Resilience of a eucalypt forest woody understorey to long-term (34–55 years) repeated burning in subtropical Australia

We investigated the effects of annual burning since 1952, triennial burning since 1973, fire exclusion since 1946 and infrequent wildfire (one fire in 61 years) on woody understorey vegetation in a dry sclerophyll eucalypt forest, south-eastern Queensland, Australia. We determined the influence of these treatments, and other site variables (rainfall, understorey density, topsoil C : N ratio, tree basal area, distance to watercourse and burn coverage) on plant taxa density, richness and composition. The richness of woody understorey taxa 0–1 m in height was not affected by burning treatments, but richness of woody plants 1–7.5 m in height was lower in the annually burnt treatment than in the triennially burnt treatment from 1989 to 2007. Fire frequency and other site variables explained 34% of the variation in taxa composition (three taxon groups and 10 species), of which 33% of the explained variance was explained by fire treatment and 46% was explained by other site variables. Annual burning between 1974 and 1993 was associated with lower understorey densities mainly due to reduced densities of eucalypts 1–7.5 m in height. Triennial burning during the same period was associated with higher densities of eucalypts 0–7.5 m in height relative to the annually burnt and unburnt treatments. Most woody taxa persisted in the frequently burnt treatments through resprouting mechanisms (e.g. lignotuberous regeneration), and fire patchiness associated with low-intensity burning was also found to be important. Persistence of plants <1 m tall demonstrates the resilience of woody taxa to repeated burning in this ecosystem, although they mainly exist in a suppressed growth state under annual burning.

Effects of recreational use and fragmentation on the understorey vegetation and soil microbial communities of urban forests in southern Finland

The impacts of fragmentation and recreational use on the hemiboreal urban forest understorey vegetation and the microbial community of the humus layer (the phospholipid fatty acid (PLFA) pattern, microbial biomass and microbial activity, measured as basal respiration) were examined in the greater Helsinki area, southern Finland. Trampling tolerance of 1) herb-rich OMT, 2) mesic MT, and 3) sub-xeric VT forests (in decreasing order of fertility) was studied by comparing relative understorey vegetation cover (urban/untrampled reference ratio) of the three forest types. The trampling tolerance of forest vegetation increased with the productivity of the site (sub-xeric < mesic < herb-rich). Wear of understorey vegetation correlated positively with the number of residents (i.e., recreational pressure) around the forest patch. An increase of 15000 residents within a radius of 1 km around a forest patch was associated with ca. 30% decrease in the relative understorey vegetation cover. The cover of dwarf shrub Vaccinium myrtillus in particular decreased with increasing levels of wear. The cover of mosses in urban forests was less than half of that in untrampled reference areas. Cover of tree saplings, mainly Sorbus aucuparia, and some resilient herbs was higher than in the reference areas. In small urban forest fragments, broad-leaved trees, grasses and herbs were more abundant and mosses were scarcer than in larger urban forest areas. Thus, due to trampling and edge effects, resilient herb and grass species are replacing sensitive dwarf shrubs, mosses and lichens in urban forests. Differences in the soil microbial community structure were found between paths and untrampled areas and the effects of paths extended more than one meter from the paths. Paths supported approximately 25-30% higher microbial biomass with a transition zone of at least 1 m from the path edge. However, microbial activity per unit of biomass was lower on paths than in untrampled areas. Furthermore, microbial biomass and activity were 30-45% lower at the first 20 m into the forest fragments, due to low moisture content of humus near the edge. The decreased microbial activity detected at forest edges and paths implies decreased litter decomposition rates, and thus, a change in nutrient cycling. Changes in the decomposition and nutrient supply may in turn affect the diversity and function of plant communities in urban forests. Keywords: boreal forest vegetation, edge effects, phospholipid fatty acids, trampling, urban woodlands, wear

Disturbance in boreal spruce forest - immediate dynamics from stand to understorey level

The immediate effects of two human-related vegetation disturbances, (1) green tree retention (GTR) patch felling and scarification by harrowing and (2) experimental understorey vegetation layer removal, were examined in boreal forest stands in Finland. Effects of GTR patch felling and scarification on tree uprootings, on coarse woody debris (CWD) and on epixylic plant community were followed in upland and in paludified forest types. Uprootings increased considerably during 2-3 years after the fellings and were more frequent (47%) in the paludified than in the upland forest (13%). Scarification reduced 68% of the CWD in the felling area. Cover and especially species richness of epixylics declined in the both areas during 1-2 years after the felling. The increasing size of GTR patch correlated positively with the species richness. Regeneration of understorey vegetation community and Vaccinium myrtillus and Vaccinium vitis-idaea after different removals of vegetation layers in an old-growth forest took four years. The regeneration occurred mainly by vegetative means and it was faster in the terms of species richness than in the cover. In the most severe treatment, recovery occurred merely by sexual reproduction. V. myrtillus recovered mainly by producing new shoots. V. vitis-idaea recovered faster than V. myrtillus, mainly by increasing length growth. For ecological reasons, use of larger GTR patches on paludified biotope would be recommendable. In felling areas, scarification by harrowing could be replaced with some other spot-wise method. After moderate intensity level disturbance, recovery occurs rapidly by vegetative regrowth of the dominating species. High level of intensity may prevent the recovery of vegetation community for years, while enabling also the genetic regeneration of the initial species. Local anthropogenic-related disturbances are currently increasing and they can interact during temporally short times, which should be taken in to account in the future forest management plans.

Evaluation of methods to estimate foliage density in the understorey of a tropical evergreen forest

Foliage density and leaf area index are important vegetation structure variables. They can be measured by several methods but few have been tested in tropical forests which have high structural heterogeneity. In this study, foliage density estimates by two indirect methods, the point quadrat and photographic methods, were compared with those obtained by direct leaf counts in the understorey of a wet evergreen forest in southern India. The point quadrat method has a tendency to overestimate, whereas the photographic method consistently and ignificantly underestimates foliage density. There was stratification within the understorey, with areas close to the ground having higher foliage densities.

Understorey vegetation as an indicator of forest site potential in Southern Finland.

The relationship between site characteristics and understorey vegetation composition was analysed with quantitative methods, especially from the viewpoint of site quality estimation. Theoretical models were applied to an empirical data set collected from the upland forests of southern Finland comprising 104 sites dominated by Scots pine (Pinus sylvestris L.), and 165 sites dominated by Norway spruce (Picea abies (L.) Karsten). Site index H100 was used as an independent measure of site quality. A new model for the estimation of site quality at sites with a known understorey vegetation composition was introduced. It is based on the application of Bayes' theorem to the density function of site quality within the study area combined with the species-specific presence-absence response curves. The resulting posterior probability density function may be used for calculating an estimate for the site variable. Using this method, a jackknife estimate of site index H100 was calculated separately for pine- and spruce-dominated sites. The results indicated that the cross-validation root mean squared error (RMSEcv) of the estimates improved from 2.98 m down to 2.34 m relative to the "null" model (standard deviation of the sample distribution) in pine-dominated forests. In spruce-dominated forests RMSEcv decreased from 3.94 m down to 3.16 m. In order to assess these results, four other estimation methods based on understorey vegetation composition were applied to the same data set. The results showed that none of the methods was clearly superior to the others. In pine-dominated forests, RMSEcv varied between 2.34 and 2.47 m, and the corresponding range for spruce-dominated forests was from 3.13 to 3.57 m.

The extended phenotype of Scots pine Pinus sylvestris structures the understorey assemblage

Heritable variation in plant secondary compounds in dominant species has been hypothesised to effect ecosystem function and the structure of associated assemblages of plants, microbes and animals. The functioning of this extended phenotype in relation to the understorey vegetation composition was tested within a boreal forest system dominated by Pinus sylvestris which contains a range of monoterpenes, the composition of which is largely under genetic control. A variance partitioning approach was adopted to identify the relative importance of tree chemistry, environment, spatial location and tree architecture in controlling the distribution of species in the ground flora under individual trees. The monoterpene composition of the pine needles appeared to contribute significantly to controlling understorey vegetation composition, but was less important than environmental factors, though similar to spatial factors. Thus there appears to be a link between variation in the chemical composition of the single, dominant tree species within this system and the pattern of occurrence and abundance in other species at the same trophic level.

Laminaria ochroleuca Bachelot de la Pylaie canopy effect on intertidal understorey benthic assemblages in northern Portugal

Dissertação de mest., Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2010

Comparative range use by three Atlantic Forest understorey bird species in relation to forest fragmentation

In this paper, we report on range use patterns of birds in relation to tropical forest fragmentation. Between 2003 and 2005, three understorey passerine species were radio-tracked in five locations of a fragmented and in two locations of a contiguous forest landscape on the Atlantic Plateau of Sao Paulo in south-eastern Brazil. Standardized ten-day home ranges of 55 individuals were used to determine influences of landscape pattern, season, species, sex and age. In addition, total observed home ranges of 76 individuals were reported as minimum measures of spatial requirements of the species. Further, seasonal home ranges of recaptured individuals were compared to examine site fidelity. Chiroxiphia caudata, but not Pyriglena leucoptera or Sclerurus scansor, used home ranges more than twice as large in the fragmented versus contiguous forest. Home range sizes of C. caudata differed in relation to sex, age, breeding status and season. Seasonal home ranges greatly overlapped in both C. caudata and in S. scansor. Our results suggest that one response by some forest bird species to habitat fragmentation entails enlarging their home ranges to include several habitat fragments, whereas more habitat-sensitive species remain restricted to larger forest patches.

Water deficit affects photosynthetic induction in Bauhinia forficata Link (Fabaceae) and Esenbeckia leiocarpa Engl. (Rutaceae) growing in understorey and gap conditions

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Understorey fire propagation and tree mortality on adjacent areas to an Amazonian deforestation fire

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Drought avoidance and the effect of local topography on trees in the understorey of Bornean lowland rain forest

The water relations of two tree species in the Euphorbiaceae were compared to test in part a hypothesis that the forest understorey plays an integral role in drought response. At Danum, Sabah, the relatively common species Dimorphocalyx muricatus is associated with ridges whilst another species, Mallotus wrayi, occurs widely both on ridges and lower slopes. Sets of subplots within two 4 -ha permanent plots in this lowland dipterocarp rain forest, were positioned on ridges and lower slopes. Soil water potentials were recorded in 1995-1997, and leaf water potentials were measured on six occasions. Soil water potentials on the ridges (-0.047 MPa) were significantly lower than on the lower slopes (-0.012 MPa), but during the driest period in May 1997 they fell to similarly low levels on both sites (-0.53 MPa). A weighted 40-day accumulated rainfall index was developed to model the soil water potentials. At dry times, D. muricatus (ridge) had significantly higher pre-dawn (-0.21 v. -0.57 MPa) and mid-day (-0.59 v. -1.77 MPa) leaf water potentials than M. wrayi (mean of ridge and lower slope). Leaf osmotic potentials of M. wrayi on the ridges were lower (-1.63 MPa) than on lower slopes (-1.09 MPa), with those for D. muricatus being intermediate (-1.29 MPa): both species adjusted osmotically between wet and dry times. D. muricatus trees were more deeply rooted than M. wrayi trees (97 v. 70 cm). M. wrayi trees had greater lateral root cross-sectional areas than D. muricatus trees although a greater proportion of this sectional area for D. muricatus was further down the soil profile. D. muricatus appeared to maintain relatively high water potentials during dry periods because of its access to deeper water supplies and thus it largely avoided drought effects, but M. wrayi seemed to be more affected yet tolerant of drought and was more plastic in its response. The interaction between water availability and topography determines these species' distributions and provides insights into how rain forests can withstand occasional strong droughts.

Primary lowland dipterocarp forest at Danum Valley, Sabah, Malaysia. Species composition and patterns in the understorey

The spatial distributions of species of tree ≥10 cm gbh were examined in two 4 ha plots and related to the local variation in topography and soil chemistry. The plots were similar in their species composition, particularly in terms of the densities of small trees, and they showed very similar edaphic characteristics. Size class distributions varied little within and between plots. Ordination of 0.25 ha subplots highlighted parallel gradients in the vegetation of both plots when the densities of trees ≥10 cm gbh were considered. Focusing on understorey trees in the 10-<50 cm gbh class at the 0.04 ha subplot scale showed a similar vegetation gradient in both plots closely associated with change from lower slope to ridge. No relationship with soil chemistry was found. On the ridges a special group of understorey species formed clumps and these species contributed importantly to the ordinations. Borneo has a regional history of occasionally severe droughts. It is suggested here that the observed patterns in the understorey are due to differential responses to low soil water supply, the ridges probably tending to dryness more than the lower slopes. Within the large and diverse family Euphorbiaceae, which dominates the understorey at Danum, there may be ecophysiological groupings of species. The long-term effects of disturbance interacting with local edaphic factors on forest structure and composition are discussed.

Primary forest dynamics in lowland dipterocarp forest at Danum Valley, Sabah, Malaysia, and the role of the understorey

Changes in species composition in two 4–ha plots of lowland dipterocarp rainforest at Danum, Sabah, were measured over ten years (1986 to 1996) for trees greater than or equal to 10 cm girth at breast height (gbh). Each included a lower–slope to ridge gradient. The period lay between two drought events of moderate intensity but the forest showed no large lasting responses, suggesting that its species were well adapted to this regime. Mortality and recruitment rates were not unusual in global or regional comparisons. The forest continued to aggrade from its relatively (for Sabah) low basal area in 1986 and, together with the very open upper canopy structure and an abundance of lianas, this suggests a forest in a late stage of recovery from a major disturbance, yet one continually affected by smaller recent setbacks. Mortality and recruitment rates were not related to population size in 1986, but across subplots recruitment was positively correlated with the density and basal area of small trees (10 to <50 cm gbh) forming the dense understorey. Neither rate was related to topography. While species with larger mean gbh had greater relative growth rates (rgr) than smaller ones, subplot mean recruitment rates were correlated with rgr among small trees. Separating understorey species (typically the Euphorbiaceae) from the overstorey (Dipterocarpaceae) showed marked differences in change in mortality with increasing gbh: in the former it increased, in the latter it decreased. Forest processes are centred on this understorey quasi–stratum. The two replicate plots showed a high correspondence in the mortality, recruitment, population changes and growth rates of small trees for the 49 most abundant species in common to both. Overstorey species had higher rgrs than understorey ones, but both showed considerable ranges in mortality and recruitment rates. The supposed trade–off in traits, viz slower rgr, shade tolerance and lower population turnover in the understorey group versus faster potential growth rate, high light responsiveness and high turnover in the overstorey group, was only partly met, as some understorey species were also very dynamic. The forest at Danum, under such a disturbance–recovery regime, can be viewed as having a dynamic equilibrium in functional and structural terms. A second trade–off in shade–tolerance versus drought–tolerance is suggested for among the understorey species. A two–storey (or vertical component) model is proposed where the understorey–overstorey species’ ratio of small stems (currently 2:1) is maintained by a major feedback process. The understorey appears to be an important part of this forest, giving resilience against drought and protecting the overstorey saplings in the long term. This view could be valuable for understanding forest responses to climate change where drought frequency in Borneo is predicted to intensify in the coming decades.