Comparative regeneration ecology of three leguminous timber species in a Bolivian tropical dry forest

A comparative study of the regeneration ecology ofthree lesser-known leguminous timber species wasconducted in the seasonally dry forests of SantaCruz, Bolivia to determine species regenerationstrategies and make silvicultural recommendationsfor these species. The study included arepresentative from each subfamily of Leguminosae:Anadenanthera colubrina (Vell. Conc.) Benth.(Mimosaceae), Copaifera chodatiana Kunth.(Caesalpinaceae), and Centrolobium microchaeteC. Martius (Fabaceae). After production in themid-late dry season, seeds of all species sufferedhigh (>30%) rates of predation. For seedssurviving predation, Anadenanthera germinatedwithin three days after the first rains and a highgermination capacity (82%), but most seedlings diedfrom inadequate light or during subsequent periodsof drought. Copaifera germinated more slowlybut had high germination capacity (85%). Centrolobium had very low germination capacity(4%) and germinative energy. Most successfulregeneration of Centrolobium occurred viasprouting from damaged roots on or near loggingroads where it had a density of 261 root sprouts/ha.Anadenanthera regenerated best from seedin areas with soil disturbance or burning. Theregeneration of these species will likely increaseunder more intensive logging and/or post-harvestcompetition control treatments in logging gaps. Themore shade-tolerant Copaifera is most suitedto the current regime of light selective logging,but all three species are likely to be responsive topost-harvest competition control treatments. Impacts of controlled and natural fire were mixed,but generally seedling regeneration and growth wereeither not significantly affected or were increasedby fire.     

Heterogeneity of peach rust disease progress within the tree canopy

Peach rust (Tranzschelia discolor) is a major foliar disease of peach that can cause severe defoliation. Few epidemiological studies have been conducted on peach rust, and there is no information concerning the spatial distribution of the disease within the canopy. This study aimed to characterise the onset and temporal progress of peach rust in three height strata in peach trees grown in two different orchards: one treated with fungicide and the second non-treated. Evaluations were conducted fortnightly between November and April for two consecutive years. Positional information for the disease within the canopy was obtained by assessing the incidence and severity of peach rust on leaves in both orchards. A linear mixed model with the position of shoots as the fixed effect and cultivars and blocks as random effects was adopted for the data analysis over both seasons, in the fungicide-treated orchard incidence and severity ranged from 60 to 90 % and 0.5 to 2 %, respectively, while in the non-treated orchard incidence and severity ranged from 90 to 100 % and 10 to 15 %, respectively. The area under the disease progress curve was greater for the upper shoots compared to the lower shoots, but the disease progress rates were similar. The logistic and exponential models best fitted the incidence and severity data, respectively. Urediniospores were detected by traps within the experimental area between late winter and early spring. Predominance of autoinfection or alloinfection is discussed.