The role of germination microsite in the establishment of sugar pine and Jeffrey pine seedlings

Mature shrubs can provide microhabitats that are beneficial to tree seedling growth and development. Sugar pine trees (Pinus lambertiana) grow in a narrow zone on the eastern slope of the Carson Range in extreme western Nevada, whereas Jeffrey pine (Pinus jeffreyi) is the dominant tree species in the region, an area extensively disturbed by wild fire. This study compares seedling establishment of sugar pine and Jeffrey pine relative to mature shrubs. In the fall of 2002 (cohort 1) and 2003 (cohort 2), 13,600 seeds of both species were planted in wire mesh enclosures, at three sites, under a variety of microhabitat treatments: under shade and in the open, under two species of shrub cover, and with and without plant litter. Seedlings were monitored for survival through two growing seasons. Even though more sugar pine seedlings emerged, more Jeffrey pine seedlings survived, and Jeffrey pine was the more drought tolerant species, better suited for the xeric climate found in the Carson Range. Litter slightly hindered seedling emergence but had no effect on survival and there was no significant species × litter interaction. Supplemental water facilitated survival in all treatments with highest survival in shade treatments. Sugar pine seedlings showed a significant increase in survival over Jeffrey pine seedlings with the addition of water, particularly in open treatments and more of both species survived under manzanita shrubs with water. The highest seedling mortality occurred when shrub canopy was removed, and seedlings experienced the effect of full sun and competition for soil water. For either species, microhabitat is a significant factor in determining success or failure in rehabilitation efforts after disturbance.     

A test of the hierarchical model of habitat selection using eastern massasauga rattlesnakes (Sistrurus c. catenatus)

Understanding the process animals follow to select habitat, rather than just documenting the habitat they use, will improve our ability to predict how the animals use habitat in other locations and how they will respond to changes in habitat. Animals are usually assumed to select habitats hierarchically, preferentially using specific macrohabitats at a landscape scale and specific microhabitats within the preferred macrohabitats. We used four years of telemetry data from 34 individuals to test this hierarchical model of habitat selection with eastern massasauga rattlesnakes (Sistrurus c. catenatus) in Ontario. Snakes were selective at the microhabitat scale, preferentially using locations with closer retreat sites and shrubs than random. Gravid females were most selective, using sites with more rock cover and less canopy closure than sites used by males and nongravid females. Snakes preferred forested habitats for hibernation and steadily increased their use of open, wetland, and edge habitats to a peak in mid-summer. Landscape-scale habitat preferences were generally mild and could be explained by the relative availability of suitable microhabitat within habitats, suggesting habitat selection was primarily driven by microhabitat preferences. The lack of selectivity at the landscape scale may be a consequence of fine-grained differences between habitats that allow massasauga rattlesnakes to find suitable microhabitats in all available macrohabitats. For species that select habitat primarily at the microhabitat scale (e.g., the rattlesnakes we studied), landscape-scale modeling of habitat use will only be effective to the extent habitats reflect the availability of suitable microhabitat within.     

Microhabitat use of wood mice ranging from a reserved belt with evergreen broad-leaved trees to a coniferous plantation

Wood mice Apodemus speciosus and Apodemus argenteus are potentially important seed dispersers and predators of Quercus and Castanopsis in Japan. We investigated the existence of two species of wood mice in warm-temperate forests ranging from a reserved belt of evergreen broad-leaved trees to a coniferous plantation, and analyzed the relationship between wood mouse occurrence and environmental factors to confirm their microhabitat use. We used two-way analysis of variance to analyze differences in the captured number of each wood mouse species in two trapping seasons as well as two stand types to confirm the interaction between the stand type and trapping season. Apodemus speciosus were often captured in the reserved belt, while captures of A. argenteus were independent of season and stand types. It is reasonable to conclude from the results of the trends in occurrence that the two species of wood mice showed different uses of the microhabitat. The result of linear discriminant analysis made it clear that the distance from the reserved belt had much to do with the difference in microhabitat use between the two species in the fruiting season of Quercus and Castanopsis. On average, A. speciosus moved 19.9 m during nonfruiting and 61.3 m during fruiting, while A. argenteus moved 8.1 m during nonfruiting, and 29.0 m during fruiting from analysis of the recapture position. The results indicate that both species of mice move around during the fruiting season more than in the nonfruiting season.     

Distribution and population patterns of the threatened palm Brahea aculeata in a tropical dry forest in Sonora, Mexico

The use of non-timber forest products (NTFPs) has great potential for the conservation of natural resources and rural development. Palms are important NTFPs, providing numerous products, including leaves. The harvest of palm leaves rarely results in the immediate death of individuals and can be considered one example of the sustainable use of forest resources. However, in most cases basic ecological information, such as distribution and abundance of the species is unknown, as is information on the ecological implications of human impacts, such as leaf harvest and livestock grazing. In the tropical dry forests of northwest Mexico, leaves from the threatened palm Brahea aculeata are harvested for roofing material and represent an important NTFP. In this study, we assessed the distribution and abundance patterns of this species across 52 plots in the tropical dry forest of Sierra de Álamos-Rio Cuchujaqui Reserve (SARCR) in Sonora, Mexico. We also evaluated patterns of leaf harvest and cattle browse intensity on palm populations. We found that B. aculeata density is highly variable across the landscape with a mean (±SE) of 121.7 ± 36.3 ha⁻¹. Results indicate that B. aculeata is primarily distributed near to arroyos and rivers. The highest densities were found in sites with low incidence radiation (<0.06 MJ cm⁻²) and narrow stream width of arroyos/rivers (<9.5 m). Palm abundance also varied within the plots, and B. aculeata attained its highest densities near to the arroyo edge (first 20 m from the edge), perhaps indicating a microhabitat effect on palm demography. Overall, fewer than 6% of the stems were seedlings. Leaf harvesting and browsing appear to affect demographic vital rates of the species; specifically we found a significant effect of harvesting and browsing activity on the proportion of reproductive active adults. Thus, low levels of seedlings in the populations may be the result of reduced fruit production by adults and higher mortality rates of seedlings due to livestock herbivory. Result from interviews with land owners also indicated that past land use, especially along arroyos might also have important impacts on the observed distribution, low densities and absence of recruitment in some areas. We believe current distribution and abundance of NTFP, such as B. aculeata at SARCR may be a result of combined effects of environmental factors and human impacts. Results from this study will be used to develop appropriate conservation, management and restoration plans of B. aculeata in the area.     

Effects of microhabitat diversity and geographical isolation on oribatid mite (Acari: Oribatida) communities in mangrove forests

The effects of microhabitat diversity and geographical isolation on the structure of oribatid communities were studied in mangrove forests on the Ryukyu Islands of Japan. The study took place at three sites on two islands 470 km apart. Oribatid mites (Oribatida) were extracted from leaves, branches, bark of trunks (0-50, 50-100, and 100-150 cm high) and of knee roots, and from forest-floor soil and littoral algae, each defined as a microhabitat of oribatid mites. At the 0-50 cm height, the species composition of the oribatid communities on the knee-root bark and the bark of trunks of Bruguiera gymnorrhiza differed significantly from that on the other microhabitats. This difference was attributed to tidal flooding of the mangrove forests. Cluster analysis showed that oribatid communities in the same microhabitat at different sites tended to be more similar than those on different microhabitats at the same site. This implies that the species composition of oribatid communities in mangrove forests is more likely to be affected by factors responsible for microhabitat diversity (characterized specifically by the flooded trunks) than by geographical distance between the islands.     

Spatial distribution of regeneration in West-Carpathian uneven-aged silver fir forests

The objective of our study was to examine whether distribution of regeneration in uneven-aged fir (Abies alba Mill.) forests is related to the spatial pattern of trees. In 12 sample plots of size 0.45–1.00 ha (in total 8.65 ha, with stand basal areas ranging from 27.6 m² ha^–1 to 39.5 m² ha^–1), all live and dead trees above 5 cm in d_1.3 were mapped and their diameters measured. In eight plots, all live and dead fir saplings were mapped. In three plots, the number of live fir saplings and seedlings was registered on small systematically distributed circular plots. The values of an analytically developed index of stand influence were compared in patches occupied and unoccupied by live or dead fir regeneration. Contrary to preliminary assumptions, only in a few cases did saplings and trees 5–15 cm in d_1.3 appear more often in gaps and looser stand patches. Rather, in many plots, the opposite tendency was observed. The seedling density showed a weak but positive correlation with the index of influence. If the spatial pattern of regeneration reflects the spatially varying mortality of juvenile trees, then no evidence was found that stand competition was the most important factor inducing this mortality. On the contrary, on the basis of the results obtained, we can presume that the survival rate of juvenile firs was higher in patches with a relatively higher local basal area. Thus, it was hypothesised that, first, dispersion of regeneration in uneven-aged fir forests is controlled by easy-to-change edaphic factors such as humus form and acidity of the upper soil horizons, and second, that these soil features are linked with the spatial pattern of trees.     

Enhancing stocks of the exploited limpet Patella candei d’Orbigny via modifications in coastal engineering

It is widely recognised that microhabitats are important for a variety of marine organisms, yet this knowledge has rarely been applied in the construction of engineered structures as a means of enhancing biodiversity or populations of species at risk. Here we examined the influence of microhabitats on the distribution and survival of the exploited limpet Patella candei on natural shores before determining the effect of introducing such habitats to an artificial seawall. On natural shores individuals were associated with pits (a natural feature of volcanic rocky shores). Animals inhabiting pits showed reduced mortality and were smaller than those on open rock. Microhabitat utilisation was similar over the vertical range of distribution of P. candei. Following observation of natural patterns, we applied this knowledge by experimentally drilling pits at varying densities and sizes in a seawall that had been constructed with simple topographical complexity. Overall, the number of animals increased in areas with experimentally increased microhabitat area. There was evidence that this was the result of immigration (larger animals) but also of increased recruitment. This study demonstrates one cost-effective way of conciliating the need to protect our coastlines while promoting the conservation and stock enhancement of over-exploited species.     

Variation between mite communities in Irish forest types – Importance of bark and moss cover in canopy

Extensive afforestation took place in Ireland during the twentieth century and the forest cover currently represents about 10% of the land area. However, approximately 50% of this forest is Sitka spruce, a non-native species introduced from the North Western United States of America. Little is known about the microarthopods of these forests and the current study examined the mites (Oribatida and Gamasina) occurring in the canopy, moss (both on the soil surface and in the canopy) and soil of oak, ash, Scots pine and Sitka spruce forests in Ireland to compare the mite assemblages in each and to determine the associations between forest type and the form of constituent microhabitats in determining the structure of this fauna. There were significant differences between the diversity and species composition of the assemblages in the different forest types with the largest species richness occurring in oak forest and the smallest in first rotation Sitka spruce forest. Analysis of our data, together with the results from other studies, suggest that the differences arise because the variation between the architecture of the tree species is reflected in the structure of microhabitats such as the form of the bark and the extent of moss cover. Thus while the ultimate factors affecting the variation in the mite fauna may be the form of the microhabitats, these are intrinsic properties of the forests associated directly with the species of tree. Finally, our results do not support the view that exotic species will necessarily have low biodiversity of mites than native forests.     

Lizard microhabitat and fire fuel management

For many species, dead vegetation is important microhabitat necessary for survival and reproduction. We compared the use of three categories of trees: living, dead standing and dead prone, within and among four species of phrynosomatid lizard (Sceloporus undulatus, Sceloporus graciosus, Urosaurus ornatus, and Uta stansburiana) on the Colorado Plateau during 1990, 1992 and 2000. All four species used dead trees (both prone and standing) more frequently than live trees, despite an opposite pattern of availability. U. ornatus used dead standing more often than dead prone trees, reflecting this lizard's arboreal nature. Tree use did not differ among lizard species, and the lizard species by tree category interaction was not significant. Current policy mandates the removal of dead vegetation and debris on US Federal lands as basic maintenance in order to decrease fire risk. Active removal of “fuel” may limit the local distribution, abundance, and diversity of these lizards, which include dead trees in their microhabitat for shelter, perching, foraging, courting, and defending territories.     

Natural regeneration of Picea abies on small clear-cuts in SE Norway

The objective was to study the influence of vegetation cover, humus depth, microrelief and distance to seed tree edge on natural regeneration of Norway spruce (Picea abies (L.) Karst.) in five small clear-cuts on bilberry woodland in southeastern Norway. The impact of the vegetation was considered at tree different scales: at the growing point, in the nearest square decimetre around the seedlings and at a 1 m² scale. Most of the regeneration (95%) developed in 1996, after a rich seed year in 1995. The microhabitat was of crucial importance to seedling establishment. Litter, Sphagnum spp. and Polytrichum commune were good substrates for establishment, while areas dominated by Deschampsia flexuosa, Dicranum spp. and Pleurozium schreberi had very few seedlings. Seedling survival after five growing seasons was slightly better in litter than in Sphagnum and other mosses, but the differences were not statistically significant. Increasing humus depth had a positive influence on regeneration, probably due to shallow soils at the sites. Even though depressions covered only 4.9% of the ground, 24.1% of the seedlings occurred here. Survival was, however, lower in depressions than in the other microrelief classes. Distance to the seed tree edge had a significant influence on establishment, with more seedlings establishing close to the edge.