MORTALITY AND DIAMETER GROWTH OF LIANAS IN A SEMIDECIDUOUS FOREST FRAGMENT IN SOUTHEASTERN BRAZIL

(Mortality and diameter growth of lianas in a semideciduous forest fragment in Southeastern Brazil). This is a 30-month study of mortality rates and diameter growth rates of lianas in a semideciduous forest fragment in Belo Horizonte, Minas Gerais State, Brazil. Results are presented for 484 specimens of lianas, of which 103 experienced individual mortality (21.3% of the sampled population). Mortality varied according to class of stem diameter, but did not vary throughout the months ofyear, or between seasons or years. Mortality rates were higher than those recorded in other studies, perhaps due to the age of this secondary forest. Stem diameter growth rates were measured for 385 lianas, the survivors after 30 months plus four plants that died just before the final census, and averaged 1.2mm/year, ranging from Ommlyear (Chioeeoea alba) to 4.8mm1year (Acaeia sp.), significantly slower than the known growth rates in tropical trees in other areas.


Introduction
Woody c\imbing plants, or lianas (Gentry 1991), gain access to the canopy by ascending over other species, saving the resources used by trees to make self-supporting trunks.Among angiosperms the c\imbing habit has evolved many times over; many genera in unrelated families have c\imbers, and in some families ali or most genera have the c\imbing habit, the case of Aristolochiaceae, Hippocrateaceae, Dioscoreaceae, Smilacaceae, Trigoniaceae and Vitaceae (Gentry 1991).
Aiming to contribute to the biological study of lianas in Brazil, in this article we present the results of a 30-month study of mortality and diameter growth of lianas in permanent plots in a fragment of a semideciduous forest in the Belo Horizonte municipality, Minas Gerais State, Brazil.

Material and methods
The municipality of Belo Horizonte is the most populated portion of Minas Gerais State.A climate, with a dry season from May to September and a rainy season from October to April characterizes the area.The vegetation around Belo Horizonte is a mosaic of fragments of semideciduous forests and rocky grasslands at higher elevations, mixed with urban zones.
Ten permanent 5x SOm plots (2.5ha) were sampled in parallel lines in the interior of a semideciduous forest fragment located in the Ecological Station of the Federal University of Minas Gerais (EE-UFMG; 19°52'40"S, 43 °58'20"W), starting at 5 to 10m from the border of the fragment.In 1997 the total monthly rainfall ranged from 428.5mm in January, to 0.1mm in July and September, the mean monthly temperature ranging from 24.6°C in February, to 18.7°C in July (data from the Pampulha Airfield Climatologic Station, ca.1.5km from study area).The first census was done in Januaryl1995 , and the last in July11997.
The EE-UFMG is a protected area of ca.150ha inside the campus ofthe Federal University of Minas Gerais, and includes several secondary habitats, including herbaceous and shrubby vegetation, swamps, transitional areas of cerrado/ semideciduous forest, and fragments of secondary forest.The sampled area is a forest fragment located on a comer of the EE-UFMG along a highway and a fence, with a ca.10m high canopy, and with some emergent trees of ca.20m high.The edges near the highway are subject to occasional anthropogenic fires, and the exposure to wind, mainly in the dry season, and treefall is common, this not, however, being measured.
All the living lianas in the plots with stem diameters 2': 0.5cm (measured at 70cm linear distance from the last rooting point) were sampled.Dense groupings of one species were considered as only one individual, these probably being rooted ramets left, after the fall of the originalliana or its canopy support (Putz 1984).Stem diameters were measured at the same point every six months with the use of calipers; only the lianas alive after the 30-month period of study were counted for diameter growth rate ca1culations.
The survival of each individual liana was recorded every two months by searching for leaves or reproductive parts in the canopy with binoculars, or by scraping the outer bark of the shoot or branch above the measurement point.Decay of the individual above this point was considered a mortality event (individual mortality), either whether the entire individual had died or only the ramet with its measurement point.
Voucher specimens of fertile lianas were collected, and specimens were deposited in the Herbarium of the Botany Department of the Biological Sciences Institute of the Federal University of Minas Gerais (BHCB).

Results and discussion
A total of 484 individual lianas were monitored in the 10 plots (l93.6/ha),belonging to 18 families and 55 species (Appendix).ThÍlty five individuaIs died before collection but were determined to family leveI; four died at the start of the study before they could be collected and determined.
Mortality -In the 484 marked individuaIs, study period (21.3% of the sampled population).Mortality occurrences were recorded only to the family levei, seeing that a great number of lianas died before proper species determination.Among families with N > 1, mortality ranged from O to 63.6% (Asteraceae) (Tab.1).
Diameter growth-A total of385 individuais were evaluated for diameter growth -the survivors after 30 months plus four plants that died just   (Putz 1990), which perhaps accounts for the small growth rates of the sampled lianas in the EE-UFMG, where lianas in the two classes wich smaller diameter are the majority (326 plants or 67.4%).This predominance oflianas with small diameter stems is probably due to the disturbance of this secondary vegetation.
The average growth rate of 1.2mm/year is, however, similar to the growth rate recorded by Putz (1990) in Barro Colorado Island, Panama, of 1.4mm/year, but significantly smaller than the growth rates recorded for tropical forest trees in Barro Colorado (9.0mm/year, Lang & Knight 1983) and Australia (2.4-4.0mm/year,Herwitz &  Young 1994).
Mortality among lianas of EE-UFMG was higher than that recorded by Putz (1990)  site 47 individuaIs (9.7% of the sampled population) died in 1995,32 in 1996 (7.1 % ofthe remaining live population of 452lianas), and 28 during January-July/1997 (5.6% of the remaining population of 428 plants).The observed higher mortality rate is perhaps due to the stage of regeneration and disturbance frequency of this secondary area subject to periodic fires and a high wind exposure.

Table I .
Families of lianas, mortality events, and the percentage of dead individuaIs in the sampled population after 30-month study in a fragment of semideciduous forest in Minas Gerais, Brazil (N = number of individuaIs at starting of study).

Table 2 .
Distribution in diameter class of the sampled lianas in a fragment of semideciduous forest in Minas Gerais, Brazil (N = number of individuaIs at starting of study).

Table 3
. Distribution of recorded death events in the lianas along the months, seasons, and years of study in a fragment of semideciduous forest in Minas Gerais, Brazil.Month or season mortality is the sum of mortality events (in 2.5 years) during the corresponding month or season (N = number of individuaIs at starting of study).

Table 4 .
Stem diameter range, extremes of diameter increase in 30 months, and mean annual secondary growth of lianas in the sampled plots in a fragment of semideciduous forest in Minas Gerais, Brazil (N = number of individuais surviving after 30-month (including four lianas that died just before lhe final census).SO = Standard deviation).

Table 4 .
for lianas on Barro Colorado (26 individuais in a population of 189 in eight years, or 1.49%/year).In our study