Palo Laziale 30 Years After - Monitoring The Situation Of Birds’ Population Of Palo Laziale Wood (1982-2012)
Project location: Italy, Palo Laziale
Project start date: December 2011 -
Project end date: October 2012
Project number: 2011-37
Beneficiary: Associazione Alsium
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1. Introduction
This site owned by the Odescalchi family, was nominated as a Site of Community Interest (SCI IT6030022 "Bosco di Palo Laziale"), and subsequently added to the Natura 2000 European Network. The residual nature of the forest and its consequent conservation value have meant that for the last several decades, the site has been managed (by WWF Italia from 1981 to 2002). Currently, the Alsium Association manages educational activities - through guided visits - and active conservation.
In 1983 the authors carried out the first census of the site's avifauna, which they repeated in 2003.
About thirty years after the first census, the Alsium Foundation promoted a similar initiative, with the support of LIPU, in order to shed light on the evolution of the bird community and its conservation status.
2. Study area
The site is in the municipality of Ladispoli (Rome) (41°56'N - 12°05'E), located between the sea and the Aurelian Way, 38 km north of Rome, and has a total surface area of 129 hectares (Fig.1).
Due to the drying of the soil and the stress this caused to the arboreal vegetation, starting in 1999 there has been an epidemic outbreak of the fungi Phytophtora sp. and Hypoxylon mediterraneum, which caused the death of a high percentage of the forest's trees. As a consequence, in 2005 a massive tree-cutting effort was carried out in the hope of eliminating these pathogenic fungi.
3. Methods
3.1. Bird census
Standardized bird surveys were carried out using the Line Transect Method.
The sample transect runs entirely in deciduous and evergreen oak forest, albeit with different structures and canopy cover; its total length is 2195 m (Fig. 2).
LIPU recorded all birds seen or heard along the sample transect within a 25-meter main belt on both sides of the transect (50 meters total), and those seen or heard beyond 25 meters from the transect (supplementary belt). Each observation was assigned a specific value:
a) Singing male, fledglings, nest, pair with hatchlings = 1 pair;
b) Individual seen or heard calling = 0.5 pair.
In total, LIPU carried out 12 visits (from late March to July 2012). Surveys were carried out in the early mornings, with no wind and rain.
The parameters and indexes LIPU developed are as follows:
frequency = relative frequency of each species, expressed as the number of individuals of a given species/total n. of individuals of all species recorded.
n°. pairs/10 hectares = species density expressed as number of pairs per ten hectares.
S = species richness;
H = diversity calculated using the Shannon & Weaver index (1963);
J = equitability index;
N. sp. dom. = number of dominant species (frequency > to 0.05);
% non-Pass. = percentage of non-passerine species;
% sp.migr. = percentage of migratory species as a total of the breeding avifauna;
we used the Kolmogorov-Smirnov test for two samples using SPSS v.17.0 for Windows.
3.2. Vegetation analysis
LIPU identified a "minimum sampling plot" with sampling stations located every 200 meters along the study transect. In accordance with botanical literature, LIPU chose sampling stations of 400 m2, which is considered adequate for woodland areas.
They recorded plant cover, height, and diameter for each vegetation layer - grass, shrubs, and trees - in ten sampling stations.
Plant cover was expressed in five classes: 1-20%, 20-40%, 40-60%, 60-80%, 80-100%, in accordance with standard usage in vegetation studies. Diameters for trees and shrub were measured ‘at breast height', about 130 cm above the ground.
4. Results obtained
4.1. Vegetation physionomy
The results of vegetation physiognomy was affected by the onset of plant disease in 1999, leading to logging in 2005 and creating a large clearing in the middle of the forest, with scattered trees and a rather uniform sclerrophyllous shrub layer. The average height of the forest in the areas sampled was 11.0 m, exactly as it was in 2003, and higher than in 1983 (9.5 m). The percentage of canopy cover was lower, 42% versus 75% in 1983 and 60% in 2003 (in cases where canopy height was 8 m or more).
4.2. The bird community
The surveys, recorded 61 bird species, 31 of which were considered to breed within the forest and 30 others which were non-breeding migrants (Tab. 1). Out of the 31 breeders, nine of the ten most common species are passerines (Sylvia atricapilla, Luscinia megarhynchos, Serinus serinus, Carduelis carduelis, Cyanistes caeruleus, Sylvia melanocephala, Turdus merula, Carduelis chloris, Parus major; cumulative frequencies = 0.61) and one is a Columbiform (Streptopelia turtur, frequency 0,045); of these ten species, six are dominant members of the community.
The community of breeding forest birds comprises mainly common and widespread species. The only uncommon and local species at the regional level is the Lesser Spotted Woodpecker Dendrocopus minor although recent data suggest the species is undergoing a rapid population expansion.
The breeding bird community in the Palo Laziale forest was analyzed using the classical parameters for this ecological level (Tab. 2).
The bird community is composed mostly of omnivorous species (n=15), followed by insectivores and predators (n=11), and finally plant-eating species (n=6).
In Tab. 3 compares the data from the three period studies (1982, 2003, 2012). Overall, these results allow LIPU to trace the ecological evolution of the Palo Laziale forest over the last 30 years from having a medium-low bird community to a mature one. Trends regarding changes, however, are hard to interpret: the community remained more or less stable for 20 years and then rapidly evolved in the last 10, going from 19 to 31 breeding species. The arboreal vegetation became simpler over time due to the onset of plant disease in 1999 and the logging that took place in response to this in 2005.
5. Conclusions
The analysis found a breeding bird community typical of mature stages of ecological successions. Some of the taxa present, such as woodpeckers, are evidence of this. This change took place over the last decade, since the survey carried out twenty years after (2003) the initial survey (1982) did not find any significant changes in terms of species number, diversity, and turnover. Nevertheless, it remains evident that the forest's structural characteristics - as a small woodland - make it an ecological island set within a broader landscape of farmland and urban settlements.
In light of the above, several observations can be made regarding the future evolution of the Palo Laziale forest. The characteristics of the biotope - is an ecological island set within a broader, homogeneous agricultural and urban landscape - prevent a stable evolution towards a mature stage, with a stable and well-defined bird community. In the near future, it is likely that island and metapopulation effects will lead to rapid changes in the bird community, with extinction dynamics probably prevailing over colonisation processes. Additionally, it we are really in the presence of a crowding effect, the risk of local extinctions, even in the short term, would increase considerably. In such an unbalanced equilibrium, it is likely that a key factor for local conservation is the conservation status of the species present in nearby forested areas (such as the Tolfa Hills), which probably serve as source populations for the bird community at Palo Laziale, at least with regards to sedentary species (e.g.. Picoides minor, Picus viridis, Fringilla coelebs).
