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

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

Maximum decomposition limits of forest litter types: A synthesis

We used long-term litter decomposition data to estimate final decomposition levels using an asymptotic function. The estimated final limit values for decomposition were compared with available chemical data for the different litter types. A total of 41 limit values were estimated from as many different decomposition studies, and 20 different litter types were incubated in eight different forest systems. The limit values estimated varied with litter type. They ranged from about 35 to about 100% decomposition and were linearly related to the initial litter concentrations of N, Mn, and Ca in the newly shed litter. For these three nutrients, there are causal relationships to lignin degradation and to the lignin-degrading microbial community. Using all available data, we made simple and multiple linear regressions and obtained a negative linear relationship between limit value and initial N concentration (Radj2. = 0.451; n = 41; P < 0.001). For needle litter alone, we obtained a better relationship (Radj2 = 0.492; n = 23; p < 0.001). Manganese concentrations in litter gave a positive relationship (Radj2 = 0.372; n = 25; p < 0.001), with a clear improvement when needle litter was tested for alone (Radj2 = 0.512; n = 16; p < 0.001). Calcium alone gave a barely significant relationship. When combining nutrients in multiple linear relationships we obtained high R2 values, indicating that the models were good. Thus for all sites and litter types, N, Mn, and Ca combined gave an Radj2value of 0.640 with n = 25 (p < 0.001). All needle litters combined gave an Radj2 o f 0.745 (n = 16; p < 0.001). The significance of this finding is discussed

Litter decomposition in earthworm-invaded northern hardwood forests: Role of invasion degree and litter chemistry

The effects of invasive earthworms on decomposition are little known, and the controls of their effect on decomposition may be different than those of microbes. Sugar maple–dominated forests previously devoid of earthworms in the western Great Lakes region (USA) exhibit different degrees of earthworm invasion, presenting a natural experiment to study its effects on litter decomposition. We hypothesized that litter decomposition would depend on the degree of earthworm invasion, the presence or absence of worms of differing sizes, and initial litter chemistry. We established an experiment using fine- and coarse-mesh litterbags (to allow access by different-sized worms) to study decomposition of 3 different litters in mixture under different degrees of earthworm invasion in 12 Minnesota sites. The effect of earthworm invasion degree on litter decomposition varied by identity of the litter, mesh size, and time of litter collection. Decomposition of Quercus rubra, the litter with the lowest initial calcium concentration and highest lignin:nitrogen, was not significantly influenced by earthworm invasion degree. In contrast, decomposition of Tilia americana, the litter with the highest calcium concentration and lowest lignin:nitrogen, was fastest in coarse-mesh litterbags. After 15 months the mass of the highest-quality litters was highest in the fine-mesh bags of heavily invaded plots, suggesting that microbially mediated decomposition slowed where earthworms had removed the forest floor