Thermal Niche for Seed Germination and Species Distribution Modelling of Swietenia macrophylla King (Mahogany) under Climate Change Scenarios

Abstract

Swietenia macrophylla is an economically important tree species propagated by seeds that lose their viability in a short time, making seed germination a key stage for the species recruitment. The objective of this study was to determine the cardinal temperatures and thermal time for seed germination of S. macrophylla; and its potential distribution under different climate change scenarios. Seeds were placed in germination chambers at constant temperatures from 5 to 45 °C and their thermal responses modelled using a thermal time approach. In addition, the potential biogeographic distribution was projected according to the Community Climate System Model version 4 (CCSM4). Germination rate reached its maximum at 37.3 ± 1.3 °C (To); seed germination decreased to near zero at 52.7 ± 2.2 °C (ceiling temperature, Tc) and at 12.8 ± 2.4 °C (base temperature, Tb). The suboptimal thermal time θ150 needed for 50% germination was ca. 190 °Cd, which in the current scenario is accumulated in 20 days. The CCSM4 model estimates an increase of the potential distribution of the species of 12.3 to 18.3% compared to the current scenario. The temperature had an important effect on the physiological processes of the seeds. With the increase in temperature, the thermal needs for germination are completed in less time, so the species will not be affected in its distribution. Although the distribution of the species may not be affected, it is crucial to generate sustainable management strategies to ensure its long-term conservation.

Potential Distribution of Cedrela odorata L. in Mexico according to Its Optimal Thermal Range for Seed Germination under Different Climate Change Scenarios

“…The variables for the ecological niche modeling in this species are in agreement with Hernández-Ramos et al [ 26 ], and they were annual precipitation, precipitation during the driest period, diurnal temperature oscillation, and altitude, with an 88.1% contribution. At the same time, the results are comparable to the potential distribution in Mexico of the optimal climate habitat for S. macrophylla (classified in the same family, Meliaceae), in which the variables with the largest contribution were precipitation during the driest month, minimum temperature of the coldest month, temperature seasonality, and annual temperature range; with a contribution of 78.1% [ 46 ], while in another study of S. macrophylla [ 45 ], the variables with the largest contribution were mean temperature during the coldest month, mean temperature, minimum temperature, and precipitation during the growing season, with a contribution of 66.7%. According to Harmann et al [ 48 ], the distribution of forest species is determined mainly by temperature.…”

“…For the drastic scenario in the intermediate future (2050) in this work, the variables precipitation during the driest period, minimum temperature of the coldest month, annual precipitation, and soil type contributed, with 86%, while for the far future (2070), they contributed with 85.7%, which is very similar for the distribution of S. macrophylla [ 46 ]. Since the thermal variables are the same, they contributed from 80.4 to 83.2% for the construction of the distribution models of this species.…”

“…For modeling the optimal distribution on the basis of its temperature thresholds, the environmental variables obtained from BioClim were used. The climate variables of BioClim have been used previously in the modeling of potential optimal distribution of forest species from Mexico, including Pinus chiapensis (Martínez) Andresen [ 42 ], Abies religiosa (Kunth) Schltdl and Cham [ 43 ], Pinus leiophylla Schiede ex Schltdl and Cham [ 44 ], Swietenia macrophylla King [ 45 , 46 ], and Cedrela odorata L. [ 26 ]. The current distribution model of C. odorata coincides with the distribution of the humid tropical forest biome and part of the seasonally dry tropical forest in Chihuahua, Sonora, Durango, and Sinaloa [ 47 ].…”

“…However, in the model of the future distribution of the species proposed by Hernández-Ramos et al [ 26 ] for 2050, the mean temperature of the warmest quarter, altitude, minimum temperature of the coldest month, and temperature seasonality contributed, with a 92% in the conservative scenario. In turn, Sampayo-Maldonado et al [ 46 ] built a model to predict the distribution of S. macrophylla in the conservative scenario for the future 2050 and 2070. The variables that contributed the most were precipitation during the driest month, minimum temperature of the coldest month, temperature seasonality, annual temperature range, and altitude, with 85.5%.…”

“…Using the same model (CCSM4), Hernández-Ramos et al [ 26 ] reported a contraction in the distribution of the species by 2050, with a model probability greater than 50%; however, they did not mention the percent of contraction. Another study used the same model (CCSM4) for the potential distribution of S. macrophylla [ 46 ], and they reported for 2050 an expansion of 18.3% in the conservative scenario and 14.4% in the drastic scenario. For 2070, they reported expansions of 17% and 12.3%, respectively, all with respect to the current distribution, with a probability greater than 20% in the construction of the models.…”