This work s general purpose was to verify intra- and interspecific interactions between seedlings of caatinga tree species, to quantify the mass allocation proportions for each species in the presence of intra- and interspecific pairs ; as also, quantify the interference of each species in their intra e inter pairs. The experiment was executed in a greenhouse with 50% shading, 168 pots of 1kg, each vase containing one pair of seedling, during 105 days. Six species of seedling trees were used in an incomplete factorial combination 6 x 2, corresponding to six species and two soils, with four repetitions. The species used were: Anadenanthera colubrine (Vell.) Brenan var. cebil (Griseb.) Altschul; Amburana cearensis (Mart.) Gillett; Schinopsis brasiliensis Engl.; Poincianella pyramidalis (Tul.) L.P.Queiroz; Aspidosperma pyrifolium Mart.; Bauhinia cheilantha (Bong.) Steud.. Among these species, Bauhinia cheilantha and Schinopsis brasiliensis demonstrated to be strong interespecifics competitors, while Amburana cearensis and Poincianella pyramidalis strong intraespecifics competitors. The mass allocations were differed by species and by nutrients availability. Similar papers utilizing these species and these approaches are scarce in the literature, but extremely important to understand the structure of dry tropical forests. / Fundação de Amparo a Pesquisa do Estado de Alagoas / O presente trabalho teve como objetivo geral verificar as interações intra e interespecíficas entre plantas jovens de espécies arbóreas da caatinga, para, assim, poder quantificar as proporções de alocação de massa para cada espécie nas presenças de pares intraespecíficos e interespecíficos; como também, quantificar a interferência de cada espécie em seus pares intra e interespecífico. O experimento foi realizado em casa de vegetação com sombreamento de 50%, com 168 vasos de 1 kg, contendo um par de cada espécie, durante 105 dias. Foram utilizadas seis espécies de plantas arbóreas em uma combinação fatorial incompleta 6 x 2, correspondendo às seis espécies e dois solos, com quatro repetições. As espécies utilizadas foram: Anadenanthera colubrina (Vell.) Brenan var. cebil (Griseb.) Altschul; Amburana cearensis (Mart.) Gillett; Schinopsis brasiliensis Engl.; Poincianella pyramidalis (Tul.) L.P.Queiroz; Aspidosperma pyrifolium Mart.; Bauhinia che lantha (Bong.) Steud.. Dentre essas espécies, Bauhinia cheilantha e Schinopsis brasiliensis demonstraram ser fortes competidoras interespecíficas, enquanto Amburana cearensis e Poincianella pyramidalis fortes competidoras intraespecíficas. As alocações de massa diferiram por espécie e por disponibilidade de nutrientes. Trabalhos semelhantes com essas espécies e nessa abordagem são escassos na literatura, mas de importância relevante para o entendimento da estruturação de florestas secas.

Trees compete for various resources such as sunlight, water, and nutrients, which can be expressed as numerical terms, called competition indices (CI). Competition between individual trees is correlated with their growth and mortality. Therefore, CIs are used as independent variables to develop, improve and modify growth and yield models. This study was conducted to test the effect of neighborhood competition on tree diameter growth among Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), western hemlock (Tsuga heterophylla (Raf.) Sarg) and red alder (Alnus rubra Bong.), in the Pacific Northwest Coast Range, USA. After testing seven distance-independent CIs and three distance-dependent CIs, only the distance-independent CIs were found to significantly affect the diameter growth model. Among them, CIs with basal area and diameter information were the most impactful. As a result, a simple CI was very effective in a model that accounts for the basal area information of different tree species.