马尾松人工林近自然化改造对植物自然更新及物种多样性的影响

中国人工林面积居世界第一位,而马尾松是中国人工林面积较大的树种之一,广泛分布于中国的亚热带区域。马尾松适应能力强,耐干旱、瘠薄,是南方低山丘陵区群落演替的先锋树种,也是荒山绿化造林的主要树种,马尾松人工林对生态防护、生态治理有着重大的意义。但是,绝大部分马尾松人工林为人工纯林,生态系统比较脆弱,生态服务功能较差。人工林的近自然改造对于增加林地生物多样性,提升人工林的生态服务功能具有重要意义。2005年,对中国林业科学院热带林业试验中心1993年造林的马尾松人工林进行4种不同强度(50%、40%、30%、20%)间伐后,套种大叶栎(Castanopsis fissa)、米老排(Mytilaria laosensis)、润楠(Machilus pingii)、红锥(C. hystrix)4个乡土阔叶树种,各种套种密度皆为120株/hm²。分别于间伐前(2004年)及2010年对群落生物多样性及人工套种树种生态情况进行调查,结果表明:(1)间伐处理后,自然更新至乔木层的物种种类和数量都有显著的增加,600 m²的样方中,物种数由(2.75±2.56)种增加到(11.17±4.32)种,个体数由(5.75±4.31)株增加到(32.17±19.09)株,群落中乔木亚层的优势种变化不大,主要有南酸枣(Choerospondias axillaris)、水锦树(Wendlandia uvariifolia),枫香(Liquidambar formosana)、破布木(Cordia dichotoma)、白背桐(Mallotus paniculatus)等。新增加到乔木层的物种大都为之前群落中灌木层的种类,主要有三桠苦(Evodia lepta)、鸭脚木(Schefflera minutistellata)、白花龙(Styrax faberi)、中平树(Macaranga denticulata)、黄毛榕(Ficus esquiroliana)、华南毛柃(Eurya ciliata)、罗浮柿(Diospyros morrisiana)、猴耳环(Pithecellobium clypearia)、木姜子(Litsea pungens)、毛黄肉楠(Actinodaphne pilosa)等。(2)间伐处理前,600 m²样方中出现的灌草种类数量为(24.63±4.24)种,间伐处理后,600 m²样方中出现的灌草种类数量为(27.58±3.80)种,不同间伐强度处理后林下灌草的优势种与间伐前大致相同,灌木层优势种为三桠苦,草本层优势种为弓果黍(Cyrtococcum patens)。不同间伐强度处理林分间,灌木层和草本层的物种丰富度指数、Shannon-Wiener指数、Simpson指数和Pielou指数均无显著差异,且与间伐前林分也无显著差异。(3)间伐促进了4个乡土树种幼树的生长,随着间伐强度的增加,大叶栎、红锥幼树的高度和胸径显著增长;50%的间伐强度的林分中,阔叶树种幼树的长势要显著好于其他间伐强度,50%的间伐强度最有利于马尾松林下套种的阔叶树种生长。(4)在马尾松林下套种的4个阔叶树种幼树的初期生长有明显差异。总体而言,大叶栎与米老排幼树的早期生长速率要明显高于红锥和润楠。

Effect of Close-to-Nature management on the natural regeneration and species diversity in a masson pine plantation

China has the world's largest total area of plantation resource, among which the most common species is masson pine (Pinus massoniana Lamb). As a pioneer tree species in hill areas of southern China, masson pine is highly resistant to drought and infertile soils and thus plays an important role in the ecological restoration. However, as most masson pine plantations are monocultures, consisting of a single dominant tree species, their ecosystem services are often poor. Close-to-nature management is of great significance for the increase of species diversity and the improvement of ecological service in plantations. In 2005, a thinning experiment was conducted in a 12-year-old masson pine plantation in the Experiment Center of Tropical Forestry of Chinese Academy of Forestry, with four different levels of thinning density (i.e. 50%, 40%, 30%, and 20%). Then, four native broad-leaved tree species, ie. Castanopsis fissa, Mytilaria laosensis, Machilus pingii and C. hystrix, were interplanted with a density of 120 trees/hm² in the thinned masson pine plantation. We investigated the community species diversity and growth conditions before the thinning experiment. Five years later, a re-investigation of the plots showed that: (1) the number of tree layer species were significant increased, with the species richness per plot (600 m²) from 2.75±2.56 to 11.17±4.32 and individual number from 5.75±2.56 to 32.17.17±19.09. In addition to the original dominant species before the experiment, nearly 10 species in original shrub layer grew into tree layer, including Evodia lepta,Schefflera minutistellata,Styrax faberi,Macaranga denticulata,Ficus esquiroliana,Eurya ciliata,Diospyros morrisiana,Pithecellobium clypearia,Litsea pungens and Actinodaphne pilosa. (2) the number of shrub and herb layer species increased only slightly from 24.63±4.24 to 27.58±3.80 per plot (600 m²). Different thinning density treatments had no significant effect on shrub-herb species in terms of Species richness index, Shannon-Wiener index, Simpson index, and Pielou index. The dominant species in shrub and herb layer were Evodia lepta and Cyrtococcum patens, respectively, which are similar with those before the thinning experiment. (3) The saplings of broad-leaved tree species benefited greatly from thinning management. The height and DBH increased significantly with the thinning intensity in Castanopsis fissa and C. hystrix. In the 50% thinning intensity stands, the broad-leaves tree saplings had significantly better performance than those in other stands, suggesting that the 50% thinning management was optimal for the growth of broad-leaves tree species. (4) There were significantly differences in early growth among the four broad-leave tree species in masson pine plantation. Overall, the early growth rates of C. fissa and Mytilaria laosensis were obviously higher than the other two species. Our results highlight the significant effects of close-to-nature management, i.e. thinning of dominant masson pine and interplanting of native tree species, on the increase of species diversity in plantations even in a relative short experimental period. As higher levels of species diversity are essential for community stability (e.g. the resistance of forest to variable disturbances), the close-to-nature management will benefit the supply of high-quality timbers and ecological services in masson pine plantations.