The succession of bird communities in the plantations of Pinus sylvestris in the Ayllón massif (Sistema Central mountains, Spain)
Authors: POTTI, J.
Published: Volume 32(2), December 1985. Pages 253-277.
Original Title: La sucesión de las comunidades de aves en los pinares repoblados de Pinus sylvestris del Macizo de Ayllón (Sistema Central)
This paper examines the bird composition and community structure of unplanted and afforested heaths in montane levels in the NE Sistema Central mountains. In order to study a succesional gradient, four stages of even-aged Scot pine growth were chosen, ranging from P-l (7 y. old; mean tree height 2.1 m.) through P-2 (25 y.; 5 m.) and P-3 (40 y.; 9 m.) to P-4 (100 y.; 14 m.). Birds were censused in these pinewoods and heath shrublands (brezal) with the line transect method in spring and winter. Community composition and bird densities (fig. 1, 2, 3, 4, 5; Appendix) undergo profound changes in the succesional gradient, otherwise comparable to those already described in the European literature, being the most striking point the quick colonization and high dominances of the Coal Tit along the series. Turnover of avian species is greater during the winter (fig. 5), seemingly because of high seasonality that promotes community overlap in the spring. Accordingly, winter communities have lower mean niche (succesional amplitude) breadth values (fig. 6). Bird density and diversity increase in both spring and winter along the succesional series (table I), although in winter some differences between P-4 and earlier stages are not statistically significant. Both parameters increase from heathland to P-2, thereafter leveling off or decreasing in P-3 and increasing again in P-4. The P-2 pinewoods seem to behave in the mode described by earlier workers as a time ecotone responsable of the first peak in density and diversity. The second one occurs in the mature managed forest P-4 (also provided with nest boxes). The evenness component of diversity behaves similarly, although low sample sizes in winter due to very low densities precludes some seasonal and interhabitat comparisons. Mean individual weight in the community does not increase along the succesion but behaves erratically, seemingly because strong structural habitat correlates of this parameter. So does a measure of spring and winter similarity (table 1), although in this case the index is distinctly higher in the pinewoods as a whole than in the heath shrubland. Mediterranean and tropical migrant bird species decrease through the series despite their low importance in highlands and pinewoods. Granivorous, granivore-insectivorous birds and flycatchers peak at the same opposite extremes of the gradient. Succesional trends in guild structure follow the logical trends linked to the development of vegetation strata and hard substrates (trunk, branches) (table II). Guilds that forage in these parts are the less heavily affected by seasonality while the converse is true for ground insectivores.It is concluded that pine afforestation of heathlands in these mountains originates a very distinctive avifauna, denser and more diverse than that of heathlands. From a conservationist standpoint, however, some management recommendations (clearing, encouragement of deciduous undergrowth, erection of nest-boxes in earlier growth stages) are made regarding the low structural diversity of some plantations (e. g. P-3) and the general unsuitability of pinewoods for oak-living and tropical migrant bird species.