Closed-canopy Sites Research Articles

Topography and canopy cover influence soil organic carbon composition and distribution across a forested hillslope in the discontinuous permafrost zone

AbstractTopography and canopy cover influence ground temperature in warming permafrost landscapes, yet soil temperature heterogeneity introduced by mesotopographic slope positions, microtopographic differences in vegetation cover, and the subsequent impact of contrasting temperature conditions on soil organic carbon (SOC) dynamics are understudied. Buffering of permafrost‐affected soils against warming air temperatures in boreal forests can reflect surface soil characteristics (e.g., thickness of organic material) as well as the degree and type of canopy cover (e.g., open cover vs. closed cover). Both landscape and soil properties interact to determine meso‐ and microscale heterogeneity of ground warming. We sampled a hillslope catena transect in a discontinuous permafrost zone near Fairbanks, Alaska, to test the small‐scale (1 to 3 m) impacts of slope position and cover type on soil organic matter composition. Mineral active layer samples were collected from backslope, low backslope, and footslope positions at depths spanning 19 to 60 cm. We examined soil mineralogical composition, soil moisture, total carbon and nitrogen content, and organic mat thickness in conjunction with an assessment of SOC composition using Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). Soils in the footslope position had a higher relative contribution of lignin‐like compounds, whereas backslope soils had more aliphatic and condensed aromatic compounds as determined using FT‐ICR‐MS. The effect of open versus closed tree canopy cover varied with the slope position. On the backslope, we found higher oxidation of molecules under open cover than closed cover, indicating an effect of warmer soil temperature on decomposition. Little to no effect of the canopy was observed in soils at the footslope position, which we attributed, in part, to the strong impact of soil moisture content in SOC dynamics in the water‐gathering footslope position. The thin organic mat under open cover on the backslope position may have contributed to differences in soil temperature and thus SOC oxidation under open and closed canopies. Here, the thinner organic mat did not appear to buffer the underlying soil against warm season air temperatures and thus increased SOC decomposition as indicated by the higher oxidation of SOC molecules and a lower contribution of simple molecules under open cover than the closed canopy sites. Our findings suggest that the role of canopy cover in SOC dynamics varies as a function of landscape position and soil properties, namely, organic mat thickness and soil moisture. Condition‐specific heterogeneity of SOC composition under open and closed canopy cover highlights the protective effect of canopy cover for soils on backslope positions.

Response of moth communities (Lepidoptera) to forest management strategies after disturbance

Spruce forests face many threats such as climate change and bark beetle outbreaks. Yet, bark beetle dynamics have a long co-evolutionary history strongly linked to spruce forest structural dynamics. Disturbed spruce forest sites resulting from bark beetle outbreaks therefore should not be regarded as degraded land, but as early successional stages following natural forest dynamics. Three post-bark-beetle disturbance sites and one closed-canopy site in the Bavarian Forest and Ĺ umava National Parks were investigated with the focus on moth communities. The three disturbed sites had undergone different post-disturbance management regimes, with one being treated by salvage logging, while at the other two forest sites deadwood was kept in the forest. To avoid the spread of bark beetles, however, the bark of dead trees was either gouged or removed. The aim was to determine how many moths can be found at the undisturbed and disturbed forest sites and if differences in community composition can be explained by different management regimes. The results highlight that natural forest disturbance can increase moth diversity, especially by favouring species that are associated with open and shrub habitats. Many rare and endangered species benefit from bark beetle outbreaks, indicating that accepting natural forest dynamics is an important part of conservation management. Post-bark beetle management seems to have a minor effect on moth communities.

Cumulative effects of spruce budworm and moose herbivory on boreal forest ecosystems

Abstract Ungulate herbivory is a key natural disturbance in many ecosystems. In forest ecosystems, ungulate herbivory often co‐occurs with other disturbances yet there are few studies looking at the cumulative impacts of ungulates and other natural disturbances on forest dynamics. We report on an 18‐year experiment to investigate the combined effects of introduced, non‐native moose and native spruce budworm herbivory on balsam fir forest recruitment and regeneration. Specifically, we measured inputs into early life‐history components of balsam fir dominant boreal forest ecosystems such as seed density, seedbed quality, seedling and sapling height and density, as well as adult density in eight paired moose exclosure and control sites across a spruce budworm disturbance gradient (i.e. no outbreak, recent outbreak, old outbreak) that resulted in closed, partially open and open canopies. Piecewise structural equation models (SEMs) revealed a strong negative effect of spruce budworm disturbance on balsam fir adult density and indirect effects of this budworm disturbance on balsam fir seedling and sapling density mediated through adult density. We observed a similar pattern of budworm disturbance effects on balsam fir seed density with the lowest densities in sites with open canopy, then partially open and closed canopies. As expected, the SEM showed a positive effect of bryophyte seedbed cover on balsam fir seedling density. The SEM showed support for a positive effect of moose exclusion on balsam fir sapling height and density. Specifically, saplings were on average taller and denser in exclosure than control plots and these differences are most pronounced at sites with partially open canopies created by spruce budworm disturbance and undisturbed or closed canopy sites. Overall, we show evidence for cumulative and interactive effects of spruce budworm and moose herbivory on all life stages of balsam fir and such effects are negatively affecting regeneration of balsam fir forests. Human activities are creating conditions that facilitate the expansion and increased impacts of herbivores on boreal ecosystem functioning. A greater understanding of how ungulate herbivory interacts with other disturbances is needed to improve our predictions of forest ecosystem dynamics under global change. A free Plain Language Summary can be found within the Supporting Information of this article.

Canopy Closure Retards Fine Wood Decomposition in Subtropical Regenerating Forests

Wood decomposition is faster in open habitats than closed-canopy forests, with the mechanisms unclear. When allowing access, termites outcompete fungi during wood decomposition. If increasing canopy density shifts the dominance from termites to fungi, decomposition rates will fall. We conducted wood decomposition experiments in 148 plots of two regenerating forest sites (Site A vs. B) in subtropical China with tree species diversity and composition (for example, specific leaf area) manipulated. Branches of seven species with varying quality were deployed and measured for wood mass-loss rates and decomposer abundance at two time steps (that is, after 1 year and 2 years). We also monitored understory microclimate and predatory ant diversity in 40 plots of Site A. We found that higher canopy density drove the shift of dominance from termites to fungi via facilitating predatory ants and wetter–cooler microclimate. Furthermore, termites promoted decomposition after 1 year especially for the species with highest wood quality, but fungi slowed decomposition after 2 years especially for two species with lower quality. Notably, canopy density negatively correlated with wood mass-loss rates in closed-canopy Site A but not so in more open Site B. Tree diversity and community-weighted mean specific leaf area increased canopy density but did not affect abundance nor decomposition. Our study highlights the importance of canopy density for retarding fine wood decomposition in closed-canopy regenerating forests, probably via shifting the dominance from more (that is, termites) to less efficient decomposer (that is, fungi). Future cross-regional studies are necessary to test the generality of canopy density effect on wood decomposition and the related mechanisms.

Carbon flux and forest dynamics: Increased deadwood decomposition in tropical rainforest tree-fall canopy gaps.

Tree mortality rates are increasing within tropical rainforests as a result of global environmental change. When trees die, gaps are created in forest canopies and carbon is transferred from the living to deadwood pools. However, little is known about the effect of tree-fall canopy gaps on the activity of decomposer communities and the rate of deadwood decay in forests. This means that the accuracy of regional and global carbon budgets is uncertain, especially given ongoing changes to the structure of rainforest ecosystems. Therefore, to determine the effect of canopy openings on wood decay rates and regional carbon flux, we carried out the first assessment of deadwood mass loss within canopy gaps in old-growth rainforest. We used replicated canopy gaps paired with closed canopy sites in combination with macroinvertebrate accessible and inaccessible woodblocks to experimentally partition the relative contribution of microbes vs. termites to decomposition within contrasting understorey conditions. We show that over a 12month period, wood mass loss increased by 63% in canopy gaps compared with closed canopy sites and that this increase was driven by termites. Using LiDAR data to quantify the proportion of canopy openings in the study region, we modelled the effect of observed changes in decomposition within gaps on regional carbon flux. Overall, we estimate that this accelerated decomposition increases regional wood decay rate by up to 18.2%, corresponding to a flux increase of 0.27MgCha-1 year-1 that is not currently accounted for in regional carbon budgets. These results provide the first insights into how small-scale disturbances in rainforests can generate hotspots for decomposer activity and carbon fluxes. In doing so, we show that including canopy gap dynamics and their impacts on wood decomposition in forest ecosystems can help improve the predictive accuracy of the carbon cycle in land surface models.

Exposure matters: Forest dynamics reveal an early Holocene conifer refugium on a north facing slope in Central Europe

Although several studies provide a broad overview of vegetation changes in the Carpathian Basin during the Holocene, stand-scale vegetation changes are lesser known because of the rarity of suitable sampling sites. In this study we investigated the sediment of a small closed-canopy site (Nagy-forrás forest hollow, 685 m a.s.l., 0.1 ha), located in the Mátra Mountains, on the north facing slope of Kékes (1014 m a.s.l.). We carried out detailed pollen, conifer stomata and plant macrofossil analyses, as well as radiocarbon dating to examine Late Glacial and Holocene dynamics of vegetation development. The site dates back to ca. 15,500 cal yr BP, when open boreal forests and wet tundra-like habitats occurred around the hollow. Closed forest cover developed around 14,600 cal yr BP, when a boreal European larch-Swiss stone pine ( Larix decidua-Pinus cembra) forest surrounded the hollow. This vegetation type remained stable up to 7700 cal yr BP. We observed a hiatus between 7700 and 2710 cal yr BP, followed by a beech ( Fagus sylvatica) dominated mixed temperate deciduous forest. Our results confirmed that the area was covered by a primary forest, as human influence was visible only from 175 cal yr BP. The relatively long lasting persistence of Pinus cembra in the Holocene at relatively low altitude was documented, which has never been found in Holocene sediments in the Pre-Carpathians before. We hypothesize that the north facing slope acted as a cold-stage refugium in the Early Holocene and could play the same role for the present-day beech forest that is threatened by recent climate change.

Development and evaluation of habitat suitability models for nesting white-headed woodpecker (Dryobates albolarvatus) in burned forest.

Salvage logging in burned forests can negatively affect habitat for white-headed woodpeckers (Dryobates albolarvatus), a species of conservation concern, but also meets socioeconomic demands for timber and human safety. Habitat suitability index (HSI) models can inform forest management activities to help meet habitat conservation objectives. Informing post-fire forest management, however, involves model application at new locations as wildfires occur, requiring evaluation of predictive performance across locations. We developed HSI models for white-headed woodpeckers using nest sites from two burned-forest locations in Oregon, the Toolbox (2002) and Canyon Creek (2015) fires. We measured predictive performance by developing one model at each of the two locations and quantifying discrimination of nest from reference sites at two other wildfire locations where the model had not been developed (either Toolbox or Canyon Creek, and the Barry Point Fire [2011]). We developed and evaluated Maxent models based on remotely sensed environmental metrics to support habitat mapping, and weighted logistic regression (WLR) models that combined remotely sensed and field-collected metrics to inform management prescriptions. Both Maxent and WLR models developed either at Canyon Creek or Toolbox performed adequately to inform management when applied at the alternate Toolbox or Canyon Creek location, respectively (area under the receiver-operating-characteristic curve [AUC] range = 0.61-0.72) but poorly when applied at Barry Point (AUC = 0.53-0.57). The final HSI models fitted to Toolbox and Canyon Creek data quantified suitable nesting habitat as severely burned or open sites adjacent to lower severity and closed canopy sites, where foraging presumably occurs. We suggest these models are applicable at locations similar to development locations but not at locations resembling Barry Point, which were characterized by more (pre-fire) canopy openings, larger diameter trees, less ponderosa pine (Pinus ponderosa), and more juniper (Juniperus occidentalis). Considering our results, we recommend caution when applying HSI models developed at individual wildfire locations to inform post-fire management at new locations without first evaluating predictive performance.

Boreal tree-rings are influenced by temperature up to two years prior to their formation: a trade-off between growth and reproduction?

Large spatial and between-tree variability has recently been observed in the response of boreal forests to ongoing climate change, spanning from growth stimulation by increasing temperatures to drought limitation. To predict future responses of boreal forests, it is necessary to disentangle the drivers modulating the temperature-growth interaction. To address this issue, we established two inventory plots (at a treeline and closed-canopy forest) and assembled site chronologies in Picea glauca stands at the transition between boreal forest and tundra in Northern Quebec, Canada. In addition to site chronologies, we established a set of chronologies containing, for each year, exclusive subsets of tree-rings with specific cambial age (young/old), tree dimensions (small/large) and tree social status (dominant/suppressed). All chronologies were correlated with climatic data to identify the course of climatic conditions driving variability in tree-ring widths. Our results show that the growth of P. glauca correlates significantly with summer temperature in tree-ring formation years and during up to two prior summers. Tree-ring width is positively influenced by summer temperatures in tree-ring formation year and two years prior to tree-ring formation. In addition, climate-growth correlations indicate a negative effect of summer temperature one year before tree-ring formation at the closed-canopy forest site. The pattern of climate-growth correlations is tightly synchronized with previously published patterns of climate-reproduction correlations of P. glauca, suggesting a growth-reproduction trade-off as a possible factor modulating the response of boreal forests to summer temperatures. Climatic signal does not differ between pairs of chronologies based on subsets of cambial ages, stem dimensions or tree competition status at the treeline site. However, the response to summer temperatures one year before tree-ring formation is significant only in mature (old, large and dominant) individuals at the closed-canopy site. The inverse pattern of temperature-growth correlations during a sequence of three years challenges predictions of how boreal forests respond to climate change.

Ecological effects and effectiveness of silvicultural restoration treatments in whitebark pine forests

Silvicultural thinning treatments to restore whitebark pine (Pinus albicaulis) are widely used in subalpine forests throughout the western United States (US) and Canada. The objectives of these treatments are to (1) improve the condition of whitebark pine at all ages, (2) to improve seedling recruitment processes, and (3) mitigate the damage caused by mountain pine beetle (MPB; Dendroctonus ponderosae) and white pine blister rust (WPBR; caused by the fungus Cronartium ribicola). However, there is some disagreement about the ecological basis of restoration and a paucity of information on the effects these activities – few treatments have been monitored to assess their success. We investigated the ecological effects of silvicultural restoration treatments in whitebark pine forests and evaluated their success by retrospectively sampling five treatment sites in the western US 6–10 years after implementation. We found strong evidence of growth release at a site previously characterized by closed-canopy stands. Growth responses in more open, park-like stands, however, were variable: we found weak growth increases at one site, weak growth decreases at another and no response at two other sites. At the site with strong growth increases, trees with previous damage from WPBR infection had growth increases similar to uninfected trees. We found low rates of whitebark pine seedling recruitment overall, and no increase in whitebark pine recruitment associated with treatments at any site. However, at one site, treated stands had higher regeneration of non-target species than did untreated stands. Post-treatment mortality (mostly from the late 2000s MPB outbreak) was significantly lower in the treated stand at the closed-canopy site; at the other sites, there was no difference in mortality between treated and untreated stands. The treatments had little detectable effect on short-term growth-climate relationships, although our analyses revealed that whitebark pine growth at our sites was more temperature limited than water limited. While some management goals were achieved, many were not, and there were some unintended consequences. Our results call for a closer examination of the ecological basis of silvicultural restoration treatments in whitebark pine and an expanded use of adaptive management.

Do disturbance and periphyton productivity affect stream invertebrate traits?

Disturbance in lotic ecosystems strongly influences which animals can survive and how those ecosystems function. Flow disturbances physically remove animals and periphyton, but it is unclear whether physical removal of individuals or the loss of food is the principal driver of effects of flow disturbances on invertebrate communities. Invertebrates possess traits that help them withstand high flows or recolonize rapidly after floods. At light-limited, closed-canopy sites, periphyton biomass should be unaffected by disturbances, so disturbance should affect invertebrate community trait composition by direct removal of animals. At open-canopy sites, disturbance should affect trait composition by both removing individuals and reducing periphyton food resources. We investigated whether a trait-based approach could elucidate drivers of effects of flow disturbance on benthic invertebrate communities and better identify potential mechanistic linkages. We sampled 10 autotrophic streams that differed in substrate-disturbance regime and varied from 100 to 0% canopy cover. We sampled 2 sites per stream, 1 in forest (closed-canopy) and 1 downstream in low-intensity agricultural grassland (open-canopy). Regardless of canopy, in streams with greater substrate disturbance, the proportion of individuals that respired with a plastron increased and proportions of individuals having 2 aquatic life stages or that were filter-feeders decreased. At open-canopy sites, the proportion of collector–gatherers with flattened bodies increased with increased substrate disturbance and decreased periphyton biomass, and the proportion of taxa having high body flexibility and 2 aquatic life stages increased with decreased substrate disturbance and increased periphyton biomass. Trait composition of these mountain stream invertebrate communities is strongly influenced by physical removal via substrate movement and by reduced periphyton resources.

The effect of land cover type and structure on evapotranspiration from agricultural and wetland sites in the Sacramento–San Joaquin River Delta, California

Water is a limited and valuable resource in California. A large proportion of the fresh water for southern California is supplied by the Sacramento and San Joaquin rivers. With recent efforts to restore large areas of land in the Sacramento–San Joaquin Delta region from farmland to managed wetlands, it is important to investigate the effect of wetland restoration on the local water cycle. We measured evapotranspiration using the eddy covariance method over six different sites in the Sacramento–San Joaquin Delta from 2013 to 2016. The three restored wetlands sites differed in time since restoration and wetland structure, i.e. the area of open water compared to closed vegetation. The three agricultural sites were a flooded rice field, an alfalfa field, and a grazed cattle pasture. In most years, annual evapotranspiration was significantly lower at the drained agricultural sites, with 652 ± 131 mm (2 year average ± standard deviation, SD) for the pasture and 901 ± 24 mm (3 year average ± SD) for the alfalfa field, compared to the two open water wetlands, with 1091 ± 144 mm (4 year average ± SD) for the Mayberry wetland and 1140 ± 67 mm (3 year average ± SD) at the East End wetland. Annual evapotranspiration at the flooded rice site (975 ± 50 mm, 4 year average ± SD) or the closed vegetation wetland (West Pond wetland, 996 ± 63 mm, 4 year average ± SD) was not significantly different from the drained alfalfa site across individual years. Our analysis showed that the structural difference between the wetlands, specifically the fraction of open water compared to closed vegetation, has a large impact on evapotranspiration dynamics. Through analysis of normalized equilibrium evaporation and nighttime evapotranspiration measurements we deduced that evapotranspiration at the wetland with a low fraction of open water surfaces was almost entirely dominated by plant transpiration with very little contribution from evaporation, despite the fact that the site was flooded and water was readily available. Both evaporation and transpiration contributed substantially to evapotranspiration at the two wetlands with larger fraction of open water surfaces. At the closed canopy site evaporation from subcanopy water seemed to be inhibited through two mechanisms: first, the closed canopy prevented heating of the water column and led to significantly cooler water temperatures, which reduced surface vapor pressure. Second, the closed canopy decoupled the water surface from the atmosphere and inhibited turbulent transport of water vapor away from the water surface. Our results provide valuable insights into the water use in California wetlands and can inform decisions on how to maximize water conservation during wetland restoration.

ROLE OF ANTHROPOGENIC CANOPY GAPS ON NATURAL REGENERATION PATTERN OF MONOSPECIFIC CERIOPS TAGAL IN RAKAWA LAGOON, SRI LANKA

Mangroves are distinctly dominated in tropical and subtropical areas as special kind of trees, palms, shrubs, vines and ferns. Ceriops tagal is one kind of mangrove species which shows monospecific distribution in Rakawa lagoon in Sri Lanka. There are certain factors which influence the natural regeneration pattern of Ceriops tagal. Light intensity is one of the factors which penetrates through canopy gaps and regulates the growth of seed, seedling and sapling and these canopy gaps are resulted mainly due to anthropogenic canopy eradication. However, the studies on the influence of man-made canopy gaps on natural regeneration pattern of mangroves are limited in Sri Lanka. Therefore, current study was carried out in Rakawa Lagoon in July 2014 to estimate the regeneration pattern of Ceriops tagal by the means of mean seedling, sapling densities and live and dead seed densities in open canopy sites with regard to closed canopy sites. Finally, to compare the mean density values of Seedling plus sapling obtained in July 2013 to get the overall knowledge on the effect of canopy gap on regeneration pattern of Ceriops tagal. Consequently mean density of seedling plus sapling were taken as regeneration class 1 and height of seedlings and saplings and the number of live and dead seeds were documented from randomly selected three homogenous plots ,(4m2 x 3) from open canopy sites and three homogenous plots (4m2 x 3) from closed canopy sites. Two –Sample T- test and Paired T-test of “MINITAB 16 software” were used to analyze and compare the data. Mean density of regeneration class 1 in open canopy sites was significantly higher p=0.02 (p<0.05) than closed canopy sites. Hence canopy gaps play major role in enhancing the natural regeneration and increasing the survivability of Ceriops tagal species. Output of this study can be used for mangroves conservation in Sri Lanka.

Contribution of soil fauna to the degradation of recalcitrant components in Cinnamomum camphora foliar litter in different-sized gaps in Pinus massoniana plantations

Forest gaps are important in forest dynamics and management, but little is known about how soil fauna influence the degradation of recalcitrant litter components in different-sized forest gaps. This investigation uses litterbags with two different mesh sizes (0.04 and 3 mm) to control the meso- and microfauna entering the bags to quantify the contribution of soil fauna to the degradation of recalcitrant components (including condensed tannins, total phenol, lignin and cellulose) during litter decomposition. The experiment was conducted in seven different forest gap sizes in Pinus massoniana plantations over 1 year. One closed-canopy site (CC) and forest gap sizes of 100, 225, 400, 625, 900, 1225 and 1600 m2 were created in a P. massoniana plantation in the Sichuan basin of China; the CC was treated as the control. Cinnamomum camphora foliage from local native trees was used in all forest gap experiments. We found the following: (1) Gap size had significant effects on the degradation rates (E) of condensed tannins and lignin and on the contributions of soil fauna; medium-sized gaps also presented high degradation rates. Soil fauna obviously contributed to the degradation of recalcitrant foliar litter components in medium-sized gaps. (2) The highest contribution to degradation (40.98%) was recorded for lignin, and the lowest contribution (0.29%) was recorded for condensed tannins. The results indicate that medium-sized gaps (900 m2) were conducive to the degradation of recalcitrant litter components by soil fauna.

Forest canopy, water level, and biopesticide interact to determine oviposition habitat selection in Aedes albopictus.

Understanding how interacting abiotic and biotic factors influence colonization rates into different habitat types is critical for both conserving and controlling species. For example, the rapid global spread of Asian tiger mosquitoes, Aedes albopictus, has reduced native species abundances and produced disease outbreaks. Fortunately, bacterial endospores of two Bacillus species (biospesticide) are highly lethal to Ae. albopictus larvae and have been commercially developed to reduce populations. Oviposition habitat selection is the first defense Ae. albopictus females possess against any control substance added to breeding sites, and considerable variation exists in their response to biopesticides. In a field experiment, I crossed the presence/absence of biopesticides, with two canopy (open, closed) and water (high, low) levels at 64 breeding sites, to examine if these interacted to influence oviposition site choice. Avoidance of biopesticide was most pronounced in closed canopy sites and those with low water levels, as all main effects and two-way interactions influenced oviposition. Oviposition habitat selection represents a possible mechanism of resistance to biopesticides and other methods used to kill mosquito larvae. Future experiments examining how larval density and mortality modify these results should allow for more effective control of this highly invasive species.

Successful translocation of the threatened New Zealand root-holoparasite Dactylanthus taylorii (Mystropetalaceae)

The conservation and translocation of threatened holoparasitic flowering plants provide added challenges due to their complete host dependency and often large knowledge gaps of their autecology. Here, we present the first successful, quantified field trial to establish from seed populations of dactylanthus (Dactylanthus taylorii, Mystropetalaceae), a threatened New Zealand endemic root-holoparasitic angiosperm. Establishment was monitored at four sites at Waipapa, Pureora Forest Park. The impact of two different sowing methods (broad- and central-sown), canopy state (as a proxy for soil moisture levels) and three dominant host species were tested. Establishment of dactylanthus was confirmed in 22 out of 24 plots 10 years after sowing, with earliest emergence after 4 years. Average and maximum inflorescence numbers per plot were similar to those of protected wild populations. The only open-canopy site performed worse in comparison with a closed-canopy site sharing the same dominant host species; differences in root availability and survival of the desiccation-sensitive seeds were regarded as the most likely explanations. Host species dominance had a significant impact on inflorescence numbers, indicating host preference in the species despite a wide host range. In contrast to longer-established wild populations, most of which are male-biased, female inflorescences strongly outnumbered males, considered as evidence of environmental sex determination and sex-switching of individuals. Findings from this study have increased our knowledge of the biology of dactylanthus, confirmed translocation as an effective tool in the conservation of the species and should be applicable for the protection of threatened parasitic plants species elsewhere in the world.

Gastropods shell utilization among hermit crabs targeted by bait fishers along a tropical mangrove fringed creek, Mida, Kenya

Mangrove gastropods and hermit crabs are frequently harvested for use as bait by artisanal trap and hook fishers, along the Kenyan coastline and elsewhere. In addition to mangrove degradation, the harvesting of shelled invertebrates, can alter shell availability and hence survival of these interdependent fauna. This study compares shell morphometric characteristics such as shell availability, adequacy and bait yield, among sites with different patterns of bait harvesting and other human disturbances. Shell morphometrics are also related to mangrove forest stand characteristics such as forest complexity, dominance, cutting intensity and sapling regeneration. Results indicate that the sampling regime, hermit crab taxa and mangrove zone influence morphometric characters of the gastropod and hermit crab. Significantly higher (P < 0.001) shell availability, adequacy and bait yield of the predominant hermit crab, Clibanarius danai, are recorded at upper and mid forested zones of sites with robust forest. This was attributed to shell selectivity of the crab, coupled with constancy of the environment at closed canopy sites. Apparently, forest structure is an important determinant of shell utilization patterns compared to prevailing bait harvesting activity. Protection of robust upper mangrove forest zones may therefore enhance sustainability of shelled bait harvesting and consequently the livelihoods support emanating from bait fishery.

Regeneration of Abies pinsapo within gaps created by Heterobasidion annosum-induced tree mortality in southern Spain

We explored the effects of tree-fall gaps caused by Heterobasidion annosum-induced tree death on the regeneration of the relict Abies pinsapo in southern Spain. We analyzed the structure and regeneration of A. pinsapo in 44 circular closed-canopy plots and 11 gaps (mean size 75 m2) located in H. annosum infection foci. We measured adult density, basal area, and height of all tree species with a diameter at breast height greater than 7.5 cm and quantified regeneration abundance. Diameter structures were analyzed using Weibull functions. A. pinsapo comprised 49-81% of total adult tree density (358-1418 trees ha-1) and total basal area (15.70-39.22 m2 ha-1). Density of A. pinsapo juveniles ranged from 129 to 416 individuals ha-1, while that of juveniles of other tree species such as Quercus ilex was much lower. A. pinsapo saplings and seedlings were more abundant within gaps than in closed-canopy sites. A. pinsapo regeneration was related to the tree species composition of the stands adjacent to gaps. The main potential species replacing A. pinsapo in H. annosum-induced gaps were, in decreasing order of importance, Quercus ilex, Q. faginea, and Juniperus oxycedrus. The current stand structure and gap-infilling processes suggest that A. pinsapo regenerates adequately within H. annosum-induced gaps. However, the relative proportion of other coexisting tree species within H. annosum-related gaps will increase substantially over time as compared with closed-canopy areas.

More cells, bigger cells or simply reorganization? Alternative mechanisms leading to changed internode architecture under contrasting stress regimes

Shading and mechanical stress (MS) modulate plant architecture by inducing different developmental pathways. Shading results in increased stem elongation, often reducing whole-plant mechanical stability, while MS inhibits elongation, with a concomitant increase in stability. Here, we examined how these organ-level responses are related to patterns and processes at the cellular level by exposing Impatiens capensis to shading and MS. Shading led to the production of narrower cells along the vertical axis. By contrast, MS led to the production of fewer, smaller and broader cells. These responses to treatments were largely in line with genetic differences found among plants from open and closed canopy sites. Shading- and MS-induced plastic responses in cellular characteristics were negatively correlated: genotypes that were more responsive to shading were less responsive to MS and vice versa. This negative correlation, however, did not scale to mechanical and architectural traits. Our data show how environmental conditions elicit distinctly different associations between characteristics at the cellular level, plant morphology and biomechanics. The evolution of optimal response to different environmental cues may be limited by negative correlations of stress-induced responses at the cellular level.

EFFECT OF CANOPY GAPS A'ND TOPOGRAPHIC REGIMES IN SEEDLINGS PERFORMANCE IN SINHARAJA RAIN FOREST, SOUTHWEST SFU LANKA

Growth and survival of tree canopy dominant seedlings in the Sinharaja lowland rain forest insouthwest Sri Lanka were monitored. Twelve canopy gaps and closed canopy sites wereselected, as four of each on different topographic positions- valley, midslope and ridgetop.Measurements of height, number of leaves and mortality were recorded over a two-year period.Hemispherical canopy photographs were taken to calculate Indirect Site Factor (ISF), Direct SiteFactor (DSF), and canopy openness. Greatest canopy openness, highest DSF values wererecorded for ridgetop sites and smallest values were recorded for valley sites. Over the two-yearperiod sixty-six (11.45%) seedlings died in the ridge top, which indicated the highest mortalityrate. Survival of seedlings in the canopy gap ani .orest understorey declined on progressingfrom valley to ridgetop sites. Seedlings of Mesua ferrea had a higher survival than other speciesin the canopy opening and understorey conditions. Height growth and leaf number were greatestin the gap sites. A significant relationship was found between DSF and maximum height growth(33.05,P&gt;O.OO) for Syzygium rubicundum. Shorea trapezlfolta, Shorea distich a and Syzygiumrubicundum showed greatest height increment .n the valley, midslope and ridgetop sitesrespectively. No relationship was found between DSF and leaf numbers in all seedlings exceptSyzygium rubicundum, where has increased with increasing DSF.

Disease risk in temperate amphibian populations is higher at closed-canopy sites.

Habitat loss and chytridiomycosis (a disease caused by the chytrid fungus Batrachochytrium dendrobatidis - Bd) are major drivers of amphibian declines worldwide. Habitat loss regulates host-pathogen interactions by altering biotic and abiotic factors directly linked to both host and pathogen fitness. Therefore, studies investigating the links between natural vegetation and chytridiomycosis require integrative approaches to control for the multitude of possible interactions of biological and environmental variables in spatial epidemiology. In this study, we quantified Bd infection dynamics across a gradient of natural vegetation and microclimates, looking for causal associations between vegetation cover, multiple microclimatic variables, and pathogen prevalence and infection intensity. To minimize the effects of host diversity in our analyses, we sampled amphibian populations in the Adirondack Mountains of New York State, a region with relatively high single-host dominance. We sampled permanent ponds for anurans, focusing on populations of the habitat generalist frog Lithobates clamitans, and recorded various biotic and abiotic factors that potentially affect host-pathogen interactions: natural vegetation, canopy density, water temperature, and host population and community attributes. We screened for important explanatory variables of Bd infections and used path analyses to statistically test for the strength of cascading effects linking vegetation cover, microclimate, and Bd parameters. We found that canopy density, natural vegetation, and daily average water temperature were the best predictors of Bd. High canopy density resulted in lower water temperature, which in turn predicted higher Bd prevalence and infection intensity. Our results confirm that microclimatic shifts arising from changes in natural vegetation play an important role in Bd spatial epidemiology, with areas of closed canopy favoring Bd. Given increasing rates of anthropogenic habitat modification and the resulting declines in temperate and tropical frogs, understanding how vegetation cover and disease interact is critical for predicting Bd spread and developing appropriate management tools for wild populations.