 3.0 cm. Preference trials suggested that leaf choice by crabs may be species-specific. Excavated crab burrows revealed maximum leaf collections of 11.75 g dry mass– 2.5 times more leaf litter than collected by square-meter leaf fall traps over several seven-day sampling periods. Additionally, experimental crab exclosures (25 m 2 ) were established using a repeated measures randomized block design to test for changes in leaf litter as a function of reduced crab density. Exclosures accumulated significantly more (5.6 ± 3.9 times) leaf litter than did control treatments during the wet, but not the dry, seasons over this two-year study. Such extensive litter relocation by land crabs may affect profiles of soil organic carbon, rooting, and seedling distributions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73250/1/j.1744-7429.2003.tb00590.x.pd

Fine-root turnover rates of European forests revisited: an analysis of data from sequential coring and ingrowth cores

Background and Aims Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values. Methods We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature. Results Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0.86 yr−1 for Fagus sylvatica and 0.88 yr−1 for Picea abies when maximum biomass data were used for the calculation, and 1.11 yr−1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula. Conclusions We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting

Biomass and morphology of fine roots in temperate broad-leaved forests differing in tree species diversity: is there evidence of below-ground overyielding?

Biodiversity effects on ecosystem functioning in forests have only recently attracted increasing attention. The vast majority of studies in forests have focused on above-ground responses to differences in tree species diversity, while systematic analyses of the effects of biodiversity on root systems are virtually non-existent. By investigating the fine root systems in 12 temperate deciduous forest stands in Central Europe, we tested the hypotheses that (1) stand fine root biomass increases with tree diversity, and (2) ‘below-ground overyielding’ of species-rich stands in terms of fine root biomass is the consequence of spatial niche segregation of the roots of different species. The selected stands represent a gradient in tree species diversity on similar bedrock from almost pure beech forests to medium-diverse forests built by beech, ash, and lime, and highly-diverse stands dominated by beech, ash, lime, maple, and hornbeam. We investigated fine root biomass and necromass at 24 profiles per stand and analyzed species differences in fine root morphology by microscopic analysis. Fine root biomass ranged from 440 to 480 g m−2 in the species-poor to species-rich stands, with 63–77% being concentrated in the upper 20 cm of the soil. In contradiction to our two hypotheses, the differences in tree species diversity affected neither stand fine root biomass nor vertical root distribution patterns. Fine root morphology showed marked distinctions between species, but these root morphological differences did not lead to significant differences in fine root surface area or root tip number on a stand area basis. Moreover, differences in species composition of the stands did not alter fine root morphology of the species. We conclude that ‘below-ground overyielding’ in terms of fine root biomass does not occur in the species-rich stands, which is most likely caused by the absence of significant spatial segregation of the root systems of these late-successional species

Litter quality and its response to water level drawdown in boreal peatlands at plant species and community level

Changes in the structure of plant communities may have much more impact on ecosystem carbon (C) cycling than any phenotypic responses to environmental changes. We studied these impacts via the response of plant litter quality, at the level of species and community, to persistent water-level (WL) drawdown in peatlands. We studied three sites with different nutrient regimes, and water-level manipulations at two time scales. The parameters used to characterize litter quality included extractable substances, cellulose, holocellulose, composition of hemicellulose (neutral sugars, uronic acids), Klason lignin, CuO oxidation phenolic products, and concentrations of C and several nutrients. The litters formed four chemically distinct groups: non-graminoid foliar litters, graminoids, mosses and woody litters. Direct effects of WL drawdown on litter quality at the species level were overruled by indirect effects via changes in litter type composition. The pristine conditions were characterized by Sphagnum moss and graminoid litters. Short-term (years) responses of the litter inputs to WL drawdown were small. In longterm (decades), total litter inputs increased, due to increased tree litter inputs. Simultaneously, the litter type composition and its chemical quality at the community level greatly changed. The changes that we documented will strongly affect soil properties and C cycle of peatlands.Peer reviewe