Postfire Vegetation Recovery in Highland Pine Forests of the Dominican Republic

We surveyed postfire vegetation at five sites at high elevations (> 2000 m) in the Cordillera Central, Dominican Republic. Highlands of the Cordillera Central are dominated by a single pine species, Pinus occidentalis, but plant communities are rich with endemics and conservation and fire management efforts in these systems are ongoing. The burns were 2–7 yr in age and had consumed nearly all shrub crowns. Pines suffered high mortality (> 50%, all sites combined), but shrubs resprouted at high rates (88%, N = 957) after fire. All shrub taxa produced basal resprouts; eight of 11 shrub taxa measured had resprouting rates > 90 percent, while Baccharis myrsinites had the lowest (56%). Most taxa grew to prefire height quickly (within 5–7 yr), with regrowth of stem diameters lagging behind. Patterns and rates of shrub recovery resembled those documented in high elevation shrublands in Costa Rica and Brazil. Pinus occidentalis does not resprout, but larger individuals can survive fire. Survival increases dramatically when trees attain > 13-cm dbh, when bark becomes thick enough to protect cambial tissue. Overall, pines are regenerating much more slowly than shrubs, but seedling establishment varied considerably between sites. Frequent fires may cause a decline in pines and an increase in shrub- or grass-dominated communities. Succession in these high elevation fire-dependent pine forests favors taxa already present in the preburn vegetation, with woody composition changing little after fire, in contrast to lower-elevation cloud forest, where postfire vegetation has been shown to bear little resemblance to mature forest even after several years.     

Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic

Aim We examined relationships between climate–disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range. Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis. Methods Climate, disturbance and vegetation data were collected over the elevation range 1100–3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high‐resolution digital elevation model in order to enable the analysis of landscape‐scale patterns of the ecotone. Results A Shipley–Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely ± 164 m (SD) over its 124‐km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non‐pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially. Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade‐wind inversion to create a narrow zone where high‐elevation fires extinguish, enabling fire‐sensitive and fire‐tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study – and of temperate and fire‐tolerant taxa in subtropical montane forests in general – highlights the importance of climate‐disturbance–biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.     

A new species of Henriettea (Melastomataceae) from the Sierra de Baoruco, the Dominican Republic

Henriettea uniflora, which is known only from a diverse moist montane forest in the vicinity of Loma Trocha de Pey (or “Monteada Nueva”), Loma Pie de Palo, and Loma Remigio, the easternmost peaks of the Sierra de Baoruco, is described and illustrated. It is compared to species of the Henriettea squamulosa complex, especially H. squamulosa and H. ciliata. The species of this complex are characterized by an indumentum of ferruginous, stellate-lepidote hairs.     

The Influence of the urban environment on the composition of terpenes in the needles of Black Pine (Pinus nigra Arnold)

 The composition of terpenoid substances in needles of Pinus nigra Arnold with respect to air pollution is discussed. Trees grown in the urban environment of the city of Nitra, which is contaminated by immissions, and trees grown in the relatively clean environment of the Mlyňany Arboretum SAS were investigated. The urban environment caused a change in the species composition and the content of terpenes. In the city of Nitra needles of P. nigra contained a smaller number of terpenoid substances (12 terpenes) in comparison with the Arboretum (15 terpenes). At Nitra P. nigra contained four terpenes with a relative portion above 1% and at the Mlyňany Arboretum P. nigra needles contained six terpenes above 1%. At the polluted site citral, eugenol, and bisabolol are completely missing in the terpene pattern of needles and myrcene, carvone and alfa-humulene were notably lower. The decrease of the alfa-pinene content and the increase of the beta-pinene content in needles from Nitra significantly lowered the ratio of alfa-pinene to beta-pinene from 2.80 to 0.86. Received: 27 October 1995 / Accepted: 29 March 1996