Oak Forest Patches Research Articles

Past Disturbance–Present Diversity: How the Coexistence of Four Different Forest Communities within One Patch of a Homogeneous Geological Substrate Is Possible

Understanding the relationship between disturbance and forest community dynamics is a key factor in sustainable forest management and conservation planning. The study aimed to determine the main factors driving unusual differentiation of forest vegetation into four communities, all coexisting on the same geological substrate. The fieldwork, conducted on the fluvioglacial sand area in Central Poland, consisted of vegetation sampling, together with soil identification and sampling, up to depths of 150 cm. Additional soil parameters were measured in the laboratory. A Geographical Information System was applied to assess variables related to topography and forest continuity. Vegetation was classified and forest communities identified. Canonical Correspondence Analysis indicated significant effects of organic horizon thickness, forest continuity, soil disturbance and soil organic matter content on vegetation composition. We found that the coexistence of four forest communities, including two Natura 2000 habitats, a Cladonia-Scots pine forest and an acidophilous oak forest (codes–91T0 and 9190 respectively), resulted from former agricultural use of the land followed by secondary succession. The lowest soil-disturbance level was observed within late-successional acidophilous oak forest patches. Nearly complete soil erosion was found within the early-successional Cladonia-Scots pine forest. We propose that both protected habitat types may belong to the same successional sere, and discuss the possibility of replacement of the early- and late-successional forest habitat types in the context of sustainable forest management and conservation.

Wildfire dynamics and impacts on a tropical Andean oak forest

Wildfires have increasingly damaged Andean tropical forests. However, both a poor understanding of wildfire dynamics and ecosystem response limits awareness about the magnitude of the problem and design management strategies. We estimate the impacts and significant drivers of wildfires by dating and mapping recent wildfires in an Andean tropical forest area, the Iguaque mountains. A large part of Iguaque hosts a population of the only Quercus species in South America, Quercus humboldtii. We used remote-sensing, official reports and social mapping to reconstruct the recent history of wildfires and change in oak forest patches in Iguaque. Between 1990 and 2017, 25 wildfires were recorded, with fire intervals between 4 and 21 years. These events burned 28.4% of the Iguaque mountains and showed a significant increasing trend in extent. Wildfires mostly occurred in the south, during the driest months, and their number and extent showed substantial interannual variations related to El Niño–Southern Oscillation cycles. Wildfires contributed to a 45% reduction in oak forests along with the fragmentation of existing populations. Our study presents evidence of the extent and impact of wildfires in Iguaque and provides new insights on fire dynamics in Andean tropical forests.

Habitat Fragmentation can Modulate Drought Effects on the Plant-soil-microbial System in Mediterranean Holm Oak (Quercus ilex) Forests

Ecological transformations derived from habitat fragmentation have led to increased threats to above-ground biodiversity. However, the impacts of forest fragmentation on soils and their microbial communities are not well understood. We examined the effects of contrasting fragment sizes on the structure and functioning of soil microbial communities from holm oak forest patches in two bioclimatically different regions of Spain. We used a microcosm approach to simulate the annual summer drought cycle and first autumn rainfall (rewetting), evaluating the functional response of a plant-soil-microbial system. Forest fragment size had a significant effect on physicochemical characteristics and microbial functioning of soils, although the diversity and structure of microbial communities were not affected. The response of our plant-soil-microbial systems to drought was strongly modulated by the bioclimatic conditions and the fragment size from where the soils were obtained. Decreasing fragment size modulated the effects of drought by improving local environmental conditions with higher water and nutrient availability. However, this modulation was stronger for plant-soil-microbial systems built with soils from the northern region (colder and wetter) than for those built with soils from the southern region (warmer and drier) suggesting that the responsiveness of the soil-plant-microbial system to habitat fragmentation was strongly dependent on both the physicochemical characteristics of soils and the historical adaptation of soil microbial communities to specific bioclimatic conditions. This interaction challenges our understanding of future global change scenarios in Mediterranean ecosystems involving drier conditions and increased frequency of forest fragmentation.

Birds, charcoal and cattle: Bird community responses to human activities in an oak forest landscape shaped by charcoal extraction

Oak forests around the world have been widely used to obtain firewood and produce charcoal and like other habitats have been affected by the increasing development of livestock activities. Oak forests from western Mexico are one of the five priority habitats for the conservation of birds at a continental level and are the repository of the highest number of endemic bird species in this megadiverse country. We studied how charcoal extraction and the use of oak forest for cattle grazing affect bird communities. We focused our work on oak forest patches with four different management units that include three successional stages that occur after most of the trees have been removed for charcoal production and cattle-grazing is conducted, and mature oak forest patches with little wood extraction and no cattle-grazing. We used unlimited radius point counts to survey avian communities, and compared their richness, composition, density, structure and similarity among the different management units. We found that resident bird species, summer migrants and Neotropical migrant bird species used the four management units differently. Resident bird species used all habitat units similarly. Winter migrants as a group were present in the different management units, however while some species used habitats with cattle, other species used habitats with no cattle-grazing. Finally, summer migrants used habitat units with tall trees and high values of tree and shrub richness, and tended to avoid the early successional unit. Both charcoal extraction and cattle grazing worked in synergy decreasing the species richness and the equity of the bird communities. Management strategies should include active conservation of undisturbed oak forest areas because they play an essential role to maintain resident bird species in the landscape.

Changes in typological and spatial boundaries between neighbouring communities of Potentitlo albae-Quercetum and Tilio-Carpinetum

The sample area of 2.8 ha, divided into 100 m<sup>2</sup> square quadrats, comprised two, distinguishable by traditional methods, oak forest patches and a fragment of a neighbouring mixed oak-hornbeam forest. The classification of quadrats was conducted by association analysis. Their identification and interpretation were performed on the basis of the systematic value and fraction of species of the characteristic oak forest combination in each distinguished quadrat group, as well as the range of distinguished communities. It appeared that due to the hornbeam invasion into the oak forest habitat, species forming the characteristic oak forest combination receded and the community area decreased. The data enabled reconstruction of the phases of oak forest recession. They corresponded to the successive phases of the encroachment of hornbeam undergrowth in the analysed area.

Fragmentation of Mediterranean oak forests affects the diversity of epiphytic lichens

The present study investigated a fragmented Mediterranean oak forest to evaluate so called edge effect on species richness and composition of epiphytic lichen communities colonizing tree trunks. The results showed that in Mediterranean oak forest patches, epiphytic lichen diversity and communities are significantly influenced by microlimatic variables related to the edge effect. Light influx rather than atmospheric humidity and temperature was the main driving factor affecting lichen diversity along the forest edge-interior gradient, while humidity is the prevailing factor inside the forest. It is concluded that forest fragmentation may have a heavy impact of epiphytic lichens, with the reduction and disappearance of typical forest species and the appearance of ubiquitous tolerant species, with an overall impoverishment and banalization of the lichen flora.

Does human-induced heterogeneity differently affect diversity in vascular plants and breeding birds? Evidences from three Mediterranean forest patches

Human-induced disturbances induce heterogeneity at patch and landscape scale, affecting plants and animals differently. In this study, we analyzed the diversity of three oak forest patches (one of them recently coppiced) in Mediterranean Central Italy. Vascular plants were censused on a raster of squares of 10,000 m2. Breeding birds were censused with the point-sampling method. In the three wood patches studied, we observed a clear pattern in diversity with similarities and differences between plants and birds. A mature wood patch (Foglino North) showed the highest total number of species (a measure of γ-diversity at wood patch scale) both for birds and plants but, at level of mean species richness (an averaged measure of α-diversity at sampling point scale), birds showed values significantly different among wood patches with the lowest value in the recently coppiced wood patch (Armellino); on the contrary, the plants did not show differences among patches. In the coppiced wood patch, birds showed the highest value of species turnover among sampling points (a measure of β-diversity at wood patch scale), while plants showed the lowest value. Data suggest that when comparing a coppiced wood patch to a mature wood patch, human-induced heterogeneity developed by coppice management may affect diversity in vascular plants and breeding birds differently at different hierarchical level (i.e., α-, β-, γ-level). This human-induced heterogeneity may decrease the α-diversity values in birds, while it may favor an increase in plants. Moreover, with coppice management, species turnover among sites (a measure of β-diversity) may decrease in plants while may increase in birds. We hypothesize that this different pattern may be due to intrinsic characterization of these two taxa (different number of species, sessile vs. vagile strategies of dispersion, different scales of the assemblages) and to different methods of sampling them.

Time-consistent rearrangement of carabid beetle assemblages by an urbanisation gradient in Hungary

To examine the impact of urbanisation on arthropod biodiversity, carabid (Coleoptera: Carabidae) assemblages were studied over 2 years along a rural–urban gradient representing increasing levels of human disturbance. Carabids were collected by pitfall trapping during their whole activity period in lowland oak forest patches in and near the city of Debrecen, Eastern Hungary, over two seasons (2001–2002). Carabid activity density was significantly higher in the rural than in the two other areas, but there was no significant difference in species richness (measured as mean number of species caught/trap). The proportion of forest specialists significantly decreased from the rural towards the urban area, and the proportion of forest specialist species was significantly higher in the rural and suburban areas than in the urban one. In contrast, the relative activity density of generalist species significantly increased along the rural–urban gradient. Both the relative number of open-habitat species and their activity density were significantly higher in the urban forest fragments than in the suburban and rural ones. The patterns found were consistent between the 2 years. Multidimensional scaling indicated pronounced changes in species composition along the gradient; the assemblages in urban forest fragments were more variable than in the other areas. A large proportion of the variation in overall activity density, species richness and the proportion of carabids with different habitat affinities could be explained by structural habitat variables (percentage cover by canopy, leaf litter, herbs and decaying wood), and prey availability.

Response of rove beetles (Staphylinidae) to various habitat types and change in Southern Mexico

We evaluated changes in levels of diversity of copro-necrophilous staphylinids attracted to piles of cattle dung and rat carrion in four contrasting habitats (continuous oak forest, oak forest patches, savannah and ravines) in southeastern Mexico during 2005 and 2006. In total, 181 morpho-species (N = 9,875 individuals) of Staphylinidae were recorded, of which 40 were coprophiles, 98 were necrophiles, and 43 were present in both substrates. Ten species accounted for 65% of the total number of individuals, 68 species were represented by singletons, whereas 103 species registered intermediate abundances. Less disturbed habitats recorded higher levels of beetle diversity. A strong seasonality effect was recorded for necrophiles, but not for coprophiles. A beta diversity analysis suggested that continuous oak forest registered the lowest fauna similarity when contrasted to other habitats; yet beetle composition among oak forest patches, savannah and ravine remained comparable. Staphylinidae body size and trophic guilds differed significantly among habitats. The results of this study suggest that key habitats such as ravines may represent a more permanent and predictable habitat for beetles in highly seasonal landscapes, even at early stages, because this habitat is characterized by a slower turnover of Staphylinidae species than in the case of tropical oak patches or savannah habitats.

Transformation of the oak forest spatial structure in the Minneapolis/St. Paul metropolitan area, Minnesota, USA over 7 years

The Twin Cities Metropolitan Area (TCMA) oak ( Quercus spp.) forest area decreased by 5.6% between 1991 and 1998. Accompanying spatial transformation of the forest can have great impacts on forest health, water flow and quality, wildlife habitat, potential for the spread of invasive species, and the quality of life of urban residents. The types of spatial transformation that occurred along with the loss of oak forest in the TCMA were investigated through the integration of remote sensing, a Geographic Information System (GIS), and landscape and patch metrics in seven ecological subsections between 1991 and 1998. Oak forest patches in the TCMA as a whole decreased in area, number, and complexity. Fragmentation of oak forest took place in all subsections and attrition occurred in three subsections. Knowledge of how the oak forest has changed over time can be integrated with land use change information to help planners make decisions about zoning and development that will minimize the impacts of increasing land conversion pressure on forest areas.

Body size inequality of carabids along an urbanisation gradient

Summary Analysis of size inequality can shed light on coexistence mechanisms and help to interpret patterns in assemblages. We tested several measures for their power to evaluate changes in carabid body size along an urbanisation gradient (city park–suburban area–rural), representing decreasing intensities of human disturbance. Carabids were collected by pitfall traps over two full activity periods in lowland oak forest patches in and near the city of Debrecen, Eastern Hungary. The average value of skewness was largest in the urban areas compared to the suburban and rural ones, indicating that small individuals were more prominent in the urban areas. The Gini coefficient also decreased from urban towards rural areas, suggesting that inequality in body size of the carabid assemblages decreased along the gradient. However, neither of these trends was significant. The Lorenz asymmetry coefficient was significantly higher in rural areas compared to suburban and urban areas indicating that there was a significant difference in inequality and/or asymmetry of body size across the gradient. This difference was primarily due to more individuals with larger body size in rural area. We suggest that the observed variation in carabid body size along the gradient is related to habitat alteration caused by urbanisation.

Carabid beetle occurrence at the edges of oak and beech forests in NW Spain

We examined the occurrence of carabid beetles (Coleoptera, Carabidae) at the edges of oak (Quercus pyrenaica) and beech (Fagus sylvatica) forests in Leon, NW Spain. Pitfall traps were used to collect beetles from April to October 2002, and leaf litter cover and depth were measured. Traps were placed at three distances (0, 50 and 100 m) from the edges of eight forest patches. A total of 5436 carabids belonging to 43 species were collected. We found no statistically significant edge effect at the carabid assemblage level, i.e. the number of species and individuals was not higher at the edge compared to the forest interior. However, individual species were affected by distance from the edge. Five of the 14 species analysed responded predictably to the edge, three of them statistically significantly so. Four species did not respond in the predicted direction, two of them statistically significantly so. We found a considerable difference between forest types in terms of carabid assemblage composition and response to the edge. Oak forests were species richer and beech forests had a higher number of individuals. These differences were probably due to small- scale habitat heterogeneity in the oak forest patches, caused by man, and the homogeneous structure of beech forests. Leaf litter appeared to be one possible factor influencing the distribution of some species from the interior to the edge of forests.

Changes in carabid beetle assemblages along an urbanisation gradient in the city of Debrecen, Hungary

Responses of carabid beetles (Coleoptera: Carabidae) to urbanisation were studied along an urban-suburban-rural gradient representing decreasing intensities of humandisturbance. Carabids were collected by pitfall trapping during their activity period in lowland oak forest patches in the city of Debrecen, Eastern Hungary. The average number of carabid species was significantly higher in the rural and urban areas compared to the suburban one. The high overall species richness in the urban area was due to the presence of species preferring open habitats. The species richness of forest specialist carabids significantly increased along the urban-rural gradient. The overall carabid abundance was significantly higher in the rural than the other two areas. The results did not support the hypothesis that overall diversity should decrease in response to habitat disturbance. They also contradicted the intermediate disturbance hypothesis: species richness was not the highest in the moderately disturbed suburban area. In the urban area, opportunistic species dominated. The average carabid body size was significantly larger in the rural and suburban areas than in the more disturbed urban area. Multivariate methods detected changes in species composition and abundance structure along the urban-rural gradient. Significant proportion of the variation in abundance and species richness was explained by the heterogeneity of environmental variables (ground temperature, surface temperature, humidity, cover of decaying wood material, herbs, canopy layer, and by the amount of prey).

Forest size and avian diversity in New Jersey woodlots with some land use implications.

The effect of forest size on avian diversity was studied in oak forest patches in rural New Jersey. Number of bird species continued to increase significantly in old oak woods up through 40 ha. This was due to the progressive addition of carnivorous species with increasing minimum forest size requirements. One large woodlot had more species than the same area subdivided into smaller woodlots. To maintain maximum regional diversity more than three large forests are required. Primary land use priority should be to protect large forests. Second priority should be to maintain a high density of small woodlots.